Activated Tcons have migrated back to the intestinal crypts and have eliminated host APCs and Tregs. Donor HP APCs that have differentiated from donor HP stem cells migrate to the colon, where they continue to present host antigens together with non-HP APCs, driving them to amplify the inflammatory cascade and to secrete large amounts of IL-33 that binds ST2 before entering the villus capillaries. Tcons have eliminated ILC3s, Paneth cells, and ISCs. Commensal bacteria (and their metabolites) no longer predominate, permitting overgrowth of potential pathogens. REG3 stored in the mucus and in Paneth cells enters the bloodstream as the epithelial barrier is lost.