Model of the immune response to
C. parvum oocysts are ingested by the host where they target the ileum of the small intestine and undergo excystation. Excysted sporozoites invade epithelial cells of the ileum where they complete asexual and sexual replication cycles. Infected epithelial cells produce pro-inflammatory cytokines, chemokines and anti-microbial peptides, which together orchestrate the immune response and recruit immune cell populations such as NK cells and γδ T cells to the site of infection. APCs such as DCs and macrophages sample antigen at the site of infection and following uptake, migrate to the draining mesenteric lymph nodes where they present antigen to CD4+ T cells. Antigen presentation together with the presence of IL-12 and IFNγ from APCs and NK cells/γδ T cells respectively, result in the generation of a Th1 CD4+ T cell response that is thought to be important during the immune response to C. parvum in humans, cattle and mice.