Antibodies (IgG) to lipopolysaccharide of Vibrio cholerae O1 mediate protection through inhibition of intestinal adherence and colonisation in a mouse model

An antiserum raised against purified lipopolysaccharide (LPS) of a Vibrio cholerae O1 strain (Co366) induced passive protection against challenge with the parent as well as other O1 organisms but not against O139 or non-O1/non-O139 organisms. A considerable level of protection against O1 strains was also observed with the IgG fraction of the antiserum which inhibited intestinal adherence and colonisation. The monovalent Fab(IgG) fragment, on the other hand, showed only a low level of protection. Interestingly, purified LPS failed to inhibit intestinal colonisation by the parent strain (Co366), thereby suggesting that the cell surface LPS moieties of vibrios may not be directly involved in the colonisation process. It may be concluded that the anti-LPS antibodies induce passive protection through microagglutination and/or immobilisation of vibrios which do not allow the organisms to adhere to and colonise the intestine.