TLR9 and colitis: Using Campylobacter jejuni infection and dextran sulfate sodium (DSS) treatment to induce colitis in mice, Jennifer R. O’Hara et al. showed a significant decrease in both IL-25 and IL-17A in mouse colonic homogenates, as well as disrupted Toll-like receptor 9 (TLR9) signaling in apical epithelium, which is responsible for maintaining colonic homeostasis (71).