Stimulator of Interferon Genes in Classical Dendritic Cells Controls Mucosal Th17 Responses to Cyclic Dinucleotides for Host Defenses Against Microbial Infections in Gut

Oral immunization of BALB/c mice with recombinant Helicobacter pylori antigens and double mutant heat-labile toxin (dmLT) induces prophylactic protective immunity against H. pylori infection

Helicobacter pylori infection and associated diseases remain a major public health problem worldwide. Much effort has been made over the last several decades in vaccine development, but there is no licensed vaccine on the market. We have previously reported that oral immunization with H. pylori lysates and double mutant heat-labile toxin (dmLT) affords prophylactic protection against H. pylori infection in mice. In the present study, we investigated the effects of oral immunization with recombinant H. pylori protein antigens (NAP/UreA/UreB) and dmLT on H. pylori challenge in BALB/c mice. We found that oral immunization with candidate antigens and dmLT significantly reduced the gastric colonization of H. pylori 6 weeks after challenge, as compared to unimmunized mice. Moreover, the subunit vaccine appeared to provide a better protection than the bacterial lysate vaccine. The immunized mice showed enhanced antigen-specific lymphocyte proliferation, and serum IgG and mucosal IgA responses. Furthermore, the immunization increased the proportion of CD4⁺ IL-17+ lymphocytes in spleen and mesenteric lymph nodes, and enhanced the production of IL-17, IL-16, IL-6 and TNF-α in lymphocyte culture supernatants. Taken together, our results suggest that oral vaccination with recombinant H. pylori antigens (NAP/UreA/UreB) and dmLT confers more effective prophylactic protection against H. pylori infection than whole bacterial lysates in BALB/c mice. The reduction of H. pylori colonization was associated with the induction of antigen-specific Th17 and local mucosal IgA immune responses.

STING-mediated intestinal barrier dysfunction contributes to lethal sepsis

Background

Gut integrity is compromised in abdominal sepsis with increased cellular apoptosis and altered barrier permeability. Intestinal epithelial cells (IEC) form a physiochemical barrier that separates the intestinal lumen from the host's internal milieu and is strongly involved in the mucosal inflammatory response and immune response. Recent research indicates the involvement of the stimulator of interferons genes (STING) pathway in uncontrolled inflammation and gut mucosal immune response.

Methods

We investigated the role of STING signaling in sepsis and intestinal barrier function using intestinal biopsies from human patients with abdominal sepsis and with an established model of abdominal sepsis in mice.

Findings

In human abdominal sepsis, STING expression was elevated in peripheral blood mononuclear cells and intestinal biopsies compared with healthy controls, and the degree of STING expression in the human intestinal lamina propria correlated with the intestinal inflammation in septic patients. Moreover, elevated STING expression was associated with high levels of serum intestinal fatty acid binding protein that served as a marker of enterocyte damage. In mice, the intestinal STING signaling pathway was markedly activated following the induction of sepsis induced by cecal ligation perforation (CLP). STING knockout mice showed an alleviated inflammatory response, attenuated gut permeability, and decreased bacterial translocation. Whereas mice treated with a STING agonist (DMXAA) following CLP developed greater intestinal apoptosis and a more severe systemic inflammatory response. We demonstrated that mitochondrial DNA (mtDNA) was released during sepsis, inducing the intestinal inflammatory response through activating the STING pathway. We finally investigated DNase I administration at 5 hours post CLP surgery, showing that it reduced systemic mtDNA and inflammatory cytokines levels, organ damage, and bacterial translocation, suggesting that inhibition of mtDNA-STING signaling pathway protects against CLP-induced intestinal barrier dysfunction.

Interpretation

Our results indicate that the STING signaling pathway can contribute to lethal sepsis by promoting IEC apoptosis and through disrupting the intestinal barrier. Our findings suggest that regulation of the mtDNA-STING pathway may be a promising therapeutic strategy to promote mucosal healing and protect the intestinal barrier in septic patients.

Fund

National Natural Science Foundation of China.

The emerging role of stimulator of interferons genes signaling in sepsis: Inflammation, autophagy, and cell death

Stimulator of interferons genes (STING) is an adaptor protein that plays a critical role in the secretion of type I interferons and pro-inflammatory cytokines in response to cytosolic nucleic acid. Recent research indicates the involvement of the STING pathway in uncontrolled inflammation, sepsis, and shock. STING signaling is significantly up-regulated in human sepsis, and STING agonists are suggested to contribute to the pathogenesis of sepsis and shock. Nevertheless, little is known about the consequences of activated STING-mediated signaling during sepsis. It has been shown that aberrant activation of the STING-dependent way can result in increased inflammation, type I interferons responses, and cell death (including apoptosis, necroptosis, and pyroptosis). In addition, autophagy modulation has been demonstrated to protect against multiple organs injuries in animal sepsis model. However, impaired autophagy may contribute to the aberrant activation of STING signaling, leading to uncontrolled inflammation and cell death. Here we present a comprehensive review of recent advances in the understanding of STING signaling, focusing on the regulatory mechanisms and the roles of this pathway in sepsis.

STING Signaling Promotes Apoptosis, Necrosis, and Cell Death: An Overview and Update

STING is a newly identified intracellular sensor of foreign and endogenous DNA. STING has been recognized as an activator of immune responses by TBK1/IRF3 and NF-κB pathways, and it is suggested to play critical roles in host defense, autoimmune diseases, and tumor immunity. Recent studies have revealed that the outcome of STING activation could vary between distinct cell types and scenarios. STING activation in certain cell types triggered cell death including apoptosis and necrosis. This effect could be critical for preventing unnecessary or excessive inflammatory events and maintaining host immune homeostasis. This review is dedicated to summarize recent evidences in the field of STING-mediated cell death and to demonstrate dual outcomes of STING signaling. Besides canonical immune responses represented by IFN and TNF productions, STING signaling can also induce cell death events in a variety of cell types. The double-faced characteristics of STING signaling requires further exploration and precious regulation before tailoring clinical strategies for associated diseases.