Abstract
B cell responses are a crucial part of the adaptive immune response to viral infection. Infection by salmonid alphavirus subtype 3 (SAV3) causes pancreas disease (PD) in Atlantic salmon (Salmo salar) and is a serious concern to the aquaculture industry. In this study, we have used intraperitoneal (IP) infection with SAV3 as a model to characterize local B cell responses in the peritoneal cavity (PerC) and systemic immune tissues (head kidney/spleen). Intraperitoneal administration of vaccines is common in Atlantic salmon and understanding more about the local PerC B cell response is fundamental. Intraperitoneal SAV3 infection clearly induced PerC B cell responses as assessed by increased frequency of IgM+ B cells and total IgM secreting cells (ASC). These PerC responses were prolonged up to nine weeks post-infection and positively correlated to the anti-SAV3 E2 and to neutralizing antibody responses in serum. For the systemic immune sites, virus-induced changes in B cell responses were more modest or decreased compared to controls in the same period. Collectively, data reported herein indicated that PerC could serve as a peripheral immunological site by providing a niche for prolonged maintenance of the ASC response in Atlantic salmon.
Highlights
Adaptive humoral immunity is an essential component of the defense against viral infections
Characterizing the resident B cell populations in naïve Atlantic salmon lays the groundwork for evaluating the effects infectious challenge triggers on the humoral immune response
A small population of IgM ASC comprising 0.6–1.4% of total leukocytes was found to reside in the systemic lymphoid tissues and peritoneal cavity (PerC), respectively, of naïve Atlantic salmon with the total IgM ASC count being highest in HK
Summary
Adaptive humoral immunity is an essential component of the defense against viral infections. Teleost fish are one of the oldest living groups of organisms possessing elements of the adaptive immune system as described in mammals. Some major differences are present making this species a useful comparative model of lower vertebrate immunology [reviewed in Ref. While lymph nodes and bone marrow are lacking, the major systemic lymphoid tissues in teleosts involved in B cell generation and activation are the anterior kidney (head kidney, HK) and spleen. Ig (immunoglobulin) class switching is absent in teleosts and they rely on un-switched IgM responses with limited affinity maturation upon repeated immune challenges [reviewed in Ref. IgM is the principal systemic Ig, which is most abundant in serum and is co-expressed with IgD on the surface of teleost B cells [2]. IgT is the predominant Ig at mucosal surfaces and is secreted
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