Dendritic cell-mediated responses to secreted Cryptosporidium effectors are required for parasite-specific CD8 + T cell responses.

Cryptosporidium causes debilitating diarrheal disease in patients with primary and acquired defects in T cell function. However, it has been a challenge to understand how this infection generates T cell responses and how they mediate parasite control. Here, 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-γ that could restrict growth of Cryptosporidium . This T cell response was dependent on the translocation of the effector and similar results were observed with another 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. These data sets highlight Cryptosporidium effectors as targets of the immune system and suggest that crosstalk between enterocytes and cDC1s is crucial for CD8 ⁺ T cell responses to Cryptosporidium .