Identification of a pharyngeal mucosal lymphoid organ in zebrafish and other teleosts: Tonsils in fish?

• Published in: Science advances Vol. 9; no. 44; p. eadj0101
• Main Authors: Resseguier, Julien, Nguyen-Chi, Mai, Wohlmann, Jens, Rigaudeau, Dimitri, Salinas, Irene, Oehlers, Stefan H., Wiegertjes, Geert F., Johansen, Finn-Eirik, Qiao, Shuo-Wang, Koppang, Erling O., Verrier, Bernard, Boudinot, Pierre, Griffiths, Gareth
• Format: Journal Article
• Language: English; Norwegian
• Published: American Association for the Advancement of Science 01.11.2023; American Association for the Advancement of Science (AAAS)
• Subjects: Earth, Environmental, Ecological, and Space Sciences; Evolutionary Biology; Life Sciences; SciAdv r-articles
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.adj0101

The constant exposure of the fish branchial cavity to aquatic pathogens causes local mucosal immune responses to be extremely important for their survival. Here, we used a marker for T lymphocytes/natural killer (NK) cells (ZAP70) and advanced imaging techniques to investigate the lymphoid architecture of the zebrafish branchial cavity. We identified a sub-pharyngeal lymphoid organ, which we tentatively named “Nemausean lymphoid organ” (NELO). NELO is enriched in T/NK cells, plasma/B cells, and antigen-presenting cells embedded in a network of reticulated epithelial cells. The presence of activated T cells and lymphocyte proliferation, but not V(D)J recombination or hematopoiesis, suggests that NELO is a secondary lymphoid organ. In response to infection, NELO displays structural changes including the formation of T/NK cell clusters. NELO and gill lymphoid tissues form a cohesive unit within a large mucosal lymphoid network. Collectively, we reveal an unreported mucosal lymphoid organ reminiscent of mammalian tonsils that evolved in multiple teleost fish families. An unknown prominent mucosal lymphoid organ has been identified in the branchial cavity of zebrafish, and other teleost fish.