Hereditary C3 hypocomplementemia in the rabbit.

Hereditary hypocomplementemia of the third component of complement (C3) was found in a strain of rabbits in which hereditary C8 alpha-gamma deficiency was also found. The serum C3 concentration, haemolytic C3 activity and total complement haemolytic activity (CH50) of these animals were, respectively, 6-12%, 8-13% and 27-37% of the normal levels. The haemolytic complement activity in the C3 hypocomplementemic (C3-hypo) rabbit serum was restored in a dose-dependent manner by the addition of purified rabbit C3. The levels of factor H and properdin and components C2 and C6 were in the normal range, and the levels of factors B and D and component C8 were higher than normal. The low level of serum C3 in C3-hypo rabbits was not due to C3 conversion, partial C3 antigenicity, presence of a C3 inhibitor or hypercatabolism of normal C3. Furthermore, no change in the ratio of C3 protein levels was observed between C3-hypo and normal rabbits, even after turpentine injection. In addition, the C8 alpha-gamma deficiency condition does not affect C3 activity and C3 catabolism in vivo. Mating tests showed that the C3 hypocomplementemia is transmitted as a simple autosomal co-dominant trait. C3-hypo rabbits have a lower survival at 3 months than normal rabbits. C3-hypo rabbit serum also has a lower bactericidal activity than normal rabbit serum. The PAGE under reducing conditions showed no difference in the molecular weights of C3 alpha and C3 beta chains between C3-hypo, heterozygous and normal animals.