Induction of inflammatory cytokines by extracellular products and LPS of the fish pathogen Aeromonas salmonicida ssp. achromogenes in mice and mouse cell cultures

Balb/c mice, injected i.p. with extracellular products (ECP) of Aeromonas salmonicida subsp. achromogenes (Asa), displayed symptoms similar to toxic shock syndrome. The LD50 observed was between 1.5 and 2.0 μg g−1 and the mice died within 19 h. Four inflammatory cytokines were measured in mice receiving sublethal ECP doses. TNF-α and IL-6 showed a sharp peak in the serum while IL-1β and IL-2 were not detected. When peritoneal macrophages were cultivated in the presence of ECP, AsaP1 (a toxic caseinolytic metallo-protease purified from ECP) or LPS, all cultures produced TNF-α, IL-6 and IL-1β. The same antigens were mitogenic in spleen cell cultures. Furthermore, IL-2 production, which is a normal T-cell response to ConA stimulation, was downregulated in spleen cell cultures from mice injected with ECP.