Stimulation of TLR7 prior to polymicrobial sepsis improves the immune control of the inflammatory response in adult mice

Knockdown of lncRNA PVT1 attenuated macrophage M1 polarization and relieved sepsis induced myocardial injury via miR-29a/HMGB1 axis

BACKGROUND

LncRNA PVT1 was reported to be elevated in septic myocardial tissue. The underlying mechanism by which PVT1 aggravated sepsis induced myocardial injury needs further investigation.

METHODS

Mice was subjected to LPS injection to mimic in vivo sepsis model. HE staining was applied to observe tissue injury. Cardiac function of mice was determined by echocardiography. Bone marrow derived macrophage (BMDM) was used to confirm the regulatory effect of PVT1 in macrophage polarization. Western blotting or qRT-PCR were performed to evaluate protein or mRNA levels, respectively. ELISA was conducted to determine cytokine levels. Interaction between PVT1 and miR-29a, miR-29a and HMGB1 were accessed by dual luciferase assay.

RESULTS

Expression of PVT1 was elevated in myocardial tissue and heart infiltrating macrophages of sepsis mice. PVT1 knockdown alleviated LPS induced myocardial injury and attenuated M1 macrophage polarization. The mechanic study suggested that PVT1 targeted miR-29a, thus elevated expression of HMGB1, which was repressed by miR-29a targeting. The effect of PVT1 on M1 macrophage polarization was dependent on targeting miR-29a.

CONCLUSION

PVT1 promoted M1 polarization and aggravated LPS induced myocardial injury via miR-29a/HMGB1 axis.

Potential of TLR agonist as an adjuvant in Leishmania vaccine against visceral leishmaniasis in BALB/c mice

Morbid infection of leishmaniasis is posing threat to humankind due to its exacerbating prevalence in newer emerging areas. Moreover, the availability of limited drugs, their toxicity, limited efficacy, the emergence of drug resistance, and unavailability of vaccines are the major obstacles in its elimination. This implies the demand for a prophylactic vaccine candidate to prevent this infection and resulting fatal disease. We evaluated gardiquimod (a toll-like receptor-7 agonist) for its action as an adjuvant with the heat-killed antigen of Leishmania donovani. BALB/c mice were immunized with a vaccine either with or without adjuvant and given challenge infection. The results depicted the low parasite burden, higher delayed-type hypersensitivity response, and higher levels of IgG2a, Th1 cytokines, and NO in immunized mice in contrast to infected control mice. Low levels of Th2 cytokines and IgG1 were also noticed in the vaccinated mice than in infected mice. The mice immunized with a combination of gardiquimod and heat-killed antigen showed maximum efficacy. The results from the present study reflect the potential of tested vaccine candidate with gardiquimod as an adjuvant.

Toll-like Receptor 7 Contributes to Inflammation, Organ Injury, and Mortality in Murine Sepsis

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

Toll-like receptor 7 responds to elevated single-stranded RNA by increasing cytokine production. Sepsis is characterized by elevated plasma levels of tissue damage (and pathogen)-associated molecular patterns, including RNA.

WHAT THIS ARTICLE TELLS US THAT IS NEW

Using murine models of bacterial sepsis, knockout of the Toll-like receptor 7 resulted in lower mortality and cytokine levels and less end-organ injury. Therefore, Toll-like receptor 7, which mediates innate immune response, contributes to harm in experimental sepsis.

BACKGROUND

Sepsis remains a critical illness with high mortality. The authors have recently reported that mouse plasma RNA concentrations are markedly increased during sepsis and closely associated with its severity. Toll-like receptor 7, originally identified as the sensor for single-stranded RNA virus, also mediates host extracellular RNA-induced innate immune responses in vitro and in vivo. Here, the authors hypothesize that innate immune signaling via Toll-like receptor 7 contributes to inflammatory response, organ injury, and mortality during polymicrobial sepsis.

METHODS

Sepsis was created by (1) cecal ligation and puncture or (2) stool slurry peritoneal injection. Wild-type and Toll-like receptor 7 knockout mice, both in C57BL/6J background, were used. The following endpoints were measured: mortality, acute kidney injury biomarkers, plasma and peritoneal cytokines, blood bacterial loading, peritoneal leukocyte counts, and neutrophil phagocytic function.

RESULTS

The 11-day overall mortality was 81% in wild-type mice and 48% in Toll-like receptor 7 knockout mice after cecal ligation and puncture (N = 27 per group, P = 0.0031). Compared with wild-type septic mice, Toll-like receptor 7 knockout septic mice also had lower sepsis severity, attenuated plasma cytokine storm (wild-type vs. Toll-like receptor 7 knockout, interleukin-6: 43.2 [24.5, 162.7] vs. 4.4 [3.1, 12.0] ng/ml, P = 0.003) and peritoneal inflammation, alleviated acute kidney injury (wild-type vs. Toll-like receptor 7 knockout, neutrophil gelatinase-associated lipocalin: 307 ± 184 vs.139 ± 41-fold, P = 0.0364; kidney injury molecule-1: 40 [16, 49] vs.13 [4, 223]-fold, P = 0.0704), lower bacterial loading, and enhanced leukocyte peritoneal recruitment and phagocytic activities at 24 h. Moreover, stool slurry from wild-type and Toll-like receptor 7 knockout mice resulted in similar level of sepsis severity, peritoneal cytokines, and leukocyte recruitment in wild-type animals after peritoneal injection.

CONCLUSIONS

Toll-like receptor 7 plays an important role in the pathogenesis of polymicrobial sepsis by mediating host innate immune responses and contributes to acute kidney injury and mortality.

Single stranded (ss)RNA-mediated antiviral response against infectious laryngotracheitis virus infection

Background

Single stranded ribonucleic acid (ssRNA) binds to toll-like receptor (TLR)7 leading to recruitment of immune cells and production of pro-inflammatory cytokines, which has been shown in mammals. In chickens, synthetic ssRNA analog, resiquimod, has been shown to elicit antiviral response against infectious bursal disease virus infection. The objective of this study was to determine the innate host responses activated by the pre-hatch in ovo administration of resiquimod against infectious laryngotracheitis virus (ILTV) infection in chickens post-hatch.

Results

First, we observed that in ovo treatment of resiquimod at embryo day (ED) 18 increases macrophage recruitment in respiratory and gastrointestinal tissues of chicken day 1 post-hatch in addition to interleukin (IL)-1β in lungs. Second, we observed that in ovo treatment of resiquimod reduces ILTV cloacal shedding at 7 days post-infection (dpi) when challenged at day 1 post-hatch coinciding with higher macrophage recruitment. In vitro, we found that resiquimod enhances production of nitric oxide (NO) and IL-1β and not type 1 interferon (IFN) activity in avian macrophages. Although, the antiviral response against ILTV is associated with the enhanced innate immune response, it is not dependent on any of the innate immune mediators observed as has been shown in vitro using avian macrophage.

Conclusion

This study provides insights into the mechanisms of antiviral response mediated by resiquimod, particularly against ILTV infection in chicken.

Intraperitoneal gardiquimod protects against hepatotoxicity through inhibition of oxidative stress and inflammation in mice with sepsis

Many reports recapitulate the contribution of reactive oxygen species (ROS) over-accumulation to the organ damage; it is of significance to strictly target ROS production. In this study, we evaluated the potential role of TLR7 agonist gardiquimod (GDQ) in oxidative stress (OS) in liver injury induced by sepsis. Here, we observed that intraperitoneal pretreatment with GDQ dramatically elevated the septic survival rate and effectively attenuated the septic liver injury. Interestingly, the increased ROS and inflammatory factor IL-6 levels were reversed after GDQ intervention. Subsequently, Western blot was employed to determine the definite mechanism. As expected, it was showed that the upregulation of c-Jun N-terminal kinase (JNK)/c-Jun pathway in liver of septic animals was considerably suppressed by GDQ pre-exposure. Our current result highlight that pre-administration of GDQ ameliorated sepsis induced hepatotoxicity and reduced the generation of IL-6 and OS responses, which was associated with downregulation of JNK/c-Jun pathway. Our strategies might be ultimately beneficial in mitigating liver injury symptom.

The role of myeloid differentiation factor 88 on mitochondrial dysfunction of peritoneal leukocytes during polymicrobial sepsis

OBJECTIVE

To investigate the role of myeloid differentiation factor 88 (MyD88) on mitochondrial dysfunction of peritoneal leukocytes during polymicrobial sepsis.

MATERIAL AND METHODS

Polymicrobial peritonitis, a clinically relevant mouse model of sepsis, was generated by cecum ligation and puncture (CLP) in both male C57BL/6J wild-type (WT) and MyD88 knockout (MyD88(-/-)) mice. Twenty-four hours after surgeries, peritoneal leukocytes were collected and four parameters of mitochondrial function, including total intracellular and mitochondrial ROS burst, mitochondrial membrane depolarization and ATP depletion, were measured by flow cytometry or ATP assay, and then compared.

RESULTS

Polymicrobial sepsis led to a marked mitochondrial dysfunction of peritoneal leukocytes with total intracellular and mitochondrial ROS overproduction, decreased mitochondrial membrane potential and reduced intracellular ATP production. In comparison, there was no significant difference in the extent of mitochondrial dysfunction of peritoneal leukocytes between WT and MyD88(-/-) septic mice.

CONCLUSIONS

MyD88 may be not sufficient to regulate mitochondrial dysfunction of peritoneal leukocytes during polymicrobial sepsis.

Prophylactic potential of resiquimod against very virulent infectious bursal disease virus (vvIBDV) challenge in the chicken

The study evaluated the prophylactic potential of resiquimod (R-848), a synthetic TLR7 agonist, against very virulent infectious bursal disease virus (vvIBDV) infection in chicken. Specific pathogen free White Leghorn chicks of three week age were treated with R-848 (50μg/bird, intramuscular) or PBS (n=26/group). Twenty four hour later, half of the birds from each group were challenged with 10(5) ELD50 of vvIBDV and observed for 10days. To understand the effect of R-848, immune response genes such as interferon (IFN)-β, IFN-γ, IL-1β, IL-4, iNOS and TLR7 were analyzed at 24 and 48h post-challenge in PBMCs ex vivo by real-time PCR (n=6/group). On day 4 post-challenge, representative birds (n=3/group) were sacrificed to study the bursal damage and IBDV antigen clearance. Immunosuppression was assessed by antibody response against live Newcastle disease virus (NDV) vaccine, which was administered on day 10 post-challenge. R-848 pre-treatment significantly upregulated the transcripts of each immune response gene studied (P<0.05). There was 50% mortality on vvIBDV challenge in control birds, while it was only 20% with R-848 group. R-848 pre-treatment reduced the bursal damage as indicated by lower bursal lesion score in histopathology, reduced IBDV antigen signal in immunohistochemistry and improved antigen clearance in agar gel immunodiffusion test. Further, it protected significantly against vvIBDV induced immunosuppression as indicated by HI antibody titre. It is concluded that pre-treatment of R-848 conferred partial protection from mortality and bursal damage while complete protection against immunosuppression in chicken when challenged with vvIBDV, which could be due to the upregulation of immune response genes.

Targeting toll-like receptors: promising therapeutic strategies for the management of sepsis-associated pathology and infectious diseases

Toll-like receptors (TLRs) are pattern recognition receptors playing a fundamental role in sensing microbial invasion and initiating innate and adaptive immune responses. TLRs are also triggered by danger signals released by injured or stressed cells during sepsis. Here we focus on studies developing TLR agonists and antagonists for the treatment of infectious diseases and sepsis. Positioned at the cell surface, TLR4 is essential for sensing lipopolysaccharide of Gram-negative bacteria, TLR2 is involved in the recognition of a large panel of microbial ligands, while TLR5 recognizes flagellin. Endosomal TLR3, TLR7, TLR8, TLR9 are specialized in the sensing of nucleic acids produced notably during viral infections. TLR4 and TLR2 are favorite targets for developing anti-sepsis drugs, and antagonistic compounds have shown efficient protection from septic shock in pre-clinical models. Results from clinical trials evaluating anti-TLR4 and anti-TLR2 approaches are presented, discussing the challenges of study design in sepsis and future exploitation of these agents in infectious diseases. We also report results from studies suggesting that the TLR5 agonist flagellin may protect from infections of the gastrointestinal tract and that agonists of endosomal TLRs are very promising for treating chronic viral infections. Altogether, TLR-targeted therapies have a strong potential for prevention and intervention in infectious diseases, notably sepsis.

Induction of pro-inflammatory cytokine production in thymocytes by the immune response modifiers Imiquimod and Gardiquimod™

An emerging role is postulated for IL-17-producing thymocytes, which in their majority consist of IL-17-producing CD4(+) cells. For these, a specific role in the immediate defense against infectious pathogens is suggested, independent from the development of an adaptive immune response in the immune periphery. Immune response modifiers, like the TLR7 ligands Imiquimod and Gardiquimod™ are effective pharmacological therapeutics applied topically against dermal tumors and virus infections and have been demonstrated to activate immune cells. In this study, we investigated the effect of Imiquimod and Gardiquimod™ on murine thymocyte cytokine production with a particular focus on IL-17. We find that both substances dose-dependently are able to trigger IFN-γ and IL-6 production, but no IL-17 production. Moreover, a strong co-stimulating effect is detected on α-CD3-induced IFN-γ, IL-6 and IL-17 production. We conclude that Imiquimod and Gardiquimod™ are not only modifiers of the adaptive immune response, but might also have additional therapeutic potential by modifying the immune activity in the thymus.

Lipopolysaccharide inhibits Sindbis virus-induced IP-10 release in human peripheral blood mononuclear cells

Chemokines play a pivotal role in the innate response to both bacterial and viral infections, and in mixed infections. To determine chemokine responses to Sindbis virus (SIN) in a co-infection model, peripheral blood mononuclear cells (PBMCs) derived from healthy volunteers were exposed to SIN in the presence and absence of lipopolysaccharide (LPS). Culture supernatants recovered at 2, 24, and 72 h post-exposure were evaluated for virus replication and analyzed for chemokines by ELISA. None of the PBMC cultures showed new virus release, GFP reporter expression, or viral RNA synthesis. While SIN had little effect on the induction of IL-8 and RANTES, the chemokines MCP-1, MIP1-α (p < 0.001), and MIP1-β (p < 0.0004) were drastically upregulated by SIN as well as LPS. Both live and UV-inactivated SIN induced secretion of IP-10 and I-TAC. Although LPS did not induce release of IP-10, it sharply inhibited (p = 0.004) SIN-mediated IP-10 secretion. On the contrary, the release of SLC was blocked by SIN. The adjuvant activity of IP-10, its antiangiogenic function, and antagonism between SIN and LPS for the release of select chemokines may be useful in understanding the pathogenesis of mixed infections, cross-talk between cellular pathways, and may have applications in cancer and sepsis.

Increased MDSC accumulation and Th2 biased response to influenza A virus infection in the absence of TLR7 in mice

Toll-like receptors (TLRs) play an important role in the induction of innate and adaptive immune response against influenza A virus (IAV) infection; however, the role of Toll-like receptor 7 (TLR7) during the innate immune response to IAV infection and the cell types affected by the absence of TLR7 are not clearly understood. In this study, we show that myeloid derived suppressor cells (MDSC) accumulate in the lungs of TLR7 deficient mice more so than in wild-type C57Bl/6 mice, and display increased cytokine expression. Furthermore, there is an increase in production of Th2 cytokines by TLR7^-/- compared with wildtype CD4+ T-cells in vivo, leading to a Th2 polarized humoral response. Our findings indicate that TLR7 modulates the accumulation of MDSCs during an IAV infection in mice, and that lack of TLR7 signaling leads to a Th2-biased response.