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Salmonella infections cause a spectrum of diseases ranging from self-limiting diarrhea to life-threatening systemic disease. Diseases caused by Salmonella are treatable with antibiotics but successful antibiotic treatment has become increasingly difficult due to antimicrobial resistance. An effective vaccine is therefore the best strategy to reduce these diseases. A clear understanding of host immunity to Salmonella is essential to aid in the development of a vaccine. Protective immunity against Salmonella depends on a wide range of innate and adaptive immune mechanisms and T cell-mediated immune responses are important in the host control of intracellular Salmonella infection. Our laboratory used an immunoproteomics approach to identify Chlamydia T cell antigens that exhibited significant protection against Chlamydia infection in mice when used as vaccines. These results demonstrate that T cell antigens identified by immunoproteomics can be successfully exploited as T cell vaccines against an intracellular pathogen. Recently we generated dendritic cells from bone marrow of C57BL/6 mice and infected with Salmonella enterica SL1344 followed by elution of MHC class I and class II-bound peptides. The sequences of the purified peptides were then identified using tandem mass spectrometry. We identified 87 MHC class II and 23 MHC class I Salmonella derived peptides. These antigens are of use in Salmonella immunobiology research and as potential Salmonella vaccine candidates.

The murine Chlamydia muridarum model demonstrates that CD4 T cells are necessary and sufficient to resolve primary infection and that either CD4 T cells or antibody is necessary and sufficient to resolve reinfection. It remains uncertain whether a Chlamydia vaccine should accelerate clearence or prevent reinfection. Using immunoproteomics we have identified five Chlamydia outer membrane proteins (PmpG, PmpE, PmpF, PmpH and MOMP) that when individually used as protein vaccine accelerated clearance of Chlamydia infection. All 5 proteins are located in the chlamydial outer membrane complex (COMC). We tested PmpG and MOMP (major outer membrane protein that constitute more than 60% of COMC) as recombinant proteins or in native conformation as part of COMC preparations for their efficacy in accelerating clearance, providing significant protection and reducing tubal pathology. Our results show that COMC, PmpG and MOMP formulated with a Th1 polarizing adjuvant accelerated clearance but that only COMC exhibited near complete protection to challenge infection and reduced genital tract pathology. High titres of Chlamydia neutralizing antibodies were only detected following COMC immunization and not following PmpG or MOMP immunization. The superior efficacy of COMC as Chlamydia vaccine may be due to native conformation of outer membrane proteins that induce functional antibodies as well as CD4 T cell responses. These results suggest COMC may be a promising Chlamydia vaccine vehicle.

Protective immunity to Chlamydia is T cell-mediated, requiring MHC class II presented antigens. Immunodominant T cell antigens are potential human Chlamydia vaccine candidates. An immunoproteomic approach was undertaken in which Chlamydia-derived peptides presented by MHC class II molecules on the surface of infected murine dendritic cells (DCs) were identified by tandem mass spectrometry. DCs from both Balb/c and C57BL/6 mice were infected with C. muridarum and DCs from C57BL/6 were infected with C. trachomatis and C. muridarum. DCs from Balb/c infected with C. muridarum yielded 14 MHC class II binding peptides from 11 different C. muridarum proteins. Only one of the 11 proteins was shared in common with 16 C. muridarum proteins that generated MHC class II binding peptides using DCs from C57BL/6 mice. However, C57BL/6 DCs infected with C. trachomatis serovar D yielded 60 MHC class II binding peptides derived from 27 proteins, 10 of which were shared between the C. muridarum and C. trachomatis proteome. Among the 10 overlapping proteins six were tested for protective immunity and all conferred protection in mice against C. muridarum genital tract infection using DDA/MPL adjuvant. Three of the protective proteins belonged to the polymorphic membrane family of proteins, which generated MHC binding epitopes at distinct sequences within the proteins. We conclude that T cell immunodominance is determined by both MHC allelic selection and inherent properties of pathogen proteins.