Focal Dermal–Epidermal Separation and Fibronectin Cleavage in Basement Membrane by Human Mast Cell Tryptase

Mast cell proteases are believed to participate in the basement membrane destruction in blistering diseases. Thus, normal human skin specimens were incubated with purified human skin tryptase or compound 48/80 (a mast cell degranulator) for up to 24 h. Thereafter, the specimens were studied immunohistochemically. Tryptase caused, in the presence and absence of 1,10-phenanthroline, focal dermal–epidermal separation above laminin and almost complete disappearance of the staining of the extra domain A region of cellular fibronectin in and beneath the basement membrane. The immunopositivity of the cell-binding region of fibronectin, laminin, and collagens IV and VII, however, was unaltered. Compound 48/80 induced almost complete dermal–epidermal separation above intact laminin and only focal reduction in the extra domain A region of cellular fibronectin staining. These alterations by compound 48/80 were prevented partially by Nα-p-tosyl-L-lysine chloromethyl ketone or 1,10-phenanthroline alone but completely when both inhibitors were present suggesting the involvement of tryptic serine proteinases, probably also tryptase, and metalloproteinases. Preventive effect of N-tosyl-L-phenylalanine chloromethyl ketone was weak suggesting minor function of chymotryptic serine proteinases. When tryptase was incubated with heparin and pure plasma fibronectin, an abrupt decrease in the adherence of cultured keratinocytes on to plastic surface coated with these substances and a gradual plasma fibronectin cleavage to 173, 161, and 28 kDa fragments in sodium dodecyl sulfate–polyacrylamide gel electrophoresis were found. In conclusion, tryptase can cause focal dermal–epidermal separation above laminin in skin specimens but it is not known to what extent the decreased keratinocyte adherence in vitro and fibronectin cleavage are related to this dermal–epidermal separation