Mast cell tryptase and chymase in the progress of cutaneous vasculitis

In animal models of vasculitis, mast cells are essential in the pathogenesis, but their involvement in human skin vasculitis is obscure. Because tryptase and chymase are potent serine proteinases in the secretory granules of mast cells, the purpose was to examine the number of mast cells expressing tryptase and chymase during the progress of cutaneous vasculitis. These numbers were correlated with the appearance of immunoreactants (C3c, fibrin, IgM, IgA and IgG) in vessel walls. For this, skin biopsies were taken from the healthy-looking skin, initial petechial lesion (IP), and palpable purpura (PP) of the leg of patients with leukocytoclastic vasculitis (n = 10). The frozen biopsies were analysed using enzyme- and immunohistochemistry and direct immunofluorescence (IF) staining. The results show that there are no marked changes in the numbers of mast cells expressing chymase or tryptase proteins. Instead, chymase enzyme activity decreased, but the score of α1-antichymotrypsin staining increased, during the progress of vasculitis. The IF positivity of fibrin correlated positively with chymase activity (p = 0.01) and the ratio of chymase activity to tryptase protein in IP (p = 0.03), as well as with mast cells showing tryptase (p = 0.03) and chymase (p = 0.01) proteins in PP. The IF positivity of C3c correlated with the ratio of chymase activity to tryptase protein in IP (p = 0.01). In conclusion, chymase is partially inactivated in vasculitis possibly due to α1-antichymotrypsin. Several positive correlations between chymase and fibrin and/or C3c in IP or PP suggest that this enzyme is involved in the deposition of immunoreactants in the vessel wall.