Involvement of spectrin in cell-surface receptor capping in lymphocytes

Human and mouse lymphocytes of T- and B-cell lineages express a protein (Mr, 240,000) that crossreacts with antibodies raised against chicken erythrocyte alpha-spectrin as judged by immunofluorescence, immunoprecipitation, and immunoautoradiography; by the same criteria, antibodies raised against chicken erythrocyte beta-spectrin do not react with any lymphocyte polypeptide. In all T and B cells analyzed, before surface-directed ligand challenge with concanavalin A and surface immunoglobulins the polypeptide antigenically related to erythrocyte alpha-spectrin is distributed diffusely at the plasma membrane. Upon challenge, the redistribution of this polypeptide is concurrent with that of the cell-surface receptors initially in patches and then in a cap. Immunoprecipitation of NaDodSO4-solubilized lymphocytes with erythrocyte alpha-spectrin antiserum shows that in all cases a polypeptide with the same apparent molecular weight as erythrocyte alpha-spectrin is precipitated. Variable amounts of another polypeptide (Mr, 235,000) are also coimmunoprecipitated. Immunoprecipitations and subsequent immunoautoradiography show that the lymphocyte polypeptide doublet has a composition similar to that of (brain) fodrin, a polypeptide doublet that previously has been found mainly in the cells of nervous tissue.