Nonhemolytic red cell autoantibodies consist of multiple immunoglobulin G populations directed against complex membrane epitopes.

Immunoglobulin G red cell autoantibodies obtained by elution from six normal blood donors with antiglobulin-positive test results were labeled with iodine 125 and characterized by adsorption studies with primate and human red cells of common and rare Rh phenotype. Adsorbable IgG was determined by exhaustive adsorption with one type of red cell and by cross-adsorption with use of two different types of red cells. All of the labeled autoantibodies studied contained multiple populations directed against epitopes variably expressed on the different types of red cells (both rare and common phenotypes) used for adsorption. At least six antibody populations defining different specificities were identified by cross-adsorption techniques with use of the red cells available. None of the antibody populations was directed against any of the major Rh alloantigens (D, C, E, c, and e) although red cells of the same Rh phenotypes from different donors adsorbed similar quantities of autoantibodies. There was remarkable consistency in the presence of similar antibody populations in all six labeled preparations in spite of the known serologic complexity of red cell autoantibodies. Autoantibody eluates were characterized as either reactive or nonreactive toward Rhnull cells on the basis of their serologic activity. Except for the antibody population specific for Rhnull, all additional specificities identified by adsorption studies were present in both types of eluates. The quantity of each antibody population, however, appeared to be unique for each individual autoantibody donor. A significant fraction (23% to 53%) of the labeled IgG in all of the autoantibodies studied was unabsorbable by any of the red cells used.(ABSTRACT TRUNCATED AT 250 WORDS)