Chlamydial protease-like activity factor mediated protection against C. trachomatis in guinea pigs.

We have comprehensively demonstrated using the mouse model that intranasal immunization with recombinant chlamydial protease-like activity factor (rCPAF) leads to a significant reduction in bacterial burden, genital tract pathology and preserves fertility following intravaginal genital chlamydial challenge. In the present report, we evaluated the protective efficacy of rCPAF immunization in guinea pigs, a second animal model for genital chlamydial infection. Using a vaccination strategy similar to the mouse model, we intranasally immunized female guinea pigs with rCPAF plus CpG deoxynucleotides (CpG; as an adjuvant), and challenged intravaginally with C. trachomatis serovar D (CT-D). Immunization with rCPAF/CpG significantly reduced vaginal CT-D shedding and induced resolution of infection by day 24, compared with day 33 in CpG alone treated and challenged animals. Immunization induced robust anti-rCPAF serum IgG 2 weeks following the last immunization, and was sustained at a high-level 4 weeks post challenge. Upregulation of antigen-specific IFN-γ gene expression was observed in rCPAF/CpG-vaccinated splenocytes. Importantly, a significant reduction in inflammation in the genital tissue in rCPAF/CpG-immunized guinea pigs compared with CpG-immunized animals was observed. Taken together, this study provides evidence of the protective efficacy of rCPAF as a vaccine candidate in a second animal model of genital chlamydial infection.

IgA modulates respiratory dysfunction as a sequela to pulmonary chlamydial infection as neonates.

Neonatal Chlamydia lung infections are associated with serious sequelae such as asthma and airway hyper-reactivity in children and adults. Our previous studies demonstrated the importance of Th-1 type cytokines, IL-12 and IFN-γ in protection against neonatal pulmonary chlamydial challenge; however, the role of the humoral arm of defense has not been elucidated. We hypothesized that B-cells and IgA, the major mucosal antibody, play a protective role in newborns against development of later life respiratory sequelae to Chlamydia infection. Our studies using neonatal mice revealed that all WT and IgA-deficient (IgA(-/-)) animals survived a sublethal pulmonary Chlamydia muridarum challenge at one day after birth with similar reduction in bacterial burdens over time. In contrast, all B-cell-deficient (µMT) mice succumbed to infection at the same challenge dose correlating to failure to control bacterial burdens in the lungs. Although IgA may not be important for bacterial clearance, we observed IgA(-/-) mice displayed greater respiratory dysfunction 5 weeks post challenge. Specifically, comparative respiratory functional analyses revealed a significant shift upward in P-V loops, and higher dynamic resistance in IgA(-/-) animals. This study provides insight(s) into the protective role of IgA in neonates against pulmonary chlamydial infection induced respiratory pathological sequelae observed later in life.

A T cell epitope-based vaccine protects against chlamydial infection in HLA-DR4 transgenic mice.

Vaccination with recombinant chlamydial protease-like activity factor (rCPAF) has been shown to provide robust protection against genital Chlamydia infection. Adoptive transfer of IFN-γ competent CPAF-specific CD4⁺ T cells was sufficient to induce early resolution of chlamydial infection and reduction of subsequent pathology in recipient IFN-γ-deficient mice indicating the importance of IFN-γ secreting CD4⁺ T cells in host defense against Chlamydia. In this study, we identify CD4⁺ T cell reactive CPAF epitopes and characterize the activation of epitope-specific CD4⁺ T cells following antigen immunization or Chlamydia challenge. Using the HLA-DR4 (HLA-DRB1*0401) transgenic mouse for screening overlapping peptides that induced T cell IFN-γ production, we identified at least 5 CPAF T cell epitopes presented by the HLA-DR4 complex. Immunization of HLA-DR4 transgenic mice with a rCPAFep fusion protein containing these 5 epitopes induced a robust cell-mediated immune response and significantly accelerated the resolution of genital and pulmonary Chlamydia infection. rCPAFep vaccination induced CPAF-specific CD4⁺ T cells in the spleen were detected using HLA-DR4/CPAF-epitope tetramers. Additionally, CPAF-specific CD4⁺ clones could be detected in the mouse spleen following Chlamydia muridarum and a human Chlamydia trachomatis strain challenge using these novel tetramers. These results provide the first direct evidence that a novel CPAF epitope vaccine can provide protection and that HLA-DR4/CPAF-epitope tetramers can detect CPAF epitope-specific CD4⁺ T cells in HLA-DR4 mice following C. muridarum or C. trachomatis infection. Such tetramers could be a useful tool for monitoring CD4⁺ T cells in immunity to Chlamydia infection and in developing epitope-based human vaccines using the murine model.