RT Journal Article T1 Lympho-Hematopoietic Microenvironments and Fish Immune System A1 Zapata González, Agustín Gregorio AB In the last 50 years information on the fish immune system has increased importantly, particularly that on species of marked commercial interest (i.e., salmonids, cods, catfish, sea breams), that occupy a key position in the vertebrate phylogenetical tree (i.e., Agnatha, Chondrichtyes, lungfish) or represent consolidated experimental models, such as zebrafish or medaka. However, most obtained information was based on genetic sequence analysis with little or no information on the cellular basis of the immune responses. Although jawed fish contain a thymus and lympho-hematopoietic organs equivalents to mammalian bone marrow, few studies have accounted for the presumptive relationships between the organization of these cell microenvironments and the known immune capabilities of the fish immune system. In the current review, we analyze this topic providing information on: (1) The origins of T and B lymphopoiesis in Agnatha and jawed fish; (2) the remarkable organization of the thymus of teleost fish; (3) the occurrence of numerous, apparently unrelated organs housing lympho-hematopoietic progenitors and, presumably, B lymphopoiesis; (4) the existence of fish immunological memory in the absence of germinal centers. PB Elsevier YR 2022 FD 2022-05-13 LK https://hdl.handle.net/20.500.14352/134184 UL https://hdl.handle.net/20.500.14352/134184 LA eng NO Zapata, A. G. (2022). Lympho-Hematopoietic Microenvironments and Fish Immune System. Biology, 11(5), 747. https://doi.org/10.3390/biology11050747 NO Funding: This research was funded by the Spanish Ministry of Science, Innovation and Universities (RTI2018–093938-B-I00), the Carlos III Health Institute (RD16/0011/0002, Cell Therapy Network, TERCEL) and the Regional Government of Madrid (S2017/BMD-3692, Avancell). Acknowledgments: We thank M.P. Herráez (University of León), Alfonso Cortés, Sara Montero Herradón and Javier García-Ceca (Complutense University of Madrid) for manuscript editing and picture preparation, and Alberto Villena Cortés (University of León) for their critical reading of the original manuscript. NO Ministerio de Ciencia, Innovación y Universidades (España) NO Instituto de Salud Carlos III (España) NO Comunidad de Madrid DS Docta Complutense RD 7 abr 2026