Th158 - Probing Intestinal Immunity Using Cryptosporidium Infection

Bethan Wallbank; Breanne Haskins; Jodi Gullicksrud; Keenan O'Dea; David Christian; Ryan Pardy; Robert Saxton; K. Christopher Garcia; Boris Striepen; Christopher Hunter

Abstract Text: Many infectious and inflammatory diseases affect the gut and associated lymphoid tissue (GALT), which houses the largest number of lymphocytes in the body. It is therefore important to understand the regulation of tissue immunity to develop better therapies to manage disease. Cryptosporidium is a unicellular parasite that is restricted to intestinal epithelial cells (IECs) that can be used to understand immune regulation in the intestine. While infection and shedding of infectious oocysts is self-limiting in immunocompetent individuals, life-threatening chronic diarrhea and liver disease can occur in acquired and primary immunodeficiencies (AIDS, CD40L/CD40 deficiency, IL-21R deficiency). Because Cryptosporidium is restricted to the gut, it is a challenge to understand local T cell responses, though it has been previously established that sterilizing immunity requires CD4+ T cells and interferon gamma (IFN-γ). In order to characterize antigen-specific responses, transgenic C. parvum was engineered to express MHCII-restricted model antigens. Antigen-specific TCR-transgenic CD4+ T cells expanded in the gut and GALT in infected mice. These cells made IFN-γ and relied on type 1 conventional dendritic cells (cDC1s) for expansion and function. A prominent CD4+ T cell-dependent but IFN-γ-independent mechanism of control exists, as humans and mice deficient in IFN-γ are not susceptible to chronic infection. Our system revealed T cells produce IL-22 that limits infection, and therapeutic targeting using engineered cytokines suppressed infection. By using Cryptosporidium fecal oocyst shedding as a readout of gut immune function, this system can dissect immunity in the gut and probe therapies aiming to augment immunity within the tissue.