NATURALLY-OCCURRING ANTI-BAND-3 ANTIBODIES BIND TO PROTEIN RATHER THAN TO CARBOHYDRATE ON BAND-3

Naturally occurring anti-band 3 antibodies were affinity purified from pooled human IgG (Sandoglobulin(R)) (Lutz, H. U., Flepp, R., and Stri ngaro-Wipf, G. (1984) J. Immunol. 133,2610-2618). They bound to the ma jor integral membrane protein of human red blood cells and its 55-kDa NH2-terminal chymotryptic fragment but not to the carbohydrate-rich 38 -kDa fragment on blots. Likewise, neither an endo-beta-galactosidase n or a neuraminidase treatment of band 3 on intact red cells reduced the ir binding to the blotted antigen. Lactoferrin (10 mug/ml) had no sign ificant effect on their binding to band 3 and to its 55-kDa chymotrypt ic fragment. Even in the presence of 20 mug/ml lactoferrin anti-band 3 antibodies bound specifically to chymotrypsin-pretreated and oxidativ ely stressed red cells. Thus, naturally occurring anti-band 3 antibodi es bind to protein rather than carbohydrate within band 3 protein, irr espective of whether the antibodies were depleted of anti-idiotypic an d other IgG-reactive antibodies or not.