Interleukin 17C is a T cell-derived cytokine that shares the sequence similarity with IL17. This cytokine was reported to stimulate the release of tumor necrosis factor alpha and interleukin 1 beta from a monocytic cell line. The expression of this cytokine was found to be restricted to activated T cells. Northern blot analysis detected an 800-bp IL17B mRNA in adult pancreas, small intestine, and stomach, whereas IL17C mRNA was not detected in several adult tissues. No expression of IL17B or IL17C mRNA was found in activated T cells. The authors found that IL17B and IL17C differ from IL17 in their patterns of expression and biologic activities. These findings, coupled with the lack of interaction with the known IL17 receptor, suggested an expanded role for the IL17 family in the proinflammatory immune response.