The localization of
mast cell tryptase in involved and noninvolved skin sections from 12 psoriatic patients was investigated using both
enzyme- and immunohistochemical staining techniques. Each involved skin section contained an increased number of
tryptase-positive mast cells in the superficial dermis as compared with corresponding noninvolved skin sections. The substrate-hydrolyzing and inhibition properties for
tryptase activity in involved and non-involved psoriatic skin sections were identical with each other as well as with those previously described in normal human skin or
mastocytoma skin sections. In four patients, epidermal
enzyme activity was observed, but only in the involved skin. None of the uninvolved sections showed
tryptase activity in the epidermis. This activity was not inhibited by
alpha 1-antitrypsin, and after removing the
enzyme-histochemical
stain with
Tween 20, positive results obtained with
tryptase-specific antibody were found in the same locations. In addition,
tryptase-positive cells were detected in close contact to lesional epidermis, but without epidermal staining in four patients. In the epidermis, the positive staining was granular, and active
tryptase was detected as far as the stratum corneum. This study is the first description of the presence of active
mast cell tryptase in psoriatic epidermis, where this
enzyme may have a role in increased cell division.