Enzyme-linked immunosorbent assay to evaluate the immunogenicity of a polyvalent Klebsiella capsular polysaccharide vaccine in humans.

A highly sensitive enzyme-linked immunosorbent assay was developed for Klebsiella capsular polysaccharide (CPS) and used to evaluate the immunoglobulin G (IgG) antibody response to a 24-valent CPS vaccine in seven adult volunteers. The median rise in titer to all vaccine antigens in samples from the volunteers was significant (twofold or greater). Significant IgG responses to 11 immunologically related serotypes not included in the vaccine were also noted. The mean cross-reacting IgG titer of 127.2 was only slightly lower than the mean titer of 175.7 to the serotypes in the vaccine (P less than 0.05). The mean 29.9-fold increase in titer to the serotypes in the vaccine was significantly higher than the mean 13.5-fold increase in titer to the additional antigens (P less than 0.001). The difference was partly because of the significantly lower (P less than 0.01) natural antibody titers in the preimmune sera to the serotypes in the vaccine, compared with those to serotypes not included in the vaccine. The selection of vaccine serotypes was based on the frequency of serotype isolation from cases of Klebsiella bacteremia. The above findings, which show low levels of natural antibody to these serotypes, support the hypothesis that anti-CPS antibody is protective against bacteremic disease.