IL-4 RENDERS MAST-CELLS FUNCTIONALLY RESPONSIVE TO ENDOTHELIN-1

It has previously been shown that mouse bone marrow-derived mast cells (BMMC) synthesize and secrete endothelin-1 (ET-1) and express ET(A)-t ype endothelin receptors (ET(A)-R). The study presented here was desig ned to elucidate the influence of different cytokine conditions for ce llular differentiation and maturation on the ability of primary mouse BMMC to respond to exogenous ET-1. BMMC were grown for 2 wk in IL-3 al one and then cultured for 2 to 3 wk with kit ligand (KL) and/or IL-3 i n the presence or absence of IL-4. ET-1 induced a very rapid (less tha n or equal to 1 min) and dose-dependent release of histamine and serot onin from BMMC cuItured in the presence of both IL-3 and IL-4. The eff ect of ET-1 was quantitatively comparable with IgE/Ag-induced mediator release and comprised up to 20% and 16% of total cellular histamine a nd serotonin, respectively. In BMMC grown with KL or KL plus IL-3, a s ubstantial effect of ET-1 on amine release was only observed when IL-4 had been included in the culture medium. These IL-4 effects could not be observed if BMMC grown in IL-3 and/or KL were preincubated for 1 o r 24 h with IL-4 before activation with ET-1, suggesting that a differ entiation process rather than a functional priming effect had been ini tiated by IL-4. In BMMC, the histamine and serotonin release induced b y ET-1 (10(-6) M) was inhibited by an ET(A)-R-specific antagonist (cyc lic [D-Asp-Pro-D-Val-Leu-D-Trp]) in a dose-dependent manner, with comp lete inhibition at an antagonist concentration of 10(-8) M. ET-1 stimu lated leukotriene C-4 biosynthesis up to 4.5-fold in BMMC cultured in the presence of IL-4. No such ET-1 effect was observed in BMMC culture d in media containing IL-3, KL, or a combination of both cytokines. Pe ritoneal cells (containing 2 to 3% serosal mast cells) obtained from B ALB/c mice released 87 +/- 2% of histamine within 1 min after challeng e with ET-1. Our results demonstrate that ET-1 can directly act as a h istamine and serotonin secretagogue and as a stimulator of leukotriene C-4 production in mast cells. IL-4 appears to be critically involved in the differentiation of immature mast cell precursors to an ET-1-rea ctive phenotype. Considering the key role of IL-4 in the development a nd function of Th2-type lymphocytes, ET-1-induced mast cell activation could be of major clinical importance in the course of Th2-dominated immune responses.