Distribution of immunoglobulinpositive cells in the spleen and kidney of Japanese flounder Paralichthys olivaceus

Abstract

The distribution of surface immunoglobulin-positive (sIg⁺) cells in the spleen, the head-kidney, and the trunk-kidney of adult Japanese flounder Paralichthys olivaceus was investigated by a flow cytometric analysis using a monoclonal antibody FB17 against flounder immunoglobulin M. Although the percentage of sIg⁺ cells varied among organs, a good correlation was revealed between the percentage in the head-kidney and that in the trunk-kidney (r = 0.996, P < 0.001). In contrast, no correlation was obtained between the percentage of sIg⁺ cells in the spleen and the head-kidney or trunk-kidney. The head-kidney and the trunk-kidney contained cells bearing fewer sIg that were stained dimly by FB17 in addition to brightly stained sIg⁺ cells regarded as mature B cells, while the spleen contained only sIg⁺ cells stained brightly. Moreover, the immunocytochemical analyses showed that the head-kidney contains plasma cells with strongly stained cytoplasm in addition to B cells with stained cell surface, which suggests that the cells with fewer sIg detected by flow cytometric analysis are presumed to be at a stage during the processes of differentiation to plasma cells. These results suggest that there are some differences between the spleen and kidney in the role of the immune system and it is considered that differentiation of B cells to plasma cells occurs in the kidney.