Human antibody responses to a Chlamydia-secreted protease factor

Characterization of fifty putative inclusion membrane proteins encoded in the Chlamydia trachomatis genome

Although the Chlamydia trachomatis genome is predicted to encode 50 inclusion membrane proteins, only 18 have been experimentally localized in the inclusion membrane of C. trachomatis-infected cells. Using fusion proteins and anti-fusion protein antibodies, we have systematically evaluated all 50 putative inclusion membrane proteins for their localization in the infected cells, distribution patterns, and effects on subsequent chlamydial infection when expressed ectopically, as well as their immunogenicity during chlamydial infection in humans. Twenty-two of the 50 proteins were localized in the inclusion membrane, and 7 were detected inside the inclusions, while the location of the remaining 21 was not defined. Four (CT225, CT228, CT358, and CT440) of the 22 inclusion membrane-localized proteins were visualized in the inclusion membrane of Chlamydia-infected cells for the first time in the current study. The seven intra-inclusion-localized proteins were confirmed to be chlamydial organism proteins in a Western blot assay. Further characterization of the 50 proteins revealed that neither colocalization with host cell endoplasmic reticulum nor inhibition of subsequent chlamydial infection by ectopically expressed proteins correlated with the inclusion membrane localization. Interestingly, antibodies from women with C. trachomatis urogenital infection preferentially recognized proteins localized in the inclusion membrane, and the immunodominant regions were further mapped to the region predicted to be on the cytoplasmic side of the inclusion membrane. These observations suggest that most of the inclusion membrane-localized proteins are both expressed and immunogenic during C. trachomatis infection in humans and that the cytoplasmic exposure may enhance the immunogenicity.

Intracellular interleukin-1alpha mediates interleukin-8 production induced by Chlamydia trachomatis infection via a mechanism independent of type I interleukin-1 receptor

Chlamydia trachomatis infection induces a wide array of inflammatory cytokines and chemokines, which may contribute to chlamydia-induced pathologies. However, the precise mechanisms by which Chlamydia induces cytokines remain unclear. Here we demonstrate that the proinflammatory cytokine interleukin-1alpha (IL-1alpha) plays an essential role in chlamydial induction of the chemokine IL-8. Cells deficient in IL-1alpha expression or IL-1alpha-competent cells treated with IL-1alpha-specific small interfering RNA failed to produce IL-8 in response to chlamydial infection. However, neutralization of extracellular IL-1alpha or blockade of or deficiency in type I IL-1 receptor (IL-1RI) signaling did not affect chlamydial induction of IL-8 in cells capable of producing IL-1alpha. These results suggest that IL-1alpha can mediate the chlamydial induction of IL-8 via an intracellular mechanism independent of IL-1RI, especially during the early stage of the infection cycle. This conclusion is further supported by the observations that expression of a transgene-encoded full-length IL-1alpha fusion protein in the nuclei enhanced IL-8 production and that nuclear localization of chlamydia-induced precursor IL-1alpha correlated with chlamydial induction of IL-8. Thus, we have identified a novel mechanism for chlamydial induction of the chemokine IL-8.

Caspase-1 contributes to Chlamydia trachomatis-induced upper urogenital tract inflammatory pathologies without affecting the course of infection

Chlamydia trachomatis infection induces inflammatory pathologies in the upper genital tract, potentially leading to ectopic pregnancy and infertility in the affected women. Caspase-1 is required for processing and release of the inflammatory cytokines interleukin-1beta (IL-1beta), IL-18, and possibly IL-33. In the present study, we evaluated the role of caspase-1 in chlamydial infection and pathogenesis. Although chlamydial infection induced caspase-1 activation and processing of IL-1beta, mice competent and mice deficient in caspase-1 experienced similar courses of chlamydial infection in their urogenital tracts, suggesting that Chlamydia-activated caspase-1 did not play a significant role in resolution of chlamydial infection. However, when genital tract tissue pathologies were examined, the caspase-1-deficient mice displayed much reduced inflammatory damage. The reduction in inflammation was most obvious in the fallopian tube tissue. These observations demonstrated that although caspase-1 is not required for controlling chlamydial infection, caspase-1-mediated responses can exacerbate the Chlamydia-induced inflammatory pathologies in the upper genital tract, suggesting that the host caspase-1 may be targeted for selectively attenuating chlamydial pathogenicity without affecting the host defense against chlamydial infection.

Induction of cross-serovar protection against genital chlamydial infection by a targeted multisubunit vaccination approach

An important consideration for antichlamydial vaccine development is the induction of cross-serovar protection, since multiple serovars (D to L) of Chlamydia trachomatis cause genital infections. We have shown previously that vaccination with C. trachomatis-derived recombinant chlamydial protease-like activity factor (rCPAF) induced significant earlier resolution of Chlamydia muridarum infection and reduced oviduct pathology. However, the vaccinated mice continued to shed chlamydiae for up to 2 weeks after challenge. In this study, C. trachomatis serovar D recombinant proteins, such as recombinant major outer membrane protein (rMOMP), recombinant inclusion membrane protein A (rIncA), and rCPAF were administered intranasally, individually or in combinations, with murine interleukin-12 (IL-12) as an adjuvant, and cross-species immunity against intravaginal C. muridarum infection was examined. Immunization with rCPAF plus IL-12 (rCPAF+IL-12), compared to immunization with rIncA+IL-12 or rMOMP+IL-12, induced the greatest antigen-specific gamma interferon production from purified CD4(+) T cells and concurrently enhanced serum antibody production. All (100%) the animals vaccinated with rCPAF+IL-12 alone or in any combination completely resolved the infection by day 18 after challenge compared to animals vaccinated with rIncA+IL-12 (50%), rMOMP+IL-12 (33%), or phosphate-buffered saline (mock vaccinated; 0%). Moreover, oviduct pathology in mice vaccinated by any regimen that included rCPAF, but not rMOMP+IL-12 or rIncA+IL-12 alone, was markedly reduced compared to mock-immunized animals. The addition of rMOMP and/or rIncA did not significantly enhance the rCPAF+IL-12-induced effect on bacterial clearance or oviduct pathology. These results suggest a greater conservation of protective linear antigenic epitopes within CPAF than MOMP or IncA across the examined serovars and the need to identify other highly conserved antigens for use with rCPAF in a multisubunit recombinant vaccine.

Live-attenuated influenza viruses as delivery vectors for Chlamydia vaccines

Effective delivery systems are needed to design efficacious vaccines against the obligate intracellular bacterial pathogen, Chlamydia trachomatis. Potentially effective delivery vehicles should promote the induction of adequate levels of mucosal T-cell and antibody responses that mediate long-term protective immunity. Antigen targeting to the nasal-associated lymphoid tissue (NALT) is effective for inducing high levels of specific immune effectors in the genital mucosa, and therefore suitable for vaccine delivery against genital chlamydial infection. We tested the hypothesis that live attenuated influenza A viruses are effective viral vectors for intranasal delivery of subunit vaccines against genital chlamydial infection. Recombinant influenza A/PR8/34 (H1N1) viruses were generated by insertion of immunodominant T-cell epitopes from chlamydial major outer membrane protein into the stalk region of the neuraminidase gene. Intranasal immunization of mice with viral recombinants resulted in a strong T helper 1 (Th1) response against intact chlamydial elementary bodies. Also, immunized mice enjoyed a significant state of protective immunity (P > 0.002) by shedding less chlamydiae and rapidly clearing the infection. Furthermore, a high frequency of Chlamydia-specific Th1 was measured in the genital mucosal and systemic draining lymphoid tissues within 24 hr after challenge of vaccinated mice. Moreover, multiple epitope delivery provided a vaccine advantage over single recombinants. Besides, long-term protective immunity correlated with the preservation of a robustly high frequency of specific Th1 cells and elevated immunoglobulin G2a in genital secretions. Because live attenuated influenza virus vaccines are safe and acceptable for human use, they may provide a new and reliable approach to deliver efficacious vaccines against sexually transmitted diseases.

Intranasal immunization with chlamydial protease-like activity factor and CpG deoxynucleotides enhances protective immunity against genital Chlamydia muridarum infection

We have reported recently that intranasal (i.n.) vaccination with chlamydial protease-like activity factor (CPAF) and interleukin-12 (IL-12) enhances protective immunity against genital chlamydial challenge. In this study, we show that i.n. or intraperitoneal (i.p.) vaccination with CPAF plus CpG deoxynucleotides (CpG), an alternative T helper 1 (Th1) adjuvant, induced robust CPAF-specific IFN-gamma responses and elevated levels of serum antibody and vaginal IgA production. CPAF+CpG vaccinated animals displayed accelerated genital chlamydial clearance, and minimal hydrosalpinx and inflammatory cellular infiltration compared to mock-immunized (PBS) challenged animals. Together, CpG dexoynucleotides are an efficacious alternative Th1 adjuvant with CPAF to induce protective anti-chlamydial immunity.

Intranasal vaccination with a secreted chlamydial protein enhances resolution of genital Chlamydia muridarum infection, protects against oviduct pathology, and is highly dependent upon endogenous gamma interferon production

There is currently no licensed vaccine against Chlamydia trachomatis, the leading cause of sexually transmitted bacterial disease worldwide. Conventional vaccination attempts using surface-exposed chlamydial antigens have achieved only partial success. We have employed a novel vaccination strategy using a secreted protein, chlamydial protease-like activity factor (CPAF), which has been shown to degrade host major histocompatibility complex transcription factors and keratin-8 and therefore may allow immune evasion and establishment of a productive infection. Intranasal immunization using recombinant CPAF (rCPAF) plus interleukin-12 (IL-12) (rCPAF+IL-12 immunization) was used to assess the protective immunity against genital Chlamydia muridarum infection in BALB/c mice. rCPAF+IL-12 immunization induced robust gamma interferon (IFN-gamma) production and minimal IL-4 production by splenocytes upon in vitro recall with rCPAF. The total and immunoglobulin G2a (IgG2a) anti-rCPAF antibody levels in serum were significantly elevated after rCPAF+IL-12 vaccination, as were the total antibody, IgG2a, and IgA levels in bronchoalveolar lavage and vaginal fluids when the animals were compared to animals that received rCPAF alone. rCPAF+IL-12-vaccinated mice displayed significantly reduced bacterial shedding upon chlamydial challenge and accelerated resolution of infection compared to mock-immunized (phosphate-buffered saline) animals. Moreover, rCPAF+IL-12-immunized animals exhibited protection against pathological consequences of chlamydial infection, including the development of hydrosalpinx and oviduct dilatation. This vaccination regimen also reduced the development of fibrosis and the influx of neutrophils into the upper genital tract when the animals were compared to mock-immunized (phosphate-buffered saline) animals after bacterial challenge. rCPAF+IL-12-mediated resolution of the bacterial infection and protection against Chlamydia-induced inflammatory disease were highly dependent on endogenous IFN-gamma production. Together, these results demonstrate that secreted chlamydial antigens may be novel vaccine candidates to induce protective immunity.

The protective efficacy of chlamydial protease-like activity factor vaccination is dependent upon CD4+ T cells

We have previously determined the protective efficacy of intranasal vaccination with chlamydial protease-like activity factor (CPAF) against genital chlamydial infection. Since T-helper 1 (Th1) responses are important for anti-chlamydial immunity, we examined the contribution of CD4(+) T cells in CPAF mediated immunity against intravaginal (i.vag.) Chlamydia muridarum infection in C57BL/6 mice. CPAF+IL-12 vaccination induced antigen-specific CD4(+) T cells that secreted elevated levels of IFN-gamma, and generated strong humoral responses. The protective effects of CPAF vaccination against genital chlamydial challenge were abrogated by anti-CD4 neutralizing antibody treatment. Moreover, anti-chlamydial immunity could be adoptively transferred to naïve recipients using CPAF-specific CD4(+) T cells. Therefore, CPAF mediated anti-chlamydial immunity is highly dependent upon antigen-specific CD4(+) T cells.

Chlamydial protease-like activity factor induces protective immunity against genital chlamydial infection in transgenic mice that express the human HLA-DR4 allele

There is no licensed vaccine available against Chlamydia trachomatis, the leading cause of bacterial sexually transmitted disease. We have found that intranasal immunization with recombinant chlamydial protease-like activity factor (CPAF) induces CD4(+) T-cell- and gamma interferon (IFN-gamma)-dependent protective immunity against murine genital chlamydial infection, thus making CPAF a viable vaccine candidate for further characterization. HLA-DR4 is the predominant allele involved in chlamydial antigen presentation to CD4(+) T cells in humans. We used engineered mice that lack endogenous major histocompatibility complex class II (MHC-II) alleles but express a human HLA allele (HLA-DR4 transgenic [tg] mice) to examine primary immune and CPAF-mediated responses against genital Chlamydia muridarum challenge. Upon primary bacterial exposure, HLA-DR4 tg mice developed Chlamydia-specific IFN-gamma and antibody production and resolved the infection within 30 days, similar to challenged conventional C57BL/6 animals. Moreover, C. muridarum-challenged HLA-DR4 tg mice exhibited CPAF-specific antibody and IFN-gamma production. Upon CPAF-plus-interleukin-12 (IL-12) vaccination, HLA-DR4 tg animals exhibited robust CPAF-specific IFN-gamma production and elevated titers of anti-CPAF total antibody and immunoglobulin G2a (IgG2a) and lower titers of IgG2b and IgG1 antibodies. HLA-DR4 tg and C57BL/6 mice vaccinated with CPAF plus IL-12 resolved the primary genital chlamydial infection significantly earlier than mock-immunized animals, whereas similarly vaccinated MHC class II-deficient mice displayed minimal antigen-specific immune responses and failed to resolve the infection even at 30 days postchallenge. Together, these results demonstrate the importance of human HLA-DR4 molecules in the recognition and presentation of CPAF epitopes, leading to the generation of protective antichlamydial immunity and making these mice a valuable model for mapping HLA-DR4-restricted chlamydial epitopes.

The hypothetical protein CT813 is localized in the Chlamydia trachomatis inclusion membrane and is immunogenic in women urogenitally infected with C. trachomatis

Using antibodies raised with chlamydial fusion proteins, we have localized a protein encoded by hypothetical open reading frame CT813 in the inclusion membrane of Chlamydia trachomatis. The detection of the C. trachomatis inclusion membrane by an anti-CT813 antibody was blocked by the CT813 protein but not unrelated fusion proteins. The CT813 protein was detected as early as 12 h after chlamydial infection and was present in the inclusion membrane during the entire growth cycle. All tested serovars from C. trachomatis but not other chlamydial species expressed the CT813 protein. Exogenously expressed CT813 protein in HeLa cells displayed a cytoskeleton-like structure similar to but not overlapping with host cell intermediate filaments, suggesting that the CT813 protein is able to either polymerize or associate with host cell cytoskeletal structures. Finally, women with C. trachomatis urogenital infection developed high titers of antibodies to the CT813 protein, demonstrating that the CT813 protein is not only expressed but also immunogenic during chlamydial infection in humans. In all, the CT813 protein is an inclusion membrane protein unique to C. trachomatis species and has the potential to interact with host cells and induce host immune responses during natural infection. Thus, the CT813 protein may represent an important candidate for understanding C. trachomatis pathogenesis and developing intervention and prevention strategies for controlling C. trachomatis infection.

Profiling of human antibody responses to Chlamydia trachomatis urogenital tract infection using microplates arrayed with 156 chlamydial fusion proteins

The available chlamydial genome sequences have made it possible to comprehensively analyze host responses to all chlamydial proteins, which is essential for further understanding of chlamydial pathogenesis and development of effective chlamydial vaccines. Microplates arrayed with 156 Chlamydia trachomatis fusion proteins were used to evaluate antibody responses in women urogenitally infected with C. trachomatis. Based on both the antibody recognition frequency and titer, seven chlamydial antigens encoded by open reading frames (ORFs) CT089, CT147, CT226, CT681, CT694, CT795, and CT858, respectively, were identified as relatively immunodominant; six of these are encoded by hypothetical ORFs. Antibody binding to these chlamydial fusion proteins was blocked by C. trachomatis-infected but not by normal HeLa cell lysates or irrelevant bacterial lysates. These results have revealed novel immune-reactive chlamydial antigens, not only indicating that the hypothetical ORF-encoded proteins are expressed during chlamydial infection in humans but also providing the proof of principle that the fusion protein-based approach can be used to profile human immune responses to chlamydial infection at the whole-genome scale.

Delivery of Chlamydia vaccines

The plethora of ocular, genital and respiratory diseases of Chlamydia, including nongonococcal urethritis, cervicitis pelvic inflammatory disease, ectopic pregnancy, tubal factor infertility, conjunctivitis, blinding trachoma and interstitial pneumonia, and chronic diseases that may include atherosclerosis, multiple sclerosis, adult onset asthma and Alzheimer's disease, still pose a considerable public health challenge to many nations. Although antibiotics are effective against Chlamydia when effectively diagnosed, asymptomatic infections are rampart, making clinical presentation of complications often the first evidence of an infection. Consequently, the current medical opinion is that an effective prophylactic vaccine would constitute the best approach to protect the human population from the most severe consequences of these infections. Clinical and experimental studies have demonstration that Chlamydia immunity in animals and humans is mediated by T cells and a complementary antibody response, and the completion of the genome sequencing of several isolates of Chlamydia is broadening our knowledge of the immunogenic antigens with potential vaccine value. Thus, major advances have been made in defining the essential elements of a potentially effective subunit vaccine design and parameters for evaluation. However, the challenge to develop effective delivery systems and human compatible adjuvants that would boost the immune response to achieve long-lasting protective immunity remains an elusive objective in chlamydial vaccine research. In response to evolving molecular and cellular technologies and novel vaccinology approaches, considerable progress is being made in the construction of novel delivery systems, such as DNA and plasmid expression systems, viral vectors, living and nonliving bacterial delivery systems, the use of chemical adjuvants, lipoprotein constructs and the codelivery of vaccines and specific immuno-modulatory biological agonists targeting receptors for chemokines, Toll-like receptors, and costimulatory molecules. The application of these novel delivery strategies to Chlamydia vaccine design could culminate in timely achievement of an efficacious vaccine.

Inhibition of proteolytic activity of a chlamydial proteasome/protease-like activity factor by antibodies from humans infected with Chlamydia trachomatis

We have previously shown that individuals infected with Chlamydia trachomatis can develop a robust antibody response to a chlamydia-secreted protein (designated chlamydial proteasome/protease-like activity factor [CPAF]). We now report that sera collected from these infected individuals neutralized the proteolytic activity of CPAF. Depletion of the serum sample with CPAF proteins to remove the CPAF-specific antibodies effectively blocked the neutralization, whereas similar depletion with the HSP60 proteins failed to do so. We further demonstrated that the CPAF central region covering residues 200 to 338 was predominantly recognized by the human neutralization antibodies. The significance of the CPAF neutralization antibodies generated in chlamydia-infected individuals is discussed.