| Summary: | Immunostimulating effects of water extract from bulbus arteriosus in tuna were examined and found to enhance IgM production by human hybridoma HB4C5 cells. When tuna bulbus arteriosus extract was heated, the IgM production-stimulating activity was decreased or lost. To identify the active substance, the extract was partially purified by anion-exchange chromatography, and proteins contained in positive fractions were analyzed by LC-MS/MS. The positive fractions contained lactate dehydrogenase, triosephosphate isomerase, enolase, and haemoglobin. Each of these four proteins was verified to enhance IgM production by HB4C5 cells with the commercially available purified proteins, suggesting that all of these four proteins are active substances in the extract. The immunostimulatory effect of these proteins was also examined on mouse primary spleen lymphocytes in vitro. Lactate dehydrogenase enhanced IgA, IgG, and IgM production and triosephosphate isomerase enhanced IgA and IgG production. In particular, lactate dehydrogenase had the strongest Ig production-stimulating effect on HB4C5 cells and on mouse primary lymphocytes. Thus, fish viscera may serve as an important raw material for the enhancement of the acquired immune system, once processed.
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