Suction blister formation in skin after acute and repeated mast cell degranulation

Mast cells and their proteases are thought to participate in the developmen t of skin blisters in various pathological conditions. Tn this study, sucti on blistering was used as an experimental model to evaluate the significanc e of mast cells in blister formation after pre-treatment of normal skin wit h intradermal injections of 100 mu g/ml compound 48/80 (a mast cell degranu lator) or with 0.1% capsaicin cream. Tryptic and chymotryptic enzyme activi ties in blister fluids were measured with sensitive p-nitroanilide substrat es, Repeated injections of compound 48/80 once a day on 3 or 5 consecutive days or capsaicin applications 3 times a day for 7 or 10 days were used to induce mast cell degranulation and inflammation in normal skin. Both treatm ents ultimately led to decreased wheal and erythema reactions before suctio n blistering, but neither treatment affected the size or formation rate of suction blisters, No suction blister fluids had detectable levels of chymot ryptic activity, but blister fluids from bullous pemphigoid, herpes tester and insect bullous eruption, used as the control, revealed clear chymotrypt ic activity. In addition, tryptic activity in suction blister fluids was no t significantly altered after compound 48/80 and capsaicin pre-treatments. However, if the wheal reaction was induced immediately before suction blist ering, a significantly increased rate in blister formation together with in creased tryptic activity was found, but, unexpectedly, no chymotryptic acti vity could be detected in blister fluids. The results show that repeated ma st cell degranulation in normal skin has no effect on the formation rate of suction blisters, which developed more rapidly on acutely whealing skin. T his is probably due to skin oedema rather than mast cell proteases, since n o chymotryptic activity was detected in suction blisters where tryptic acti vity exhibited high individual variation.