Enhancement of anti- Aeromonas salmonicida activity in Atlantic salmon ( Salmo salar ) macrophages by a mannose-binding lectin
We investigated the effects of a calcium-dependent mannose-binding lectin isolated from the serum of Atlantic salmon on Aeromonas salmonicida viability and the anti- A . salmonicida activity of Atlantic salmon macrophages. In the absence of other factors, binding of this lectin at concentrations of 0.8, 4.0 and 20.0 ng ml −1 to virulent A. salmonicida failed to significantly reduce ( P >0.05) cell viability. However, binding of the lectin to A. salmonicida did result in significant ( P ≤0.05) dose-dependent increases in phagocytosis, and bactericidal activity. Significant increases ( P ≤0.05) were also observed in phagocyte respiratory burst activity within the lectin concentration range of 4.0–20.0 ng ml −1 but the stimulation was not dose dependent at these lectin concentrations. At the lowest lectin concentration tested (0.32 ng ml −1 ), a significant decrease ( P ≤0.05) in respiratory burst was observed. The structure and activity of this lectin are similar to that of mammalian mannose-binding lectins, which are known to play a pivotal role in innate immunity. The presence of this lectin may be an important defense mechanism against Gram-negative bacteria such as A. salmonicida.