{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,27]],"date-time":"2026-10-27T22:52:52Z","timestamp":1793141572070,"version":"4.5.0"},"reference-count":37,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,3,6]],"date-time":"2026-03-06T00:00:00Z","timestamp":1772755200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Immunol."],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Atlantic cod lack functional MHC class II and CD4, raising fundamental questions about how vaccination generates protection in this species.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>\n                      We combined single-cell transcriptomic profiling of splenic cells with qRT-PCR across complementary active vaccination and passive serum-transfer experiments to define cellular and transcriptional correlates of immunity to\n                      <jats:italic>Vibrio anguillarum<\/jats:italic>\n                      .\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      Bath-vaccinated fish and recipients of immune serum showed effective containment of infection, with bacterial signals largely restricted to gills and minimal detection in spleen or head kidney, whereas na\u00efve fish frequently developed high systemic bacterial loads by day 3 post-infection. All groups exhibited increased splenic macrophage abundance following challenge, but only na\u00efve fish showed strong and sustained inflammatory activation, consistent with their higher pathogen burden. Vaccinated fish and immune-serum recipients displayed only transient or weak myeloid responses despite similar early neutrophil activation. Across both experimental models, a transcriptionally distinct B-cell subset expanded at the peak of infection. This population showed increased immunoglobulin and MHC class I expression together with innate sensing features, consistent with an activated B-cell state. Although this B-cell subset increased in all groups, the largest expansions were observed in vaccinated fish and immune-serum recipients. Overall, these findings are consistent with antigen-specific IgM enhancing early B-cell activation and contributing to protection against\n                      <jats:italic>V. anguillarum<\/jats:italic>\n                      through coordinated humoral and innate-like B-cell responses.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Discussion<\/jats:title>\n                    <jats:p>\n                      These findings identify an antibody-driven mode of immune coordination that operates independently of classical CD4\n                      <jats:sup>+<\/jats:sup>\n                      T-cell help and provide insight into how effective vaccination can be achieved in vertebrates with divergent adaptive immune architectures.\n                    <\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fimmu.2026.1771403","type":"journal-article","created":{"date-parts":[[2026,3,6]],"date-time":"2026-03-06T05:29:57Z","timestamp":1772774997000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":2,"title":["IgM-mediated protection drives early B-cell activation and mucosal containment of Vibrio anguillarum in Atlantic cod (Gadus morhua)"],"prefix":"10.3389","volume":"17","author":[{"given":"Naomi Croft","family":"Guslund","sequence":"first","affiliation":[{"name":"Section for Physiology and Cell Biology, Department of Biosciences, University of Oslo","place":["Oslo, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alexandra","family":"Jonsson","sequence":"additional","affiliation":[{"name":"Section for Physiology and Cell Biology, Department of Biosciences, University of Oslo","place":["Oslo, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Anders K.","family":"Krabber\u00f8d","sequence":"additional","affiliation":[{"name":"Section for Genetics and Evolutionary Biology, Department of Biosciences, University of Oslo","place":["Oslo, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Adri\u00e1n","family":"L\u00f3pez-Porras","sequence":"additional","affiliation":[{"name":"Section for Physiology and Cell Biology, Department of Biosciences, University of Oslo","place":["Oslo, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Simen F.","family":"N\u00f8rsteb\u00f8","sequence":"additional","affiliation":[{"name":"Department of Preclinical Sciences and Pathology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences","place":["\u00c5s, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Henning","family":"S\u00f8rum","sequence":"additional","affiliation":[{"name":"Department of Paraclinical Sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences","place":["\u00c5s, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kjetill S.","family":"Jakobsen","sequence":"additional","affiliation":[{"name":"Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo","place":["Oslo, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Finn-Eirik","family":"Johansen","sequence":"additional","affiliation":[{"name":"Section for Physiology and Cell Biology, Department of Biosciences, University of Oslo","place":["Oslo, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shuo-Wang","family":"Qiao","sequence":"additional","affiliation":[{"name":"Department of Immunology, Institute of Clinical Medicine, University of Oslo","place":["Oslo, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,3,6]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1444-2906.2005.01052.x","article-title":"Why is the antibody response of Atlantic cod so poor? 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