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The Dependence of Agglomeration of Stored Erythrocytes on Fibrinogen and pH

In a previous study we have reported that stored erythrocytes have an augmented tendency to agglomeration in 0.25 M sucrose, at pH 7.2. In the present study we determined the role of protein coating of the erythrocyte membrane and the effect of pH in the agglomeration phenomenon. Erythrocytes, which did not agglomerate and had no protein coating when fresh, agglomerated with storage; although no membrane gamma globulin was detectable, their surface contained fibrinogen. When fresh erythrocytes were coated with albumin, gamma globulin, fibrinogen or hemoglobin, they did not agglomerate. The incubation of fresh washed erythrocytes in ACD or PBS at pH 5.5, in the presence or absence of plasma, induced agglomeration, and the cells reacted with antibody to fibrinogen. Fresh cells from patients with immune disorders, including multiple myeloma, immune‐hemolytic anemia, and rheumatoid arthritis, did not agglomerate. Erythrocytes of these patients were stored in the presence and absence of their plasma, at different buffer systems. Agglomeration after storage was independent of the protein level and the pH of the system appeared to be the major factor. Agglomeration also occurred after several weeks of storage at constant pH of 7.1 and absence of proteins. The findings are consistent with the hypothesis that traces of fibrinogen are adsorbed to circulating erythrocytes, but are only accessible to the antibody reagent after metabolic membrane alterations had occurred after storage. These changes can also be induced by lowering the pH. It appears that the interaction of these factors is mainly responsible for the agglomeration phenomenon.