LPS-based conjugate vaccines composed of O-polysaccharide from Pseudomonas aeruginosa IATS 6 and 11 bound to a carrier protein

Lipopolysaccharide (LPS) is the major surface antigen of Pseudomonas aeruginosa and elicits protective antibodies in animals. No cross reaction was observed between LPSs of P. aeruginosa International Antigenic Typing Scheme (IATS) 6 and 11 strains using rabbit polyclonal antibodies raised against the whole cells. The O-polysaccharides (O-PSs) from IATS 6 and 11, the antigenic determinant of LPS, were directly coupled to bovine serum albumin (BSA) by carbodiimide mediated condensation reaction. The molar ratios of saccharide repeating units to BSA in the prepared conjugates were 15:1 and 26:1 for IATS 6 and 11 conjugates, respectively. Mice were immunized with the conjugates emulsified with monophosphoryl lipid A (MPL), Freund, and Alum adjuvants. The conjugates emulsified with MPL adjuvant elicited the highest IgM antibody, followed by Freund. While both MPL and Freund adjuvants elicited high IgG antibody. Good correlation was observed between the IgG and IgM levels with the bactericidal activities of the sera against homologous strains. In addition, immunization of mice with the prepared conjugates emulsified with MPL and Freund adjuvants provided high protection against ten times the LD₅₀ of P. aeruginsoa IATS 6 and 11, which showed a good correlations with the IgG titer.