SERUM ANTI-LPS ANTIBODY-PRODUCTION BY RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) IN RESPONSE TO THE ADMINISTRATION OF FREE AND LIPOSOMALLY-INCORPORATED LPS FROM AEROMONAS-SALMONICIDA

The lipopolysaccharide (LPS) from Aeromonas salmonicida was incorporat ed into liposomes in order to examine the potential of these formulati ons to enhance the immunogenicity of LPS in rainbow trout (Oncorhynchu s mykiss). Repeated intraperitoneal (i.p.) injection of free LPS resul ted in the generation of anti-LPS reactivity in the serum which remain ed elevated for 2-4 weeks after the final injection of LPS. When admin istered i.p., LPS incorporated into multilamellar vesicles (MLV/LPS) o r large unilamellar vesicles produced via extrusion through 200 nm por e size filters (LUVET200/LPS) prolonged the period over which serum an ti-LPS antibody levels remained elevated to 6-14 weeks. Administration of two doses of either positively-or negatively-charged MLV/LPS prior to exposure to free LPS generated an anti-LPS antibody response which persisted for several weeks longer than immunisation with LPS alone. Positively-and negatively-charged LUVET200/LPS administered i.p. also resulted in extended durations of serum anti-LPS antibody responses. I njection of liposomally incorporated LPS i.p. also induced anti-lipid A antibodies in sera. The data suggests that, when administered i.p., liposomally-incorporated LPS from A. salmonicida is capable of prolong ing humoral immune responses against LPS in rainbow trout. (C) 1997 Ac ademic Press Limited.