Ultrastructural quantitation of desmosome and differentiation-related keratinocyte membrane antigen

The keratinocyte membrane antigen KM 48 was defined by a new monoclonal antibody obtained after mouse immunization with normal human epidermal cell suspension. Specific reactivity of the antibody with desmosomal regions of keratinocyte cell membrane was demonstrated by immunoelectronmicroscopy. Langerhans cells, melanocytes, and indeterminate cells did not express the KM 48 antigen. Immunogold labelling permitted ultrastructural quantitation of KM 48 antibody binding on keratinocytes from various epidermal layers. A gradual increase in desmosome-related KM 48 antigen expression accompanied differentiation of keratinocytes during their transit from basal to granular layer. Distribution of the antigen on individual cells was uneven. The upper pole of a keratinocyte facing overlying more differentiated cells was always found to be laden with an immunogold marker about twice that of the opposite, lower surface of the cell. The results support the previous reports on gradual development of desmosomes during epidermal cell maturation and open up new possibilities for keratinocyte differentiation studies. They also underline the virtues of the immunogold-labelling method used for cell-surface antigen tracing and quantitation.