Discovery of a Novel Lymphoid Structure in the Nasal Cavity of Fish: Implications in Responses to Vaccination

1,2Fen Dong, 1Elisa Casadei, 3Julien Resseguier, 1Irene Salinas

 1 Department of Biology, University of New Mexico, Albuquerque, New Mexico, USA; 2 Department of Aquatic Animal Medicine, College of Fisheries, Huazhong Agricultural University, Wuhan, Hubei, 430070, China; 3 Department of Biosciences, University of Oslo, Norway

ABSTRACT

Fish mucosa-associated lymphoid tissues (MALT) protect teleosts from pathogen invasion and infection. Teleost MALT have thought to consist exclusively of diffuse immune cells, lacking organized structures such as mammalian tonsils and Peyer’s patches. Organized mucosa-associated lymphoid tissues (O-MALT) are considered inductive sites in mammals, serving as continuous sources of memory B and T cells that then move to mucosal effector sites. We previously described the presence of a nasopharynx-associated lymphoid tissue in the olfactory mucosa of rainbow trout (Oncorhynchus mykiss) characterized by the presence of scattered innate and adaptive immune cells. Trout nasal-associated lymphoid tissues (NALT) is stimulated upon intranasal vaccination and during infection. Intranasal vaccination is highly protective against bacterial and viral pathogens and causes local modification of the B cell repertoire. Here we report the presence of a novel lymphoid structure present at the entry of the nasal cavity in rainbow trout and zebrafish (Danio rerio). Immunofluorescence staining reveals that rainbow trout organized NALT (O-NALT) mainly consists of CD4+ and CD8+ T cells as well as some IgM+ B cells and a few IgT+ B cells. A large cluster of T cells is also observed in the same location in the nasal cavity of adult zebrafish. Laser-capture microdissection of control rainbow trout O-NALT and diffuse NALT (dNALT) followed by RT-qPCR indicates that O-NALT is enriched in expression of T cell markers, the chemokine CCL19, and the activation induced deaminase (AID) responsible for maturation of the adaptive immune response compared to dNALT. Intranasal vaccination with live attenuated infectious hematopoietic necrosis virus (IHNV) vaccine results in changes in trout O-NALT immune cell composition, with increased proportions of CD8+ T cells 1 day and 30 days post-vaccination. IgM+ B cells increase in O-NALT 1 day post-vaccination, decrease 7 days post-vaccination and remain unchanged thereafter. A trend toward increased IgT+ B cell numbers in O-NALT occurs 90 days post IHNV intranasal vaccination. Current efforts aim to evaluate the changes in the B and T cell repertoire in the O-NALT of control and vaccinated trout and in response to a secondary booster vaccination. Our results indicate that O-NALT is an overlooked MALT in teleosts and that it actively participates in the immune response to mucosal vaccines.