Cholera toxin B induced activation of murine macrophages exposed to a fixed bacterial immunogen

ER-transiting bacterial toxins amplify STING innate immune responses and elicit ER stress

The cGAS/STING sensor system drives innate immune responses to intracellular microbial double-stranded DNA (dsDNA) and bacterial cyclic nucleotide second messengers (e.g., c-di-AMP). STING-dependent cell-intrinsic responses can increase resistance to microbial infection and speed pathogen clearance. Correspondingly, STING activation and signaling are known to be targeted for suppression by effectors from several bacterial pathogens. Whether STING responses are also positively regulated through sensing of specific bacterial effectors is less clear. We find that STING activation through dsDNA, by its canonical ligand 2'-3' cGAMP, or the small molecule DMXAA is potentiated following intracellular delivery of the AB5 toxin family member pertussis toxin from Bordetella pertussis or the B subunit of cholera toxin from Vibrio cholerae. Entry of pertussis toxin or cholera toxin B into mouse macrophages triggers markers of endoplasmic reticulum (ER) stress and enhances ligand-dependent STING responses at the level of STING receptor activation in a manner that is independent of toxin enzymatic activity. Our results provide an example in which STING responses integrate information about the presence of relevant ER-transiting bacterial toxins into the innate inflammatory response and may help to explain the in vivo adjuvant effects of catalytically inactive toxins.

The Functions of Cholera Toxin Subunit B as a Modulator of Silica Nanoparticle Endocytosis

The gastrointestinal tract is the main target of orally ingested nanoparticles (NPs) and at the same time is exposed to noxious substances, such as bacterial components. We investigated the interaction of 59 nm silica (SiO2) NPs with differentiated Caco-2 intestinal epithelial cells in the presence of cholera toxin subunit B (CTxB) and compared the effects to J774A.1 macrophages. CTxB can affect cellular functions and modulate endocytosis via binding to the monosialoganglioside (GM1) receptor, expressed on both cell lines. After stimulating macrophages with CTxB, we observed notable changes in the membrane structure but not in Caco-2 cells, and no secretion of the pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) was detected. Cells were then exposed to 59 nm SiO2 NPs and CtxB sequentially and simultaneously, resulting in a high NP uptake in J774A.1 cells, but no uptake in Caco-2 cells was detected. Flow cytometry analysis revealed that the exposure of J774A.1 cells to CTxB resulted in a significant reduction in the uptake of SiO2 NPs. In contrast, the uptake of NPs by highly selective Caco-2 cells remained unaffected following CTxB exposure. Based on colocalization studies, CTxB and NPs might enter cells via shared endocytic pathways, followed by their sorting into different intracellular compartments. Our findings provide new insights into CTxB's function of modulating SiO2 NP uptake in phagocytic but not in differentiated intestine cells.

Association between post-diagnostic use of cholera vaccine and risk of death in prostate cancer patients

Recent evidence suggests that cholera toxin might have multiple functions regarding the ability to regulate the immune system. However, it is unknown whether subsequent administration of cholera vaccine might affect the mortality rate in patients with prostate cancer. Here we report that patients in Sweden, who were diagnosed with prostate cancer between July 2005 and December 2014 and used cholera vaccine, have a decreased risk of death from prostate cancer (HR, 0.57; 95% CI, 0.40-0.82) as compared to patients with prostate cancer but without cholera vaccine use, adjusted for a range of confounding factors. In addition, patients using cholera vaccine show a decreased risk of death overall (HR, 0.53; 95% CI, 0.41-0.69). The decreased mortality rate is largely consistent, irrespective of patients' age or tumor stage at diagnosis. In this population-based study, we suggest that subsequent administration of cholera vaccine after prostate cancer diagnosis might reduce the mortality rate.

Utilization of cholera toxin B as a mucosal adjuvant elicits antibody-mediated protection against S. pneumoniae infection in mice

BACKGOUND

The introduction of the pneumococcal conjugate and polysaccharide vaccines have been valuable tools for combating invasive pneumococcal infection in children and healthy adults. Despite the available vaccination strategies, pneumococcal pneumonia and associated diseases continue to cause substantial morbidity and mortality, particularly in individuals with chronic disease and ageing populations. Next-generation pneumococcal vaccines will need to be highly immunogenic across patient populations providing both mucosal and systemic protective immunity. Mucosal immunization is an effective strategy for stimulating the immune response at the site of pathogen entry while increasing systemic immunity. In this study we utilized intranasal immunization with pneumococcal surface protein A (PspA), in combination with the mucosal adjuvant cholera toxin B (CTB), to characterize the immune components providing protection against S. pneumoniae challenge.

METHODS

Mice were immunized intranasally with CTB and PspA individually, and in combination, followed by lethal bacterial challenge with S. pneumoniae, strain A66.1. Animals were monitored for survival and tested for lung bacterial burden, cytokine production as well as S. pneumoniae-specific antibody titer in mouse sera. The primary immunological contributor to the observed protection was confirmed by cytokine neutralization and serum passive transfer.

RESULTS

The combination of CTB and PspA provided complete protection against bacterial challenge, which coincided with a significant decrease in lung bacterial burden. Increases in the T-helper (Th) 1 cytokines, interferon (IFN)-γ and interleukin (IL)-2 were observed in the lung 24 h post-challenge while decreases in proinflammatory mediators IL-6 and tumor necrosis factor (TNF)-α were also recorded at the same time point. The adjuvanted PspA immunization induced significant titers of S. pneumoniae-specific antibody in the serum of mice prior to infection. Serum adoptive transfer passively protected animals against subsequent challenge while IFN-γ neutralization had no impact on the outcome of immunization, suggesting a primary role for antibody-mediated protection in the context of this immunization strategy.

CONCLUSION

Mucosal immunization with CTB and PspA induced a local cellular immune response and systemic humoral immunity which resulted in effective reduction of pulmonary bacterial burden and complete protection against S. pneumoniae challenge. While induction of the pleiotropic cytokine IFN-γ likely contributes to control of infection through activation of effector pathways, it was not required for protection. Instead, immunization with PspA and CTB-induced S. pneumoniae-specific antibodies in the serum prior to infection that were sufficient to protect against mucosal challenge.