Monoclonal antibodies to two different epitopes in a 30-kD CNBr peptide of the K1 and K2 keratins.

Two anti-keratin monoclonal antibodies, Kab-2 and Kab-3, with specificities for different epitopes of type II (basic) human epidermal keratins, were produced. These antibodies had different immunofluorescent staining patterns on human fetal epidermis. Western blots and solid phase RIA showed both antibodies bound to 65-67-kD basic keratins (K1 and K2) extracted from foreskin epidermis. Competitive binding studies with the two Kab antibodies and other anti-keratin monoclonal antibodies showed that Kab-2 and Kab-3 recognized related epitopes, distinct from the epitopes recognized by other anti-keratin antibodies AE-1, 2, and 3. Kab-2 and Kab-3 epitopes were distinguished by differences in their reactivity with peptides generated by Staphylococcus aureus V8 protease digestion of the K1 keratin; the antibodies recognized both common and unique peptides. Western blots of cyanogen bromide digests of the K1 keratin showed that both Kab antibodies reacted with a 30-kD fragment of the molecule presumed to be the N-terminal CNBr peptide. We interpret these data to indicate that in tissues, portions of the N-terminal region of the K1 keratin are differentially available for reaction with these monoclonal antibodies and that morphologic differences in staining with monoclonal antibodies to the same molecule can reflect epitope specificity or epitope availability related to supramolecular organization.