Human mast cells express inducible PGE synthase and generate PGE2 in response to TLR2-dependent activation

Abstract

Rationale Mast cells (MCs) are effectors of both innate and adaptive immunity. MC activation through Fc epsilon RI results in their generation of leukotriene (LT)C4 through the 5-lipoxygenase/leukotriene C4 synthase (5-LO/LTC4S) pathway, and of prostaglandin (PG)D2 through the cyclooxygenase (COX)/PGD2 synthase pathway. PGE2 is generated by both constitutive and inducible enzymatic systems and serves a key role in cell activation and gene induction; its generation by MCs has not been recognized. Methods Cultured human MCs (hMCs) derived from cord blood were stimulated by either Fc epsilon RI cross-linkage, or by staphylococcal peptidoglycan (PGN), a ligand for Toll-like receptor (TLR)2. Eicosanoids were measured by ELISA, and relevant enzymes and proteins were assessed by western blots. Results Unexpectedly, both ligands elicited the generation of PGE2, as well as LTC4 and PGD2. Whereas Fc epsilon RI-dependent activation was far more potent for LTC4 and PGD2 generation, PGN was more potent for PGE2 generation, which occurred with a strikingly delayed kinetics (maximal at 24 h). Both activation stimuli induced the expression of COX-2 and two terminal synthases, mPGES-1 and mPGES-2. Delayed-phase PGE2 generation was completely prevented by NS-398, a selective PGHS-2 inhibitor. Conclusions MCs express an inducible system for PGE2 generation, and likely produce different respective profiles of eicosanoids in innate and adaptive immune responses. The inducible COX-2/mPGES system may form a pathogenetic link between MCs and non-allergic diseases in which PGE2 plays a major role.