Posttranslational Regulation of IL-23 Production Distinguishes the Innate Immune Responses to Live Toxigenic versus Heat-Inactivated Vibrio cholerae.

infection provides long-lasting protective immunity, while oral, inactivated cholera vaccines (OCV) result in more-limited protection. To identify characteristics of the innate immune response that may distinguish natural infection from OCV, we stimulated differentiated, macrophage-like THP-1 cells with live versus heat-inactivated with and without endogenous or exogenous cholera holotoxin (CT). Interleukin 23A gene () expression was higher in cells exposed to live than in cells exposed to inactivated organisms (mean change, 38-fold; 95% confidence interval [95% CI], 4.0 to 42;  < 0.01). IL-23 secretion was also higher in cells exposed to live than in cells exposed to inactivated (mean change, 5.6-fold; 95% CI, 4.4 to 11;  < 0.001). This increase in IL-23 secretion was more marked than for other key innate immune cytokines (e.g., IL-1β and IL-6) and dependent on exposure to the combination of both live and CT. While IL-23 secretion was reduced following stimulation with either heat-inactivated wild-type or a live isogenic mutant of , the addition of exogenous CT restored IL-23 secretion in combination with the live isogenic mutant , but not when it was paired with stimulation by heat-inactivated The posttranslational regulation of IL-23 under these conditions was dependent on the activity of the cysteine protease cathepsin B. In humans, IL-23 promotes the differentiation of Th17 cells to T follicular helper cells, which maintain and support long-term memory B cell generation after infection. Based on these findings, the stimulation of IL-23 production may be a determinant of protective immunity following infection. An episode of cholera provides better protection against reinfection than oral cholera vaccines, and the reasons for this are still under study. To better understand this, we compared the immune responses of human cells exposed to live with those of cells exposed to heat-killed (similar to the contents of oral cholera vaccines). We also compared the effects of active cholera toxin and the inactive cholera toxin B subunit (which is included in some cholera vaccines). One key immune signaling molecule, IL-23, was uniquely produced in response to the combination of live bacteria and active cholera holotoxin. Stimulation with that did not produce the active toxin or was killed did not produce an IL-23 response. The stimulation of IL-23 production by cholera toxin-producing may be important in conferring long-term immunity after cholera.