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 immune response. The effect of vasoactive intestinal peptide (VIP) and of serotonin and its antagonists on the challenge phase of allergic contact dermatitis in humans were tested. The substances were injected intracutaneously shortly before and 6 h after application of patch tests with nickel sulphate in nickel-allergic patients and the test areas were measured after a further 18 h. Biopsy specimens were also taken for immunohistochemistry. The diameter of the nickel sulphate-induced test reaction was significantly reduced 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 subjects to nickel sulphate, when added at the same time as the antigen. No effect on the cell proliferative rate was seen, except for an inhibitory effect 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 stimulated by 5-HT at 10(-4) mol/l and by ketanserin at 10(-6) mol/l. In conclusion, our results show that when injected intracutaneously in the challenge phase of allergic contact dermatitis, VIP has an inhibitory effect, which might be explained by enhanced leukocyte production of interferon gamma.