Antigen-induced release of macrophage activating factor from rainbow trout Oncorhynchus mykiss leucocytes

The production of macrophage-activating factor (MAF) by rainbow trout, Oncorhynchus mykiss, head kidney leucocytes at varying times post-immunisation, with the fish bacterial pathogen, Aeromonas salmonicida, was investigated and correlated with head kidney lymphocyte proliferation and serum antibody production. MAF production was preceded by lymphocyte proliferation and both responses were highest using whole bacterial cells as the in vitro stimulant. MAF production and antibody production increased 2-3 weeks post-immunisation, and peaked 4-5 weeks post-immunisation. The relative importance of MAF activated phagocytes in the immunological armoury of disease-resistant, vaccinated fish requires further investigation.