Immunocytochemical study on liver, spleen and intestine of rainbow trout immunized with Vibrio anguillarum lipopolysaccharide

Background: Vibriosis has been recognized as a major bacterial disease in aquaculture industry. The development of effective vaccines has significantly reduced the impact of this disease. Objectives: The aim of this study was to follow distribution of the antigenic Vibrio anguillarum cell wall lipopolysaccharide (LPS) in liver, spleen and anterior intestinal cells of rainbow trout (Oncorhynchus mykiss) using immunocytochemistry. Methods: Rainbow trout was intraperitoneally injected with V. anguillarum LPS. One hour later, liver, spleen and anterior intestine samples were collected to study the LPS distribution in the tissue sections using immunocytochemistry and Transmission Electron Microscope. Rabbit polyclonal antibody against the protein-A gold (pAg) labeled-LPS was applied to show electron density of the pAg using an indirect immunocytochemical method at the site of antigen- antibody interaction on the fish tissues. A pre-absorbed immune rabbit antibody and a pre-immune rabbit serum were considered as negative controls. Results: Results showed that the labels were evenly distributed over cell cytoplasm, nucleus, intracellular spaces, basal membrane and connective tissue in the liver, spleen and anterior intestine. In most cases, more labels were detected in cytoplasm than nucleus while no label was observed in negative controls. Conclusions: Immunocytochemical study of tissues and cells in the immunized fish with V. anguillarum LPS showed extensive distribution of the antigen in hepatocytes, splenocytes and enterocytes.