Serum vibriocidal antibody assay has been used to evaluate the immunogenicity of cholera vaccines formulated with killed whole-cell of Vibrio cholerae. However, serum antibodies representing the vibriocidal activity are not fully characterized. In this study, we examined which isotype is associated with the vibriocidal activity using human convalescent sera with high virbiocidal activity and 20 clinical serum samples obtained from human subjects who had been vaccinated with a killed, whole-cell cholera vaccine. Total IgG, IgA or IgM antibody levels were not correlated with the vibriocidal activity in the 20 human clinical sera. When IgG, IgA and IgM antibodies specific to each of the heat-killed V. cholerae, lipopolysaccharide (LPS), or outer membrane protein U were measured in the 20 clinical serum samples, anti-LPS IgM antibody showed the highest correlation with the vibriocidal activity (Pearson correlation coefficient r = 0.818). Depletion of IgM antibodies in the convalescent sera produced a significant (P<0.05) decrease in the vibriocidal activity (16-fold decrease), whereas little change was observed with depletion of IgG and/or IgA. Furthermore, size-exclusion column chromatography followed by vibriocidal assay and analysis of antibody isotypes demonstrated the co-elution of vibriocidal activity and IgM antibody. Collectively, these results suggest that LPS-specific IgM could be a potential serologic marker for the vibriocidal antibody assay.
- Copyright © 2011 by The American Association of Immunologists, Inc.