Immunocytochemical enhancement of basement membrane antigens by pepsin: applications in diagnostic pathology.

Basement membrane zone antigens, laminin, Type IV collagen, and Type V collagen each are enhanced selectively in formalin-fixed, paraffin-embedded sections by pretreatment with pepsin (1 mg pepsin/mL 0.5 M acetic acid). Highly specific antibodies to laminin, Type IV collagen, and Type V collagen each demonstrate intense linear staining of epithelial and endothelial basement membranes in fresh tissue, but this staining is diminished markedly and often completely abolished in paraffin-embedded tissue. Pretreatment of this paraffin-embedded tissue with standard immunoperoxidase enhancement technics such as trypsin fails to increase immunoreactivity of these antigens. Pretreatment with other proteases with known collagenolytic activities such as bacterial collagenase and Type IV collagenase is likewise ineffective. In contrast, pepsin pretreatment markedly enhances immunoreactivity of laminin, Type IV collagen, and Type V collagen. Previous immunocytochemical studies of the basement membrane useful in the distinction of invasive tumors from their benign counterparts, for example, tubular carcinoma of the breast from sclerosing adenosis, which only could be done prospectively in fresh tissue now can be performed retrospectively in paraffin-embedded tissue.