In vitro responsiveness of subpopulations of leucocytes from Atlantic salmon, Salmo salar L., to Aeromonas salmonicida

Although passive immunization studies have shown that antibodies to A. salmonicida can be protective against furunculosis (McCarthy, Amend, Johnson & Bloom 1983; Shieh 1985; Cipriano 1983), several studies indicate that cellular mechanisms are important. Pourreau, Koopman, Hendriks, Evenberg & van Muiswinkel (1987) observed that cellular and extracellular antigens from an avirulent strain of A. salmonicida had stimulatory effects on carp leucocytes in vitro. Furthermore, in a study of antigen-induced blastogenesis of head kidney leucocytes of Atlantic salmon to antigens from A. salmonicida, Tatner (1990) observed that certain antigens induced lymphocyte proliferation. In agreement with these findings, peripheral blood leucocytes of non-vaccinated Atlantic salmon were found to respond by proliferation when stimulated with whole A. salmonicida cells (Reitan & Thuvander 1991). However, the proliferative response was significantly higher in fish immunized with the bacteria. From these studies, it seems obvious that A. salmonicida exerts stimulatory effects on fish lymphocytes which are of both mitogenic and antigen specific nature.