Lysophosphatidic acid induces human mast cell activation in an IL-4-dependent manner

Abstract

Rationale Lysophosphatidic acid (LPA) is a lipid constituent of human serum that functions as a signaling molecule through binding to 4 known G protein-coupled receptors, designated LPA1-4. LPA has previously been shown to act as a growth factor for human mast cells (hMCs) cultured under serum-free conditions. We now investigate the role of LPA in hMC activation. Methods hMCs were cultured from umbilical cord-derived mononuclear cells using serum-free medium with recombinant human stem cell factor, IL-6, IL-10, and supplemental LPA (5μM). Cells were primed with IL-4 (0.1-50 ng/mL) for up to 5 days. RT-PCR was performed to characterize LPA receptor expression. LPA-induced calcium flux was measured in Fura-2AM-loaded hMCs. For activation studies, hMCs were incubated with LPA (10-50μM) for 30 minutes to 6 hours. Histamine release, eicosanoids, and cytokine production were measured by ELISA. Kit (CD117) expression was measured by FACS analysis. Results mRNA encoding LPA1-4 are expressed by hMCs. LPA (20-50μM) induced calcium flux. LPA (10-50μM) induced MIP-1β production only in the presence of IL-4 priming. IL-4 enhanced MIP-1β generation in a dose-dependent manner, reaching 53 ± 13% (mean ± SEM, n=4) of the level produced by FcϵRI cross-link, compared with negligible levels in unprimed cells (p=0.04). In contrast, LPA did not induce hMC exocytosis or eicosanoid production. IL-4 priming significantly down-regulated Kit expression. Conclusions LPA induces cytokine generation by hMCs in an IL-4-dependent manner by a pathway that does not elicit exocytosis or eicosanoid generation.