Immunogenicity of soluble haemagglutinin-lipopolysaccharide complex of classical vibrio cholerae

Soluble haemagglutinin-lipopolysaccharide complexes were found to be good antigens since it elicited high levels of the antibodies in the intestine especially of the IgA class. These specific antibodies sustained for a long period of time at the significantly high levels (longer than 6 months). The enteric memory primed by the antigens in the intestinal tract were longer than 3 months. Pools of intestinal fluids obtained from mice immunized with single dose of SH-LPS at 1 week, 1 month and 3 months after the antigen stimulation conferred protection against the homologous challenge. Better protection was found in the corresponding specimens collected from mice which received antigen booster at 3 months after the first stimulation. Multiple oral doses of the antigens (three doses at weekly intervals) did not have any advantage over the single dose immunization. The intestinal fluids obtained from the former group conferred similar degree of protection as those from the latter though the serum specimens offered higher PD50. The protection against cholera does not correlate with the levels of vibriocidal antibody in the body fluids which seems to confirm the hypothesis that the mechanism of protection against cholera by intestinal antibody is by reducing or preventing the attachment of the vibrios to the epithelium either via agglutinating process or via masking of the vibrio adhesive sites.