Relationship between the skin and innert defense mechanisms in fish

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Opsonic activity of the skin mucus lectin against neutrophils was examined in the Japanese eel, Anguilla japonica, to elucidate if the defense mechanisms in the skin mucus has some meaning for the defense mechansms, e.g.leucocytes, when the infection occur via integument. Leuctin was extracted from the epithelial tissue and separated by gel filtration. This lectin agglutinated rabbit red blood cells (rRBC) with specificity to lactose. Eel neutrophils separated by Percoll density gradients were incubated with rRBC pretreated with the lectin, and phagocytic activity was estimated under microscopy. The lectin was found to enhance the phagocytosis of neutrophils, phagocytic index against lectin-bound rRBC was significantly higher than against normal rRBC with an increase in numbers of phagocytized rRBC.The activation of phagocytosis was inhibited by additive lectin inhibitor, i.e., lactose in the process of lectin treatment of rRBC.The skin mucus lectin in eel thus exhibited opsonic activity against eel neutrophils. Phagocytosis was influenced, e.g., enhanced or reduced accordingly by coexistent lymphocytes, showing modulational function of the lymphocytes. These findings show that the defense mechanisms of the skin surface have interrelationship with internal mechanisms.