ANTIGENIC CROSS-REACTIONS AMONG IMMUNOGLOBULIN OF DIVERSE VERTEBRATES (ELASMOBRANCHS TO MAN) DETECTED USING XENOANTISERA

1. Antisera raised in rabbits and goats against intact immunoglobulins or their constituent light and heavy chains from man, mouse and the galapagos shark (Carcharhinus galapagenesis) were tested for their reactivity with immunoglobulins of elasmobranchs, other lower vertebrates and eutherian and prototherian mammals. 2. Xenoantisera directed against human heavy chain isotypes allowed the serological identification of IgM and IgG immunoglobulins in the echidna (Tachyglossus aculeatus), a monotreme which is one of the most primitive species of extant mammals. 3. The antisera to heavy chains reacted to varying degrees with purified immunoglobulins of non-mammalian species, including the chicken, teleost fish and elasmobranchs in a fashion that was specific for immunoglobulins, but was not related to defined human isotypic markers. 4. The reactions of some antisera seem to skip species known to possess homologous immunoglobulins. 5. Antisera directed against isotypic markers of human kappa and lambda light chains reacted with shark light chains in a manner that was specific for light chain determinants but was not isotype-related. 6. Antisera directed against heavy chains of either sharks or mammals reacted with heavy chains, but not with light chains of diverse species. 7. A rabbit antiserum specific for shark light chain reacted with human and murine monoclonal lambda-chains and with two synthetic peptides corresponding to human V-lambda Fr3 and Fr4 sequences. 8. These results establish that a variety of antigenic markers including conformational and linear determinants can be shared among immunoglobulins of vertebrates species that had an ancestral divergence more than 400 million years ago.