Broad phylogenetic expression of heavy-chain determinants detected by rabbit antisera to VHa allotypes

Immunoglobulin molecules from diverse vertebrate species were examined, using an enzyme-linked immunosorbent assay (ELISA), for the expression of determinants detectable by rabbit antisera to VHa allotypes. The data indicate that immunoglobulins of elasmobranchs, teleosts, amphibians and birds express determinants cross-reactive with those specified by the a1, a2 and a3 alleles in the domestic rabbit. We localize VHa cross-reactive specificity to the denatured heavy chain of a primitive vertebrate, the Galapagos shark (Carcharhinus galapagensis). Furthermore, the N-terminal amino acid sequence of the shark heavy chain shows significant homology with rabbit heavy chains of known VHa type at positions where allotype-correlated differences have been implicated. VHa-related determinants are shared by immunoglobulins of a wide range of vertebrates from sharks to man and thus seem to be epitopes which have been conserved during vertebrate evolution. The determinants detected on immunoglobulins of lower vertebrates by rabbit anti-VHa allotype sera most probably are VH-subgroup rather than allotypic markers. Their distribution demonstrates a strong phylogenetic conservation of VH-regions.