Humoral immune response of Japanese eel, Anguilla japonica Temminck & Schlegel, to Pleistophora anguillarum Hoshina, 1951 (Microspora)

A humoral response of Japanese eel, Anguilla japonica Temminck & Schlegel, to the microsporean Pleistophora anguillarum Hoshina was demonstrated using immunoblotting and an enzyme-linked immunosorbent assay (ELISA). Japanese eel immunoglobulin was purified by affinity chromatography. The immunoglobulin was composed of 25-kDa light chains and 72-kDa heavy chains. The ELISA values of P. anguillarum antibodies in naturally infected fish sera were significantly higher than those of clinically healthy fish. Spore proteins from the microsporean were separated by electrophoresis and subjected to analysis by Western blot. Sera from naturally infected fish showed different reaction patterns to the spore proteins. While the sera randomly selected from naturally infected eels all showed a significant positive reaction to P. anguillarum antigens, the mucus from only three out of the nine infected eels reacted positively in the ELISA test. Subsequent analyses indicated that there was no significant difference in the amount of mucus immunoglobulin among the tested eels. Therefore, the generally lower ELISA values of mucosal anti-P. anguillarum antibodies from the infected eels tested were evidently not caused by a lack of immunoglobulin per se, but seem to be the result of a lack of anti-P. anguillarum antibodies in the mucus and/or a lower affinity in the anti-P. anguillarum antibodies that were present.