Immunological cross-reactivity between thyroglobulins of mammals and reptiles

Purified thyroglobulins of four mammalian species (pig, sheep, horse, rabbit), two reptilian species (python, crocodile), and one avian species (duck) were tested for immunological cross-reactivity in two test systems. One was the double diffusion in agar immunoprecipitation technique of Ouchterlony. In the other test system (immunoassay) the various thyroglobulins were permitted to compete with, or inhibit a homologous radioactive thyroglobulin reacting with its specific antibody. The second technique enabled measurement of the degree of inhibition. In the immunoprecipitation the mammalian thyroglobulins (TG) cross-reacted to various degrees, but a nonmammalian thyroglobulin never precipitated with an antisheep TG or antipig TG antibody. In the radioimmunoassay the two reptilian thyroglobulins inhibited the homologous antigen-antibody reaction as well as several mammalian thyroglobulins. Duck thyroglobulin never cross-reacted in this way. It appears from these initial experiments that there is some degree of molecular or immunochemical resemblance between mammalian and reptilian thyroglobulins. Thyroglobulin of the one avian species tested (duck) showed no such resemblance.