Complement components detected on normal red blood cells taken into EDTA and CPD.

Normal red blood cells (RBC) from fresh EDTA and CPD blood and from stored CPD blood were examined for the presence of bound subcomponents of C3 and C4. By serologic agglutination tests, only C3d was detectable on the cells. Incubation in compatible fresh normal serum (FNS) at 37 degrees C appeared to increase the amount of 3Cd on the RBC. C3b was serologically detectable only on stored CPD cells and only after incubation in compatible FNS. No. C4 components were detected on the cell surfaces in agglutination tests. Using an indirect labeling technique, small, but significant, amounts of C3d and C4d were found on all three types of untreated cells. C3b was present on stored CPD cells only. The indirect labeling technique showed a significant increase in C3d and C4d on all cells following incubation i- compatible FNS, whereas bound C3b was significantly increased only with stored CPD cells. There was no increase in bound C4b following serum incubation. The average number of C3d molecules per cell on normal EDTA cells was 557 and average Ko was 3.6 x 10(7) l/mol.