A monoclonal antibody labelling the keratinocyte membrane: a marker of epidermal differentiation.

A murine hybridoma secreting an IgM monoclonal antibody (KL3) was produced by cell fusion of mouse myeloma cells with spleen cells from mice immunized with human epidermal keratins. On normal human epidermis KL3 stained the intercellular spaces from the stratum germinatum to the stratum granulosum with a fluorescence intensity increasing from the basal layer to the upper layers. Basal cells were not stained on the side facing the basement membrane. About 90% of free keratinocytes isolated after trypsinization were labelled by KL3 in a punctate staining. Immunoelectron microscopy allowed us to show that the antigen recognized by KL3 was exclusively localized on the keratinocyte membrane especially in the desmosomal plaques. KL3 reactivity was not modified by preincubation of skin sections with lectins showing a selective intercellular labelling of upper layers of epidermis or pemphigus antisera, nor by adsorption of the antibody on NP40 soluble proteins of the epidermis. Though KL3 reactivity was completely abolished after adsorption of purified keratins, no immunological reactivity of KL3 was detected with epidermal keratin polypeptides blotted on nitrocellulose paper. In psoriatic epidemis and epidermal tumors KL3 reactivity was drastically modified. These results suggest that KL3 recognized a keratinocyte membrane antigen implied in the epidermal differentiation process.