Complement components of a haemolytically deficient strain of rabbits.

A strain of complement (C′) deficient rabbits was studied. No C′ haemolytic activity was found in the sera of these rabbits. Both haemolytic and leucocidal activities were stored upon adding purified C′ isolated from either normal rabbits or normal guinea-pigs. The mixture of deficient serum with sensitized sheep cells resulted in the generation of active C′ sites, SAbC′ since lysis occurred after the addition of highly purified C′, C′, C′ and C′ to the washed cells. These rabbits possess a heat labile substance which is considerably heavier than C′. This C′ inactivator reacts specifically with the intermediate complex, EAbC′. The product of the reaction appears to be incapable of combining with the next component in the haemolytic sequence, C′. The inactivator is not depleted from the fluid phase during interaction with cells possessing active C′ sites. The elution characteristics from DEAE- and CM-cellulose and the sedimentation constants C′ and of the inactivator, as well as of certain other rabbit C′ components, were determined. C′ inactivator was also found in normal rabbit serum. A mechanism to explain the variability in results of homotransplant rejection in C′ deficient rabbits is offered.