title: The invention of lymphocytes.
abstract: Lamprey and hagfish are surviving representatives of the most ancient vertebrates. They possess adaptive immune systems based on a vast, somatically diversified repertoire of lymphocyte-bound antigen receptors. Despite these similarities to antibody and T cell receptors (TCR) of later vertebrates, the variable lymphocyte receptors (VLR) are not related to the immunoglobulin (Ig)-superfamily of genes; and instead of V(D)J recombination VLR are somatically assembled by a gene conversion process. However, recent studies have revealed two lamprey lymphocyte subsets so closely resembling B cells and T cells that separate lymphocyte lineages must have already existed in the ancestral vertebrate, before Ig/TCR emergence. VLR and Ig/TCR arose independently, but the convergent evolution they display actually reflects their selection in cells with specialized functions.
authors.affiliation: Department of Physiology and Pharmacology, State University of New York and Health Science Center at Brooklyn, Brooklyn, NY 11203, USA. hsue@hscbklyn.edu
authors.forename: Ellen
authors.initials: E
authors.lastname: Hsu
mesh_terms: D056704:Adaptive Immunity; D000818:Animals; D019143:Evolution, Molecular; D006801:Humans; D008214:Lymphocytes / Q000276:immunology*; D011946:Receptors, Antigen / Q000276:immunology
chemical_list: D011946:Receptors, Antigen