Study of A100 allotypic specificity of rabbit immunoglobulins: the cross-reactivity between A100, a1 and a3

Evidence for the genetic determination of A100 allotypic specificity suggests that it is the product of an allele at the alpha locus. The A100 allotypic specificity was detected in a wild rabbit lacking all the known specificities of the a series. None of the 8 rabbits possessing the A100 allotypic specificity possessed two allotypic specificities of the a series. The concentration of A100+ molecules is larger in the serum of a presumably homozygous rabbit than in that of a presumably heterozygous rabbit. In the sera of heterozygous A100+ rabbits, the A100 allotypic specificity and the known specificity of the a series are carried by different molecules. The determinants responsible for the A100 allotypic specificity are present both on IgG and IgM. They are located on the heavy chain and the Fab fragment of IgG. A family of variants of A100 specificity has been detected and cross-reactivity between A100, a1 and a3 specificities has been found. This was detected and studied with anti-a3 antisera. It seems that A100 allotypic specificity is closer to a3 specificity than a1 is to a3 specificity.