NEUTRAL POLYMERS ELICIT, AND ANTIBODIES TO SPECTRIN, BAND-4.1 PROTEINAND CYTOPLASMIC DOMAIN OF BAND-3 PROTEIN INHIBIT THE CONCANAVALIN A-MEDIATED AGGLUTINATION OF HUMAN ERYTHROCYTES

Concanavalin A (Con A) is known to agglutinate human erythrocytes if t he cells are pre-treated with a proteinase or neuraminidase. We report that untreated cells can also be made to agglutinate with the lectin if the lectin-bound cells are treated with anti-Con A antibodies, or i f a neutral polymer such as serum albumin, polyvinylpyrrolidone or Fic oll is added. Thus, Con A falls in the category of 'incomplete' lectin s. The polymer induces Con A-agglutinability without altering the rece ptor number, or deformability of the cells. If the polymer is sequeste red within erythrocyte ghosts, Con A is unable to agglutinate them; bu t the presence of the polymer only on the outer surface (as in intact cells) or on both the surfaces permits agglutinability, Thus, the site of the polymer effect resides on the outer surface of the membrane. T he polymer, however, is unable to induce agglutinability in erythrocyt e vesicles, whose membrane lacks skeletal proteins. The result suggest s a positive role for the membrane skeleton in the process of agglutin ation brought about by the polymer, as is true also for the agglutinat ion of proteinase-treated cells. In order to obtain detailed informati on on the proteins participating in agglutination, monospecific antibo dies to spectrins, band 4.1 protein, ankyrin and the cytoplasmic domai n of band 3 protein were internalized in erythrocytes. It is found tha t anti-spectrin and anti-band 3 cytoplasmic domain, but not their Fab' s, inhibit the Con A-mediated agglutinability partially, and anti-4.1 antibodies, as well as the Fab's, inhibit the agglutinability substant ially. Anti-ankyrin, however, was without any effect. The results conf irm a positive role for the membrane skeleton in the Con A-mediated ag glutination of normal erythrocytes in the presence of a neutral polyme r, or in proteinase treated cells. We also provide evidence for requir ement of Mg-ATP in the agglutination process.