HMGB1 regulates IL-33 expression in acute respiratory distress syndrome

Interesting effects of interleukins and immune cells on acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a medical condition characterized by widespread inflammation in the lungs with consequent proportional loss of gas exchange function. ARDS is linked with severe pulmonary or systemic infection. Several factors, including secretory cytokines, immune cells, and lung epithelial and endothelial cells, play a role in the development and progression of this disease. The present study is based on Pubmed database information (1987-2022) using the words "Acute respiratory distress syndrome", "Interleukin", "Cytokines" and "Immune cells". Cytokines and immune cells play an important role in this disease, with particular emphasis on the balance between pro-inflammatory and anti-inflammatory factors. Neutrophils are one of several important mediators of Inflammation, lung tissue destruction, and malfunction during ARDS. Some immune cells, such as macrophages and eosinophils, play a dual role in releasing inflammatory mediators, recruitment inflammatory cells and the progression of ARDS, or releasing anti-inflammatory mediators, clearing the lung of inflammatory cells, and helping to improve the disease. Different interleukins play a role in the development or inhibition of ARDS by helping to activate various signaling pathways, helping to secrete other inflammatory or anti-inflammatory interleukins, and playing a role in the production and balance between immune cells involved in ARDS. As a result, immune cells and, inflammatory cytokines, especially interleukins play an important role in the pathogenesis of this disease Therefore, understanding the relevant mechanisms will help in the proper diagnosis and treatment of this disease.

Natural products for treating cytokine storm-related diseases: Therapeutic effects and mechanisms

BACKGROUND

A cytokine storm (CS) is a rapidly occurring, complex, and highly lethal systemic acute inflammatory response induced by pathogens and other factors. Currently, no clinical therapeutic drugs are available with a significant effect and minimal side effects. Given the pathogenesis of CS, natural products have become important resources for bioactive agents in the discovery of anti-CS drugs.

PURPOSE

This study aimed to provide guidance for preventing and treating CS-related diseases by reviewing the natural products identified to inhibit CS in recent years.

METHODS

A comprehensive literature review was conducted on CS and natural products, utilizing databases such as PubMed and Web of Science. The quality of the studies was evaluated and summarized for further analysis.

RESULTS

This study summarized more than 30 types of natural products, including 9 classes of flavonoids, phenols, and terpenoids, among others. In vivo and in vitro experiments demonstrated that these natural products could effectively inhibit CS via nuclear factor kappa-B, mitogen-activated protein kinase, and Mammalian target of rapamycin (mTOR) signaling pathways. Moreover, the enzyme inhibition assays revealed that more than 20 chemical components had the potential to inhibit ACE2, 3CL-protease, and papain-like protease activity. The experimental results were obtained using advanced technologies such as biochips and omics.

CONCLUSIONS

Various natural compounds in traditional Chinese medicine (TCM) extracts could directly or indirectly inhibit CS occurrence, potentially serving as effective drugs for treating CS-related diseases. This study may guide further exploration of the therapeutic effects and biochemical mechanisms of natural products on CS.

The Correlation of Serum Calpain 1 Activity and Concentrations of Interleukin 33 in COVID-19 Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is one of the most severe complications of the COVID-19 disease. The role of IL-33 and calpain 1 was previously described in lung infections and lung tissue damage. Our study examined the association between serum calpain 1 activity and IL-33 concentration in patients with COVID-19 ARDS. In the research, we included 80 subjects who had COVID-19 pneumonia and divided them into 2 groups: 40 subjects with ARDS and 40 subjects without ARDS. The basis of the research was the collection of subjects' data and the sampling of peripheral venous blood. The concentration of IL-33 was determined by the ELISA method and the activity of calpain 1 by the fluorometry method. Our research showed elevated calpain 1 activity and IL-33 concentration in the serum of COVID-19 patients who developed ARDS compared to those who did not develop ARDS and a positive correlation between them was established. Further, a positive correlation was established between the examined parameters and the severity of the disease, proinflammatory markers, and the use of mechanical ventilation. These results indicate a possible association and role of calpain 1 and IL-33 with the development of ARDS in COVID-19 patients.

Serum HMGB1 and soluble urokinase plasminogen activator receptor levels aid diagnosis and prognosis prediction of sepsis with acute respiratory distress syndrome

Objective: To study the clinical application of serum HMGB1 and soluble urokinase plasminogen activator receptor (suPAR) expression in sepsis with acute respiratory distress syndrome (ARDS). Methods: Clinical data of 303 septic patients with/without ARDS were documented. Levels of serum inflammatory markers and HMGB1/suPAR were measured. ARDS patients were subdivided into high and low HMGB1/suPAR expression groups and followed up. Results: Serum HMGB1 and suPAR were upregulated in ARDS patients and positively correlated with inflammatory markers. The combination of HMGB1 with suPAR surpassed HMGB1 or suPAR alone in aiding diagnosis of sepsis with ARDS. CRP, PCT, IL-6, HMGB1 and suPAR were independent risk factors for ARDS. High HMGB1/suPAR expression might be linked to poor prognosis. Conclusion: Serum HMGB1/suPAR levels might aid diagnosis and predict poor prognosis of septic patients with ARDS.

Jin-Zhen oral liquid for pediatric coronavirus disease (COVID-19): A randomly controlled, open-label, and non-inferiority trial at multiple clinical centers

Background: As the coronavirus disease 2019 (COVID-19) pandemic progressed, especially with the emergence of the Omicron variant, the proportion of infected children and adolescents increased significantly. Some treatment such as Chinese herbal medicine has been administered for COVID-19 as a therapeutic option. Jin-Zhen Oral Liquid is widely used for pediatric acute bronchitis, while the efficacy and safety in the treatment of pediatric COVID-19 are unclear. Methods: We conducted a randomized controlled, open-label, multicenter, non-inferiority clinical study involving hospitalized children with mild to moderate COVID-19. Children eligible for enrollment were randomly assigned in a 1:1 ratio to Jin-Zhen Oral Liquid (the treatment group) and Jinhua Qinggan Granules (the positive control group) and received the respective agent for 14 days, followed by a 14-day follow-up after discontinuation of the treatment. The primary efficacy endpoint was the time to first negative viral testing. The secondary endpoints were the time and rate of major symptoms disappearance, duration of hospitalization, and the proportion of symptoms changed from asymptomatic or mild to moderate or severe/critical illness. In addition, the safety end points of any adverse events were observed. Results: A total of 240 child patients were assigned randomly into the Jin-Zhen Oral Liquid (117 patients) and Jinhua Qinggan Granules (123 patients) groups. There was no significant difference of the baselines in terms of the clinical characteristics and initial symptoms between the two groups. After 14-day administration, the time to first negative viral testing in the Jin-Zhen group (median 6.0 days, 95% CI 5.0-6.0) was significantly shorter compared with the positive control Jinhua Qinggan Granules group (median 7.0 days, 95% CI 7.0-8.0). The time and rate of major clinical symptoms disappearance were comparable to the positive control. The symptom disappearance time of pharyngalgia and hospitalization duration were significantly shortened in the Jin-zhen Oral Liquid group. No participants in either group experienced post-treatment exacerbation to severe or critical illness. No adverse events were observed in the Jin-Zhen Oral Liquid treatment group (0.0%) while 1 patient with adverse events occurred in the positive control Jinhua Qinggan granules group (0.8%). No serious adverse events were observed during the study period in both groups. Conclusion: Jin-Zhen Oral Liquid is safe and effective in the treatment of mild to medium COVID-19 in children. It is non-inferior to Jinhua Qinggan granules in shortening the time to first negative viral testing, the time and rate of major clinical symptoms disappearance, and the hospitalization duration. The results suggest that Jin-Zhen Oral Liquid can be a recommended drug for treatment of pediatric COVID-19 patients.

IL-33 Promotes ST2-Dependent Fibroblast Maturation via P38 and TGF-β in a Mouse Model of Epidural Fibrosis

BACKGROUND

Recent evidence suggests that IL-33, a novel member of the IL-1β family, is involved in organ fibrosis. However, the roles of IL-33 and its receptor ST2 in epidural fibrosis post spine operation remain elusive.

METHODS

A mouse model of epidural fibrosis was established after laminectomy. IL-33 in the wound tissues post laminectomy was measured with Western blotting, ELISA and immunoflurosence imaging. The fibroblast cell line NIH-3T3 and primary fibroblasts were treated with IL-33 and the mechanisms of maturation of fibroblasts into myofibroblasts were analyzed. To explore roles of IL-33 and its receptor ST2 in vivo, IL-33 knockout (KO) and ST2 KO mice were employed to construct the model of laminectomy. The epidural fibrosis was evaluated using H&E and Masson staining, western-blotting, ELISA and immunohistochemistry.

RESULTS

As demonstrated in western blotting and ELISA, IL-33 was increased in epidural wound tissues post laminectomy. The immunoflurosence imaging revealed that endothelial cells (CD31⁺) and fibroblasts (α-SAM⁺) were major producers of IL-33 in the epidural wound tissues. In vitro, IL-33 promoted fibroblast maturation, which was blocked by ST2 neutralization antibody, suggesting that IL-33-promoted-fibroblasts maturation was ST2 dependent. Further, IL-33/ST2 activated MAPK p38 and TGF-β pathways. Either p38 inhibitor or TGF-β inhibitor decreased fibronectin and α-SAM production from IL-33-treated fibroblasts, suggesting that p38 and TGF-β were involved with IL-33/ST2 signal pathways in the fibroblasts maturation. In vivo, IL-33 KO or ST2 KO decreased fibronectin, α-SMA and collagen deposition in the wound tissues of mice that underwent spine surgery. In addition, TGF-β1 was decreased in IL-33 KO or ST2 KO epidural wound tissues.

CONCLUSION

In summary, IL-33/ST2 promoted fibroblast differentiation into myofibroblasts via MAPK p38 and TGF-β in a mouse model of epidural fibrosis after laminectomy.

Glycyrrhizic Acid Alleviates Lipopolysaccharide (LPS)-Induced Acute Lung Injury by Regulating Angiotensin-Converting Enzyme-2 (ACE2) and Caveolin-1 Signaling Pathway

Acute lung injury (ALI) is mainly caused by severe infection, shock, trauma, and burn, which causes the extensive release of inflammatory factors and other mediators. As a major bioactive constituent of traditional Chinese herb licorice, glycyrrhizic acid (GA) plays an important effect on inflammatory regulation. Nevertheless, the exact mechanism of this effect remains unclear. The present study aims to explore the potential protective effect of GA on LPS-induced ALI. Our results showed that GA significantly attenuated LPS-induced ALI and decreased the production of inflammatory factors, including IL-1β, MCP-1, COX2, HMGB1, and adhesion molecules, such as E-selectin, VCAM-1, and modulated expression of angiotensin-converting enzyme 2 (ACE2). Moreover, treatment of ACE2 inhibitor (MLN-4760) reversed the effects of GA on the secretion of pro-inflammatory factors in ALI. Additionally, GA exerts its protective effect by regulating the ACE2 and caveolin-1/NF-κB signaling pathway. In conclusion, this study showed that GA alleviated LPS-induced ALI by upregulating ACE2 and inhibiting the caveolin-1/NF-κB signaling pathway.

Interplay between hypoxia and inflammation contributes to the progression and severity of respiratory viral diseases

History of pandemics is dominated by viral infections and specifically respiratory viral diseases like influenza and COVID-19. Lower respiratory tract infection is the fourth leading cause of death worldwide. Crosstalk between resultant inflammation and hypoxic microenvironment may impair ventilatory response of lungs. This reduces arterial partial pressure of oxygen, termed as hypoxemia, which is observed in a section of patients with respiratory virus infections including SARS-CoV-2 (COVID-19). In this review, we describe the interplay between inflammation and hypoxic microenvironment in respiratory viral infection and its contribution to disease pathogenesis.

HMGB1 suppress the expression of IL-35 by regulating Naïve CD4+ T cell differentiation and aggravating Caspase-11-dependent pyroptosis in acute lung injury

OBJECTIVES

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a severe form of inflammatory lung disease. Its development and progression are regulated by cytokines. The purpose of this study was to determine the effects of HMGB1 involved in the regulation of Treg cells and IL-35.

METHODS

A cecal ligation and puncture (CLP)-induced ALI model was used to investigate the changes in IL-35, Tregs, and the expression of RAGE and caspase-11 after HMGB1 inhibition (glycyrrhizin was used as an inhibitor of HMGB1). CD4+ naïve T cells sorted from C57BL/6 mice spleens were cultured to explore the role of HMGB1 in the differentiation from CD4+ naïve T cells to Tregs.

RESULTS

HMGB1 promoted lung injury and uncontrolled inflammation in the CLP mouse model. HMGB1, NF-κB p65, RAGE, and caspase-11 expression in the lungs of CLP mice decreased significantly after pretreatment with glycyrrhizin. We found that the Treg proportion and IL-35 expression were upregulated in the serum and lung of CLP mice after inhibiting HMGB1. In our in vitro experiments, we found that recombinant HMGB1 significantly suppressed the proportion of CD4+CD25+FOXP3+Tregs differentiated from CD4+ naïve T cells.

CONCLUSIONS

The inhibition of HMGB1 increased the proportion of Treg and expression of IL-35 and alleviated lung injury in the CLP-induced ALI model. Furthermore, inhibition of HMGB1 reduced caspase-11-dependent pyroptosis in the lungs of the CLP-induced ALI model.

Recombinant thrombomodulin protects against LPS-induced acute respiratory distress syndrome via preservation of pulmonary endothelial glycocalyx

Background and Purpose

Disruption of the endothelial glycocalyx is causally related to microvascular endothelial dysfunction, a characteristic of sepsis‐induced acute respiratory distress syndrome (ARDS). Recombinant human thrombomodulin (rhTM) attenuates vascular endothelial injuries, but the underlying mechanism remains elusive. Here, we investigated the structural basis and molecular mechanisms of rhTM effects on vascular endothelial injury in a model of sepsis.

Experimental Approach

LPS (20 mg·kg⁻¹) was intraperitoneally injected into 10‐week‐old male C57BL6 mice, and saline or rhTM was intraperitoneally injected 3 and 24 h after LPS injection. Using serum and/or lung tissue, histological, ultrastructural, and microarray analyses were performed.

Key Results

Survival rate of rhTM‐treated mice was significantly higher than that of control mice 48 h after LPS injection. Serum concentrations of IL‐6 and high‐mobility group box 1 were lower in the rhTM‐treated group than in the control. Injury to the endothelial glycocalyx in pulmonary capillaries was attenuated by rhTM treatment. Gene set enrichment analysis revealed up‐regulation of gene sets corresponding to cell proliferation/differentiation and anti‐inflammation, such as the TGF‐β pathway, and negative regulation of IL‐6, upon rhTM treatment. Gene expression of heparan sulfate 6‐O‐sulfotransferase 1 and endothelial cell‐specific molecule 1 (components of the endothelial glycocalyx) was significantly preserved by rhTM treatment, and their protein expression levels were maintained in endothelial cells.

Conclusion and Implications

Our findings show that rhTM treatment affected inflammation, cell proliferation/differentiation, and glycocalyx synthesis in serum and lung tissue, subsequently attenuating ARDS caused by endothelial injury.

Glycyrrhizin: An alternative drug for the treatment of COVID-19 infection and the associated respiratory syndrome?

Safe and efficient drugs to combat the current COVID-19 pandemic are urgently needed. In this context, we have analyzed the anti-coronavirus potential of the natural product glycyrrhizic acid (GLR), a drug used to treat liver diseases (including viral hepatitis) and specific cutaneous inflammation (such as atopic dermatitis) in some countries. The properties of GLR and its primary active metabolite glycyrrhetinic acid are presented and discussed. GLR has shown activities against different viruses, including SARS-associated Human and animal coronaviruses. GLR is a non-hemolytic saponin and a potent immuno-active anti-inflammatory agent which displays both cytoplasmic and membrane effects. At the membrane level, GLR induces cholesterol-dependent disorganization of lipid rafts which are important for the entry of coronavirus into cells. At the intracellular and circulating levels, GLR can trap the high mobility group box 1 protein and thus blocks the alarmin functions of HMGB1. We used molecular docking to characterize further and discuss both the cholesterol- and HMG box-binding functions of GLR. The membrane and cytoplasmic effects of GLR, coupled with its long-established medical use as a relatively safe drug, make GLR a good candidate to be tested against the SARS-CoV-2 coronavirus, alone and in combination with other drugs. The rational supporting combinations with (hydroxy)chloroquine and tenofovir (two drugs active against SARS-CoV-2) is also discussed. Based on this analysis, we conclude that GLR should be further considered and rapidly evaluated for the treatment of patients with COVID-19.

IL-33 and its increased serum levels as an alarmin for imminent pulmonary complications in polytraumatized patients

Background

According to recently published findings, we hypothesized that serum interleukin-33 (IL-33) may qualify for predicting pulmonary complications in polytraumatized patients.

Methods

One hundred and thirty patients (age ≥ 18 years, ISS ≥ 16) were included in our prospective analysis after primary admission to our level I trauma center during the first post-traumatic hour. Serum samples immediately after admission and on day 2 after trauma were obtained and analyzed.

Results

Median initial IL-33 levels (in picograms per milliliter) were higher in polytrauma victims (1) with concomitant thoracic trauma [5.08 vs. 3.52; p = 0.036], (2) sustaining parenchymal lung injury (PLI) [5.37 vs. 3.71; p = 0.027], and (3) developing acute respiratory distress syndrome (ARDS) [6.19 vs. 4.48; p = 0.003], compared to the respective rest of the study group. The median initial IL-33 levels were higher in patients experiencing both PLI and ARDS compared to those sustaining PLI and not developing ARDS [6.99 vs. 4.69; p = 0.029]. ROC statistics provided an AUC of 0.666 (p = 0.003) and a cut-off value of 4.77 (sensitivity, 71.8%; specificity, 75.7%) for predicting ARDS. Moreover, a higher initial median IL-33 level was revealed in the deceased compared to the survivors [12.25 vs. 4.72; p = 0.021]. ROC statistics identified the initial level of IL-33 as a predictor of death with 11.19 as cut-off value (sensitivity, 80.0%; specificity, 80.0%; AUC = 0.805; p = 0.021).

Conclusions

Following tissue damage, IL-33 is abundantly released in the serum of polytraumatized patients immediately after their injuries occurred. As initial IL-33 levels were particularly high in individuals experiencing both PLI and ARDS, IL-33 release after trauma seems to be involved in the promotion of ARDS and might serve already at admission as a solid indicator of impending death in polytraumatized patients.

Different intensity of autophagy regulate interleukin-33 to control the uncontrolled inflammation of acute lung injury

OBJECTIVES

Cytokines participate in the progression of acute respiratory distress syndrome (ARDS), and uncontrolled inflammation is a central issue of acute lung injury (ALI). Interleukin (IL)-33 is a nuclear protein that has been reported to have a proinflammatory role in ARDS. Studies have shown that excessive autophagy may lead to the increased mortality of patients with ARDS, while several investigations indicated that IL-33 and autophagy interact with one another. The present study sought to clarify the relation between autophagy and IL-33's proinflammatory role in ARDS.

METHODS

We built a lipopolysaccharide (LPS)-induced lung injury mouse model. To study the relationship between IL-33 and autophagy, mice were pretreated with rapamycin (RAPA; a promoter of autophagy) and 3-methyladenine (3-MA; an inhibitor of autophagy) prior to LPS administration. The expression of IL-33 in serum and bronchoalveolar lavage fluid (BALF) was measured. Immunohistochemistry of IL-33 in lung tissue was examined. Th1,Th2 cytokines/chemokine levels in serum and BALF were tested. Further, the severity of lung injury was evaluated. And the nuclear factor-kappa B (NF-κB)'s nuclear translocation in lung tissue was detected.

RESULTS

In comparison with the control group, the levels of IL-33 in serum and BALF were increased after LPS injection. Th1 cytokines/chemokine levels were significantly increased in serum and BALF, while Th2 cytokine levels changed only a little. The levels of IL-33 in serum and BALF of the RAPA group was significantly increased after LPS was injected as compared with the LPS group; additionally, the levels of IL-33 in serum and BALF of the 3-MA group was significantly reduced after LPS was injected as compared with the LPS group, and that lung injury was ameliorated after 3-MA pretreatment. Th1 cytokines and chemokines in both serum and BALF were also decreased in the 3-MA group. Furthermore, we found that the nuclear translocation of NF-κB increased after LPS administration, and NF-κB's nuclear translocation was significantly increased in comparison with the LPS group after RAPA pretreatment. In contrast, NF-κB's nuclear translocation decreased after 3-MA pretreatment as compared with the LPS group.

CONCLUSIONS

These findings showed that autophagy might regulate IL-33 by activating or inhibiting NF-κB to control the uncontrolled inflammation of acute lung injury.

Elevated IL-33 promotes expression of MMP2 and MMP9 via activating STAT3 in alveolar macrophages during LPS-induced acute lung injury

Background

Pulmonary inflammation and endothelial barrier permeability increase in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) induced by pro-inflammatory cytokines and matrix metalloproteinases (MMPs). However, the relationship between pro-inflammatory cytokines and MMPs in ALI/ARDS remains poorly understood.

Methods

A lipopolysaccharide (LPS)-induced ALI rat model was established through intratracheal instillation. The wet/dry ratios of lung tissues were measured, and bronchoalveolar lavage fluid (BALF) was collected to test protein concentrations, total cell/macrophage numbers, and pro-inflammatory cytokine levels. LPS-treated alveolar macrophages were utilized in in vitro experiments. The expression and secretion of MMPs were respectively detected using quantitative PCR, Western blotting and ELISA assays.

Results

The levels of IL-33 and MMP2/9 in BALF increased in all the ALI rats with severe lung injury. LPS-induced IL-33 autocrine upregulated the expression of MMP2 and MMP9 through activating STAT3. Neutralizing IL-33 in culture medium with specific antibodies suppressed the expression and secretion of MMP2 and MMP9 in LPS-treated alveolar macrophages. Consistently, eliminating IL-33 decreased the levels of MMP2 and MMP9 in BALF and alleviated lung injury in ALI rats.

Conclusion

The IL-33/STAT3/MMP2/9 regulatory pathway is activated in alveolar macrophages during acute lung injury, which may exacerbate the pulmonary inflammation.

DNA binding protein HMGB1 secreted by activated microglia promotes the apoptosis of hippocampal neurons in diabetes complicated with OSA

Type 2 diabetes mellitus (T2DM) complicated with obstructive sleep apnea (OSA) may cause neuronal apoptosis and cognitive deficits, but the underlying mechanisms remain unclear. We aimed to determine the relationship between the activation of microglia and the apoptosis of hippocampal neurons, specifically in terms of high mobility group box-1 (HMGB1), after high glucose (HG) and intermittent hypoxia (IH) exposure. Diabetic KK-Ay mice and non-diabetic C57BL/6J mice (C57 mice) underwent IH or normoxia (control) exposure for 4 weeks. Cognitive function, microglial activation and hippocampal neuronal apoptosis were assessed after IH or normoxia exposure. Compared with C57 control mice, KK-Ay control mice exhibited increased cognitive dysfunction, microglial activation and hippocampal neuronal apoptosis. There were no differences between untreated KK-Ay control mice and C57 mice that had been exposed to IH. The abovementioned responses were aggravated in IH-exposed KK-Ay mice compared with control KK-Ay mice. In vitro, a cellular co-culture experiment showed that HG combined with IH could activate BV2 microglia, leading to the release of neuroinflammatory factors (ROS, TNF-α, IL-1β) and mediating the apoptosis of HT22 cells via the PI3K/Akt/GSK-3β signaling pathway. Meanwhile, HMGB1 was actively secreted into the extracellular environment from activated BV2 microglia. As a proinflammatory factor, it was able to sustain microglial activation by directly acting on those cells. The activation promoted positive feedback and aggravated neuronal damage further. In a cellular monoculture or co-culture system, HMGB1 siRNA was able to alleviate the activation of BV2 cells and the apoptosis of HT22 cells induced by HG combined with IH. Our object is to show that inhibition of HMGB1 may break the vicious cycle to prevent or treat neuroinflammation and hippocampal neuronal apoptosis caused by T2DM complicated with OSA.

Cyclic stretch induced IL-33 production through HMGB1/TLR-4 signaling pathway in murine respiratory epithelial cells

Interleukin 33 (IL-33), an inflammatory and mechanically responsive cytokine, is an important component of a TLR4-dependent innate immune process in mucosal epithelium. Although TLR4 also plays a role in sensing biomechanical stretch, a pathway of stretch-induced TLR4-dependent IL-33 biosynthesis has not been revealed. In the current study, we show that short term (6 h) cyclic stretch (CS) of cultured murine respiratory epithelial cells (MLE-12) increased intracellular IL-33 expression in a TLR4 dependent fashion. There was no detectable IL-33 in conditioned media in this interval. CS, however, increased release of the notable alarmin, HMGB1, and a neutralizing antibody (2G7) to HMGB1 completely abolished the CS mediated increase in IL-33. rHMGB1 increased IL-33 synthesis and this was partially abrogated by silencing TLR4 suggesting additional receptors for HMGB1 are involved in its regulation of IL-33. Collectively, these data reveal a HMGB1/TLR4/IL-33 pathway in the response of respiratory epithelium to mechanical stretch.