Mast cells in developing subepidermal bullous diseases: Emphasis on tryptase, chymase and protease inhibitors

The possible involvement of mast cell tryptase and chymase in subepidermal bullous diseases was studied enzyme-histochemically in specimens from eryth ematous and vesicular skin and from non-involved skin of patients with derm atitis herpetiformis, bullous pemphigoid, erythema multiforme, infective bu llous eruption and linear IgA dermatosis. Patients with pemphigus were biop sied for comparison. The immunoreactivity of chymase inhibitors, al-protein ase inhibitor (alpha(1)-PT) and alpha(1)-antichymotrypsin (alpha(1)-AC), in mast cells was demonstrated using the sequential double staining method. T ryptase-positive mast cells were unchanged or only slightly increased in nu mber in erythematous lesions and slightly decreased in blistering skin comp ared with healthy-looking skin. Only occasionally were mast cells seen in a pparent contact with the basement membrane zone. Chymase-positive mast cell s and the chymase/tryptase ratio steadily decreased during the development of the lesions in each subepidermal bullous disease. The percentage of alph a(1)-PI+ and/or alpha(1)-AC(+) mast cells increased simultaneously, which c ould explain the disappearance of chymase activity. Similar results were ob tained regardless of the bullous disease, The results were also similar in pemphigus, which is an intraepidermal bullous disease. In conclusion, these results show significant alterations in mast cell chymase and protease inh ibitors in a range of different bullous diseases, suggesting mast cell invo lvement. The apparent inactivation of chymase could be due to the action of chymase inhibitors detected in numerous mast cells. However, these alterat ions probably reflect general inflammation rather than a specific reaction in a certain bullous disease.