THE ROLE OF DENDRITIC CELLS IN THE GENERATION OF CD8+ T CELL RESPONSES DURING CRYPTOSPORIDIUM INFECTION

Cryptosporidium is an intracellular intestinal parasite that causes debilitating diarrheal disease in individuals with primary and acquired defects in T cell function. However, because of a paucity of tools to study parasite-specific responses it has been a challenge to understand how this infection generates T cell responses and how they mediate parasite control. In Chapter 2, Cryptosporidium was engineered to express a parasite effector protein (MEDLE-2) that contains the MHC-I restricted SIINFEKL epitope which is recognized by TCR transgenic OT-I CD8+ T cells. These modified parasites induced expansion of endogenous SIINFEKL-specific and OT-I CD8+ T cells that were a source of IFN-g that could restrict growth of Cryptosporidium. This T cell response was dependent on the translocation of MEDLE-2 into the host cell and similar results were observed with the secreted parasite effector ROP1. Although infection and these translocated effector proteins are restricted to intestinal epithelial cells (IEC), type I dendritic cells (cDC1) were required to generate CD8+ T cell responses to these model antigens. In numerous experimental settings, the ability of the cDC1 subset of dendritic cells (DCs) to present antigen, provide a platform for CD4+ T cell help canonically mediated by CD40L, and produce the cytokine IL-12 are associated with the activation and maintenance of CD8+ T cells. The studies in Chapter 3 revealed that CCR7 was required for DC migration from infected gut to the mesenteric lymph nodes and the ability of cDC1s to express MHC-I was critical for priming of OT-I cells. These early events were dependent on CD40/CD40L signaling but independent of the ability of cDC1 to produce IL-12p40 or CD4+ T cells. Thus, only a subset of canonical functions of cDC1 are required to generate CD8+ T cell responses to Cryptosporidium. Additionally, while the loss of MHC-I expression on enterocytes did not alter OT-I priming, it was required in the intestine for optimal parasite control. Together, these data sets highlight Cryptosporidium effectors as potential targets of the immune system and suggest a model in which CD8+ T cells require sequential MHC-I signals provided by cDC1 and IEC to provide protection against Cryptosporidium.