Polymorphism of the fourth complement component in the dog.

The polymorphism of the fourth complement component was studied in 118 unrelated dogs from different breeds and 73 unrelated beagles. In the mixed breed population, five different variants were observed with the following gene frequencies: C41 = 3.9%; C42 = 13.6%; C421 = 6.0%; C43 = 9.0% and C44 = 51.1%. In beagles, only four variants could be identified with gene frequencies of C42 = 24.2%; C421 = 1.4%; C43 = 20.6% and C4*4 = 46.3%. In both populations analyzed positive linkage disequilibria between certain DLA antigens and C4 variants were recognized. The biochemical analysis of the canine C4 revealed a double-banding pattern for the C4 alpha chain which gives preliminary evidence for two gene loci encoding for the fourth complement component in the dog.