Intestinal cDC1s provide IL-12 dependent and independent functions required for CD4 ⁺ T cell-mediated resistance to Cryptosporidium

Cryptosporidium is an enteric pathogen that is a prominent cause of diarrheal disease. Control of this infection requires CD4 + T cells, though the processes that lead to T cell-mediated resistance have been difficult to assess. Here, Cryptosporidium parasites that express MHCII-restricted model antigens were generated to dissect the early events that influence CD4 + T cell priming and effector function. These studies highlight that parasite-specific CD4 + T cells are primed in the draining mesenteric lymph node (mesLN) and differentiate into Th1 cells in the gut, where they mediate IFN-γ-dependent control of the infection. Although type 1 conventional dendritic cells (cDC1s) were not required for initial priming of CD4 + T cells, cDC1s were required for CD4 + T cell expansion and gut homing. cDC1s were also a major source of IL-12 that was not required for priming but promoted full differentiation of CD4 + T cells and local production of IFN-γ. Together, these studies reveal distinct roles for cDC1s in shaping CD4 + T cell responses to enteric infection: first to drive early expansion in the mesLN and second to drive effector responses in the gut. Summary Cryptosporidium parasites that express model antigens were generated to dissect how parasite-specific CD4 + T cells are primed and mediate effector functions required to control this enteric pathogen. cDC1s produced IL-12p40 and were required for early expansion and gut homing of CD4 + T cells. However, IL-12p40 was only required for the development of Th1 CD4 + T cell effector function in the gut.