AUTHOR=Ferreira Inês A. , Peixoto Diogo , Losada Ana Paula , Quiroga María Isabel , Vale Ana do , Costas Benjamín 

TITLE=Early innate immune responses in European sea bass (Dicentrarchus labrax L.) following Tenacibaculum maritimum infection

JOURNAL=Frontiers in Immunology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.1254677

DOI=10.3389/fimmu.2023.1254677

ISSN=1664-3224

ABSTRACT=<sec><title>Introduction</title><p>The marine aquaculture industry has been witnessing a worldwide emergence of tenacibaculosis, a poorly understood bacterial disease caused by <italic>Tenacibaculum maritimum</italic> that affects commercially important fish. So far, knowledge on the <italic>T. maritimum</italic> virulence mechanisms is scarce and the pathogen-host interaction operating in tenacibaculosis remain to be disclosed. This study aimed at contributing to a better understanding of this disease, by evaluating the early innate immune response triggered in European sea bass (<italic>Dicentrarchus labrax</italic>) by a bath-challenge with <italic>T. maritimum</italic>.</p></sec><sec><title>Methods</title><p>Groups of sea bass were bath-challenged with <italic>T. maritimum</italic> (challenged fish) or mock-challenged. Undisturbed fish were used as controls (time 0). Samples of blood, liver and mucosal organs (skin, gills and posterior-intestine) were collected at 0 h (control) and at 6, 24, 48 and 72 h post-challenge (n=12). Mucosal organs were used for analyzing the expression of immune-related genes by RT-qPCR, as well as blood samples for assessing haematological and innate humoral parameters and liver for oxidative stress assessment.</p></sec><sec><title>Results</title><p>An increased expression of <italic>il-1β</italic>, <italic>il8</italic>, <italic>mmp9</italic> and <italic>hamp1</italic> was detected in all mucosal organs of infected fish when compared with control and mock-challenged fish, suggesting a pro-inflammatory response against <italic>T. maritimum</italic> transversal to all organs. The faster induction of these pro-inflammatory genes was observed in the gills. Regarding the systemic response, challenged fish presented neutrophilia, monocytosis, signs of anemia, and a decrease of bactericidal and lysozyme activities in plasma. Almost no variations were observed regarding hepatic oxidative stress.</p></sec><sec><title>Discussion/Conclusions</title><p>The present study suggests that <italic>T. maritimum</italic> induces a local innate immune response upon bath infection not only in the skin of European sea bass, but also in the gills and posterior-intestine, likely triggered by the <italic>T. maritimum</italic>’s capacity to adhere, colonize and damage these organs that can function as entry ways to bacteria, leading ultimately to the seen host’s systemic response.</p></sec>