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 erythematous and vesicular skin and from non-involved skin of patients with dermatitis herpetiformis, bullous pemphigoid, erythema multiforme, infective bullous eruption and linear IgA dermatosis. Patients with pemphigus were biopsied for comparison. The immunoreactivity of chymase inhibitors, alpha1-proteinase inhibitor (alpha1-PI) and alpha1-antichymotrypsin (alpha1-AC), in mast cells was demonstrated using the sequential double staining method. Tryptase-positive mast cells were unchanged or only slightly increased in number in erythematous lesions and slightly decreased in blistering skin compared with healthy-looking skin. Only occasionally were mast cells seen in apparent contact with the basement membrane zone. Chymase-positive mast cells and the chymase/tryptase ratio steadily decreased during the development of the lesions in each subepidermal bullous disease. The percentage of alpha1-PI+ and/or alpha1-AC+ mast cells increased simultaneously, which could explain the disappearance of chymase activity. Similar results were obtained 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 inhibitors in a range of different bullous diseases, suggesting mast cell involvement. The apparent inactivation of chymase could be due to the action of chymase inhibitors detected in numerous mast cells. However, these alterations probably reflect general inflammation rather than a specific reaction in a certain bullous disease.