Effect of experimental Flavobacterium columnare infection on IgM production in Japanese Eel anguilla japonica

To study IgM production in Japanese eel infected with Flavobacterium column are, we measured serum IgM concentration (SIC), IgM constitution of total s erum protein (ICT) and the number of antibody secretary cells (NASC) isolat ed from the blood, spleen and kidney. The fish were exposed to a bacterial suspension after removal of skin mucus in the tail region, and reared at 25 degreesC. The values of SIG, ICT and NASC were significantly decreased 48 to 72 h after inoculation. When the eels were intraperitoneally injected wi th extracellular product (ECP) of the bacterium, a significant decrease in SIG, ICT and NASC isolated from the spleen was also observed 12 h after inj ection. In addition, ECP showed in vitro cytotoxicity against kidney lympho cytes of eel. It is considered that ECP is the major factor causing the dec rease of IgM production.