Biochemical characterization of the epithelial basement membrane antigen defined by the monoclonal antibody KF-1

The KF-1 monoclonal antibody has been shown to identify a noncollageneous component of the lamina densa of the basement membrane zone of human skin. In the present work, the monoclonal antibody and the antigen were further characterized. KF-1 monoclonal antibody is an IgG3 immunoglobulin with no binding to staphylococcal protein A. Two squamous carcinoma cell lines--namely, TR131 and TR146--quantitatively express the antigen. Immunofluorescence techniques showed that the antigen is a cell surface antigen, is sensitive to Triton X-100 extraction, and is concentrated in cell areas from which actin fibers are excluded. Immunoblot analysis showed that this monoclonal antibody identifies a 72 kD polypeptide present in TR131 cell extract as well as in cultured human keratinocyte cell extract.