Protease treatment combined with immunohistochemistry reveals heterogeneity of normal and neoplastic basement membranes.

Heterogeneity of normal tissue and neoplastic basement membranes was investigated immunohistochemically with monoclonal antibodies and polyclonal antisera to laminin and collagen type IV. Cryostat sections of normal and neoplastic human tissues were digested with bacterial protease or trypsin. The duration of digestion and the concentration of enzyme were varied to determine whether laminin and collagen type IV could be removed differentially from basement membranes from distinct anatomic sites. After digestion, the residual antigenicity of glycoprotein was assessed immunohistochemically. Laminin could be removed more easily from all tissues than could collagen IV, and also much more easily from malignant tumors than from benign tumors or normal tissues. On the basis of susceptibility to proteolytic digestion, basement membranes from normal human tissues were classified as susceptible (e.g., heart and smooth muscle of gastrointestinal tract and uterus), moderately resistant (e.g., nerve, skeletal muscle, epithelial basement membrane of skin, smooth muscle of arteries), and very resistant (e.g., glomerulus). Differential susceptibility to proteolytic digestion most likely reflects quantitative and possibly also qualitative differences in the composition of basement membranes.