Monoclonal Antibody GB3, a New Probe for the Study of Human Basement Membranes and Hemidesmosomes

A monoclonal antibody, GB3, has been raised against human amnion. Not only does GB3 bind to amniotic basement membrane, but it also recognizes an antigenic structure expressed by epidermal as well as by some other human basement membranes. This antigen is synthesized (and excreted) by cultured normal human epidermal keratinocytes. It is expressed to a lesser extent by the A431 epidermoid carcinoma cell line, but is not expressed by the SV40 virus-transformed SVK14 keratinocyte cell line. In ultrastructural studies, this antigen was located in the epidermal basement membrane, both in the lamina densa and in the lamina lucida, associated with hemidesmosomes. It was identified as a protein by in vitro proteolytic cleavage studies. The radio-immunoprecipitates from cultured human keratinocytes, analysed by SDS-PAGE, showed that GB3 recognized five polypeptides of 93.5, 125, 130, 146 and 150 kD under reducing conditions. They were probably linked by disulfide bonds. The tissue distribution of the antigen and the molecular weights (MWs) of its constitutive polypeptides suggest that it is different from other known components of basement membranes. It may provide a biochemical marker for hemidesmosomes. Furthermore, GB3 represents an interesting and original clinical probe, since the antigenic structure recognized by GB3 is lacking in Junctional Epidermolysis Bullosa, a lethal genodermatosis in which a dermo-epidermal splitting occurs at the level of lamina lucida.