SemOpenAlex |

SemOpenAlex

Matches in SemOpenAlex for { <https://semopenalex.org/work/W2080454590> ?p ?o ?g. }

Showing items 1 to 100 of ±103 with 100 items per page.

W2080454590 endingPage "17836" @default.
W2080454590 startingPage "17828" @default.
W2080454590 abstract "Human granulocytic ehrlichiosis (HGE) is caused by infection with an obligatory intracellular bacterium, the HGE agent. We previously cloned a gene encoding HGE agent 44-kDa major outer membrane protein and designated it p44. In this study, we (i) identified five different mRNAs that are transcribed fromp44-homologous genes in the HGE agent cultivated in HL-60 cells; (ii) cloned genes corresponding to the mRNAs from the genomic DNA of the HGE agent; (iii) showed that the genes being expressed were not clustered in the HGE agent genome; (iv) estimated that a minimum copy number of the p44-homologous genes in the genome is 18; (v) detected two different P44-homologous proteins expressed by the HGE agent; and (vi) demonstrated existence of antibodies specific to the two proteins in sera from patients with HGE. These findings showed that p44 multigenes have several active expression sites and the expression is regulated at transcriptional level, suggesting a potentially unique mechanism for generating the diversity in major antigenic outer membrane proteins of the HGE agent. Characterization of p44-homologous genes expressed by the HGE agent in a tissue culture would assist in understanding a role of the p44 multigene family in pathogenesis and immune response in HGE. Human granulocytic ehrlichiosis (HGE) is caused by infection with an obligatory intracellular bacterium, the HGE agent. We previously cloned a gene encoding HGE agent 44-kDa major outer membrane protein and designated it p44. In this study, we (i) identified five different mRNAs that are transcribed fromp44-homologous genes in the HGE agent cultivated in HL-60 cells; (ii) cloned genes corresponding to the mRNAs from the genomic DNA of the HGE agent; (iii) showed that the genes being expressed were not clustered in the HGE agent genome; (iv) estimated that a minimum copy number of the p44-homologous genes in the genome is 18; (v) detected two different P44-homologous proteins expressed by the HGE agent; and (vi) demonstrated existence of antibodies specific to the two proteins in sera from patients with HGE. These findings showed that p44 multigenes have several active expression sites and the expression is regulated at transcriptional level, suggesting a potentially unique mechanism for generating the diversity in major antigenic outer membrane proteins of the HGE agent. Characterization of p44-homologous genes expressed by the HGE agent in a tissue culture would assist in understanding a role of the p44 multigene family in pathogenesis and immune response in HGE. Human granulocytic ehrlichiosis (HGE), 1The abbreviations used are: HGE, human granulocytic ehrlichiosis; RT, reverse transcription; PCR, polymerase chain reaction; IFA, indirect fluorescent antibody; KLH, keyhole limpet hemacyanin; PFGE, pulsed-field gel electophoresis; ORF, open reading frame; kb, kilobase(s); bp, base pair(s); rP44, recombinant P44. 1The abbreviations used are: HGE, human granulocytic ehrlichiosis; RT, reverse transcription; PCR, polymerase chain reaction; IFA, indirect fluorescent antibody; KLH, keyhole limpet hemacyanin; PFGE, pulsed-field gel electophoresis; ORF, open reading frame; kb, kilobase(s); bp, base pair(s); rP44, recombinant P44. a tick-borne zoonosis, was first reported in 1994 and increasingly recognized in the United States (1Bakken J.S. Krueth J. Wilson-Nordskog C. Tilden R.L. Asanovich K. Dumler J.S. J. Am. Med. Assoc. 1996; 275: 199-205Crossref PubMed Google Scholar, 2Chen S.-M. Dumler J.S. Bakken J.S. Walker D.H. J. Clin. Microbiol. 1994; 32: 589-595Crossref PubMed Google Scholar, 3Goodman J.L.C. Nelson C. Vitale B. Madigan J.E. Dumler J.S. Kurtti T.J. Munderloh U.G. N. Engl. J. Med. 1996; 334: 209-215Crossref PubMed Scopus (401) Google Scholar). Serologic and PCR analyses suggest that HGE also exists in Europe (4Brouqui P. Dumler J.S. Lienhard R. Brossard M. Raoult D. Lancet. 1995; 346: 782-783Abstract PubMed Scopus (105) Google Scholar, 5Pusterla N. Huder J.B. Wolfensberger C. Litschi B. Parvis A. Lutz H. J. Clin. Microbiol. 1997; 35: 2307-2309Crossref PubMed Google Scholar, 6Pusterla N. Huder J. Feige K. Lutz H. J. Clin. Microbiol. 1998; 36: 2035-2037Crossref PubMed Google Scholar). HGE is characterized by chills, headache, myalgia, and hematological abnormalities, including leukopenia and thrombocytopenia. It frequently requires prolonged hospitalization, and when the treatment is delayed due to misdiagnosis or in immunocompromized patients, HGE can be fatal (7Hardalo C.J. Quagliarello V. Dumler J.S. Clin. Infect. Dis. 1995; 21: 910-914Crossref PubMed Scopus (106) Google Scholar). HGE is caused by infection with an obligatory intracellular bacterium, HGE agent. Comparison of 16 S rRNA gene sequences (2Chen S.-M. Dumler J.S. Bakken J.S. Walker D.H. J. Clin. Microbiol. 1994; 32: 589-595Crossref PubMed Google Scholar) and ultrastructure (8Rikihisa Y. Zhi N. Wormser G.P. Wen B.H. Horowitz H.W. Hechemy K.E. J. Infect. Dis. 1997; 175: 210-213Crossref PubMed Scopus (94) Google Scholar) indicates that the HGE agent is closely related to Ehrlichia phagocytophila, the agent of tick-borne fever, and Ehrlichia equi, the agent of equine ehrlichiosis. The HGE agent is transmitted by the Ixodes sp. tick (9Telford III, S.R. Dawson J.E. Katavolos P. Warner C.K. Kolbert C.P. Persing D.H. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 6209-6214Crossref PubMed Scopus (431) Google Scholar), and the white-footed mouse is considered to be the major reservoir of the HGE agent in the United States (9Telford III, S.R. Dawson J.E. Katavolos P. Warner C.K. Kolbert C.P. Persing D.H. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 6209-6214Crossref PubMed Scopus (431) Google Scholar).Although the successful culture isolation of the organism was accomplished in 1995, little is known about the pathogenesis and intracellular parasitism of the HGE agent at the molecular level. Recent studies of the HGE agent showed that 38–49-kDa proteins of this organism are dominant antigens recognized by the sera from patients with HGE (10Asanovich K.M. Bakken J.S. Madigan J.E. Aguero-Rosenfeld M. Wormser G.P. Dumler J.S. J. Infect. Dis. 1997; 176: 1029-1034Crossref PubMed Scopus (106) Google Scholar, 11Ijdo J.W. Zhang Y. Hodzic E. Magnarelli L.A. Wilson M.L. Telford III, S.R. Barthold S.W. Fikrig E. J. Infect. Dis. 1997; 176: 687-692Crossref PubMed Scopus (53) Google Scholar, 12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar, 13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar). We demonstrated that these proteins are present in the outer membrane fraction of our five human patient isolates of the HGE agent and of a tick isolate (USG3) of the granulocyticEhrlichia (GE) sp. (12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar). More recently, we cloned, sequenced, and expressed in Escherichia coli a gene encoding a 44-kDa protein of the HGE agent (HZ isolate (8Rikihisa Y. Zhi N. Wormser G.P. Wen B.H. Horowitz H.W. Hechemy K.E. J. Infect. Dis. 1997; 175: 210-213Crossref PubMed Scopus (94) Google Scholar), also called isolate 13 (12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar, 13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar, 14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar)), and designated it p44 (13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar). Another ORF homologous to the p44 gene was found in the area downstream from the p44. This ORF lacked the universal start codon (AUG) and had two conserved sequences consisting of 59 and 65 amino acid residues identical to those of the p44 gene, which flanked a central hypervariable region. Genomic Southern blot analysis revealed more than 10 bands bound to the p44 gene probe, suggesting the existence of additional p44-homologous genes in the HGE agent genome. By Western blot analysis, a mouse antiserum against the recombinant P44 (rP44) protein recognized two to six P44-homologous proteins in each of the five isolates of the HGE agent and in USG3 isolate. Three monoclonal antibodies that react to the rP44 recognized one to four 44-kDa-range proteins in the whole organism as well as in the outer membrane fraction from these six isolates (14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar). Passive immunization with these antibodies induced a partial protection against infection with the live HGE agent in mice. These studies suggest that multiple antigenically cross-reactive proteins of 38–49 kDa are expressed in each isolate of the HGE and USG3 isolate in HL-60 cell culture and are potential protective antigens in HGE infection.Murphy et al. (15Murphy C.I. Storey J.R. Recchia J. Doros-Richert L.A. Gingrich-Baker C. Munroe K. Bakken J.S. Coughlin R.T. Beltz G.A. Infect. Immun. 1998; 66: 3711-3718Crossref PubMed Google Scholar) cloned three p44-homologous genes (msp-2a, msp-2b, and msp-2c) of USG3 isolate. The chemically determined amino acid sequences at N termini or internal segments of native 43- and 45-kDa proteins of the isolate approximately match with the segments of amino acid sequences predicted from one to two each of the three cloned genes. However, due to existence of highly conserved amino acid sequences among these P44-homologous proteins, whether these genes are actually expressed by the isolate was not conclusive in that study. Ijdo et al.(16Ijdo J.W. Sun W. Zhang Y. Magnarelli L.A. Fikrig E. Infect. Immun. 1998; 66: 3264-3296Crossref PubMed Google Scholar) cloned a p44-homologous gene (hge-44) from the NCH-1 isolate of HGE agent and showed by RT-PCR and sequencing the product that this gene is expressed by the HGE agent in HL-60 cells.So far, little is known about the relationship between the diversity of antigenically cross-reactive proteins of 38–49 kDa and multiplep44-homologous genes in the HGE agent. In this study, we characterized the structure, distribution, and expression of thep44-homologous genes of the HGE agent cultivated in HL-60 cells. Thereby, the study is expected to facilitate understanding of a role of the p44 multigene family in pathogenesis and immune responses in HGE infection and also to be helpful in designing a vaccine candidate by using these gene products.DISCUSSIONThis study demonstrated that multiple p44 genes are expressed by the HGE agent in HL-60 cells and probably in patients, which may be the reason why multiple bands of 38–49 kDa were found in our previous Western blot analysis studies with patients' sera (12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar) or with monoclonal antibodies (14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar). Our data set the framework for a better understanding of the mechanism(s) underpinning the expression ofp44 multigenes in the HGE agent. Four of expressedp44-homologous genes (p44-2, p44-12, p44-15, andp44-18) and one silent gene (p44) from the genomic DNA were cloned. The proteins encoded by thesep44-homologous genes were found to consist of a single central hypervariable region of approximately 94 amino acid residues and N- and C-terminal regions highly conserved among the homologs. It appears that two kinds of mechanisms may involve in the expressions ofp44-homologous genes: (i) the normal expression of the genes, such as p44-2 and p44-12, with complete ORFs from the respective expression sites, and (ii) the unique expression with a specific event, probably transcriptional modification such as splicing, of the genes, such as p44-18 andp44-15, which lack a universal start codon. The latter mechanism may come to existence to overcome the deficiency in creating antigenic diversity by a common mechanism, such as recombination.p44 multigenes are homologous to two A. marginale msp2 genes that had been cloned (∼ 45% amino acid similarity (13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar, 15Murphy C.I. Storey J.R. Recchia J. Doros-Richert L.A. Gingrich-Baker C. Munroe K. Bakken J.S. Coughlin R.T. Beltz G.A. Infect. Immun. 1998; 66: 3711-3718Crossref PubMed Google Scholar, 16Ijdo J.W. Sun W. Zhang Y. Magnarelli L.A. Fikrig E. Infect. Immun. 1998; 66: 3264-3296Crossref PubMed Google Scholar)). Recently, the study on A. marginale revealed that multiple (at least 4) msp2 genes were expressed in each peak of rickettsemia that occurred at 6–8-week intervals in two cattle (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar). The distribution of the genes in the genome (broad distribution throughout the genome) and the protein structure (e.g. a central hypervariable region flanked with conserved regions) are similar between msp2 genes and p44 multigenes. Because the copy number of msp2 multigenes in A. marginale was estimated as 10 (21Palmer G.H. Eid G. Barbet A.F. McGuire T.C. McElwain T.F. Infect. Immun. 1994; 62: 3808-3816Crossref PubMed Google Scholar), the relative ratio (4 in 10) of expressed genes against the total copy number of msp2multigenes at a given stage of infection is higher than that (5 in 18) of p44 multigenes of the HGE agent. In other words, the HGE agent may have more potential genetic capacity to generate the diversity of the P44-homologous proteins. Because for A. marginale, the msp2 genes corresponding to the transcripts were not identified, the expression mechanism is unknown.Among rickettsia closely related to HGE agent, persistent infection and recurrence after recovery from the clinical disease are known forEhrlichia canis, Ehrlichia platys, E. phagocytophila, Cowdria ruminantium, and A. marginale (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar, 23Rikihisa Y. Clin. Microbiol. Rev. 1991; 4: 286-308Crossref PubMed Scopus (356) Google Scholar). The HGE agent was detected in the serum of one untreated patient by PCR at 30 day after onset of illness (24Dumler J.S. Bakken J.S. J. Infect. Dis. 1996; 173: 1027-1030Crossref PubMed Scopus (56) Google Scholar), suggesting that the HGE agent may also cause persistent infection in humans. In addition, persistence of the HGE agent in reservoir rodent host would be an important adaptation that allows greater access of uninfected tick populations to an infectious blood meal. French et al. (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar) proposed that the expression of distinct sets of msp2 genes at each rickettsemia peak in A. marginale infection of cattle may allow immunoevation of anaplasma to persist in immunocompetent hosts. Multiple expression of p44 multigenes may be also related to immunoavoidance in human and rodent hosts and potential persistence.The expression mechanisms of the several multigene families in the human pathogens Neisseria gonorrhoeae (pil (25Haas R. Meyer T.F. Cell. 1986; 44: 107-115Abstract Full Text PDF PubMed Scopus (234) Google Scholar) and opa (26Stern A. Brown M. Nickel P. Meyer T.F. Cell. 1986; 47: 61-71Abstract Full Text PDF PubMed Scopus (303) Google Scholar)), Borrelia hermsii (vmp(27Barbour A.G. Annu. Rev. Microbiol. 1990; 44: 155-171Crossref PubMed Scopus (133) Google Scholar)), Borrelia burgdorferi (vls(28Zhang J.R. Hardham J.M. Barbour A.G. Norris S.J. Cell. 1997; 89: 275-285Abstract Full Text Full Text PDF PubMed Scopus (516) Google Scholar)), African trypanosomes (vsg (29Vanhamme L. Pays E. Microbiol. Rew. 1995; 59: 223-240Crossref PubMed Google Scholar)), and Plasmodium falciparum (var (30Scherf A. Hernandez-Rivas R. Buffet P. Bottius E. Benatar C. Pouvelle B. Gysin J. Lanzer M. EMBO J. 1998; 17: 5418-5426Crossref PubMed Scopus (451) Google Scholar)), have been well studied. These multigene families are involved in pathogenesis, e.g.antigenic variation (or phase variation) and cytoadhesin. The switching of gene expression can be divided into two major mechanisms: one depends on DNA rearrangement, and another occurs at transcriptional level. In pil, vmp, vls, andvsg, switching of expression between members of the corresponding gene families occurs through programmed DNA rearrangements (gene conversion), moving a transcriptionally silent gene into an active expression site. In opa, expression is regulated by a reversible frameshift mutation of DNA, i.e. a slipped-strand mispairing of the number of pentanucleotide coding repeat units in the single peptides (26Stern A. Brown M. Nickel P. Meyer T.F. Cell. 1986; 47: 61-71Abstract Full Text PDF PubMed Scopus (303) Google Scholar), whereas in the vargene of P. falciparum, each parasite expresses only a single and distinct var gene product. Each var gene is an independent transcription unit in which promoter activity determines the expression status. p44 multigene expression appears to be different from those of pil, vmp,vls, and vsg in that multiple expressedp44 genes are located in several large DNA fragments in the HGE agent genome, i.e. the transcription of the genes apparently does not occur from a unique expression site. The expressionp44 multigene, therefore, may not involve DNA rearrangement. Expressions of p44 multigenes, as well as msp2genes (21Palmer G.H. Eid G. Barbet A.F. McGuire T.C. McElwain T.F. Infect. Immun. 1994; 62: 3808-3816Crossref PubMed Google Scholar), are also different from that of var genes, because a single organism appear to express more than two gene products.In ehrlichiae, recently, additional multigene families encoding major outer membrane proteins have been discovered. We identified theomp-1 gene family of Ehrlichia chaffeensis (31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar) and the p30 gene family ofE. canis (19Ohashi N. Unver A. Zhi N. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 2671-2680Crossref PubMed Google Scholar). More than a dozen copies of theomp-1 and p30 gene families are tandemly arranged in the genome, in contrast to p44 multigenes andmsp2 genes. Furthermore the protein structures encoded by the omp-1 and p30 gene families is distinct from those of p44 and msp2, consisting of three short, hypervariable segments interposed with relatively conserved segments (19Ohashi N. Unver A. Zhi N. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 2671-2680Crossref PubMed Google Scholar, 31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar). This suggests that the expression mechanism ofomp-1 and p30 gene families is probably different from those of p44 and msp2. Immunization with a recombinant P28 protein (one of the omp-1 multigene products) of E. chaffeensis and native MSP2 of A. marginale has been demonstrated to induce almost complete and partial protections against the infection in mice and cattle, respectively (31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar, 32Palmer G.H. Oberle S.M. Barbet A.F. Goff W.L. Davis W.C. McGuire T.C. Infect. Immun. 1988; 56: 1526-1531Crossref PubMed Google Scholar). We previously observed that passive immunization with monoclonal antibodies specific to P44-homologous proteins of the HGE agent induced partial protection against challenge with the HGE agent in mice (14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar). Active immunization with the recombinant P44 protein also partially protected mice from HGE infection. 2N. Zhi, N. Ohashi, and Y. Rikihisa, unpublished data. This indicates that the p44 multigene family encodes a potential protective antigen. However, because only a fraction of genes is differentially expressed as shown in this study, it seems to be essential to determine which genes are expressed in the host for identification of the most protective antigen.By a GenBankTM data base homology search, the P44-homologous proteins of the HGE agent were found to possess a similarity (∼64%) with the N-terminal region of Hsf protein (surface fibrils) involved in binding of Hemophilus influenzae type b to human epithelial cells (33St. Geme III, J.W. Cutter D. Barenkamp S.J. J. Bacteriol. 1996; 178: 6281-6287Crossref PubMed Google Scholar). The similar sequence identified was located in the center of all P44 homologs, including the hypervariable domain (span of approximately 200 amino acid residues). This finding suggests that P44s may have a similar function, such as cytoadhesion to human granulocytes.The basic information obtained in this study would facilitate the understanding of the role of the p44 multigene family in causing disease in humans, in the persistence of HGE agent in white-footed mice, and in transmission of this agent from tick to human. Further analysis of expression mechanism of these genes and the genes encoding more protective antigens would assist in designing an effective vaccine candidate against the human ehrlichiosis. Human granulocytic ehrlichiosis (HGE), 1The abbreviations used are: HGE, human granulocytic ehrlichiosis; RT, reverse transcription; PCR, polymerase chain reaction; IFA, indirect fluorescent antibody; KLH, keyhole limpet hemacyanin; PFGE, pulsed-field gel electophoresis; ORF, open reading frame; kb, kilobase(s); bp, base pair(s); rP44, recombinant P44. 1The abbreviations used are: HGE, human granulocytic ehrlichiosis; RT, reverse transcription; PCR, polymerase chain reaction; IFA, indirect fluorescent antibody; KLH, keyhole limpet hemacyanin; PFGE, pulsed-field gel electophoresis; ORF, open reading frame; kb, kilobase(s); bp, base pair(s); rP44, recombinant P44. a tick-borne zoonosis, was first reported in 1994 and increasingly recognized in the United States (1Bakken J.S. Krueth J. Wilson-Nordskog C. Tilden R.L. Asanovich K. Dumler J.S. J. Am. Med. Assoc. 1996; 275: 199-205Crossref PubMed Google Scholar, 2Chen S.-M. Dumler J.S. Bakken J.S. Walker D.H. J. Clin. Microbiol. 1994; 32: 589-595Crossref PubMed Google Scholar, 3Goodman J.L.C. Nelson C. Vitale B. Madigan J.E. Dumler J.S. Kurtti T.J. Munderloh U.G. N. Engl. J. Med. 1996; 334: 209-215Crossref PubMed Scopus (401) Google Scholar). Serologic and PCR analyses suggest that HGE also exists in Europe (4Brouqui P. Dumler J.S. Lienhard R. Brossard M. Raoult D. Lancet. 1995; 346: 782-783Abstract PubMed Scopus (105) Google Scholar, 5Pusterla N. Huder J.B. Wolfensberger C. Litschi B. Parvis A. Lutz H. J. Clin. Microbiol. 1997; 35: 2307-2309Crossref PubMed Google Scholar, 6Pusterla N. Huder J. Feige K. Lutz H. J. Clin. Microbiol. 1998; 36: 2035-2037Crossref PubMed Google Scholar). HGE is characterized by chills, headache, myalgia, and hematological abnormalities, including leukopenia and thrombocytopenia. It frequently requires prolonged hospitalization, and when the treatment is delayed due to misdiagnosis or in immunocompromized patients, HGE can be fatal (7Hardalo C.J. Quagliarello V. Dumler J.S. Clin. Infect. Dis. 1995; 21: 910-914Crossref PubMed Scopus (106) Google Scholar). HGE is caused by infection with an obligatory intracellular bacterium, HGE agent. Comparison of 16 S rRNA gene sequences (2Chen S.-M. Dumler J.S. Bakken J.S. Walker D.H. J. Clin. Microbiol. 1994; 32: 589-595Crossref PubMed Google Scholar) and ultrastructure (8Rikihisa Y. Zhi N. Wormser G.P. Wen B.H. Horowitz H.W. Hechemy K.E. J. Infect. Dis. 1997; 175: 210-213Crossref PubMed Scopus (94) Google Scholar) indicates that the HGE agent is closely related to Ehrlichia phagocytophila, the agent of tick-borne fever, and Ehrlichia equi, the agent of equine ehrlichiosis. The HGE agent is transmitted by the Ixodes sp. tick (9Telford III, S.R. Dawson J.E. Katavolos P. Warner C.K. Kolbert C.P. Persing D.H. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 6209-6214Crossref PubMed Scopus (431) Google Scholar), and the white-footed mouse is considered to be the major reservoir of the HGE agent in the United States (9Telford III, S.R. Dawson J.E. Katavolos P. Warner C.K. Kolbert C.P. Persing D.H. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 6209-6214Crossref PubMed Scopus (431) Google Scholar). Although the successful culture isolation of the organism was accomplished in 1995, little is known about the pathogenesis and intracellular parasitism of the HGE agent at the molecular level. Recent studies of the HGE agent showed that 38–49-kDa proteins of this organism are dominant antigens recognized by the sera from patients with HGE (10Asanovich K.M. Bakken J.S. Madigan J.E. Aguero-Rosenfeld M. Wormser G.P. Dumler J.S. J. Infect. Dis. 1997; 176: 1029-1034Crossref PubMed Scopus (106) Google Scholar, 11Ijdo J.W. Zhang Y. Hodzic E. Magnarelli L.A. Wilson M.L. Telford III, S.R. Barthold S.W. Fikrig E. J. Infect. Dis. 1997; 176: 687-692Crossref PubMed Scopus (53) Google Scholar, 12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar, 13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar). We demonstrated that these proteins are present in the outer membrane fraction of our five human patient isolates of the HGE agent and of a tick isolate (USG3) of the granulocyticEhrlichia (GE) sp. (12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar). More recently, we cloned, sequenced, and expressed in Escherichia coli a gene encoding a 44-kDa protein of the HGE agent (HZ isolate (8Rikihisa Y. Zhi N. Wormser G.P. Wen B.H. Horowitz H.W. Hechemy K.E. J. Infect. Dis. 1997; 175: 210-213Crossref PubMed Scopus (94) Google Scholar), also called isolate 13 (12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar, 13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar, 14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar)), and designated it p44 (13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar). Another ORF homologous to the p44 gene was found in the area downstream from the p44. This ORF lacked the universal start codon (AUG) and had two conserved sequences consisting of 59 and 65 amino acid residues identical to those of the p44 gene, which flanked a central hypervariable region. Genomic Southern blot analysis revealed more than 10 bands bound to the p44 gene probe, suggesting the existence of additional p44-homologous genes in the HGE agent genome. By Western blot analysis, a mouse antiserum against the recombinant P44 (rP44) protein recognized two to six P44-homologous proteins in each of the five isolates of the HGE agent and in USG3 isolate. Three monoclonal antibodies that react to the rP44 recognized one to four 44-kDa-range proteins in the whole organism as well as in the outer membrane fraction from these six isolates (14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar). Passive immunization with these antibodies induced a partial protection against infection with the live HGE agent in mice. These studies suggest that multiple antigenically cross-reactive proteins of 38–49 kDa are expressed in each isolate of the HGE and USG3 isolate in HL-60 cell culture and are potential protective antigens in HGE infection. Murphy et al. (15Murphy C.I. Storey J.R. Recchia J. Doros-Richert L.A. Gingrich-Baker C. Munroe K. Bakken J.S. Coughlin R.T. Beltz G.A. Infect. Immun. 1998; 66: 3711-3718Crossref PubMed Google Scholar) cloned three p44-homologous genes (msp-2a, msp-2b, and msp-2c) of USG3 isolate. The chemically determined amino acid sequences at N termini or internal segments of native 43- and 45-kDa proteins of the isolate approximately match with the segments of amino acid sequences predicted from one to two each of the three cloned genes. However, due to existence of highly conserved amino acid sequences among these P44-homologous proteins, whether these genes are actually expressed by the isolate was not conclusive in that study. Ijdo et al.(16Ijdo J.W. Sun W. Zhang Y. Magnarelli L.A. Fikrig E. Infect. Immun. 1998; 66: 3264-3296Crossref PubMed Google Scholar) cloned a p44-homologous gene (hge-44) from the NCH-1 isolate of HGE agent and showed by RT-PCR and sequencing the product that this gene is expressed by the HGE agent in HL-60 cells. So far, little is known about the relationship between the diversity of antigenically cross-reactive proteins of 38–49 kDa and multiplep44-homologous genes in the HGE agent. In this study, we characterized the structure, distribution, and expression of thep44-homologous genes of the HGE agent cultivated in HL-60 cells. Thereby, the study is expected to facilitate understanding of a role of the p44 multigene family in pathogenesis and immune responses in HGE infection and also to be helpful in designing a vaccine candidate by using these gene products. DISCUSSIONThis study demonstrated that multiple p44 genes are expressed by the HGE agent in HL-60 cells and probably in patients, which may be the reason why multiple bands of 38–49 kDa were found in our previous Western blot analysis studies with patients' sera (12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar) or with monoclonal antibodies (14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar). Our data set the framework for a better understanding of the mechanism(s) underpinning the expression ofp44 multigenes in the HGE agent. Four of expressedp44-homologous genes (p44-2, p44-12, p44-15, andp44-18) and one silent gene (p44) from the genomic DNA were cloned. The proteins encoded by thesep44-homologous genes were found to consist of a single central hypervariable region of approximately 94 amino acid residues and N- and C-terminal regions highly conserved among the homologs. It appears that two kinds of mechanisms may involve in the expressions ofp44-homologous genes: (i) the normal expression of the genes, such as p44-2 and p44-12, with complete ORFs from the respective expression sites, and (ii) the unique expression with a specific event, probably transcriptional modification such as splicing, of the genes, such as p44-18 andp44-15, which lack a universal start codon. The latter mechanism may come to existence to overcome the deficiency in creating antigenic diversity by a common mechanism, such as recombination.p44 multigenes are homologous to two A. marginale msp2 genes that had been cloned (∼ 45% amino acid similarity (13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar, 15Murphy C.I. Storey J.R. Recchia J. Doros-Richert L.A. Gingrich-Baker C. Munroe K. Bakken J.S. Coughlin R.T. Beltz G.A. Infect. Immun. 1998; 66: 3711-3718Crossref PubMed Google Scholar, 16Ijdo J.W. Sun W. Zhang Y. Magnarelli L.A. Fikrig E. Infect. Immun. 1998; 66: 3264-3296Crossref PubMed Google Scholar)). Recently, the study on A. marginale revealed that multiple (at least 4) msp2 genes were expressed in each peak of rickettsemia that occurred at 6–8-week intervals in two cattle (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar). The distribution of the genes in the genome (broad distribution throughout the genome) and the protein structure (e.g. a central hypervariable region flanked with conserved regions) are similar between msp2 genes and p44 multigenes. Because the copy number of msp2 multigenes in A. marginale was estimated as 10 (21Palmer G.H. Eid G. Barbet A.F. McGuire T.C. McElwain T.F. Infect. Immun. 1994; 62: 3808-3816Crossref PubMed Google Scholar), the relative ratio (4 in 10) of expressed genes against the total copy number of msp2multigenes at a given stage of infection is higher than that (5 in 18) of p44 multigenes of the HGE agent. In other words, the HGE agent may have more potential genetic capacity to generate the diversity of the P44-homologous proteins. Because for A. marginale, the msp2 genes corresponding to the transcripts were not identified, the expression mechanism is unknown.Among rickettsia closely related to HGE agent, persistent infection and recurrence after recovery from the clinical disease are known forEhrlichia canis, Ehrlichia platys, E. phagocytophila, Cowdria ruminantium, and A. marginale (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar, 23Rikihisa Y. Clin. Microbiol. Rev. 1991; 4: 286-308Crossref PubMed Scopus (356) Google Scholar). The HGE agent was detected in the serum of one untreated patient by PCR at 30 day after onset of illness (24Dumler J.S. Bakken J.S. J. Infect. Dis. 1996; 173: 1027-1030Crossref PubMed Scopus (56) Google Scholar), suggesting that the HGE agent may also cause persistent infection in humans. In addition, persistence of the HGE agent in reservoir rodent host would be an important adaptation that allows greater access of uninfected tick populations to an infectious blood meal. French et al. (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar) proposed that the expression of distinct sets of msp2 genes at each rickettsemia peak in A. marginale infection of cattle may allow immunoevation of anaplasma to persist in immunocompetent hosts. Multiple expression of p44 multigenes may be also related to immunoavoidance in human and rodent hosts and potential persistence.The expression mechanisms of the several multigene families in the human pathogens Neisseria gonorrhoeae (pil (25Haas R. Meyer T.F. Cell. 1986; 44: 107-115Abstract Full Text PDF PubMed Scopus (234) Google Scholar) and opa (26Stern A. Brown M. Nickel P. Meyer T.F. Cell. 1986; 47: 61-71Abstract Full Text PDF PubMed Scopus (303) Google Scholar)), Borrelia hermsii (vmp(27Barbour A.G. Annu. Rev. Microbiol. 1990; 44: 155-171Crossref PubMed Scopus (133) Google Scholar)), Borrelia burgdorferi (vls(28Zhang J.R. Hardham J.M. Barbour A.G. Norris S.J. Cell. 1997; 89: 275-285Abstract Full Text Full Text PDF PubMed Scopus (516) Google Scholar)), African trypanosomes (vsg (29Vanhamme L. Pays E. Microbiol. Rew. 1995; 59: 223-240Crossref PubMed Google Scholar)), and Plasmodium falciparum (var (30Scherf A. Hernandez-Rivas R. Buffet P. Bottius E. Benatar C. Pouvelle B. Gysin J. Lanzer M. EMBO J. 1998; 17: 5418-5426Crossref PubMed Scopus (451) Google Scholar)), have been well studied. These multigene families are involved in pathogenesis, e.g.antigenic variation (or phase variation) and cytoadhesin. The switching of gene expression can be divided into two major mechanisms: one depends on DNA rearrangement, and another occurs at transcriptional level. In pil, vmp, vls, andvsg, switching of expression between members of the corresponding gene families occurs through programmed DNA rearrangements (gene conversion), moving a transcriptionally silent gene into an active expression site. In opa, expression is regulated by a reversible frameshift mutation of DNA, i.e. a slipped-strand mispairing of the number of pentanucleotide coding repeat units in the single peptides (26Stern A. Brown M. Nickel P. Meyer T.F. Cell. 1986; 47: 61-71Abstract Full Text PDF PubMed Scopus (303) Google Scholar), whereas in the vargene of P. falciparum, each parasite expresses only a single and distinct var gene product. Each var gene is an independent transcription unit in which promoter activity determines the expression status. p44 multigene expression appears to be different from those of pil, vmp,vls, and vsg in that multiple expressedp44 genes are located in several large DNA fragments in the HGE agent genome, i.e. the transcription of the genes apparently does not occur from a unique expression site. The expressionp44 multigene, therefore, may not involve DNA rearrangement. Expressions of p44 multigenes, as well as msp2genes (21Palmer G.H. Eid G. Barbet A.F. McGuire T.C. McElwain T.F. Infect. Immun. 1994; 62: 3808-3816Crossref PubMed Google Scholar), are also different from that of var genes, because a single organism appear to express more than two gene products.In ehrlichiae, recently, additional multigene families encoding major outer membrane proteins have been discovered. We identified theomp-1 gene family of Ehrlichia chaffeensis (31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar) and the p30 gene family ofE. canis (19Ohashi N. Unver A. Zhi N. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 2671-2680Crossref PubMed Google Scholar). More than a dozen copies of theomp-1 and p30 gene families are tandemly arranged in the genome, in contrast to p44 multigenes andmsp2 genes. Furthermore the protein structures encoded by the omp-1 and p30 gene families is distinct from those of p44 and msp2, consisting of three short, hypervariable segments interposed with relatively conserved segments (19Ohashi N. Unver A. Zhi N. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 2671-2680Crossref PubMed Google Scholar, 31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar). This suggests that the expression mechanism ofomp-1 and p30 gene families is probably different from those of p44 and msp2. Immunization with a recombinant P28 protein (one of the omp-1 multigene products) of E. chaffeensis and native MSP2 of A. marginale has been demonstrated to induce almost complete and partial protections against the infection in mice and cattle, respectively (31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar, 32Palmer G.H. Oberle S.M. Barbet A.F. Goff W.L. Davis W.C. McGuire T.C. Infect. Immun. 1988; 56: 1526-1531Crossref PubMed Google Scholar). We previously observed that passive immunization with monoclonal antibodies specific to P44-homologous proteins of the HGE agent induced partial protection against challenge with the HGE agent in mice (14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar). Active immunization with the recombinant P44 protein also partially protected mice from HGE infection. 2N. Zhi, N. Ohashi, and Y. Rikihisa, unpublished data. This indicates that the p44 multigene family encodes a potential protective antigen. However, because only a fraction of genes is differentially expressed as shown in this study, it seems to be essential to determine which genes are expressed in the host for identification of the most protective antigen.By a GenBankTM data base homology search, the P44-homologous proteins of the HGE agent were found to possess a similarity (∼64%) with the N-terminal region of Hsf protein (surface fibrils) involved in binding of Hemophilus influenzae type b to human epithelial cells (33St. Geme III, J.W. Cutter D. Barenkamp S.J. J. Bacteriol. 1996; 178: 6281-6287Crossref PubMed Google Scholar). The similar sequence identified was located in the center of all P44 homologs, including the hypervariable domain (span of approximately 200 amino acid residues). This finding suggests that P44s may have a similar function, such as cytoadhesion to human granulocytes.The basic information obtained in this study would facilitate the understanding of the role of the p44 multigene family in causing disease in humans, in the persistence of HGE agent in white-footed mice, and in transmission of this agent from tick to human. Further analysis of expression mechanism of these genes and the genes encoding more protective antigens would assist in designing an effective vaccine candidate against the human ehrlichiosis. This study demonstrated that multiple p44 genes are expressed by the HGE agent in HL-60 cells and probably in patients, which may be the reason why multiple bands of 38–49 kDa were found in our previous Western blot analysis studies with patients' sera (12Zhi N. Rikihisa Y. Kim H.Y. Wormser G.P. Horowitz H.W. J. Clin. Microbiol. 1997; 35: 2606-2611Crossref PubMed Google Scholar) or with monoclonal antibodies (14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar). Our data set the framework for a better understanding of the mechanism(s) underpinning the expression ofp44 multigenes in the HGE agent. Four of expressedp44-homologous genes (p44-2, p44-12, p44-15, andp44-18) and one silent gene (p44) from the genomic DNA were cloned. The proteins encoded by thesep44-homologous genes were found to consist of a single central hypervariable region of approximately 94 amino acid residues and N- and C-terminal regions highly conserved among the homologs. It appears that two kinds of mechanisms may involve in the expressions ofp44-homologous genes: (i) the normal expression of the genes, such as p44-2 and p44-12, with complete ORFs from the respective expression sites, and (ii) the unique expression with a specific event, probably transcriptional modification such as splicing, of the genes, such as p44-18 andp44-15, which lack a universal start codon. The latter mechanism may come to existence to overcome the deficiency in creating antigenic diversity by a common mechanism, such as recombination. p44 multigenes are homologous to two A. marginale msp2 genes that had been cloned (∼ 45% amino acid similarity (13Zhi N. Ohashi N. Rikihisa Y. Wormser G.P. Horowitz H.W. Hechemy K.E. J. Clin. Microbiol. 1998; 36: 1666-1673Crossref PubMed Google Scholar, 15Murphy C.I. Storey J.R. Recchia J. Doros-Richert L.A. Gingrich-Baker C. Munroe K. Bakken J.S. Coughlin R.T. Beltz G.A. Infect. Immun. 1998; 66: 3711-3718Crossref PubMed Google Scholar, 16Ijdo J.W. Sun W. Zhang Y. Magnarelli L.A. Fikrig E. Infect. Immun. 1998; 66: 3264-3296Crossref PubMed Google Scholar)). Recently, the study on A. marginale revealed that multiple (at least 4) msp2 genes were expressed in each peak of rickettsemia that occurred at 6–8-week intervals in two cattle (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar). The distribution of the genes in the genome (broad distribution throughout the genome) and the protein structure (e.g. a central hypervariable region flanked with conserved regions) are similar between msp2 genes and p44 multigenes. Because the copy number of msp2 multigenes in A. marginale was estimated as 10 (21Palmer G.H. Eid G. Barbet A.F. McGuire T.C. McElwain T.F. Infect. Immun. 1994; 62: 3808-3816Crossref PubMed Google Scholar), the relative ratio (4 in 10) of expressed genes against the total copy number of msp2multigenes at a given stage of infection is higher than that (5 in 18) of p44 multigenes of the HGE agent. In other words, the HGE agent may have more potential genetic capacity to generate the diversity of the P44-homologous proteins. Because for A. marginale, the msp2 genes corresponding to the transcripts were not identified, the expression mechanism is unknown. Among rickettsia closely related to HGE agent, persistent infection and recurrence after recovery from the clinical disease are known forEhrlichia canis, Ehrlichia platys, E. phagocytophila, Cowdria ruminantium, and A. marginale (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar, 23Rikihisa Y. Clin. Microbiol. Rev. 1991; 4: 286-308Crossref PubMed Scopus (356) Google Scholar). The HGE agent was detected in the serum of one untreated patient by PCR at 30 day after onset of illness (24Dumler J.S. Bakken J.S. J. Infect. Dis. 1996; 173: 1027-1030Crossref PubMed Scopus (56) Google Scholar), suggesting that the HGE agent may also cause persistent infection in humans. In addition, persistence of the HGE agent in reservoir rodent host would be an important adaptation that allows greater access of uninfected tick populations to an infectious blood meal. French et al. (20French D.M. McElwain T.F. McGuire T.C. Palmer G.H. Infect. Immun. 1998; 66: 1200-1207Crossref PubMed Google Scholar) proposed that the expression of distinct sets of msp2 genes at each rickettsemia peak in A. marginale infection of cattle may allow immunoevation of anaplasma to persist in immunocompetent hosts. Multiple expression of p44 multigenes may be also related to immunoavoidance in human and rodent hosts and potential persistence. The expression mechanisms of the several multigene families in the human pathogens Neisseria gonorrhoeae (pil (25Haas R. Meyer T.F. Cell. 1986; 44: 107-115Abstract Full Text PDF PubMed Scopus (234) Google Scholar) and opa (26Stern A. Brown M. Nickel P. Meyer T.F. Cell. 1986; 47: 61-71Abstract Full Text PDF PubMed Scopus (303) Google Scholar)), Borrelia hermsii (vmp(27Barbour A.G. Annu. Rev. Microbiol. 1990; 44: 155-171Crossref PubMed Scopus (133) Google Scholar)), Borrelia burgdorferi (vls(28Zhang J.R. Hardham J.M. Barbour A.G. Norris S.J. Cell. 1997; 89: 275-285Abstract Full Text Full Text PDF PubMed Scopus (516) Google Scholar)), African trypanosomes (vsg (29Vanhamme L. Pays E. Microbiol. Rew. 1995; 59: 223-240Crossref PubMed Google Scholar)), and Plasmodium falciparum (var (30Scherf A. Hernandez-Rivas R. Buffet P. Bottius E. Benatar C. Pouvelle B. Gysin J. Lanzer M. EMBO J. 1998; 17: 5418-5426Crossref PubMed Scopus (451) Google Scholar)), have been well studied. These multigene families are involved in pathogenesis, e.g.antigenic variation (or phase variation) and cytoadhesin. The switching of gene expression can be divided into two major mechanisms: one depends on DNA rearrangement, and another occurs at transcriptional level. In pil, vmp, vls, andvsg, switching of expression between members of the corresponding gene families occurs through programmed DNA rearrangements (gene conversion), moving a transcriptionally silent gene into an active expression site. In opa, expression is regulated by a reversible frameshift mutation of DNA, i.e. a slipped-strand mispairing of the number of pentanucleotide coding repeat units in the single peptides (26Stern A. Brown M. Nickel P. Meyer T.F. Cell. 1986; 47: 61-71Abstract Full Text PDF PubMed Scopus (303) Google Scholar), whereas in the vargene of P. falciparum, each parasite expresses only a single and distinct var gene product. Each var gene is an independent transcription unit in which promoter activity determines the expression status. p44 multigene expression appears to be different from those of pil, vmp,vls, and vsg in that multiple expressedp44 genes are located in several large DNA fragments in the HGE agent genome, i.e. the transcription of the genes apparently does not occur from a unique expression site. The expressionp44 multigene, therefore, may not involve DNA rearrangement. Expressions of p44 multigenes, as well as msp2genes (21Palmer G.H. Eid G. Barbet A.F. McGuire T.C. McElwain T.F. Infect. Immun. 1994; 62: 3808-3816Crossref PubMed Google Scholar), are also different from that of var genes, because a single organism appear to express more than two gene products. In ehrlichiae, recently, additional multigene families encoding major outer membrane proteins have been discovered. We identified theomp-1 gene family of Ehrlichia chaffeensis (31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar) and the p30 gene family ofE. canis (19Ohashi N. Unver A. Zhi N. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 2671-2680Crossref PubMed Google Scholar). More than a dozen copies of theomp-1 and p30 gene families are tandemly arranged in the genome, in contrast to p44 multigenes andmsp2 genes. Furthermore the protein structures encoded by the omp-1 and p30 gene families is distinct from those of p44 and msp2, consisting of three short, hypervariable segments interposed with relatively conserved segments (19Ohashi N. Unver A. Zhi N. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 2671-2680Crossref PubMed Google Scholar, 31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar). This suggests that the expression mechanism ofomp-1 and p30 gene families is probably different from those of p44 and msp2. Immunization with a recombinant P28 protein (one of the omp-1 multigene products) of E. chaffeensis and native MSP2 of A. marginale has been demonstrated to induce almost complete and partial protections against the infection in mice and cattle, respectively (31Ohashi N. Zhi N. Zhang Y. Rikihisa Y. Infect. Immun. 1998; 66: 132-139Crossref PubMed Google Scholar, 32Palmer G.H. Oberle S.M. Barbet A.F. Goff W.L. Davis W.C. McGuire T.C. Infect. Immun. 1988; 56: 1526-1531Crossref PubMed Google Scholar). We previously observed that passive immunization with monoclonal antibodies specific to P44-homologous proteins of the HGE agent induced partial protection against challenge with the HGE agent in mice (14Kim H.Y. Rikihisa Y. J. Clin. Microbiol. 1998; 36: 3278-3284Crossref PubMed Google Scholar). Active immunization with the recombinant P44 protein also partially protected mice from HGE infection. 2N. Zhi, N. Ohashi, and Y. Rikihisa, unpublished data. This indicates that the p44 multigene family encodes a potential protective antigen. However, because only a fraction of genes is differentially expressed as shown in this study, it seems to be essential to determine which genes are expressed in the host for identification of the most protective antigen. By a GenBankTM data base homology search, the P44-homologous proteins of the HGE agent were found to possess a similarity (∼64%) with the N-terminal region of Hsf protein (surface fibrils) involved in binding of Hemophilus influenzae type b to human epithelial cells (33St. Geme III, J.W. Cutter D. Barenkamp S.J. J. Bacteriol. 1996; 178: 6281-6287Crossref PubMed Google Scholar). The similar sequence identified was located in the center of all P44 homologs, including the hypervariable domain (span of approximately 200 amino acid residues). This finding suggests that P44s may have a similar function, such as cytoadhesion to human granulocytes. The basic information obtained in this study would facilitate the understanding of the role of the p44 multigene family in causing disease in humans, in the persistence of HGE agent in white-footed mice, and in transmission of this agent from tick to human. Further analysis of expression mechanism of these genes and the genes encoding more protective antigens would assist in designing an effective vaccine candidate against the human ehrlichiosis." @default.
W2080454590 created "2016-06-24" @default.
W2080454590 creator A5003482762 @default.
W2080454590 creator A5040274093 @default.
W2080454590 creator A5076111953 @default.
W2080454590 date "1999-06-01" @default.
W2080454590 modified "2023-10-12" @default.
W2080454590 title "Multiple p44 Genes Encoding Major Outer Membrane Proteins Are Expressed in the Human Granulocytic Ehrlichiosis Agent" @default.
W2080454590 cites W1545787051 @default.
W2080454590 cites W1776877792 @default.
W2080454590 cites W1838246889 @default.
W2080454590 cites W1956842074 @default.
W2080454590 cites W1981349143 @default.
W2080454590 cites W1993249060 @default.
W2080454590 cites W1999044786 @default.
W2080454590 cites W2017184491 @default.
W2080454590 cites W2044272539 @default.
W2080454590 cites W2044595671 @default.
W2080454590 cites W2061265918 @default.
W2080454590 cites W2062677544 @default.
W2080454590 cites W2083417553 @default.
W2080454590 cites W2099184115 @default.
W2080454590 cites W2102106844 @default.
W2080454590 cites W2104648036 @default.
W2080454590 cites W2110368176 @default.
W2080454590 cites W2116759905 @default.
W2080454590 cites W2122064356 @default.
W2080454590 cites W2124645143 @default.
W2080454590 cites W2132538774 @default.
W2080454590 cites W2133427302 @default.
W2080454590 cites W2136733880 @default.
W2080454590 cites W2141752248 @default.
W2080454590 cites W2153897827 @default.
W2080454590 cites W2155277883 @default.
W2080454590 cites W2157471263 @default.
W2080454590 cites W2158591166 @default.
W2080454590 cites W2160129094 @default.
W2080454590 cites W2160976992 @default.
W2080454590 cites W2165379126 @default.
W2080454590 cites W2180855780 @default.
W2080454590 doi "https://doi.org/10.1074/jbc.274.25.17828" @default.
W2080454590 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/10364227" @default.
W2080454590 hasPublicationYear "1999" @default.
W2080454590 type Work @default.
W2080454590 sameAs 2080454590 @default.
W2080454590 citedByCount "104" @default.
W2080454590 countsByYear W20804545902012 @default.
W2080454590 countsByYear W20804545902013 @default.
W2080454590 countsByYear W20804545902014 @default.
W2080454590 countsByYear W20804545902015 @default.
W2080454590 countsByYear W20804545902016 @default.
W2080454590 countsByYear W20804545902019 @default.
W2080454590 countsByYear W20804545902020 @default.
W2080454590 crossrefType "journal-article" @default.
W2080454590 hasAuthorship W2080454590A5003482762 @default.
W2080454590 hasAuthorship W2080454590A5040274093 @default.
W2080454590 hasAuthorship W2080454590A5076111953 @default.
W2080454590 hasBestOaLocation W20804545901 @default.
W2080454590 hasConcept C104317684 @default.
W2080454590 hasConcept C125411270 @default.
W2080454590 hasConcept C144647389 @default.
W2080454590 hasConcept C146587185 @default.
W2080454590 hasConcept C159047783 @default.
W2080454590 hasConcept C169760540 @default.
W2080454590 hasConcept C2778101375 @default.
W2080454590 hasConcept C2779620486 @default.
W2080454590 hasConcept C41625074 @default.
W2080454590 hasConcept C54355233 @default.
W2080454590 hasConcept C547475151 @default.
W2080454590 hasConcept C86803240 @default.
W2080454590 hasConceptScore W2080454590C104317684 @default.
W2080454590 hasConceptScore W2080454590C125411270 @default.
W2080454590 hasConceptScore W2080454590C144647389 @default.
W2080454590 hasConceptScore W2080454590C146587185 @default.
W2080454590 hasConceptScore W2080454590C159047783 @default.
W2080454590 hasConceptScore W2080454590C169760540 @default.
W2080454590 hasConceptScore W2080454590C2778101375 @default.
W2080454590 hasConceptScore W2080454590C2779620486 @default.
W2080454590 hasConceptScore W2080454590C41625074 @default.
W2080454590 hasConceptScore W2080454590C54355233 @default.
W2080454590 hasConceptScore W2080454590C547475151 @default.
W2080454590 hasConceptScore W2080454590C86803240 @default.
W2080454590 hasIssue "25" @default.
W2080454590 hasLocation W20804545901 @default.
W2080454590 hasOpenAccess W2080454590 @default.
W2080454590 hasPrimaryLocation W20804545901 @default.
W2080454590 hasRelatedWork W1473677910 @default.
W2080454590 hasRelatedWork W1693554971 @default.
W2080454590 hasRelatedWork W1931933672 @default.
W2080454590 hasRelatedWork W2146899109 @default.
W2080454590 hasRelatedWork W2358088849 @default.
W2080454590 hasRelatedWork W2768043139 @default.
W2080454590 hasRelatedWork W2922253088 @default.
W2080454590 hasRelatedWork W4214754676 @default.
W2080454590 hasRelatedWork W4308345274 @default.
W2080454590 hasRelatedWork W95411467 @default.
W2080454590 hasVolume "274" @default.
W2080454590 isParatext "false" @default.