VIBRIOCIDAL ANTIBODY-RESPONSES IN NORTH-AMERICAN VOLUNTEERS EXPOSED TO WILD-TYPE OR VACCINE VIBRIO-CHOLERAE O139 - SPECIFICITY AND RELEVANCE TO IMMUNITY

The emergence of a new agent of cholera, Vibrio cholerae O139, has pro mpted a reevaluation of the vibriocidal antibody assay, This assay, pr imarily directed to lipopolysaccharide, is an important correlate of O 1 immunity, V. cholerae O139 strains are encapsulated, rendering them relatively resistant to killing by serum, Recent reports suggest that there is strain-to-strain variability in the sensitivity of the vibrio cidal assay to fully encapsulated O139 strains, We have assessed a mod ified vibriocidal assay for fully encapsulated O139 strain AI-1837 and its unencapsulated mutant 2L in sera from 53 volunteers given wild-ty pe AI-1837 or its attenuated derivative CVD 112 and from 48 controls c hallenged with V. cholerae O1 or strains of the family Enterobacteriac eae. Vibriocidal responses to the AI-1837 and 2L strains were seen in 67 and 89% of volunteers, respectively, following a single exposure to the wild-type strain, However, > 50% of all controls had low-level vi briocidal responses to both strains, These nonspecific responses were transient and of the immunoglobulin G isotype. No binding activity aga inst purified O139 lipopolysaccharide (LPS) by immunoblotting was seen in control sera, In contrast, vibriocidal assay and strain 2L LPS res ponses by immunoblotting were detectable in 91% of tested volunteers f ollowing a single exposure to O139, The presence of vibriocidal antibo dy to AI-1837 or 2L was not associated with protection in rechallenge studies with O139 strain AI-1837, The vibriocidal assay with unencapsu lated strain 2L may be used to detect exposure to O139 strain AI-1837 in controlled research trials, However, its lack of specificity does n ot make it useful for determining exposure to V. cholerae O139 in the field.