Cytokine-mediated antimicrobial immune response of catfish,Clarias gariepinus, as a defence againstAeromonas hydrophila

The proliferative response of head kidney (HK) leucocytes from catfish (Clarias gariepinus) immunised againstAeromonas hydrophilastrain PPD 134/91 was significantly increased compared with that of naive HK leucocytes using whole bacterial cells as thein vitrostimulant. A correlation between the proliferation of immune HK leucocytes and the production of macrophage-activating factor (MAF) was also observed. The production of reactive oxygen and nitrogen intermediates from the resident phagocytes of control fish was enhanced after incubating with the MAF-containing supernatants for 48 h. Both cytokine-containing supernatants and the incubated phagocytes of the immune fish also exhibited a significant increase of bactericidal activity. The study also showed that nitric oxide (NO) production and microbicidal activity of the antigen-activated phagocytes were partially blocked with NG-monomethyl-L-arginine (NG-MMLA), suggesting that NO might be an important antimicrobial effector in fish phagocytes as in mammals.