Genetic polymorphism of the complement C2 in Japanese.

Genetic polymorphism of the second component of human complement (C2) was investigated in 521 unrelated healthy adult Japanese using isoelectric focusing in polyacrylamide gel followed by a specific hemolytic overlay method. Besides the phenotypes reported previously (C, AC and BC), a relatively infrequent double-banded phenotype (tentatively named A'C) was observed. Moreover, a homozygous variant (A) and a heterozygous "double" variant (AB) were observed. The estimated frequencies for the common allele, C2c(= C2(1)), and the variant alleles, C2A, C2B(= C2(2)) and C2A' were 0.939, 0.034, 0.022, and 0.006, respectively. The results of further typing for HLA-A, -B, -C specificities indicated the presence of significant associations of C2A with HLA-B15 and with A26, and of C2B with HLA-Bw61. These findings support our previous observation that in Japanese there are allelic combinations showing linkage disequilibrium between C2 and HLA loci which are different from those in Caucasians, and that the C2 structural locus is more closely linked to HLA-B than to HLA-A. C2 hemolytic activities of each phenotypes were assayed. The mean activity of type AC sera was significantly higher than that of type C or type BC, while there were no differences in the activities among the types C, BC or A'C. Also presented are two pedigrees demonstrating the segregation of C2 with HLA alleles in which a homozygous C2 A or C2 B individual was observed.