Modifications of the thymocyte membrane during redistribution of concanavalin A receptors

The modifications of the thymocyte membrane which are induced by concanavalin A (Con A) were studied by means of the variation of electrophoretic mobility which the lectin induces on the cell. The electrophoretic mobility of thymocytes is increased when Con A is used under conditions expected to induce a cap formation and the subsequent endocytosis. This increase persists as long as the lectin is present in the medium and disappears as soon as the lectin is eliminated. The redistribution of the Con A receptors into spots and caps may partially explain this electrical modification. The ionized groups of the thymocyte membrane are drastically modified during these phenomena with: 1) a diminution by 61% in the density of the sialic carboxyl groups, 2) a decrease of 40% in the density of phosphate groups and of 60% in the density of amino groups, 3) a 20 times higher density of unidentified negatively charged groups. The electrophoretic mobility of normal human blood lymphocytes is similarly increased by Con A. A marginal difference exists in the shape of the dose response curves obtained when normal and cancerous thymocytes react with increasing doses of Con A. No measurable electrical modification was observed during redistribution of H-2 and Thy-1.2 antigens on EL4 cells. Some experiments suggest a possible correlation between the mitogenicity of the lectin and a measurable modification of the cell electrophoretic mobility.