INHIBITION OF C3 CONVERSION AFTER ALLOTRANSPLANTATION

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Abstract
After kidney or heart allotransplantation in man and dogs, an inhibition of the conversion of C3 by an immune complex is generated. This inhibitor is found both in the serum and attached to the graft, and it blocks the action of rather than the formation of itself. Not only can this inhibitor block the conversion of serum C3 by C3 convertase but also can block the C3 conversion mediated by zymosan and C3NeF. This has led to the conclusion that either the inhibitor stabilizes native C3 so that it no longer can react with these enzymes or it is an effective competitive substrate. Kinetic studies with C3 convertase support the fact that the inhibition is of a competitive reversible nature. In semiisolated form, the inhibitor can block the hemolysis and immune adherence of sensitized sheep erythrocytes by normal human serum. In addition, the inhibitor appears to be able to fix to a receptor site on the surface of B-type lymphocytes and, in so doing, is capable of blocking rosette formation with complement-coated cells. Evidence is presented which indicates that the inhibitor appears during lymphocyte transformation but only after a specific stimulus, such as an allotransplant.

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