Differential lectin binding to mammalian keratinocytes and melanocytes in vitro

Guinea pig melanocytes and keratinocytes in primary mixed epidermal cell cultures were investigated as to their differential lectin binding capacities. Cultures were exposed to a battery of fluorescent (FITC and TRITC) lectins and lectin derivatives for ultrastructural visualization (HRP-labeled lectins for a one-step technique and biotinylated lectins followed by avidin-HRP in a two-step technique). Most of the lectins bound to both melanocytes and keratinocytes. Lectins with specificity for N-acetyl-galactosamine and terminal D-galactose bound only to keratinocytes; melanocytes were reactive, though, at contact sites of dendrites with keratinocyte cell bodies. Ulex europaeus (specific for L-fucose) bound to neither melanocytes no keratinocytes. Neuraminidase pretreatment restored the capacity of melanocytes to bind all lectins except Ulex europeaus. It is concluded that the melanocytes receptor sites for N-acetyl-galactosamine and terminal D-galactose are masked by sialic acid residues; they appear to emerge, though, under conditions of cell-to-cell contact as in the course of pigment transfer. Masking and demasking processes may therefore bear a functional significance.