Dissociation of immune determinants of outer membrane proteins of Chlamydia psittaci strain guinea pig inclusion conjunctivitis

Seventy Years of Chlamydia Vaccine Research - Limitations of the Past and Directions for the Future

Chlamydia is a major bacterial pathogen that infects humans, as well as a wide range of animals, including marsupials, birds, cats, pigs, cattle, and sheep. Antibiotics are the only treatment currently available, however, with high rates of re-infection, there is mounting pressure to develop Chlamydia vaccines. In this review, we analyzed how Chlamydia vaccine trials have developed over the past 70 years and identified where future trials need to be focused. There has been a strong bias toward studies targeting C. muridarum and C. trachomatis within mice and a lack of studies matching chlamydial species to their end target host. Even though a large number of specific antigenic targets have been studied, the results from whole-cell vaccine targets show slightly more promising results overall. There has also been a strong bias toward systemic vaccine delivery systems, despite the finding that mucosal delivery systems have shown more promising outcomes. However, the only successful vaccines with matched chlamydial species/infecting host are based on systemic vaccine delivery methods. We highlight the extensive work done with mouse model trials and indicate that whole cell antigenic targets are capable of inducing an effective response, protecting from disease and reducing shedding rates. However, replication of these results using antigen preparations more conducive to commercial vaccine production has proven difficult. To date, the Major Outer Membrane Protein (MOMP) has emerged as the most suitable substitute for whole cell targets and its delivery as a combined systemic and mucosal vaccine is most effective. Finally, although mouse model trials are useful, differences between hosts and infecting chlamydial strains are preventing vaccine formulations from mouse models to be translated into larger animals or intended hosts.

Protective efficacy against Chlamydophila psittaci by oral immunization based on transgenic rice expressing MOMP in mice

Avian chlamydiosis is caused by Chlamydophila psittaci (Cp. psittaci) and major outer membrane protein (MOMP) of Cp. psittaci is an excellent vaccine candidate. In this study, the MOMP gene was expressed in rice callus by the Agrobacterium tumefaciens vector. The production of protein in transgenic rice seeds was confirmed and quantified by Western-blot and ELISA, the results demonstrating that the antigen was expressed stably. The transgenic rice seeds expressing the MOMP protein were administered by the oral route to BALB/c mice, which developed MOMP-specific serum IgG and fecal IgA antibodies and a splenocyte MOMP-specific proliferative response and significant levels of IFN-γ, IL-2, IL-4, IL-5 and TGF-β production. Immunization with MOMP transgenic seeds induced partial protection (50%) against a lethal challenge with the highly virulent Cp. psittaci 6BC strain. Lung function after challenge was less affected compared non-MOMP immunized animals. The results demonstrate the feasibility of using transgenic rice seeds as an oral vaccine to generate protective immunity and reduce the lung lesions in mice against virulent Cp. psittaci 6BC strain. This finding has implications for further development of an oral vaccine against avian chlamydiosis.

Comprehensive in silico prediction and analysis of chlamydial outer membrane proteins reflects evolution and life style of the Chlamydiae

Background

Chlamydiae are obligate intracellular bacteria comprising some of the most important bacterial pathogens of animals and humans. Although chlamydial outer membrane proteins play a key role for attachment to and entry into host cells, only few have been described so far. We developed a comprehensive, multiphasic in silico approach, including the calculation of clusters of orthologues, to predict outer membrane proteins using conservative criteria. We tested this approach using Escherichia coli (positive control) and Bacillus subtilis (negative control), and applied it to five chlamydial species; Chlamydia trachomatis, Chlamydia muridarum, Chlamydia (a.k.a. Chlamydophila) pneumoniae, Chlamydia (a.k.a. Chlamydophila) caviae, and Protochlamydia amoebophila.

Results

In total, 312 chlamydial outer membrane proteins and lipoproteins in 88 orthologous clusters were identified, including 238 proteins not previously recognized to be located in the outer membrane. Analysis of their taxonomic distribution revealed an evolutionary conservation among Chlamydiae, Verrucomicrobia, Lentisphaerae and Planctomycetes as well as lifestyle-dependent conservation of the chlamydial outer membrane protein composition.

Conclusion

This analysis suggested a correlation between the outer membrane protein composition and the host range of chlamydiae and revealed a common set of outer membrane proteins shared by these intracellular bacteria. The collection of predicted chlamydial outer membrane proteins is available at the online database pCOMP http://www.microbial-ecology.net/pcomp and might provide future guidance in the quest for anti-chlamydial vaccines.

Construction and immunogenicity of recombinant adenovirus expressing the major outer membrane protein (MOMP) of Chlamydophila psittaci in chicks

Avian chlamydiosis is caused by Chlamydophila psittaci. The major outer membrane protein (MOMP) encoded by the outer membrane protein 1 (omp1) gene is an excellent candidate for genetic engineering of a vaccine against avian chlamydiosis. In this study, the MOMP gene was amplified by PCR and cloned into the transfer vector pShuttle-CMV. The recombinant plasmid was obtained by recombination between the plasmid pShuttle-CMV-MOMP and skeleton vector pAdEasy-1 in Escherichia coli strain BJ5183. The titer of recombinant adenovirus containing the MOMP gene (rAd-MOMP) of C. psittaci was 3.4x10(10)TCID(50)/ml in human embryonic kidney 293 (HEK293) monolayer cells. The expression of the MOMP in HEK293 cells infected with rAd-MOMP was confirmed by an indirect immunofluorescence assay. Specific pathogen free (SPF) chicks were inoculated with 10(6), 10(8), and 10(10)TCID(50) of rAd-MOMP/chick. Inoculated chicks generated antibodies against MOMP of C. psittaci, which were detected by an indirect hemagglutination test (IHA). The vaccinated chicks were challenged with a virulent Chinese field isolate. Nine out of 10 chicks in the vaccinated group were protected, while birds in the wild-type adenovirus control group and the PBS control group all showed clinical signs after challenge. The results indicate that the recombinant adenovirus containing the MOMP gene of C. psittaci might be a candidate vaccine against avian chlamydiosis.

Recognition of the 60 kilodalton cysteine-rich outer membrane protein OMP2 by CD4(+) T cells from humans infected with Chlamydia trachomatis

T cell-mediated immunity is important in the control of chlamydia infection but chlamydia-specific T cells are also implicated in the inflammation and tissue damage which characterize chlamydia associated diseases. To investigate target antigens of the T cell-mediated immune response to chlamydia infection, Chlamydia trachomatis-specific CD4+ T cell clones were isolated from a patient with chlamydia-induced reactive arthritis. T cell immunoblotting indicated that an antigen of approximately 60 kilodaltons molecular mass was recognized, and recombinant 60 kilodalton cysteine-rich outer membrane 2 (OMP2) proved to be stimulatory. By using deletion constructs and synthetic peptides an epitope presented by HLA-DRB1*0401 was defined and proved to contain the nonamer peptide within the OMP2 sequence predicted to have the greatest binding affinity for DRB1*0401 The sequence of the epitope is conserved in all C. trachomatis strains but not in C. pneumoniae. Investigation of patients with acute urethritis and additional patients with sexually acquired reactive arthritis showed that OMP2-reactive T cells were readily detectable in peripheral blood and synovial fluid. Thus OMP2 is a target antigen of the T cell-mediated immune response to CT infection.

Interaction of outer envelope proteins of Chlamydia psittaci GPIC with the HeLa cell surface

The chlamydial life cycle involves the intimate interaction of components of the infectious elementary body (EB) surface with receptors on the susceptible eukaryotic cell plasma membrane. We have developed an in vitro ligand binding assay system for the identification and characterization of detergent-extracted EB envelope proteins capable of binding to glutaraldehyde-fixed HeLa cell surfaces. With this assay, the developmentally regulated cysteine-rich envelope protein Omp2 of Chlamydia psittaci strain guinea pig inclusion conjunctivitis was shown to bind specifically to HeLa cells. HeLa cells bound Omp2 selectively over other cell wall-associated proteins, including the major outer membrane protein, and the binding of Omp2 was abolished under conditions which alter its conformation. Furthermore, trypsin treatment, which reduces EB adherence, resulted in the proteolytic removal of a small terminal peptide of Omp2 at the EB surface and inactivated Omp2 in the ligand binding assay, while having a negligible effect on the major outer membrane protein. Collectively, our results suggest that Omp2 possesses the capacity to engage in a specific interaction with the host eukaryotic cell. We speculate that, since Omp2 is present only in the infectious EB form, the observed in vitro interaction may be representative of a determining step of the chlamydial pathogenic process.

Deviation of immune response to Chlamydia psittaci outer membrane protein in lipopolysaccharide-hyporesponsive mice

The outcome of infection is determined by both the quantity and the quality of an induced immune response. In particular, it has been demonstrated for selected pathogens that induction of TH1 or TH2 type helper T-cell subsets determines whether an immune response gives rise to protective immunity or disease-associated immunopathology. The nature of the antigen and the type of antigen-presenting cells recruited in the induction of a response are critical factors that influence the quality of the immune response. Of particular interest in this respect is the immune response to bacterial particles and the impact of cell wall-associated lipopolysaccharide (LPS) on that response. Nonspecific activation of macrophages and B lymphocytes by LPS could skew the phenotype of activated antigen-presenting cells and selectively alter the immunoglobulin isotypes and helper T-cell subsets that are induced following infection. In an initial attempt to detect immune deviation associated with LPS stimulation, we have compared the immunoglobulin isotypes of antibodies specific for the cysteine-rich outer membrane protein Omp2 induced in normal and LPS-hyporesponsive mice following immunization with Chlamydia psittaci strain guinea pig inclusion conjunctivitis whole elementary bodies. We report that there is a dramatic shift of Omp2-specific antibody from predominantly immunoglobulin G2a (IgG2a) isotype in LPS-hyporesponsive mice to high levels of IgG1 isotype in LPS-responder strains. The dependence of the IgG1 isotype shift on the LPS responder status is linked to the structure of the antigen and its natural processing pathway since LPS-hyporesponsive mice are not, in general, deficient in IgG1 antibody production. In particular, the antibody response to purified recombinant Omp2 is predominantly of the IgG1 isotype even in LPS-hyporesponsive mice.