Protective efficacy and immunogenicity of Escherichia coli K13 diphtheria toxoid conjugate against experimental ascending pyelonephritis

In the present study, protective efficacy of Escherichia coli capsular antigen, K13, was evaluated in a mouse model of pyelonephritis. Unconjugated capsular polysaccharide failed to provide any protection. However, coupling of K13 to diphtheria toxoid (DT) enhanced its immunogenicity and led to significant production of anticapsular antibodies in mice. Immunization of animals with K13–DT conjugate also caused significant improvement in cell-mediated immune response as indicated by an increase in lymphoblastogenic response and in the CD4+/CD8+ cell ratio of splenic lymphocytes. Significant decrease in bacterial load and renal severity scores were observed in K13–DT immunized animals. Suitability of K13–DT conjugate as an effective vaccine candidate against urinary tract infections caused by E. coli has been discussed.