In man the structural genes for the HLA antigens are encoded on the short arm of chromosome 6 and constitute a linkage group with structural genes of the complement components Bf, C2, and C4 (Allen 1974, Fu et al. 1974, Rittner et al. 1975). The gene products of the whole group are characterized by codominant inheritance and extreme polymorphism. The C4 complement component in man consists of two structural genes (C4A and C4B) that are located to all probability between the HLB-B and HLA-D, DR loci (O'Neill et al. 1978, Hawkins et al. 1980). Analogous to the humanHLA, the species dog possesses a blood group system named DLA (dog leukocyte antigens). Until now published data were not available about a linkage between the DLA system and the above-mentioned complement components (Vriesendorp et al. 1977). Furthermore, specific heterologous antibodies toward the respective canine complement components were not described. After observing that a commercial antiserum toward human C4 precipitates protein in dog serum or plasma, we decided to study the possible polymorphism of the canine C4 complement component and their linkage to DLA.
According to the method described by Awdeh and co-workers (1979), neuraminidase-treated EDTA-plasma aliquots were subjected to high voltage agarosegel-electrophoresis and subsequently incubated with a goat-anti-human-C4-serum (Atlantic Antibodies, Scarborough, Maine, Cat. No. 006-03). The precipitated bands were visualized by Coomassie-blue staining. Where indicated after high voltage electrophoresis agarose gels were subjected to an hemolytic overlay with sheep erythrocytes that were sensitized priorly by amboceptor and C4deficient guinea pig serum to demonstrate the functional activity of canine C4 (Mauffet al. 1983). In a pilot study, electrophoresis of desialized EDTA-plasma from randomly selected beagle dogs revealed distinct protein bands with different