Immunization with a Peptide Corresponding to Chlamydial Heat
Shock Protein 60 Increases the Humoral Immune Response in C3H Mice
to a Peptide Representing Variable Domain 4 of the Major Outer
Membrane Protein of Chlamydia trachomatis |
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| Authors: | Vladimir L. Motin,Luis M. de la Maza,Ellena&# M. Peterson |
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| Affiliation: | Department of Pathology, University of California—Irvine, Irvine, California 92697-4800 |
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| Abstract: | C3H (H-2k) mice are susceptible to a vaginal challenge with human strains of Chlamydia trachomatis and thus are a useful strain for testing potential Chlamydia vaccine candidates. However, C3H mice are fairly poor responders in terms of the level of antibody resulting from immunization with potential protective peptides representing variable domains (VDs) of the major outer membrane protein (MOMP). C57BL/6 (H-2b) mice, on the other hand, are moderately resistant to a vaginal challenge but are good responders to the chlamydial MOMP VDs. Peptides representing universal T-cell helper epitopes were employed to determine whether the antibody response to a peptide representing VD4 of the MOMP, which has been shown to contain neutralizing epitopes, could be enhanced in C3H and C57 mice. Universal T-cell helper peptides from tetanus toxin, the pre-S2 region of hepatitis B virus, and the mouse heat shock protein 60, as well as the corresponding segment of the Chlamydia heat shock protein 60 (hspct), were coadministered with the VD4 peptide. Peptides were coencapsulated in liposomes containing the adjuvant monophosphoryl lipid A and administered by using a combination of mucosal and intramuscular injection. The only T-cell helper peptide that improved the immune response as judged by antibody level, in vitro neutralization assays, and T-cell proliferation was hspct. The response in the C57BL/6 strain was not significantly enhanced with hspct over levels achieved with VD4 alone; however, in C3H mice the levels of serum antibody to C. trachomatis increased to that seen in C57 mice. However, the molecular specificity and immunoglobulin subclass distribution differed from those of the C57 response, and the neutralizing titers and T-cell proliferation responses were lower. In both strains of mice, titers of vaginal antibody to C. trachomatis were low. In summary, of the T-helper peptides used, only hspct significantly enhanced the immune response of C3H mice to the VD4 peptide, but it had only a modest effect on the immune response of C57 mice.Chlamydia trachomatis, being a leading cause of sexually transmitted diseases, has been the focus of efforts to develop a protective vaccine (4, 31, 37). Central to this effort has been the identification of host factors that may protect against infections caused by this pathogen as well as the definition of chlamydial components that confer pathogenic potential to this organism. To date the major outer membrane protein (MOMP) has been the most widely investigated vaccine candidate of the chlamydial proteins (17). Within the MOMP there are four variable domains (VDs), which differ among the serovars and are regions in which there are neutralizable epitopes (3, 17, 24, 30, 33, 40). In vitro experiments using monoclonal antibodies directed at the VDs have shown that attenuation of infection is narrow in terms of the number of serovars that are neutralized when any one epitope is targeted (24, 30, 40). Since neutralization of all serovars is not achieved by using antibodies directed at any one epitope, a subunit vaccine that incorporates an array of protective epitopes has been proposed (4, 31, 37). For the few attempts to utilize recombinant MOMP or peptides representing VD neutralizing epitopes to immunize mice, only modest attenuation of the infection has been reported (36, 38). There may be several reasons for this, including the requirement for T-cell help to boost and direct the immune response to critical regions within these peptides, the failure to elicit an adequate mucosal immune response, the requirement for a conformational epitope not provided by short synthetic peptides, and inherent differences in inbred mouse strains used in the vaccine trials.It has been shown that mouse strains of different H-2 haplotypes vary dramatically in their responses to a genital challenge with C. trachomatis (8, 9). As an example, C57BL/6 (H-2b) mice are fairly resistant to a vaginal challenge with a human serovar, with vaginal cultures, depending on the challenge dose, being positive for only 1 to 2 weeks following inoculation. In contrast, C3H (H-2k) mice are infected with lower numbers of organisms, and C. trachomatis can be cultured from the vagina for up to 4 to 6 weeks following challenge (9, 26). Therefore, because of the longer duration of infection, C3H mice are an attractive strain in which to test peptide vaccine candidates. However, it has been shown that a peptide representing VD4 of the MOMP was immunogenic in C57BL/6 (H-2b) mice but was significantly less effective in eliciting a humoral response in C3H/HeJ and B10.BR/SgSnJ mice, both of which are of the H-2k haplotype (29, 34).The purpose of this study was to determine whether universal T-cell helper peptides could enhance the immune response to a VD4 peptide in the otherwise nonresponsive C3H mouse or modify the response in C57 mice. Since the long-term goal is to protect against a genital mucosal challenge, the immunization strategy used was to coadminister, through a combination of systemic and mucosal routes, T-cell helper peptides and a VD4 peptide coentrapped in liposomes. Eliciting an immune response in the permissive but low- or nonresponsive C3H strain is essential for the future development and testing of subunit vaccines in this animal model. |
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