Roles of an endogenous serum lectin in the immune protection of blue gourami, Trichogaster trichopterus (Pallus) against Aeromonas hydrophila

The serum of blue gourami, Trichogaster trichopterus (Pallus), contains a calcium-dependent, N-acetyl-galactosamine-binding lectin (BGL) which efficiently activates and enhances the non-specific immune response of fish towards a virulent strain of Aeromonas hydrophila. In the in vitro studies, a lectin concentration range of 0·05–1·0 ng ml−1was found to significantly promote phagocytic uptake of the bacteria by macrophages. This effect was further augmented when purified lectin was combined with laminarin (β-1,3-D-glucan). Supernatants obtained from these lectin-stimulated macrophage cultures also exhibited significant bacteria-killing activities. In addition, complement from naı̈ve fish serum, in the presence of purified BGL, was able to kill A. hydrophila. Finally, challenge experiments demonstrated that BGL could confer effective immune protection to naı̈ve blue gourami against anAeromonas infection.