title: Evolution of vertebrate adaptive immunity: immune cells and tissues, and AID/APOBEC cytidine deaminases.
abstract: All surviving jawed vertebrate representatives achieve diversity in immunoglobulin-based B and T cell receptors for antigen recognition through recombinatorial rearrangement of V(D)J segments. However, the extant jawless vertebrates, lampreys and hagfish, instead generate three types of variable lymphocyte receptors (VLRs) through a template-mediated combinatorial assembly of different leucine-rich repeat (LRR) sequences. The clonally diverse VLRB receptors are expressed by B-like lymphocytes, while the VLRA and VLRC receptors are expressed by lymphocyte lineages that resemble αβ and γδ T lymphocytes, respectively. These findings suggest that three basic types of lymphocytes, one B-like and two T-like, are an essential feature of vertebrate adaptive immunity. Around 500 million years ago, a common ancestor of jawed and jawless vertebrates evolved a genetic program for the development of prototypic lymphoid cells as a foundation for an adaptive immune system. This acquisition preceded the convergent evolution of alternative types of clonally diverse receptors for antigens in all vertebrates, as reviewed in this article.
authors.affiliation: Department of Pathology and Laboratory Medicine, Emory Vaccine Center, Emory University, Atlanta, GA, USA.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hirano
mesh_terms: D056704:Adaptive Immunity / Q000235:genetics*; D000818:Animals; D003564:Cytidine Deaminase / Q000502:physiology*; D019143:Evolution, Molecular; D006801:Humans; D008214:Lymphocytes / Q000201:enzymology / Q000276:immunology*; D008221:Lymphoid Tissue / Q000201:enzymology / Q000276:immunology*; D011946:Receptors, Antigen / Q000235:genetics
chemical_list: D011946:Receptors, Antigen; D003564:Cytidine Deaminase
keywords: AID/APOBEC; adaptive immunity; evolution; lymphocytes; lymphoid tissues