Investigating mast cell responses and the functional role of Toll-Like Receptor 2 in Chlamydia pathogenesis

Abstract

Chlamydia trachomatis (Ct) is a Gram-negative obligate intracellular bacterium that can cause severe reproductive tract complications in females. In this thesis, I have investigated two aspects of the immune response in Chlamydia infection and pathogenesis: (i) the role of mast cells and (ii) the role of Toll-like receptor 2 (TLR2). We hypothesized that mast cells, which are common at mucosal barriers, may contribute to responses to Ct infection. Human primary mast cells exposed to Ct took up the bacteria but did not support its replication. Ct-activated mast cells exhibited homotypic aggregation and significantly enhanced gene expression of IL1B, CCL3, NFKB1, CXCL8 and IL6. Endocytic blockade reduced the gene expression of IL6, IL1B and CCL3 suggesting intracellular and extracellular Ct-mast cell interactions. In a mast cell-deficient in vivo mouse model of Chlamydia infection we observed attenuated CXCL2 production and significantly reduced numbers of neutrophils, eosinophils, and B cells, but no effect on oviduct cyst development. Therefore, mast cells are reactive to Chlamydia spp. and are important in shaping immune responses to Chlamydia through both effector cell recruitment and modification of the chemokine microenvironment. TLR2 is expressed in the female reproductive tract (FRT) and is known to bind to Chlamydia and activate innate and adaptive host immune responses. We hypothesized that TLR2 was essential steering protective host responses and controlling pathology. TLR2-deficient mice (TLR2KOs) exhibited significantly larger cysts at day 72 post-infection. TLR2KOs demonstrated dysregulated early cytokine and chemokine responses in the FRT with decreased IL-6, CCL2, and CXCL10 responses. At day 16 post-infection, TLR2KOs had reduced infiltration of neutrophils and inflammatory monocytes into the FRT and severely reduced T cell infiltration into oviduct cysts. Furthermore, TLR2KOs had a dampened T cell response and were notably deficient in the Th17 response. Thus, TLR2 is critical for early protective host responses and the lack of effective acquired immune response and T cell mobilization is associated with chronic and persistent cysts. Overall, these studies provide evidence for important roles of both mast cells and TLR2 in the response to Chlamydia infection, which may help inform vaccine or other disease prevention or treatment strategies.