Zapata González, Agustín Gregorio2026-03-202026-03-202022-05-13Zapata, A. G. (2022). Lympho-Hematopoietic Microenvironments and Fish Immune System. Biology, 11(5), 747. https://doi.org/10.3390/biology1105074710.3390/biology11050747https://hdl.handle.net/20.500.14352/134184Funding: 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.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.engAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/journal article2079-7737https://doi.org/10.3390/biology11050747open access597:612.017Teleost fish ImmunityThymusPeripheral lymphoid organsMALT T and B lymphocytesGerminal centers and immune memoryBiología celular (Biología)Biología molecular (Biología)InmunologíaGenética2407 Biología Celular2412 Inmunología2415 Biología Molecular2409 Genética