title: On the origins of the adaptive immune system: novel insights from invertebrates and cold-blooded vertebrates.
abstract: When and how adaptive immunity emerged is one of the fundamental questions in immunology. Accumulated evidence suggests that the key components of adaptive immunity, rearranging receptor genes and the MHC, are unique to jawed vertebrates. Recent studies in protochordates, in particular, the draft genome sequence of the ascidian Ciona intestinalis, are providing important clues for understanding the origin of antigen receptors and the MHC. We discuss a group of newly identified protochordate genes along with some cold-blooded vertebrate genes, the ancestors of which might have provided key elements of antigen receptors. The organization of the proto-MHCs in protochordates provides convincing evidence that the MHC regions of jawed vertebrates emerged as a result of two rounds of chromosomal duplication.
authors.affiliation: Department of Biosystems Science, School of Advanced Sciences, The Graduate University for Advanced Studies (Sokendai), Shonan Village, Hayama 240-0193, Japan. kasahara@soken.ac.jp
authors.forename: Masanori
authors.initials: M
authors.lastname: Kasahara
authors.forename: Takashi
authors.initials: T
authors.lastname: Suzuki
authors.forename: Louis Du
authors.initials: LD
authors.lastname: Pasquier
mesh_terms: D000818:Animals; D002816:Chordata, Nonvertebrate / Q000235:genetics* / Q000276:immunology; D019143:Evolution, Molecular; D023061:Gene Order / Q000235:genetics; D015322:Gene Rearrangement, B-Lymphocyte / Q000235:genetics; D015329:Gene Rearrangement, T-Lymphocyte / Q000235:genetics; D006801:Humans; D007110:Immunity, Active / Q000235:genetics*; D007113:Immunity, Innate / Q000235:genetics*; D007694:Killer Cells, Natural / Q000276:immunology / Q000378:metabolism; D008214:Lymphocytes / Q000276:immunology / Q000378:metabolism; D008285:Major Histocompatibility Complex / Q000235:genetics / Q000276:immunology; D010802:Phylogeny; D014714:Vertebrates / Q000235:genetics* / Q000276:immunology