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Cultured human intestinal mast cells express functional IL‐3 receptors and respond to IL‐3 by enhancing growth and IgE receptor‐dependent mediator release

Mast cells are immunoregulatory effector cells capable of releasing different mediators and cytokines implicated in inflammatory tissue processes. Previous studies suggested that IL‐3 regulates growth and function of murine mast cells and human mast cell precursors, but does not affect mature human mast cells. In the present study, we found expression of IL‐3 receptors (IL‐3R) in freshlyisolated human intestinal mast cells by reverse transcriptase (RT)‐PCR and in mast cells cultured with stem cell factor (SCF) using RT‐PCR and flow cytometry. IL‐3R expression was enhanced when theculture medium was supplemented with IL‐4 in addition to SCF. In the presence of SCF, IL‐3 significantly enhanced mast cell growth in a dose‐dependent fashion (179±51% of control, p⩽0.004, n=9, ED50 ≈ 15 ng/ml) by decreasing mast cell apoptosis rather than inducing proliferation. Furthermore, IL‐3 selectively enhanced histamine (from 39.6±12.4 to 51.2±15.7% specific release, p<0.02, n=8) and leukotriene C4 (LTC4, 5.1±3.4 to 10.8±5.5 ng/106 mast cells, p<0.03, n=6) release triggered by IgE receptor cross‐linking without affecting prostaglandin D2 production. In conclusion, our data show that human intestinal mast cells express functional IL‐3R, indicating that IL‐3 not only regulates growth and function of immature, but also that of mature human mast cells.