Modulation of histamine release from mast cells by interleukin-2 is affected by nedocromil sodium

We have previously demonstrated that histamine release from immunologically activated mast cells (MC) is enhanced by their preincubation (1 h) with interleukin-2 (IL-2), and that IL-2 induces slow-chronic histamine release by MC in long-term cultures (6 days). In the present study we assessed whether nedocromil sodium can interfere with IL-2 modulation of MC histamine release. IL-2 enhancing effects and nedocromil sodium activity were studied in cocultures of rat peritoneal MC with 3T3 fibroblasts (MC/3T3). MC/3T3 were preincubated for 1 h with IL-2 (50 μg/ml) and activated with either rabbit anti-rat IgE or compound 48/80. In chronic experiments MC/3T3 were long-term (5-6 days) incubated with IL-2 (50 pg/ml). Nedocromil sodium was used at 10^-5 M. Nedocromil sodium markedly inhibited the enhancing effect of IL-2 on compound 48/80 and anti-IgE mediated MC activation both when added during the preincubation period (no tachyphylaxis was present) and when added together with the MC activators (30-50% inhibition). Washing out IL-2 before addition of the anti-IgE antibodies did not affect its histamine-release enhancing activity. Removal of nedocromil sodium before addition of the stimulus completely abrogated its effect. Continuous presence of IL-2 in the culture medium enhanced spontaneous histamine release by 37% and this effect was completely abolished in the presence of nedocromil sodium. Furthermore, nedocromil sodium decreased MC basal histamine release by 23% in long-term cocultures. Since IL-2 is known to be elevated in some pathological conditions, our results show that nedocromil sodium inhibits MC activation in an in vitro system which may represent a close resemblance to the in vivo allergic response.