Somatic diversification of antigen receptors across metazoans: multiple solutions for individual and specific responses to bioaggressors.

The specific immunity left by an infectious confrontation constitutes a remarkable feature of the immune system. Such an immune memory requires a specific recognition of antigens and molecular motifs from bio aggressors. The specificity and reminiscence of the immune response were explained by the theory of the clonal selection of specialized cells – the lymphocytes – proposed by Jerne and by Burnet sixty years ago. The universe of antigenic motifs was matched to a large population of lymphocytes through specific recognition of an epitope by a given receptor unique to a lymphocyte clone. The huge diversity of antigen receptors required by this model was later explained by the somatic recombination of Ig (and T cell receptors) genes. The complexity of this system and its regulation challenges our understanding of the immunity to infection, but also of the self non self recognition and resilience mechanisms.
This system of specific “adaptive immunity” is restricted to jaw vertebrates, ie sharks, fishes, amphibians reptiles birds and mammals. However, somatic mechanisms of antigen receptor diversification have been discovered in other phyla, and their complexity challenges our understanding of the immunity to microbes. We will examine conserved molecular patterns and fundamental differences between immune repertoires in different groups of animals. This comparative approach provides insights into the plasticity of (adaptive) defense systems.