PARADOXICAL RECONSTITUTION OF COMPLEMENT ACTIVITY FOLLOWING PLASMA TRANSFUSION OF AN INDIVIDUAL WITH DEFICIENCY OF THE 7TH-COMPONENT OF COMPLEMENT

A subject deficient in the seventh component of complement (C7) was pl asmapheresed with 660 ml C7-sufficient plasma. The expected reconstitu tion of C7 activity, followed by exponential decay, was not observed. During day 1, serum haemolytic C7 and total haemolytic complement were undetectable and C7 levels were very low by C7 ELISA. However, low le vels of circulating fluid phase terminal complement complex (TCC) were detected. On day 2 about mu g C7/ml serum was detected and this rose to 6 mu g/ml by day 17. Functional complement activity was also presen t. At day 28 the serum C7 and total haemolytic complement had dropped to pretransfusion levels. A low level of C5b6 was present in pretransf usion serum and this increased markedly immediately following transfus ion when the patient's serum also acquired C7 consuming activity. Thro ughout the study low levels of anti-C7 antibodies were present but the re was no evidence that antibody was directly responsible for the C7 c onsumption. Nevertheless antibody-antigen interactions could have gene rated circulating C5b6. C5b6 has been shown previously to have the cap acity to inhibit C7 activity in vitro. Investigations of the C7 circul ating on days 2-17 demonstrated normal molecular weight, functionally active C7. The donor sera and the recirculating C7 allotyped C7-1 by i soelectric focusing; however, the recirculating C7 showed additional w eak bands with C7 functional activity, suggesting a possible genetic o r acquired abnormality. Although the disappearance of C7 immediately p ost-transfusion may be explained by the presence of C5b6, there is no satisfactory explanation for the rising C7 levels on days 2-17 and we cannot exclude temporary C7 secretion by the patient.