The pyloric caeca area is a major site for IgM+ and IgT+ B cell recruitment in response to oral vaccination in rainbow trout

Abstract

Although previous studies have characterized some aspects of the immune response of the teleost gut in response to diverse pathogens or stimuli, most studies have focused on the posterior segments exclusively. However, there are still many details of how teleost intestinal immunity is regulated that remain unsolved, including the location of IgM + and IgT + B cells along the digestive tract and their role during the course of a local stimulus. Thus, in the current work, we have studied the B cell response in five different segments of the rainbow trout (Oncorhynchus mykiss) digestive tract in both naïve fish and fish orally vaccinated with an alginate-encapsulated DNA vaccine against infectious pancreatic necrosis virus (IPNV). IgM + and IgT + cells were identified all along the tract with the exception of the stomach in naïve fish. While IgM + cells were mostly located in the lamina propria (LP), IgT + cells were primarily localized as intraepithelial lymphocytes (IELs). Scattered IgM + IELs were only detected in the pyloric caeca. In response to oral vaccination, the pyloric caeca region was the area of the digestive tract in which a major recruitment of B cells was demonstrated through both real time PCR and immunohistochemistry, observing a significant increase in the number of both IgM + and IgT + IELs. Our findings demonstrate that both IgM + and IgT + respond to oral stimulation and challenge the paradigm that teleost IELs are exclusively T cells. Unexpectedly, we have also detected B cells in the fat tissue associated to the digestive tract that respond to vaccination, suggesting that these cells surrounded by adipocytes also play a role in mucosal defense.

Time after seawater transfer influences immune cell abundance and responses to SAV3 infection in Atlantic salmon

“…The MHC class II + and IgM + cells detected in pyloric caeca in the present study in control fish might represent the subset of leucocytes observed in teleosts in previous reports (Hetland et al., ; Press & Evensen, ). In agreement with our results, low numbers of MHC class II + cells have also been reported in hearts of Atlantic salmon at ~1 year post‐seawater transfer (Yousaf et al., ), and the presence of IgM + and IgT + cells in pyloric caeca in naïve rainbow trout has also been observed (Ballesteros et al., ). The control fish in Phase‐B fish have been exposed to environmental antigens in the seawater for a longer time compared with the Phase‐A fish.…”

“…In addition, the increase in CD8 + cells in the Phase‐B fish in the pyloric caeca indicates the role of this organ during virus infection and warrants further study. The presence of IgM + and IgT + cells in the pyloric caeca of rainbow trout in response to oral IPNV DNA vaccine has been observed in a previous study (Ballesteros et al., ). These results suggest an immunological role of pyloric caeca in addition to nutrient digestion and absorption.…”

Identification of the First Teleost CD5 Molecule: Additional Evidence on Phenotypical and Functional Similarities between Fish IgM+ B Cells and Mammalian B1 Cells

“…Blood was extracted from the caudal vein of freshly killed rainbow trout using a heparinized needle/syringe. Transcardial perfusion using teleost Ringer's solution (pH 7.4) containing 0.1% procaine was undertaken to remove all blood from fish tissues as previously described (44). Thymus, head kidney, gills, spleen, intestine, skin, gonad, muscle, heart, and liver samples were then collected and placed in TRIzol (45,46).…”

Rainbow trout mount a robust specific immune response upon anal administration of thymus-independent antigens

“…Despite the important structural differences between the mammalian and the teleost immune system that include the lack of lymph nodes, bone marrow (with the kidney being the main hematopoietic organ) or cognate germinal centers, the presence of these functionally and phenotypically different B cell subsets has been demonstrated in teleost ( Ye et al, 2011 ). In many teleost species, including rainbow trout ( Oncorhynchus mykiss ), B cells have also been identified in the intestinal mucosa both within the lamina propria and as intraepithelial lymphocytes ( Rombout et al, 2011 ; Ballesteros et al, 2013 ). However, to date, little work has focused on how teleost B cells differentiate to ASCs upon encounter with different antigens and how these cells in diverse differentiation stages are distributed throughout the teleost immune tissues during the immune response ( Bromage et al, 2004 ; Ma et al, 2013 ).…”