Neutralisation of peritoneal IL-17A markedly improves the prognosis of severe septic mice by decreasing neutrophil infiltration and proinflammatory cytokines

The role of the peripheral system dysfunction in the pathogenesis of sepsis-associated encephalopathy

Sepsis is a condition that greatly impacts the brain, leading to neurological dysfunction and heightened mortality rates, making it one of the primary organs affected. Injury to the central nervous system can be attributed to dysfunction of various organs throughout the entire body and imbalances within the peripheral immune system. Furthermore, central nervous system injury can create a vicious circle with infection-induced peripheral immune disorders. We collate the pathogenesis of septic encephalopathy, which involves microglial activation, programmed cell death, mitochondrial dysfunction, endoplasmic reticulum stress, neurotransmitter imbalance, and blood-brain barrier disruption. We also spotlight the effects of intestinal flora and its metabolites, enterocyte-derived exosomes, cholinergic anti-inflammatory pathway, peripheral T cells and their cytokines on septic encephalopathy.

Novel Aspects of the Immune Response Involved in the Peritoneal Damage in Chronic Kidney Disease Patients under Dialysis

Chronic kidney disease (CKD) incidence is growing worldwide, with a significant percentage of CKD patients reaching end-stage renal disease (ESRD) and requiring kidney replacement therapies (KRT). Peritoneal dialysis (PD) is a convenient KRT presenting benefices as home therapy. In PD patients, the peritoneum is chronically exposed to PD fluids containing supraphysiologic concentrations of glucose or other osmotic agents, leading to the activation of cellular and molecular processes of damage, including inflammation and fibrosis. Importantly, peritonitis episodes enhance peritoneum inflammation status and accelerate peritoneal injury. Here, we review the role of immune cells in the damage of the peritoneal membrane (PM) by repeated exposure to PD fluids during KRT as well as by bacterial or viral infections. We also discuss the anti-inflammatory properties of current clinical treatments of CKD patients in KRT and their potential effect on preserving PM integrity. Finally, given the current importance of coronavirus disease 2019 (COVID-19) disease, we also analyze here the implications of this disease in CKD and KRT.

Protective effect of Secukinumab on severe sepsis model rats by neutralizing IL-17A to inhibit IKBα/NFκB inflammatory signal pathway

Secukinumab is a specific neutralizing antibody for IL-17A. At present, numerous studies have confirmed the important role of IL-17A in sepsis, but the role of secukinumab in sepsis has not been studied. The present study explored the protective effect and underlying mechanism of secukinumab in severe sepsis model rats. We established a severe sepsis rat model using cecal ligation and puncture (CLP). The optimal dose of secukinumab was determined by observing the 7-day survival rate of severe sepsis model rats. The expression levels of TNF-α, IL-6, and IL-17A in plasma and lung tissue were determined by enzyme-linked immunosorbent assay. The degree of pathological damage to lung tissue was evaluated by hematoxylin–eosin (H–E) staining and pathological damage scale. The expressions of IKBα/NFκB pathway proteins and downstream-related inflammatory factors were detected by western blotting and real-time quantitative polymerase chain reaction (RT-qPCR). Our results show that high-dose secukinumab can inhibit the activation of the IKBα/NFκB inflammatory pathway by neutralizing IL-17A and reducing the gene expression of pathway-related inflammatory cytokines, thereby reducing the levels of inflammatory cytokines in lung tissue and plasma, thereby reducing the damage of lung tissue in severe sepsis model rats and improving the systemic inflammatory response.

Contributory Role of BLT2 in the Production of Proinflammatory Cytokines in Cecal Ligation and Puncture-Induced Sepsis

BLT2 is a low-affinity receptor for leukotriene B4, a potent lipid mediator of inflammation generated from arachidonic acid via the 5-lipoxygenase pathway. The aim of this study was to investigate whether BLT2 plays any role in sepsis, a systemic inflammatory response syndrome caused by infection. A murine model of cecal ligation and puncture (CLP)-induced sepsis was used to evaluate the role of BLT2 in septic inflammation. In the present study, we observed that the levels of ligands for BLT2 (LTB4 [leukotriene B4] and 12(S)-HETE [12(S)-hydroxyeicosatetraenoic acid]) were significantly increased in the peritoneal lavage fluid and serum from mice with CLP-induced sepsis. We also observed that the levels of BLT2 as well as 5-LO and 12-LO, which are synthesizing enzymes for LTB4 and 12(S)-HETE, were significantly increased in lung and liver tissues in the CLP mouse model. Blockade of BLT2 markedly suppressed the production of sepsis-associated cytokines (IL-6 [interleukin-6], TNF-α [tumor necrosis factor alpha], and IL-1β [interleukin-1β] as well as IL-17 [interleukin-17]) and alleviated lung inflammation in the CLP group. Taken together, our results suggest that BLT2 cascade contributes to lung inflammation in CLP-induced sepsis by mediating the production of inflammatory cytokines. These findings suggest that BLT2 may be a potential therapeutic target for sepsis patients.

Neuroinflammation in Sepsis: Molecular Pathways of Microglia Activation

Frequently underestimated, encephalopathy or delirium are common neurological manifestations associated with sepsis. Brain dysfunction occurs in up to 80% of cases and is directly associated with increased mortality and long-term neurocognitive consequences. Although the central nervous system (CNS) has been classically viewed as an immune-privileged system, neuroinflammation is emerging as a central mechanism of brain dysfunction in sepsis. Microglial cells are major players in this setting. Here, we aimed to discuss the current knowledge on how the brain is affected by peripheral immune activation in sepsis and the role of microglia in these processes. This review focused on the molecular pathways of microglial activity in sepsis, its regulatory mechanisms, and their interaction with other CNS cells, especially with neuronal cells and circuits.

γδ T/Interleukin-17A Contributes to the Effect of Maresin Conjugates in Tissue Regeneration 1 on Lipopolysaccharide-Induced Cardiac Injury

The mechanisms underlying sepsis-induced cardiomyopathy (SIC) remain poorly understood, and there are no specific therapeutics for SIC. We investigated the effects of maresin conjugates in tissue regeneration 1 (MCTR1) on SIC and explored its potential mechanisms. The experiments were conducted using an endotoxemia model induced by lipopolysaccharide (LPS). Mice were given MCTR1 intravenously 6 h after LPS stimulation. Echocardiography was performed to assess cardiac function 12 h after LPS administration. Treatment with MCTR1 significantly enhanced cardiac function and reduced LPS-induced increase of mRNA expression levels of inflammation cytokines. Transcriptomic analysis indicated that MCTR1 inhibited neutrophil chemotaxis via the IL-17 signaling pathway. We confirmed that MCTR1 reduced the expressions of neutrophil chemoattractants and neutrophil infiltration in the LPS-stimulated hearts. MCTR1 also resulted in a considerable reduction in IL-17A production mainly derived from γδ T cells. Moreover, our results provided the first evidence that neutralizing IL-17A or depletion of γδ T cells markedly decreased neutrophil recruitment and enhanced cardiac function in LPS-induced cardiac injury. These results suggest that MCTR1 alleviates neutrophil infiltration thereby improves cardiac function in LPS-induced cardiac injury via the IL-17 signaling pathway. Thus, MCTR1 represented a novel therapeutic strategy for patients with SIC.

Regulation of the Nfkbiz Gene and Its Protein Product IkBζ in Animal Models of Sepsis and Endotoxic Shock

Sepsis is a life-threatening condition that arises from a poorly regulated inflammatory response to pathogenic organisms. Current treatments are limited to antibiotics, fluid resuscitation, and other supportive therapies. New targets for monitoring disease progression and therapeutic interventions are therefore critically needed. We previously reported that lipocalin-2 (Lcn2), a bacteriostatic mediator with potent proapoptotic activities, was robustly induced in sepsis. Other studies showed that Lcn2 was a predictor of mortality in septic patients. However, how Lcn2 is regulated during sepsis is poorly understood. We evaluated how IkBζ, an inducer of Lcn2, was regulated in sepsis using both the cecal ligation and puncture (CLP) and endotoxemia (lipopolysaccharide [LPS]) animal models. We show that Nfkbiz, the gene encoding IkBζ, was rapidly stimulated but, unlike Lcn2, whose expression persists during sepsis, mRNA levels of Nfkbiz decline to near basal levels several hours after its induction. In contrast, we observed that IkBζ expression remained highly elevated in septic animals following CLP but not LPS, indicating the occurrence of a CLP-specific mechanism that extends IkBζ half-life. By using an inhibitor of IkBζ, we determined that the expression of Lcn2 was largely controlled by IkBζ. Altogether, these data indicate that the high IkBζ expression in tissues likely contributes to the elevated expression of Lcn2 in sepsis. Since IkBζ is also capable of promoting or repressing other inflammatory genes, it might exert a central role in sepsis.

IL-17A as a Potential Therapeutic Target for Patients on Peritoneal Dialysis

Chronic kidney disease (CKD) is a health problem reaching epidemic proportions. There is no cure for CKD, and patients may progress to end-stage renal disease (ESRD). Peritoneal dialysis (PD) is a current replacement therapy option for ESRD patients until renal transplantation can be achieved. One important problem in long-term PD patients is peritoneal membrane failure. The mechanisms involved in peritoneal damage include activation of the inflammatory and immune responses, associated with submesothelial immune infiltrates, angiogenesis, loss of the mesothelial layer due to cell death and mesothelial to mesenchymal transition, and collagen accumulation in the submesothelial compact zone. These processes lead to fibrosis and loss of peritoneal membrane function. Peritoneal inflammation and membrane failure are strongly associated with additional problems in PD patients, mainly with a very high risk of cardiovascular disease. Among the inflammatory mediators involved in peritoneal damage, cytokine IL-17A has recently been proposed as a potential therapeutic target for chronic inflammatory diseases, including CKD. Although IL-17A is the hallmark cytokine of Th17 immune cells, many other cells can also produce or secrete IL-17A. In the peritoneum of PD patients, IL-17A-secreting cells comprise Th17 cells, γδ T cells, mast cells, and neutrophils. Experimental studies demonstrated that IL-17A blockade ameliorated peritoneal damage caused by exposure to PD fluids. This article provides a comprehensive review of recent advances on the role of IL-17A in peritoneal membrane injury during PD and other PD-associated complications.

Identification of progranulin as a novel diagnostic biomarker for early-onset sepsis in neonates

Neonatal early-onset sepsis (EOS) is associated with high morbidity and mortality. Accurate early diagnosis is crucial for prompt treatment and a better clinical outcome. We aimed to identify new biomarkers for the diagnosis of EOS. A total of 152 neonates with a risk of EOS were divided into an EOS group and a non-EOS group according to the conventional diagnostic criteria. Blood samples were collected within 0-24, 24-48, and 48-72 h after birth. Serum levels of progranulin (PGRN), interleukin (IL)-33, IL-17a, IL-23, IL-6, tumor necrosis factors α (TNF-α), interferon γ (IFN-γ), granulocyte-macrophage colony-stimulating factor (GM-CSF), procalcitonin (PCT), and C-reactive protein (CRP) were determined. PGRN levels were significantly elevated in the EOS neonates compared with the levels in the non-EOS neonates (1.53 vs. 0.77 ng/ml (median), P < 0.001), with an area under the receiver operating characteristic (ROC) curve (AUC) of 0.76 (P < 0.001). Compared with PGRN, IL-33, IL-17a, IL-23, IL-6, PCT, and CRP showed significant (AUC > 0.70) but slightly less predictive power for EOS within the same time range. Stepwise multivariate regression analysis identified PGRN, IL-33, and PCT as independent predictors of EOS. In addition, the combined measurements of PGRN, IL-33, and PCT showed significantly higher predictive power for EOS than any of the three markers alone. PGRN showed greater efficacy for predicting EOS than the traditional markers PCT and CRP as well as other potential markers tested in this study. PGRN may serve as an effective biomarker for the early diagnosis of EOS.

Neutralization of interleukin-17A alleviates burn-induced intestinal barrier disruption via reducing pro-inflammatory cytokines in a mouse model

Background

The intestinal barrier integrity can be disrupted due to burn injury, which is responsible for local and systemic inflammatory responses. Anti-inflammation strategy is one of the proposed therapeutic approaches to control inflammatory cascade at an early stage. Interleukin-17A (IL-17A) plays a critical role in inflammatory diseases. However, the role of IL-17A in the progression of burn-induced intestinal inflammation is poorly understood. In this study, we aimed to investigate the effect of IL-17A and associated pro-inflammatory cytokines that were deeply involved in the pathogenesis of burn-induced intestinal inflammatory injury, and furthermore, we sought to determine the early source of IL-17A in the intestine.

Methods

Mouse burn model was successfully established with infliction of 30% total body surface area scald burn. The histopathological manifestation, intestinal permeability, zonula occludens-1 expression, pro-inflammatory cytokines were determined with or without IL-17A-neutralization. Flow cytometry was used to detect the major source of IL-17A⁺ cells in the intestine.

Results

Burn caused intestinal barrier damage, increase of intestinal permeability, alteration of zonula occludens-1 expressions, elevation of IL-17A, IL-6, IL-1β and tumor necrosis factor-α (TNF-α), whereas IL-17A neutralization dramatically alleviated burn-induced intestinal barrier disruption, maintained zonula occludens-1 expression, and noticeably, inhibited pro-inflammatory cytokines elevation. In addition, we observed that the proportion of intestinal IL-17A⁺Vγ4⁺ T subtype cells (but not IL-17A⁺Vγ1⁺ T subtype cells) were increased in burn group, and neutralization of IL-17A suppressed this increase.

Conclusions

The main original findings of this study are intestinal mucosa barrier is disrupted after burn through affecting the expression of pro-inflammatory cytokines, and a protective role of IL-17A neutralization for intestinal mucosa barrier is determined. Furthermore, Vγ4⁺ T cells are identified as the major early producers of IL-17A that orchestrate an inflammatory response in the burn model. These data suggest that IL-17A blockage may provide a unique target for therapeutic intervention to treat intestinal insult after burn.

IL-17A activated by Toll-like receptor 9 contributes to the development of septic acute kidney injury

Toll-like receptor 9 (TLR9), which is activated by endogenously released mtDNA during sepsis, contributes to the development of polymicrobial septic acute kidney injury (AKI). However, downstream factors of TLR9 to AKI remain unknown. We hypothesized that IL-17A activated by TLR9 may play a critical role in septic AKI development. To determine the effects of TLR9 on IL-17A production in septic AKI, we used a cecal ligation and puncture (CLP) model in Tlr9 knockout (Tlr9KO) mice and wild-type (WT) littermates. We also investigated the pathway from TLR9 activation in dendritic cells (DCs) to IL-17A production by γδT cells in vitro. To elucidate the effects of IL-17A on septic AKI, Il-17a knockout (Il-17aKO) mice and WT littermates were subjected to CLP. We further investigated the relationship between the TLR9-IL-17A axis and septic AKI by intravenously administering recombinant IL-17A or vehicle into Tlr9KO mice and assessing kidney function. IL-17A levels in both plasma and the peritoneal cavity and mRNA levels of IL-23 in the spleen were significantly higher in WT mice after CLP than in Tlr9KO mice. Bone marrow-derived DCs activated by TLR9 induced IL-23 and consequently promoted IL-17A production in γδT cells in vitro. Knockout of Il-17a improved survival, functional and morphological aspects of AKI, and splenic apoptosis after CLP. Exogenous IL-17A administration aggravated CLP-induced AKI attenuated by knockout of Tlr9. TLR9 in DCs mediated IL-17A production in γδT cells during sepsis and contributed to the development of septic AKI.

Blockade of IL-17A/IL-17R Pathway Protected Mice from Sepsis-Associated Encephalopathy by Inhibition of Microglia Activation

Sepsis-associated encephalopathy (SAE) is a poorly understood condition that leads to long-term cognitive impairment and increased mortality in survivors. Recent research revealed that IL-17A/IL-17R might serve as a checkpoint in microglia-mediated neuroinflammation. The present study was designed to determine the specific role of IL-17A-mediated microglia activation in the development of SAE. A mouse model of SAE was induced by cecal ligation and puncture (CLP), and behavior performance was evaluated by the inhibitory avoidance test and the open field test. Cytokine expression and microglia activation in brain tissue were determined at 6 h, 12 h, 24 h, 48 h, and day 7 post surgery. Further, septic mice were intracerebral ventricle- (i.c.v.-) injected with recombinant IL-17A, anti-IL-17A ab, anti-IL-17R ab, or isotype controls to evaluate the potential effects of IL-17A/IL-17R blockade in the prevention of SAE. Septic peritonitis induced significant impairment of learning memory and exploratory activity, which was associated with a higher expression of IL-17A, IL-1β, and TNF-α in the brain homogenate. Fluorescence intensity of Iba-1 and IL-17R in the hippocampus was significantly increased following CLP. Treatment with recombinant IL-17A enhanced the neuroinflammation and microglia activation in CLP mice. On the contrary, neutralizing anti-IL-17A or anti-IL-17R antibodies mitigated the CNS inflammation and microglia activation, thus alleviating the cognitive dysfunction. Furthermore, as compared to the sham control, microglia cultured from CLP mice produced significantly higher levels of cytokines and expressed with higher fluorescence intensity of Iba-1 in response to IL-17A or LPS. Pretreatment with anti-IL-17R ab suppressed the Iba-1 expression and cytokine production in microglia stimulated by IL-17A. In conclusion, blockade of the IL-17A/IL-17R pathway inhibited microglia activation and neuroinflammation, thereby partially reversing sepsis-induced cognitive impairment. The present study suggested that the IL-17A/IL-17R signaling pathway had an important, nonredundant role in the development of SAE.

IL-17, IL-27, and IL-33: A Novel Axis Linked to Immunological Dysfunction During Sepsis

Sepsis is a major cause of morbidity and mortality worldwide despite numerous attempts to identify effective therapeutics. While some sepsis deaths are attributable to tissue damage caused by inflammation, most mortality is the result of prolonged immunosuppression. Ex vivo, immunosuppression during sepsis is evidenced by a sharp decrease in the production of pro-inflammatory cytokines by T cells and other leukocytes and increased lymphocyte apoptosis. This allows suppressive cytokines to exert a greater inhibitory effect on lymphocytes upon antigen exposure. While some pre-clinical and clinical trials have demonstrated utility in targeting cytokines that promote lymphocyte survival, this has not led to the approval of any therapies for clinical use. As cytokines with a more global impact on the immune system are also altered by sepsis, they represent novel and potentially valuable therapeutic targets. Recent evidence links interleukin (IL)-17, IL-27, and IL-33 to alterations in the immune response during sepsis using patient serum and murine models of peritonitis and pneumonia. Elevated levels of IL-17 and IL-27 are found in the serum of pediatric and adult septic patients early after sepsis onset and have been proposed as diagnostic biomarkers. In contrast, IL-33 levels increase in patient serum during the immunosuppressive stage of sepsis and remain high for more than 5 months after recovery. All three cytokines contribute to immunological dysfunction during sepsis by disrupting the balance between type 1, 2, and 17 immune responses. This review will describe how IL-17, IL-27, and IL-33 exert these effects during sepsis and their potential as therapeutic targets.

Neutralization of Interleukin-17A Attenuates Lipopolysaccharide-Induced Mastitis by Inhibiting Neutrophil Infiltration and the Inflammatory Response

Mastitis has been recognized as a common and major disease of cows with a strong impact on dairy farming. Interleukin-17A (IL-17A) has been shown to mediate crucial crosstalk between the immune system and various epithelial tissues, initiating a series of defensive mechanisms against bacterial and fungal infections. This crosstalk is especially involved in neutrophil infiltration. To evaluate the role of IL-17A in immune defense in the mammary gland in mice, we tested the effects of depleting IL-17A on changes in pathology, neutrophil infiltration, and pro-inflammatory cytokine levels in the mammary gland stimulated by lipopolysaccharide (LPS). Further, the effects of IL-17A on the activation of the nuclear factor-κB (NF-κB) signaling pathway during mastitis induced by LPS were also studied. The results showed that the production of IL-17A was significantly elevated during mastitis induced by LPS. IL-17A blockade via an intraperitoneal antibody injection protected against LPS-induced mastitis, as indicated by decreased neutrophil infiltration, myeloperoxidase activity, pro-inflammatory cytokines levels, and NF-κB signaling pathway molecule phosphorylation in response to LPS. In conclusion, an elevated IL-17 level plays a crucial role during mastitis, and anti-IL-17A antibody blockade protects against LPS-induced mammary gland inflammation induced through the NF-κB signaling pathway, which provides a new potential treatment target for mastitis.

TIPE2 Suppresses Pseudomonas aeruginosa Keratitis by Inhibiting NF-κB Signaling and the Infiltration of Inflammatory Cells

Background

The role of tumor necrosis factor α (TNF-α) induced protein 8-like-2 (TIPE2) in Pseudomonas aeruginosa (PA) keratitis was explored.

Methods

Eight-week-old TIPE2 knockout (TIPE2−/−) C57BL/6 mice and their wild-type (WT) littermates were used. Corneal disease was graded at 1, 2, and 3 days postinfection, and slit lamp, clinical score, histopathology, and immunostaining were performed in the infected corneas. The corneas were harvested, and messenger ribonucleic acid (mRNA) levels of TNF-α, interleukin-1β (IL-1β), and interleukin-6 (IL-6) were tested. Enzyme-linked immunosorbent assay (ELISA) determined the protein levels, and nuclear factor κ-light-chain-enhancer of activated B cell (NF-κB) signaling molecules were tested by Western blot. In vitro human corneal epithelial cells (HCECs) were used to determine the relationship between TIPE2 and TAK1. The HCECs were treated with TIPE2 short hairpin ribonucleic acid (shRNA) and lipopolysaccharide (LPS) to test the NF-κB signaling molecules by Western blot.

Results

Pseudomonas aeruginosa infection induced a decreased expression of TIPE2 in mouse corneas 2 days postinfection. Compared with the control group, TIPE2-deficient mice were susceptible to infection with PA and showed increased corneal inflammation. Reduced NF-κB signaling and inflammatory cell infiltration were required in the TIPE2-mediated immune modulation.

Conclusions

TIPE2 promoted host resistance to PA infection by suppressing corneal inflammation via regulating TAK1 signaling negatively and inhibiting the infiltration of inflammatory cells.

IL-17A - A regulator in acute inflammation: Insights from in vitro, in vivo and in silico studies

Acute inflammation following sterile injury is both inevitable and necessary to restore homeostasis and promote tissue repair. However, when excessive, inflammation can jeopardize the viability of organs and cause detrimental systemic effects. Identifying key-regulators of the immune cascade induced by surgery is vital to attenuating excessive inflammation and its subsequent effects. In this review, we describe the emerging role of IL-17A as a key-regulator in acute inflammation. The role of IL-17A in chronic disease states, such as rheumatoid arthritis, psoriasis and cancer has been well documented, but its significance in acute inflammation following surgery, sepsis, or traumatic injury has not been well studied. We aim to highlight the role of IL-17A in acute inflammation caused by trauma, liver ischemia, and organ transplantation, as well as in post-operative surgical infections. Further investigation of the roles of this cytokine in acute inflammation may stimulate novel therapies or diagnostic modalities.

IL-17 in neonatal health and disease

Over the last few years, scientific interest in the cytokine IL-17A has intensified as its role in human health and disease has been elucidated. Discovered almost a quarter century ago, IL-17A is known to have poor biologic activity when acting alone, but attains robust actions when working synergistically with potent mediators of proinflammatory immune responses, such as IL-6 and IL-8. IL-17A is produced by specialized innate immune cells that protect host barriers from the outside world. Like sentries, these innate immune cells can "sound the alarm" through increased production of IL-17A, causing activation and recruitment of primed neutrophils and monocytes when pathogens escape initial host defenses. In this way, IL-17A promulgates mechanisms responsible for pathogen death and clearance. However, when IL-17A pathways are triggered during fetal development, due to chorioamnionitis or in utero inflammatory conditions, IL-17A can instigate and/or exacerbate fetal inflammatory responses that increase neonatal morbidities and mortality associated with common neonatal conditions such as sepsis, bronchopulmonary dysplasia (BPD), patent ductus arteriosus (PDA), and necrotizing enterocolitis (NEC). This review details the ontogeny of IL-17A in the fetus and newborn, discusses how derangements in its production can lead to pathology, and describes known and evolving therapies that may attenuate IL-17A-mediated human conditions.

Interleukin-17A Aggravates Middle Ear Injury Induced by Streptococcus pneumoniae through the p38 Mitogen-Activated Protein Kinase Signaling Pathway

Acute otitis media (AOM) is one of the most common bacterial infectious diseases in children aged 2 to 7 years worldwide. We previously demonstrated that interleukin-17A (IL-17A) promotes an acute inflammatory response characterized by the influx of neutrophils into the middle ear cavity during Streptococcus pneumoniae-induced AOM. In general, the inflammatory response is viewed as an effector that frequently causes local tissue damage. However, little is known about the pathogenic effects of IL-17A in AOM. Here, we investigated the pathogenic effects of IL-17A by using wild-type (WT) and IL-17A knockout (KO) mouse models. The results showed that the pathogenic effects of AOM, including weight loss, histopathological changes, and proinflammatory cytokine production, were more severe in WT mice than in IL-17A KO mice, suggesting that IL-17A aggravates tissue damage in AOM. Furthermore, these pathogenic effects were found to be dependent on p38 mitogen-activated protein kinase (MAPK) and could be reversed in the presence of a p38 MAPK-specific inhibitor. It was also demonstrated that IL-17A promoted the production of neutrophil myeloperoxidase (MPO) through the p38 MAPK signaling pathway, which was responsible for the middle ear tissue injury. These data support the conclusion that IL-17A contributes to middle ear injury through the p38 MAPK signaling pathway.

Lung-resident γδ T cells and their roles in lung diseases

γδ T cells are greatly enriched in mucosal and epithelial sites, such as the skin, respiratory, digestive and reproductive tracts, and they are defined as tissue-resident immune cells. In these tissues, the characteristics and biological roles of γδ T cells are distinguished from each other. The lungs represent the most challenging immunological dilemma for the host, and they have their own effective immune system. The abundance of γδ T cells, an estimated 8-20% of resident pulmonary lymphocytes in the lung, maintains lung tissue homeostasis. In this review, we summarize the recent research progress regarding lung-resident γδ T cells, including their development, residency and immune characteristics, and discuss the involvement of γδ T cells in infectious diseases of the lung, including bacterial, viral and fungal infections; lung allergic disease; lung inflammation and fibrosis; and lung cancer.

Knockout of interleukin-17A protects against sepsis-associated acute kidney injury

Background

Sepsis-associated acute kidney injury (SA-AKI) is an independent risk factor for death in patients with sepsis, but treatment for it is limited. To improve the diagnosis and treatment of SA-AKI, we must first understand its pathogenesis. Recently, interleukin (IL)-17A has been shown to be associated with the pathogenesis of acute kidney injury and sepsis, but its role in SA-AKI remains unclear.

Methods

SA-AKI was induced in male C57BL/6 and IL-17A^−/− mice using cecal ligation and puncture (CLP) operations for 24 h.

Results

At 7 days, only seven mice survived in the wild-type septic group, but nine survived in the IL-17A^−/− septic group, corresponding to survival rates of 25 % and 45 %, respectively. At 24 h after CLP operations, both wild-type and IL-17A^−/− septic mice developed kidney injury. The IL-17A^−/− septic mice exhibited decreased serum creatinine and blood urea nitrogen levels and an improved acute tubular necrosis score. The IL-17A^−/− septic mice exhibited decreased IL-6, interferon-γ, tumor necrosis factor-α, CXCL1, CXCL2, and CXCL5 expression in kidney tissue, but increased IL-10 expression. In addition, renal neutrophil infiltration was attenuated significantly in the IL-17A^−/− septic group. Moreover, IL-17A^−/− septic mice showed significantly decreased apoptosis of tubular epithelial cells, including decreased TUNEL-positive tubular cell number and cleaved caspase-3 level, compared with the wild-type CLP group. Their Bax/Bcl-2 expression ratio was also increased.

Conclusions

Our study demonstrates that IL-17A knockout could protect against SA-AKI. We show that IL-17A plays a pathogenic role in SA-AKI by increasing the levels of proinflammatory cytokines and chemokines, and by inducing neutrophil infiltration and apoptosis of tubular epithelial cells. Accordingly, IL-17A may be a novel target in SA-AKI.

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0157-1) contains supplementary material, which is available to authorized users.

Innate Lymphoid Cells Are the Predominant Source of IL-17A during the Early Pathogenesis of Acute Respiratory Distress Syndrome

RATIONALE

IL-17A is purported to help drive early pathogenesis in acute respiratory distress syndrome (ARDS) by enhancing neutrophil recruitment. Although IL-17A is the archetypal cytokine of T-helper 17 cells, it is produced by a number of lymphocytes, the source during ARDS being unknown.

OBJECTIVES

To identify the cellular source and the role of IL-17A in the early phase of lung injury.

METHODS

Lung injury was induced in wild-type (C57BL/6) and IL-17 knockout (KO) mice with aerosolized LPS (100 μg) or Pseudomonas aeruginosa infection. Detailed phenotyping of the cells expressing RORγt, the transcriptional regulator of IL-17 production, in the mouse lung at 24 hours was performed by flow cytometry.

MEASUREMENTS AND MAIN RESULTS

A 100-fold reduction in neutrophil infiltration was observed in the lungs of the IL-17A KO compared with wild-type mice. The majority of RORγt(+) cells in the mouse lung were the recently identified group 3 innate lymphoid cells (ILC3s). Detailed characterization revealed these pulmonary ILC3s (pILC3s) to be discrete from those described in the gut. The critical role of these cells was verified by inducing injury in recombinase-activating gene 2 KO mice, which lack T cells but retain innate lymphoid cells. No amelioration of pathology was observed in the recombinase-activating gene 2 KO mice.

CONCLUSIONS

IL-17 is rapidly produced during lung injury and significantly contributes to early immunopathogenesis. This is orchestrated largely by a distinct population of pILC3s. Modulation of the activity of pILC3s may potentiate early control of the inflammatory dysregulation seen in ARDS, opening up new therapeutic targets.

Pathophysiology of septic shock: From bench to bedside

Our understanding of sepsis and its resultant outcomes remains a paradox. On the one hand, we know more about the pathophysiology of sepsis than ever before. However, this knowledge has not been successfully translated to the bedside, as the vast majority of clinical trials for sepsis have been negative. Yet even in the general absence of positive clinical trials, mortality from sepsis has fallen to its lowest point in history, in large part due to educational campaigns that stress timely antibiotics and hemodynamic support. While additional improvements in outcome will assuredly result from further compliance with evidence based practices, a deeper understanding of the science that underlies the host response in sepsis is critical to the development of novel therapeutics. In this review, we outline immunopathologic abnormalities in sepsis, and then look at potential approaches to therapeutically modulate them. Ultimately, an understanding of the science underlying sepsis should allow the critical care community to utilize precision medicine to combat this devastating disease on an individual basis leading to improved outcomes.

Regulation of inflammatory biomarkers by intravenous methylprednisolone in pediatric ARDS patients: Results from a double-blind, placebo-controlled randomized pilot trial

OBJECTIVE

A double-blind, randomized controlled trial showed that low-dose glucocorticoid therapy in pediatric ARDS patients is feasible and may improve both ventilation and oxygenation indices in these patients. However, the molecular mechanisms underlying potential changes in outcomes remain unclear. Based on these clinical findings, this study was designed to examine the effects of intravenous methylprednisolone on circulating inflammatory biomarkers in pediatric ARDS patients.

DESIGN

Double-blind, placebo-controlled randomized trial with blood collection on study entry and day 7.

SETTING

Tertiary care children's hospital.

PATIENTS

Children (0-18years) with ARDS undergoing mechanical ventilation.

INTERVENTIONS

35 children were randomized within 72h of mechanical ventilation. The glucocorticoid group received methylprednisolone 2mg/kg loading dose followed by 1mg/kg/day continuous infusion from days 1 to 7. Both groups were ventilated following the ARDSnet recommendations. WBC and differential cell counts, plasma cytokines and CRP levels, and coagulation parameters were analyzed on days 0 and 7.

RESULTS

At study entry, the placebo group had higher IL-15 and basophil levels. On day 7, in comparison to study entry, the placebo group had lower IL-1α, IFN-γ and IL-10 levels. The glucocorticoid group had lower INF-α, IL-6, IL-10, MCP-1, G-CSF and GM-CSF levels, and higher IL-17α levels on day 7 in comparison to study entry. Total and differential cell counts remained unchanged within the placebo group between days 0 and 7, whereas in the glucocorticoid group total WBC and platelets counts were increased on day 7. Pearson's correlation studies within the placebo and glucocorticoid groups revealed positive and negative correlations between cytokine levels, cell counts, coagulation parameters and relevant clinical parameters of disease severity identified in our previous study. Multiple regression models identified several cytokines as predictors for alterations in clinical parameters of disease severity.

CONCLUSION

This pilot study shows the feasibility of simultaneously measuring multiple inflammatory cytokines, cell counts and coagulation parameters in pediatric ARDS patients. We report statistical models that may be useful for future, larger trials to predict ARDS severity and outcomes.

Milk fat globule-epidermal growth factor-factor VIII downregulates interleukin-17 expression in sepsis by modulating STAT3 activation

BACKGROUND

Milk fat globule-epidermal growth factor-factor VIII (MFG-E8) is a secretory glycoprotein with a known role in inflammation. In sepsis, interleukin (IL)-17 acts as a proinflammatory cytokine to exaggerate systemic inflammation. We hypothesize that MFG-E8 downregulates IL-17 expression in sepsis.

METHODS

Sepsis was induced in 8-week-old male C57BL/6 mice by cecal ligation and puncture (CLP). Recombinant mouse MFG-E8 (rmMFG-E8) at a dosage of 20 μg/kg body weight or phosphate-buffered saline was concurrently injected. After 10 hours, blood and spleen samples were harvested for analysis. For in vitro studies, splenocytes isolated from healthy mice pretreated with rmMFG-E8 and splenocytes from MFG-E8 knockout (mfge8(-/-)) mice were stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin, followed by measurement of IL-17 expression with either quantitative PCR or enzyme-linked immunosorbent assay.

RESULTS

At 10 hours after CLP, rmMFG-E8 inhibited the elevated levels of IL-17 protein in serum by 31%, compared with the vehicle. In the spleen, rmMFG-E8 reduced the upregulated IL-17 mRNA and protein levels by 81% and 51%, respectively. This correlated with a significant reduction in organ injury markers AST and ALT in sepsis after administration of rmMFG-E8. In vitro treatment of splenocytes isolated from healthy mice with rmMFG-E8 showed significant downregulation in PMA/ionomycin-induced IL-17 expression. In contrast, CD4 T-cells from mfge8(-/-) mice showed significant upregulation of IL-17 compared with wild-type mice. The phosphorylated level of signal transducer and activator of transcription 3 (STAT3) was downregulated in spleen tissue of septic mice treated with rmMFG-E8. Conversely, mfge8(-/-) mice showed increased phosphorylated STAT3 compared with wild-type mice after sepsis.

CONCLUSION

Our findings demonstrate MFG-E8-mediated downregulation of IL-17 expression, implicating its potential as a novel therapeutic agent against sepsis.

Treatment with a neutralising anti-rat interleukin-17 antibody after multiple-trauma reduces lung inflammation

BACKGROUND

It has been well recognised that a deficit of numbers and function of CD4(+)CD25(+)Foxp3(+) cells (Treg) is attributed to the development of autoimmune diseases and inflammatory diseases; additionally, IL-17-producing cells (Th17) have a pro-inflammatory role. The balance between Th17 and Treg may be essential for maintaining immune homeostasis and has long been thought as one of the important factors in the development/prevention of autoimmune diseases and inflammatory diseases. In our previous research, we explored that cytokines (IL-17) and the balance of Treg/Th17 had a significant relevance with tissue (lung) inflammation and injury in acute-phase after multiple-trauma.

OBJECTIVE

To more verify whether an imbalance of Treg/Th17 is characteristic of rats suffering from multiple trauma.

METHODS AND SUBJECTIVE

Using IL-17 monoclonal antibody (IL-17mAb)-treated multiple-trauma rat, we tested the pathogenic role of IL-17 in the development of multiple-trauma. Rat models were treated respectively with IL-17mAb or rat IgG 2A isotype control or phosphate-buffered solution after model was established. Normal rats only received anaesthesia and cannulation were taken as sham. Rats in each group were killed respectively at the end of 1h, 4h, 8h after injection. Collected serum and lung samples for assessment dynamically of MPO, IL-17, IL-6, and TGF-β-mRNA, and cytokine (IL-17, IL-6, TGF-β) and lung tissue for pulmonary histological analysis.

RESULTS

Neutralisation of IL-17 with anti-IL-17 can decrease serum IL-17 level and the IL-17-mRNA transcript level in lung, and ameliorate tissue inflammatory, defer disease course.

CONCLUSION

Our data suggest that IL-17 is crucially involved in the pathogenesis of multiple-trauma in rat, IL-17 inhibition might ameliorate the lung inflammation in acute-phase after multiple-trauma.

Blockage of Eosinopoiesis by IL-17A Is Prevented by Cytokine and Lipid Mediators of Allergic Inflammation

Interleukin- (IL-) 17A, a pleiotropic mediator of inflammation and autoimmunity, potently stimulates bone-marrow neutrophil production. To explore IL-17A effects on eosinopoiesis, we cultured bone-marrow from wild-type mice, or mutants lacking inducible nitric oxide synthase (iNOS−/−), CD95 (lpr), IL-17RA, or IL-4, with IL-5, alone or associated with IL-17A. Synergisms between IL-17A-activated, NO-dependent, and NO-independent mechanisms and antagonisms between IL-17A and proallergic factors were further examined. While IL-17A (0.1–10 ng/mL) had no IL-5-independent effect on eosinopoiesis, it dose-dependently suppressed IL-5-induced eosinophil differentiation, by acting during the initial 24 hours. Its effectiveness was abolished by caspase inhibitor, zVAD-fmk. The effect of IL-17A (0.1–1 ng/mL) was sensitive to the iNOS-selective inhibitor aminoguanidine and undetectable in iNOS−/− bone-marrow. By contrast, a higher IL-17A concentration (10 ng/mL) retained significant suppressive effect in both conditions, unmasking a high-end iNOS-independent mechanism. Lower IL-17A concentrations synergized with NO donor nitroprusside. Eosinopoiesis suppression by IL-17A was (a) undetectable in bone-marrow lacking IL-17RA or CD95 and (b) actively prevented by LTD4, LTC4, IL-13, and eotaxin. Sensitivity to IL-17A was increased in bone-marrow lacking IL-4; adding IL-4 to the cultures restored IL-5 responses to control levels. Therefore, effects of both IL-17A and proallergic factors are transduced by the iNOS-CD95 pathway in isolated bone-marrow.

Murine IL-17+ Vγ4 T lymphocytes accumulate in the lungs and play a protective role during severe sepsis

Background

Lung inflammation is a major consequence of the systemic inflammatory response caused by severe sepsis. Increased migration of γδ T lymphocytes into the lungs has been previously demonstrated during experimental sepsis; however, the involvement of the γδ T cell subtype Vγ4 has not been previously described.

Methods

Severe sepsis was induced by cecal ligation and puncture (CLP; 9 punctures, 21G needle) in male C57BL/6 mice. γδ and Vγ4 T lymphocyte depletion was performed by 3A10 and UC3-10A6 mAb i.p. administration, respectively. Lung infiltrating T lymphocytes, IL-17 production and mortality rate were evaluated.

Results

Severe sepsis induced by CLP in C57BL/6 mice led to an intense lung inflammatory response, marked by the accumulation of γδ T lymphocytes (comprising the Vγ4 subtype). γδ T lymphocytes present in the lungs of CLP mice were likely to be originated from peripheral lymphoid organs and migrated towards CCL2, CCL3 and CCL5, which were highly produced in response to CLP-induced sepsis. Increased expression of CD25 by Vγ4 T lymphocytes was observed in spleen earlier than that by αβ T cells, suggesting the early activation of Vγ4 T cells. The Vγ4 T lymphocyte subset predominated among the IL-17⁺ cell populations present in the lungs of CLP mice (unlike Vγ1 and αβ T lymphocytes) and was strongly biased toward IL-17 rather than toward IFN-γ production. Accordingly, the in vivo administration of anti-Vγ4 mAb abrogated CLP-induced IL-17 production in mouse lungs. Furthermore, anti-Vγ4 mAb treatment accelerated mortality rate in severe septic mice, demonstrating that Vγ4 T lymphocyte play a beneficial role in host defense.

Conclusions

Overall, our findings provide evidence that early-activated Vγ4 T lymphocytes are the main responsible cells for IL-17 production in inflamed lungs during the course of sepsis and delay mortality of septic mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-015-0098-8) contains supplementary material, which is available to authorized users.

Lymph node fibroblastic reticular cell transplants show robust therapeutic efficacy in high-mortality murine sepsis

Sepsis is an aggressive inflammatory syndrome and a global health burden estimated to kill 7.3 million people annually. Single-target molecular therapies have not addressed the multiple disease pathways triggered by septic injury. Cell therapies might offer a broader set of mechanisms of action that benefit complex, multifocal disease processes. We describe a population of immune-specialized myofibroblasts derived from lymph node tissue, termed fibroblastic reticular cells (FRCs). Because FRCs have an immunoregulatory function in lymph nodes, we hypothesized that ex vivo-expanded FRCs would control inflammation when administered therapeutically. Indeed, a single injection of ex vivo-expanded allogeneic FRCs reduced mortality in mouse models of sepsis when administered at early or late time points after septic onset. Mice treated with FRCs exhibited lower local and systemic concentrations of proinflammatory cytokines and reduced bacteremia. When administered 4 hours after induction of lipopolysaccharide endotoxemia, or cecal ligation and puncture (CLP) sepsis in mice, FRCs reduced deaths by at least 70%. When administered late in disease (16 hours after CLP), FRCs still conveyed a robust survival advantage (44% survival compared to 0% for controls). FRC therapy was dependent on the metabolic activity of nitric oxide synthase 2 (NOS2) as the primary molecular mechanism of drug action in the mice. Together, these data describe a new anti-inflammatory cell type and provide preclinical evidence for therapeutic efficacy in severe sepsis that warrants further translational study.

Interleukin 17 regulates Mer tyrosine kinase-positive cells in Pseudomonas aeruginosa keratitis

PURPOSE

To determine if IL-17 regulates Mer tyrosine kinase-positive (MerTK+) cells in Pseudomonas aeruginosa keratitis.

METHODS

Interleukin 17 was tested in normal and infected cornea of susceptible C57BL/6 and resistant BALB/c mice. The latter were treated with recombinant mouse (rm) IL-17; both groups were treated with IL-17 neutralizing antibody. Mice were infected, and clinical score, PCR, ELISA, and myeloperoxidase (MPO) assays tested expression of proinflammatory and anti-inflammatory mediators and polymorphonuclear neutrophilic leukocyte (PMN) infiltrate. Fas and Fas ligand (FasL) protein levels were assessed in both mouse strains, while MerTK+ cells were examined by immunostaining and cell sorting before and after IL-17 neutralization.

RESULTS

The IL-17 mRNA and protein were higher in C57BL/6 versus BALB/c cornea after infection. The rmIL-17 treatment of BALB/c mice modified proinflammatory and anti-inflammatory mediators, but clinical score and MPO assay revealed no differences. However, only BALB/c mice treated with IL-17 neutralizing antibody showed increased disease, macrophage inflammatory protein (MIP) 2, and MPO levels. Fas and FasL protein levels, elevated earlier in BALB/c versus C57BL/6 mice, correlated with significantly more MerTK+ cells in BALB/c cornea at 3 days after infection. Neutralization of IL-17 in C57BL/6 mice elevated MerTK+ cells, while similar treatment of BALB/c mice significantly decreased them.

CONCLUSIONS

These data provide evidence that IL-17 expression is higher in C57BL/6 versus BALB/c cornea after infection and that the latter group has more MerTK+ cells. Exogenous rmIL-17 failed to shift the disease response in resistant mice, but its neutralization resulted in worsened disease and reduced MerTK+ cells. Neutralization of IL-17 in C57BL/6 mice increased MerTK+ cells but did not dramatically shift the disease response.