Antigen competition: Evolutionary and functional considerations in amphibia

Antigen competition was studied in two amphibia, Notophthalmus viridescens and Xenopus laevis, using sheep and horse erythrocytes injected simultaneously or sequentially. Members of these two species are known to differ with regard to evolutionary, anatomical, developmental, and functional aspects of immunity. The antigen competition response pattern of the more primitive Notophthalmus differed from that of Xenopus. Our results suggest that in evolution new immunologic mechanisms may have developed which provide (a) a capacity to respond when two non-cross-reacting immunogens are presented simultaneously, and (b) a more effective inhibition of responsivity to the second immunogen when they are presented sequentially. Both may have arisen as a consequence of the evolution of genetic diversity providing functional restriction of individual lymphocytes. Data derived from the exploration of dosage, adult thymectomy, LPS, and colloidal carbon effects on antigen competition in Xenopus suggest that it depends on high doses of competing immunogen, maybe thymus independent, and may involve regulatory phagocytes.