Inhibitory effect of vasoactive intestinal polypeptide and ketanserin on established allergic contact dermatitis in man.

Neuromediators may influence the immune response. To investigate their potential immunomodulating role in established allergic contact dermatitis in man, the following neuromediators were tested: vasoactive intestinal polypeptide (VIP), serotonin, and the serotonin antagonists ketanserin, methiotepine and ICS-205-930. Positive patch test reactions were elicited by application of nickel sulphate for 48 h. The neuromediators were applied under patch test conditions after another 24 h. The test areas were measured before and 24 h after application of the neuromediators and biopsy specimens were taken for immunohistochemistry. After application of VIP at a concentration of 10(-5) mol/l, and of ketanserin at a concentration of 10(-4) mol/l, there was a significant reduction in the diameter of the test reaction. In addition, with VIP there was a reduction in the number of Leu 3a+ cells. Also tested was the influence of the neuromediators on the proliferative response of peripheral blood mononuclear cells from nickel-allergic subjects to nickel sulphate. The cells were cultured for 6 days and the neuromediators were added after 3 days. There was no effect on the proliferative response, except for slight inhibition by serotonin and by ketanserin at 10(-4) mol/l. More interferon gamma was found in the supernatants when VIP was added at 10(-5) and 10(-6) mol/l than in the control cultures. Thus, VIP and ketanserin may have an inhibitory effect on established allergic contact dermatitis. The effect of VIP is possibly mediated by an increased production of interferon gamma.