title: The evolutionary history of lymphoid organs.
abstract: Lymphoid organs are important regulators of lymphocyte development and immune responses. During vertebrate evolution, primary lymphoid organs appeared earlier than secondary lymphoid organs. Among the sites of primary lymphopoiesis during evolution and ontogeny, those for B cell differentiation have differed considerably, although they often have had myelolymphatic characteristics. In contrast, only a single site for T cell differentiation has occurred, exclusively the thymus. Based on those observations and the known features of variable-diversity-joining gene recombination, we propose a model for the successive specification of different lymphocyte lineages during vertebrate evolution. According to our model, T cells were the first lymphocytes to acquire variable-diversity-joining-type receptors, and the thymus was the first lymphoid organ to evolve in vertebrates to deal with potentially autoreactive, somatically diversified T cell receptors.
authors.affiliation: Max Planck Institute of Immunobiology, D-79279 Freiburg, Germany. boehm@immunbio.mpg.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Boehm
authors.forename: Conrad C
authors.initials: CC
authors.lastname: Bleul
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002454:Cell Differentiation / Q000276:immunology; D008208:Lymphatic System / Q000276:immunology*; D008214:Lymphocytes / Q000166:cytology / Q000276:immunology; D011946:Receptors, Antigen / Q000276:immunology; D045567:VDJ Recombinases / Q000276:immunology / Q000378:metabolism
chemical_list: D011946:Receptors, Antigen; D045567:VDJ Recombinases