PSMs induce specific activation and degranulation of mFpr2-expressing RBL cells. PSMs specifically do not activate mFpr1–transfected RBL cells (A, C), but activate mFpr2 (B, D) at indicated concentrations. Data represent means ± sem of at least 3 independent experiments. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 vs. corresponding medium control (53), as calculated by Student’s t test.