| Summary: | Trabajo presentado en 3rd International Conference on Fish and Shellfish Immunology (ISFSI), celebrada en Gran Canaria (España), del 16 al 20 de junio de 2019 Fish spleen is an organ rich in lymphocytes, particularly, in B lymphocytes, playing a relevant role in the adaptive immune response after vaccination. After fish vaccination by intraperitoneal injection, there is a strong migration of antigen containing cells to the spleen, where antigen presentation occurs. In the present study, we have analysed the B cell populations (IgM, IgT or IgD positive cells) and the gene expression (IgM, IgT, IgD, MHCII, and several immune related genes) in the spleen of turbot immunized with a vaccine containing an oleous adjuvant and a particulated Philasterides dicentrarchi antigen. Fish were immunized at days 0 and 30, and samples were obtained at dasy 3, 7, 33, 37 and 60. The vaccine provoked a significant increase in specific and total serum IgM at 37 dpi and at 60 dpi, but the specific IgT levels did not vary significantly in vaccinated fish. No significant regulation of sIgT, mIgT, sIgM, mIgM and IgD was found before 37 dpi, whereas at 37 and 60 dpi, overexpression of sIgT and mIgT was detected in fish injected with adjuvant alone or with the vaccine. The identification of B lymphocytes by immunofluorescence allowed their classification in four groups: IgMþIgD-IgT- (the majority of IgMþ cells), IgMþIgDþIgT-, IgM-IgDþIgT- (very few cells; which probably correspond with lymphocytes with low levels of IgM), and IgM-IgD-IgTþ cells. The IgMþ and IgTþcells were scattered throughout the parenchyma, and grouped around large vessels and surrounding melanomacrophage centres (MMC). IgMþ cells, IgTþ cells or a mixture of the two populations were associated frequently to MMC. Cell proliferation was estimated by using a combination of antibodies anti-IgT, anti-IgM and anti-PCNA. Proliferation of both IgMþ and IgTþ B cells was found in several areas of the spleen. In addition, vaccinated fish showed PCNA þ/IgM þ and PCNAþ/ IgTþ B ...
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