IMMUNOHISTOCHEMICAL ANALYSIS OF SENSORY NERVES AND NEUROPEPTIDES, ANDTHEIR CONTACTS WITH MAST-CELLS IN DEVELOPING AND MATURE PSORIATIC LESIONS

The distribution of the neuropeptides substance P (SP), vasoactive int estinal polypeptide (VIP) and calcitonin gene related peptide (CGRP) w as studied immunohistochemically in psoriatic skin during the Koebner response (6 h, 2 days, 7 days, 14 days, 21 days), and in mature psoria tic plaques, of 37 psoriatic patients. The morphological association o f sensory nerves, SP and VIP with papillary mast cells was also monito red. The nerves containing SP, VIP or CGRP were very scanty in control skin, and in non-lesional and Koebner-negative psoriatic skin. The fi rst psoriatic lesions were seen 7 days after tape stripping the sympto mless psoriatic skin. SP- and VIP-containing nerves were slightly incr eased in Koebner-positive specimens, but the increase was very promine nt in dermal papillae of mature psoriatic plaques. In the plaques, ner ve-mast cell contacts were significantly increased (p < 0.001) compare d with non-lesional psoriatic skin. Only SP-positive fibres were detec ted in the epidermis and in contact with papillary mast cells. VIP was mainly located around capillaries where SP was also found. No change was noted in CGRP-positive fibres between lesional and non-lesional sp ecimens. The appearance of SP and VIP in the capillary walls is morpho logical evidence for their function as vasodilators in psoriatic lesio n. A slight increase in SP- and VIP-positive fibres in Koebner-positiv e specimens suggests that these neuropeptides may participate in the i nflammatory reaction at an early stage. Their prominence in mature pso riatic plaques in turn indicates a role for them in the maintenance of psoriatic lesions. Morphological contacts between mast cells and SP-c ontaining nerves give further evidence to the view that SP is capable of amplifying the inflammatory reaction also through the axon-reflex m echanism.