Vasoactive intestinal polypeptide inhibits the established allergic contact dermatitis in humans.

There is increasing evidence indicating that the nervous system influences the immune response. In the present study the potential immunomodulatory role of vasoactive intestinal polypeptide (VIP) in established allergic contact dermatitis in humans was investigated. Positive patch-test reactions were elicited by application of nickel sulphate for 48 h. VIP was applied under patch-test conditions after another 24-h period. The test areas were measured before and 24 h after application of VIP and biopsy specimens were taken for immunohistochemistry. After application of VIP at 10(-5) mol/L, there was a significant reduction in the diameter of the test reaction. In addition, there was a reduction in the number of Leu 3a+ cells. The influence of VIP on the proliferative response of peripheral blood mononuclear cells from nickel-allergic subjects to nickel sulphate was also tested. The cells were cultured for 6 days and VIP was added after 3 days. There was no effect on the proliferative response. However, when VIP was added at 10(-6) and 10(-5) mol/L, a higher level of interferon gamma was found in the nickel-treated cell cultures compared to the controls. In conclusion, VIP may have an inhibitory effect on established allergic contact dermatitis. This inhibitory effect is possibly mediated through an increased production of interferon gamma by peripheral blood mononuclear cells.