Reactivity of VacA mutant proteins with a monoclonal anti-VacA antibody. Wild-type H. pylori strain 60190 and strains expressing mutant VacA proteins were grown in broth culture, and secreted VacA proteins were normalized as described in Methods. Wells of ELISA plates were coated with broth culture supernatants, and reactivity of the proteins with an anti-VacA monoclonal antibody (5E4) that recognizes a conformational epitope was determined by ELISA. Reactivity of a vacA null mutant was subtracted as background. Relative VacA concentrations are indicated. Values represent the mean ± SD from triplicate samples.