Interaction between the nervous and immune systems in allergic contact dermatitis : a clinical and experimental study with emphasis on the role of VIP and serotonin

The interaction between the nervous and immune systems was investigated in allergic contact dermatitis (ACD) with emphasis on the role of vasoactive intestinal peptide (VIP) and serotonin (S-HT).

Dual dose-dependent effects of VIP on the migration of mononuclear and polymorphonuclear leukocytes were found. Serotonin and the serotonin antagonists ketanserin, methiotepin and tropisetron had an inhibitory effect on the migration of mononuclear leukocytes while no effect on polymorphonuclear leukocytes. In pharmacological concentrations at least, VIP may protect lymphocytes from metal toxicity.

Topical application of VIP on the established patch test reaction to nickel sulphate and intracutaneous injection of VIP in the challenge phase caused a reduction of the diameter of the test reaction. In addition, CD4+ cells were reduced in number when VIP was topically applied. The secretion of interferon gamma increased when VIP was added to cultures of peripheral blood mononuclear cells from nickel-allergic subjects in both challenge and proliferative phase. Of serotonin and its antagonists, ketanserin reduced the diameter of the test reaction when applied topically.

Basal epidermal serotonin immunoreactive (IR) cells found were possibly melanocytes. These cells became more dendritic and migrated upwards in the epidermis in the ACD reaction, compared with in control skin. There was also an increased concentration of serotonin in ACD vis-a-vis control skin.

There was no significant difference in either distribution of VIP fibres or concentration of VIP between ACD-involved and uninvolved skin. However, the number of dermal mononuclear cells showing VIP2 receptor-IR in ACD skin was reduced. In conclusion, VIP and serotonin may play a pathophysiological role in ACD, and both VIP and ketanserin may have therapeutic potential.