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

Abstract

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 V. cholerae infection from OCV, we stimulated differentiated, macrophage-like THP-1 cells with live versus heat-inactivated V. cholerae with and without endogenous or exogenous cholera holotoxin (CT). Interleukin 23A gene (IL23A) expression was higher in cells exposed to live V. cholerae than in cells exposed to inactivated organisms (mean change, 38-fold; 95% confidence interval [95% CI], 4.0 to 42; P < 0.01). IL-23 secretion was also higher in cells exposed to live V. cholerae than in cells exposed to inactivated V. cholerae (mean change, 5.6-fold; 95% CI, 4.4 to 11; P < 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 V. cholerae and CT. While IL-23 secretion was reduced following stimulation with either heat-inactivated wild-type V. cholerae or a live isogenic ctxAB mutant of V. cholerae, the addition of exogenous CT restored IL-23 secretion in combination with the live isogenic ctxAB mutant V. cholerae, but not when it was paired with stimulation by heat-inactivated V. cholerae. 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 V. cholerae infection. IMPORTANCE 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 Vibrio cholerae with those of cells exposed to heat-killed V. cholerae (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 V. cholerae 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 V. cholerae may be important in conferring long-term immunity after cholera.

Vibrio cholerae at the Intersection of Immunity and the Microbiome

“…cholerae infection activates several hubs of innate immune signaling (30, 33). This has been observed in biopsy specimens from patients with acute cholera and can be modeled in vitro (30, 33, 36, 37). Some of the major innate signaling pathways which are upregulated in response to V.…”

Gut Microbiota and Development of Vibrio cholerae-Specific Long-Term Memory B Cells in Adults after Whole-Cell Killed Oral Cholera Vaccine

“…The development of long-term protective immune responses to V. cholerae infection is thought to be partially directed by the innate immune response to infection ( 31 – 34 ). We compared baseline fecal metabolites between study participants with high or low MBC responses to learn if baseline innate immune activation was associated with the postvaccination MBC response.…”

Systemic, Mucosal, and Memory Immune Responses following Cholera

“…While the innate immune system does not entirely prevent infection—since most immunologically naïve individuals who ingest enough organisms will become infected—it nonetheless plays an essential role in directing the adaptive immune response. For example, the innate immune response to live pathogenic V. cholerae results in the expression of key cytokines such as IL-23 that promote B- and T-cell differentiation [ 74 ].…”