Binding of autologous IgG to human red blood cells before and after ATP-depletion. Selective exposure of binding sites (autoantigens) on spectrin-free vesicles.
Binding of autologous IgG to fresh, ATP-depleted red blood cells as well as to spectrin-free vesicles was studied by a non-equilibrium binding assay using 125I-iodinated protein A from Staphylococcus aureus. IgG binding was 14-times higher to spectrin-free vesicles than to ATP-maintaining red blood cells and 4-times higher than to ATP-depleted erythrocytes from which these vesicles were released. Protein A binding to vesicles that were released from washed and nutrient-deprived erythrocytes, was dependent on added autologous IgG. However, spectrin-free vesicles that were spontaneously released from erythrocytes conserved in whole blood, bound similar amounts of protein A with or without added autologous IgG (0.45-0.55 ng/micrograms band 3 protein). These findings demonstrate that opsonization of spectrin-free vesicles by autologous IgG occurs not only in the test tube, but also under blood blank conditions. The binding characteristics of IgG to spectrin-free vesicles are indicative of a natural autoantibody rather than an unspecific binding of autologous IgG. The preferential binding of IgG to spectrin-free vesicles implies a selective exposure of corresponding autoantigens in membrane regions that have lost cytoskeletal anchorage and bud off.
D000255:Adenosine Triphosphate / Q000378:metabolism*; D001457:Anion Exchange Protein 1, Erythrocyte; D000941:Antigens; D001324:Autoantigens; D001665:Binding Sites; D001798:Blood Proteins / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D008565:Membrane Proteins; D013049:Spectrin; D013205:Staphylococcal Protein A / Q000378:metabolism
D001457:Anion Exchange Protein 1, Erythrocyte; D000941:Antigens; D001324:Autoantigens; D001798:Blood Proteins; D007074:Immunoglobulin G; D008565:Membrane Proteins; D013205:Staphylococcal Protein A; D013049:Spectrin; D000255:Adenosine Triphosphate