A large percentage of peritoneal IL-33R⁺ cells are mast cells that are activated in vitro to secrete cytokines and chemokines. (A) Expression of T1/ST2, c-Kit, and FcϵRI on peritoneal cells. (B) Secretion of cytokines (top panel) and chemokines (bottom panel) in PCMCs treated with 10 or 100 ng/mL rIL-33 in vitro. In panel A, 1 representative of 3 experiments is shown. In panel B, values are presented as mean ± SEM (n = 4-8) *P < .05, **P < .01, ***P < .001.