Quantitation of the third component of complement on stored red cells

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Abstract
By means of an automated anti-C3c consumption technique the molecules of the 3rd component of human complement (containing the C3c fragment) that accumulate on red cells (RBC) were quantitated during liquid whole-blood storage. Calibrated C3-sensitized zymosan particles (ZyC3) were used as standards for bound C3. Although the dose-response curves of anti-C3c neutralization by ZyC3 and stored RBC were similar, mathematical analysis showed that the shapes of these 2 sigmoidal curves were significantly different. The large C3 molecules bound to stored RBC apparently differed antigenically from those bound to ZyC3. Despite this difference, the former could be quantitated adequately by the automated anti-C3c consumption technique. Red cell-bound large C3 molecules were measured following various periods of storage at 4.degree. C of whole blood samples (n = 102). An average of 48 molecules were detected on RBC stored for 21 days. Statistical analysis of these data indicated that during storage at 4.degree. C there was a continuous accumulation of C3 on RBC, followed by cleavage of C3c fragments. The degree of agglutination of stored RBC with anti-C3c was proportional to the number of cell-bound large C3 molecules.