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Identification of Novel Human Basement Membrane Zone Components by Monoclonal Antibodies

When visualized through the electron microscope, the basement membrane zone of the dermal-epidermal junction appears as a trilaminar region with anchoring filaments attaching the hemidesmosomes of basal cells to the underlying lamina densa and anchoring fibrils extending to the lamina densa from the subjacent connective tissue. In addition, thin elastic fibers, also called oxytalan, have been seen to course through the dermis parallel to each other and perpendicular to the dermal-epidermal junction, intersecting the lamina densa. Most known basement membrane components are present in all basement membranes. However, in addition to the ultrastructural elements mentioned, the skin blistering diseases of bullous pemphigoid and epidermolysis bullosa indicate the presence of unique antigens in the dermal-epidermal basement membrane zone. Using immunogens derived from pepsin digestions of human amnion, we have constructed monoclonal antibodies which bind to three distinct sets of antigens. One set binds to a unique basement membrane zone antigen, the novel protein (NP) antigen, present in skin and amnion, but not in blood vessels, muscle, placenta, kidney, lung, liver, stomach, bladder, or intestine. We have previously reported this unique antigen.’ A monoclonal antibody which binds specifically to human type VII collagen, which we have suggested may be the anchoring fibril protein: displays exactly the same basement membrane zone immunofluorescent staining pattern and restricted tissue distribution as the NP antigen. The third set of antibodies binds to a distinctly fibrillar antigen (FA) which bears a striking resemblance to descriptions of oxytalan. Representative immunofluorescent patterns are shown in FIGURE 1. Treatment of tissues with bovine testicular hyaluronidase or acetic acid/pepsin in acetic acid does not “unmask” any of these antigens in normally unstained regions of the tissue. When tissues are treated with pepsin before performing immunofluorescence, NP antibody binding is almost eliminated and FA antibody binding is significantly disrupted and diminished. Under the same conditions, anti-type VII collagen staining is unchanged. We have screened various cell cultures for production of the antigens. Human skin fibroblasts, fixed in either acetone or 3% paraformaldehyde, are stained by anti-