naomiac

• Guslund, Naomi Croft; Jonsson, Alexandra; Krabberød, Anders Kristian; Porras, Adrian Lopez; Nørstebø, Simen Foyn & Sørum, Henning [Show all 9 contributors for this article] (2026). IgM-mediated protection drives early B-cell activation and mucosal containment of Vibrio anguillarum in Atlantic cod (Gadus morhua). Frontiers in Immunology. 17. doi: 10.3389/fimmu.2026.1771403. Full text in Research Archive Show summary

  Background: Atlantic cod lack functional MHC class II and CD4, raising fundamental questions about how vaccination generates protection in this species. Methods: 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 Vibrio anguillarum. Results: 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 naïve fish frequently developed high systemic bacterial loads by day 3 post-infection. All groups exhibited increased splenic macrophage abundance following challenge, but only naïve 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 V. anguillarum through coordinated humoral and innate-like B-cell responses. Discussion: These findings identify an antibody-driven mode of immune coordination that operates independently of classical CD4+ T-cell help and provide insight into how effective vaccination can be achieved in vertebrates with divergent adaptive immune architectures.

• Jonsson, Alexandra; Porras, Adrian Lopez; Nørstebø, Simen Foyn; Guslund, Naomi Croft; Sørum, Henning & Qiao, Shuo-Wang [Show all 7 contributors for this article] (2025). Protective IgM-mediated immunity against Vibrio anguillarum in Atlantic cod with evolutionary losses of mhc class II and cd4. Frontiers in Immunology. 16. doi: 10.3389/fimmu.2025.1579541. Full text in Research Archive Show summary

  The unique adaptive immune system of the Atlantic cod ( Gadus morhua ), with genetic loss of the mhc class II and cd4 , poses questions about the protective role of specific antibodies in this species. We investigate the IgM response against Vibrio anguillarum , a common pathogen in aquaculture. Juvenile Atlantic cod were bath-immunized with formalin-fixed V. anguillarum serotype O2a. Vaccinated cod were fully protected against lethal vibriosis when challenged by immersion with serotype O2a and partially protected against challenge with serotype O2b. Serum IgM from immunized cod reacted specifically with V. anguillarum O2a in ELISA, with some crossreactivity towards the O2b serotype. Bath-immunized cod were also protected against intracelomic challenge with V. anguillarum O2a, supporting the induction of systemic immunity by bath vaccination. Passive transfer experiments were conducted to evaluate the protective efficacy of IgM. Naive cod that received total serum or purified IgM from immunized donors were protected against lethal vibriosis; whereas, naive cod that received naive serum were not protected. Western blotting revealed that these protective antibodies recognized a proteinase K-sensitive antigen rather than lipopolysaccharides. These insights enhance our understanding of cod immunity and provide guidance for developing future vaccination strategies in aquaculture.

• Guslund, Naomi Croft; Krabberød, Anders Kristian; Nørstebø, Simen Foyn; Solbakken, Monica Hongrø; Jakobsen, Kjetill Sigurd & Johansen, Finn-Eirik [Show all 7 contributors for this article] (2022). Lymphocyte subsets in Atlantic cod (Gadus morhua) interrogated by single-cell sequencing. Communications Biology. 5:689(1), p. 1–9. doi: 10.1038/s42003-022-03645-w. Full text in Research Archive Show summary

  Abstract Atlantic Cod ( Gadus morhua ) has lost the major histocompatibility complex class II presentation pathway. We recently identified CD8-positive T cells, B cells, and plasma cells in cod, but further characterisation of lymphocyte subsets is needed to elucidate immune adaptations triggered by the absence of CD4-positive T lymphocytes. Here, we use single-cell RNA sequencing to examine the lymphocyte heterogeneity in Atlantic cod spleen. We describe five T cell subsets and eight B cell subsets and propose a B cell trajectory of differentiation. Notably, we identify a subpopulation of T cells that are CD8-negative. Most of the CD8-negative T lymphocytes highly express the homologue of monocyte chemotactic protein 1b , and another subset of CD8-negative T lymphocytes express the homologue of the scavenger receptor m130 . Uncovering the multiple lymphocyte cell sub-clusters reveals the different immune states present within the B and T cell populations, building a foundation for further work.

• Parker, Jamie; Guslund, Naomi Croft; Jentoft, Sissel & Roth, Olivia (2022). Characterization of Pipefish Immune Cell Populations Through Single-Cell Transcriptomics. Frontiers in Immunology. 13:820152, p. 1–11. doi: 10.3389/fimmu.2022.820152. Full text in Research Archive Show summary

  Teleost adaptive immune systems have evolved with more flexibility than previously assumed. A particularly enigmatic system to address immune system modifications in the evolutionary past is represented by the Syngnathids, the family of pipefishes, seahorses and seadragons. These small fishes with their unique male pregnancy have lost the spleen as an important immune organ as well as a functional major histocompatibility class II (MHC II) pathway. How these evolutionary changes have impacted immune cell population dynamics have up to this point remained unexplored. Here, we present the first immune cell repertoire characterization of a syngnathid fish ( Syngnathus typhle ) using single-cell transcriptomics. Gene expression profiles of individual cells extracted from blood and head-kidney clustered in twelve putative cell populations with eight belonging to those with immune function. Upregulated cell marker genes identified in humans and teleosts were used to define cell clusters. While the suggested loss of CD4+ T-cells accompanied the loss of the MHC II pathway was supported, the upregulation of specific subtype markers within the T-cell cluster indicates subpopulations of regulatory T-cells ( il2rb ) and cytotoxic T-cells ( gzma ). Utilizing single-cell RNA sequencing this report is the first to characterize immune cell populations in syngnathids and provides a valuable foundation for future cellular classification and experimental work within the lineage.

• Sudworth, Amanda; Segers, Filip; Yilmaz, Bahtiyar; Guslund, Naomi Croft; Macpherson, Andrew J. & Dissen, Erik [Show all 8 contributors for this article] (2022). Innate lymphoid cell characterization in the rat and their correlation to gut commensal microbes. European Journal of Immunology. ISSN 0014-2980. 52(5), p. 717–729. doi: 10.1002/eji.202149639. Full text in Research Archive Show summary

  Innate lymphoid cells (ILCs) are important for tissue immune homeostasis, and are thoroughly characterized in mice and humans. Here, we have performed in-depth characterization of rat ILCs. Rat ILCs were identified based on differential expression of transcription factors and lack of lineage markers. ILC3s represented the major ILC population of the small intestine, while ILC2s were infrequent but most prominent in liver and adipose tissue. Two major subsets of group 1 ILCs were defined. Lineage–T-bet+Eomes+ cells were identified as conventional NK cells, while lineage–T-bet+Eomes– cells were identified as the probable rat counterpart of ILC1s based on their selective expression of the ILC marker CD200R. Rat ILC1s were particularly abundant in liver and intestinal tissues, and were functionally similar to NK cells. Single-cell transcriptomics of spleen and liver cells confirmed the main division of NK cells and ILC1-like cells, and demonstrated Granzyme A as an additional ILC1 marker. We further report differential distributions of NK cells and ILCs along the small and large intestines, and the association of certain bacterial taxa to frequencies of ILCs. In conclusion, we provide a framework for future studies of ILCs in diverse rat experimental models, and novel data on the potential interplay between commensals and intestinal ILCs.

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