['We previously localized protease-activated receptor 2 (PAR-2) on human spermatozoa and demonstrated that activation of PAR-2 by the mast cell (MC) product tryptase inhibits sperm motility. Importantly, tryptase-secreting MCs are encountered in the male and female genital tract, implying that MC-spermatozoa interactions may be as yet unrecognized factors affecting sperm fertilizing ability. In order to elucidate how tryptase via activation of PAR-2 acts in human spermatozoa, we studied intracellular signal transduction events.', 'Impairment of sperm motility by tryptase was not dependent on the presence of extracellular Ca2+ and tryptase did not alter intracellular Ca2+ levels. Pre-incubation with pertussis toxin (PTX) failed to prevent tryptase effects on sperm motility. Western blot analyses revealed that tryptase increased phosphorylation of the mitogen-activated protein kinases (MAPK) ERK1/2, an effect which was blocked by the MAPK pathway inhibitor PD98059. Pre-treatment of spermatozoa with this inhibitor also blocked the inhibtion of sperm motility evoked by tryptase.'] Does tryptase inhibit motility of human spermatozoa mainly by activation of the mitogen-activated protein kinase pathway?