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 c alcium-dependent, N-acetyl-galactosamine-binding lectin (BGL) which efficie ntly activates and enhances the non-specific immune response of fish toward s a virulent strain of Aeromonas hydrophila. In the in vitro studies, a lec tin concentration range of 0.05-1.0 ng ml(-1) was found to significantly pr omote phagocytic uptake of the bacteria by macrophages: This effect was fur ther augmented when purified lectin was combined with laminarin (beta -1,3- D-glucan). Supernatants obtained from these lectin-stimulated macrophage cu ltures also exhibited significant bacteria-killing activities. In addition, complement from naive fish serum, in the presence of purified BCTL, was ab le to kill A. hydrophila. Finally, challenge experiments demonstrated that BGL could confer effective immune protection to naive blue gourami against an Aeromonas infection. (C) 2001 Academic Press.