Enhancement of anti-Aeromonas salmonicida activity in Atlantic salmon (Salmo sellar) macrophages by a mannose-binding lectin

We investigated the effects of a calcium-dependent mannose-binding lectin i solated from the serum of Atlantic salmon on Aeromonas salmonicida viabilit y and the anti-A. salmonicida activity of Atlantic salmon macrophages. In t he 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 significantl y reduce (P > 0.05) cell viability. However, binding of the lectin to A. sa lmonicida did result in significant (P less than or equal to 0.05) dose-dep endent increases in phagocytosis, and bactericidal activity. Significant in creases (P less than or equal to 0.05) were also observed in phagocyte resp iratory 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 concentr ations. At the lowest lectin concentration tested (0.32 ng ml(-1)), a signi ficant decrease (P less than or equal to 0.05) in respiratory burst was obs erved. The structure and activity of this lectin are similar to that of mam malian mannose-binding lectins, which are known to play a pivotal role in i nnate immunity. The presence of this lectin may be an important defense mec hanism against Gram-negative bacteria such as A. salmonicida. (C) 1999 Else vier Science Inc. Ail rights reserved.