Inhibitory effect of vasoactive intestinal peptide on the challenge phase of allergic contact dermatitis in humans

There is increasing evidence that the nervous system has influence on the i mmune response. The effect of vasoactive intestinal peptide (VIP) and of se rotonin and its antagonists on the challenge phase of allergic contact derm atitis in humans were tested. The substances were injected intracutaneously shortly before and 6 h after application of patch tests with nickel sulpha te in nickel-allergic patients and the test areas were measured after a fur ther 18 h, Biopsy specimens were also taken for immunohistochemistry. The d iameter of the nickel sulphate-induced test reaction was significantly redu ced after injection of VIP at 10(-6)-10(-5) mol/l, but was not affected by serotonin or ketanserin. Also tested was the influence of the substances on the response of peripheral blood mononuclear cells from nickel-allergic su bjects to nickel sulphate, when added at the same time as the antigen. No e ffect on the cell proliferative rate was seen, except for an inhibitory eff ect of serotonin and its antagonists at 10(-5)-10(-4) mol/l. VIP, at 10(-5) mol/l and serotonin at 10(-4) mol/l stimulated the secretion of interferon gamma. The interleukin-2 soluble receptor secretion was slightly stimulate d by 5-HT at 10-4 mol/l and by ketanserin at 10(-6) mol/l. In conclusion, o ur results show that when injected intracutaneously in the challenge phase of allergic contact dermatitis, VIP has an inhibitory effect, which might b e explained by enhanced leukocyte production of interferon gamma.