MAST-CELL TRYPTASE AND CHYMASE ARE POTENTIAL REGULATORS OF NEUROGENICINFLAMMATION IN PSORIATIC SKIN

Background. Tryptase and chymase are proteinases present only in mast cells. In psoriatic lesions, mast cells are increased in number. Certa in neuropeptides are also more abundant in lesional than nonlesional p soriatic skin. Based on some earlier results as well as the results of the present study, a hypothesis is presented concerning the regulator y action of mast cell tryptase and chymase on neuropeptides in psoriat ic inflammation. Methods. Forty patients were biopsied, 13 for a matur e psoriatic plaque and 9 patients of 27 for a developing (1-3 weeks) p soriatic lesion induced by tape stripping (Koebner reaction). Each les ion had its nonlesional control from the same patient. Mast cell trypt ase and chymase, and the neuropeptides Substance P (SP) vasoactive int estinal polypeptide (VIP), and calcitonin-gene-related peptide (CGRP) were stained by enzyme- and immunohistochemical methods. Morphological contacts between mast cells and neuropeptides were visualized using d ouble stains and quantitated in the upper dermis. Results. As the lesi on aged, MC(TC) mast cells displaying tryptase activity increased in n umber, whereas chymase activity in these cells decreased. All neuropep tides showed some increase along with the development of the lesion, b ut SP was most abundant in mature lesions. Substance P-positive nerves had also more contacts with mast cells compared to VIP- or CGRP-conta ining fibers, the contact count being highest in mature lesions. Concl usions. Tryptase is known to degrade VIP and CGRP, but not SP. Chymase is capable of cleaving both SP and VIP, but is rendered partially ina ctive in psoriatic skin. These data together with the results of the p resent study strongly suggest that SP has potency to act as an importa nt mediator in different stages of the psoriatic inflammation.