Conservation among the immunoglobulins of carcharhine sharks and phylogenetic conservation of variable region determinants

To study primitive vertebrate recognition molecules we have purified the immunoglobulins of three species of carcharhine sharks. The tiger ( Galeocerdo cuvieri), the sandbar ( Carcharhinus plumbeus) and the galapagos sharks ( Carcharhinus galapagensis) possess 18S high molecular weight and 7S low molecular weight immunoglobulin forms. Both within and between species these forms closely resemble each other in polypeptide chain composition, heavy chain mass, carbohydrate content, amino acid composition, antigenic character and amino terminal sequence. These carcharhine species are separated by at least 30 million years of evolutionary time and it is remarkable that so little diversification of immunoglobulin structure has occurred during their evolution. By several criteria carcharhine immunoglobulins most closely resemble mammalian IgM. Studies of serological cross-reactions indicate that some immunoglobulin determinants have been conserved over a broad phylogenetic range of vertebrate classes; most notably J H and V Ha-related markers are shared between forms as diverse as sharks and mammals.