Immune response of eel to Edwardsiella tarda lipopolysaccharide.

Abstract

To clarify the protective properties of Edwardsiella tarda lipopolysaccharide (LPS) reported previously, immunogenicity, antigenicity and chemical characteristics were examined using crude LPS, pure LPS, polysaccharide and lipid A prepared from one strain of E. tarda. The eels immunized by intramuscular injection with the four preparations showed an increase in agglutination titer in comparison to control group. The highest titers were recorded in eels immunized with crude LPS preparation and the lowest with the lipid A preparation. However, titer did not correlate with the survival rate after challenge. The highest survival was demonstrated in the eels immunized with the polysaccharide preparation and some resistance was shown in the eels immunized with the crude LPS preparation. The eels immunized with pure LPS and lipid A preparations did not show protection to challenge. Using Ouchterlony immunodiffusion, it was shown that the antigenicity of the polysaccharides were lower than pure LPS where no precipitin lines were observed. Chemical analysis showed a high degree of heterogeneity in the crude LPS with a small amount of protein and high content of nucleic acids. After further purification, protein and nucleic acids were reduced, but present. From these results it was concluded that the main protective substance in the E. tarda crude LPS preparation was polysaccharide.