Thymic stromal lymphopoietin mediates the host response and increases mortality during sepsis

TSLP protects against sepsis-induced liver injury by inducing autophagy via activation of the PI3K/Akt/STAT3 pathway

BACKGROUND

Liver injury is the main factor in multiple organ failure caused by sepsis. Thymic stromal lymphopoietin (TSLP) is derived from epithelial cells and plays an important role in inflammation, allergies and cancer. The role of TSLP in sepsis-induced liver injury (SILI) is unclear. The purpose of this study was to investigate the effect of TSLP on sepsis-induced liver injury and to clarify the mechanism.

METHODS

Wild-type (WT) mice and TSLPR knockout (TSLPR^-/-) mice were subjected to cecal ligation and puncture (CLP) to generate a SILI model. Liver injury was assessed by measuring the levels of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), histologic liver injury scores, hepatocyte death, and liver inflammatory factors. Signal pathways were explored in vivo to identify possible mechanisms for TSLP in SILI.

RESULTS

The expression of TSLP and TSLPR increased during SILI. Deletion of TSLPR exacerbated liver injury in terms of serum ALT, AST, histologic liver injury scores, and liver inflammatory factors. Compared with controls, administration of exogenous recombinant mouse TSLP reduced liver injury in WT mice during SILI, but failed to reduce liver injury in TSLPR^-/- mice. TSLP induced autophagy in hepatocytes during SILI. Mechanistically, Akt and STAT3 were activated in WT mice during SILI. The opposite results were observed in TSLPR^-/- mice. In addition, the protective effects of TSLP in WT mice were blocked by PI3K inhibitor, LY294002, during SILI.

CONCLUSION

These results suggest that TSLP can improve liver injury caused by sepsis and its specific mechanism may be related to inducing autophagy through the PI3K/Akt/STAT3 signaling pathway.

TSLP up-regulates inflammatory responses through induction of autophagy in T cells

Thymic stromal lymphopoietin (TSLP), a type I cytokine belonging to the IL-2 cytokine family, promotes Th2-mediated inflammatory responses. The aim of this study is to investigate whether TSLP increases inflammatory responses via induction of autophagy using a murine T cell lymphoma cell line, EL4 cells, and lipopolysaccharide (LPS)-injected mice. TSLP increased expression levels of autophagy-related factors, such as Beclin-1, LC3-II, p62, Atg5, and lysosome associated membrane protein 1/2, whereas these factors increased by TSLP disappeared by neutralization of TSLP in EL4 cells. TSLP activated JAK1/JAK2/STAT5/JNK/PI3K, while the blockade of JAK1/JAK2/STAT5/JNK/PI3K signaling pathways reduced the expression levels of Beclin-1, LC3-II, and p62 in TSLP-stimulated EL4 cells. In addition, TSLP simultaneously increased levels of inflammatory cytokines via induction of autophagy by activation of JAK1/JAK2/STAT5/JNK/PI3K signaling pathways. In an LPS-induced acute liver injury (ALI) mouse model, exogenous TSLP increased expression levels of Beclin-1 and LC3-II, whereas functional deficiency of TSLP by TSLP siRNA resulted in lower expression of Beclin-1, LC3-II, and inflammatory cytokines, impairing their ability to form autophagosomes in ALI mice. Thus, our findings show a new role of TSLP between autophagy and inflammatory responses. In conclusion, regulating TSLP-induced autophagy may be a potential therapeutic strategy for inflammatory responses.

Potential Targets to Mitigate Trauma- or Sepsis-Induced Immune Suppression

In sepsis and trauma, pathogens and injured tissue provoke a systemic inflammatory reaction which can lead to overwhelming inflammation. Concurrent with the innate hyperinflammatory response is adaptive immune suppression that can become chronic. A current key issue today is that patients who undergo intensive medical care after sepsis or trauma have a high mortality rate after being discharged. This high mortality is thought to be associated with persistent immunosuppression. Knowledge about the pathophysiology leading to this state remains fragmented. Immunosuppressive cytokines play an essential role in mediating and upholding immunosuppression in these patients. Specifically, the cytokines Interleukin-10 (IL-10), Transforming Growth Factor-β (TGF-β) and Thymic stromal lymphopoietin (TSLP) are reported to have potent immunosuppressive capacities. Here, we review their ability to suppress inflammation, their dynamics in sepsis and trauma and what drives the pathologic release of these cytokines. They do exert paradoxical effects under certain conditions, which makes it necessary to evaluate their functions in the context of dynamic changes post-sepsis and trauma. Several drugs modulating their functions are currently in clinical trials in the treatment of other pathologies. We provide an overview of the current literature on the effects of IL-10, TGF-β and TSLP in sepsis and trauma and suggest therapeutic approaches for their modulation.

TSLP induces a proinflammatory phenotype in circulating innate cells and predicts prognosis in sepsis patients

Thymic stromal lymphopoietin (TSLP) has been identified as a crucial inflammatory cytokine in immune homeostasis. Previous studies have reported conflicting effects of TSLP on sepsis in mice, and the effect of TSLP on sepsis in humans has not been investigated. In this study, we used the ELISA to measure serum levels of TSLP in patients with sepsis, and used flow cytometry and ELISA to evaluate the proinflammatory phenotype of circulating immune cells. In addition, we used quantitative RT-PCR to examine the expression of proinflammatory cytokines [interleukin (IL)-1β, IL-6, tumor necrosis factor-α, transferrin growth factor-β, IL-10, and matrix metalloproteinase] between patients with high and low levels of TSLP. Flow cytometry analysis was performed to evaluate the phagocytic and respiratory burst of circulating neutrophils. A significant increase in the production of proinflammatory cytokines by nonclassical monocytes and the number of interferon (IFN)-γ+  CD4+ monocytes was observed in patients with high levels of TSLP. Furthermore, the number of IL-10+ regulatory T cells was observed to be increased in patients with high levels of TSLP. We found that TSLP values greater than 350 pg·mL-1 were associated with a higher mortality rate and longer stays in intensive care (sensitivity of 89% and specificity of 79%). In patients with low levels of neutrophils, the area under curve was only 0.71 (based on the cutoff value in the diagnostic test evaluation; sensitivity of 62% and specificity of 68%). Our findings suggest that the serum levels of TSLP may be suitable as a biomarker for prediction of prognosis in a subgroup of patients with sepsis who are exhibiting hyperleukocytosis and a high neutrophil ratio.

TSLP Exacerbates Septic Inflammation via Murine Double Minute 2 (MDM2) Signaling Pathway

Thymic stromal lymphopoietin (TSLP) is crucial for Th2-mediated inflammation. Sepsis is a serious systemic inflammatory reaction with organ dysfunction by infection. However, the function of TSLP during sepsis is poorly understood. Thus, we investigated a role and regulatory mechanism of TSLP during sepsis. Sepsis was induced by lipopolysaccharides (LPS) or Escherichia coli DH5α injection in mice. TSLP levels were measured in human subjects, mice, and macrophages. TSLP deficiency or murine double minute 2 (MDM2) deficiency was induced using siRNA or an MDM2 inhibitor, nutlin-3a. We found that TSLP levels were elevated in serum of patients and mice with sepsis. TSLP deficiency lowered liver damage and inflammatory cytokine levels in mice with sepsis. TSLP was produced by the MDM2/NF-κB signaling pathway in LPS-stimulated macrophages. TSLP downregulation by an MDM2 inhibitor, nutlin-3a, alleviated clinical symptoms and septic inflammatory responses. Pharmacological inhibition of TSLP level by cisplatin reduced the septic inflammatory responses. Altogether, the present results show that TSLP exacerbates septic inflammation via the MDM2 signaling pathway, suggesting that TSLP may be a potential target for the treatment of sepsis.

Group 2 Innate Lymphoid Cells (ILC2s) Are Key Mediators of the Inflammatory Response in Polymicrobial Sepsis

Sepsis remains a major public health concern, characterized by marked immune dysfunction. Innate lymphoid cells develop from a common lymphoid precursor but have a role in orchestrating inflammation during innate response to infection. Here, we investigate the pathologic contribution of the group 2 innate lymphoid cells (ILC2s) in a murine model of acute septic shock (cecal ligation and puncture). Flow cytometric data revealed that ILC2s increase in number and percentage in the small intestine and in the peritoneal cells and inversely decline in the liver at 24 hours after septic insult. Sepsis also resulted in changes in ILC2 effector cytokine (IL-13) and activating cytokine (IL-33) in the plasma of mice and human patients in septic shock. Of interest, the sepsis-induced changes in cytokines were abrogated in mice deficient in functionally invariant natural killer T cells. Mice deficient in IL-13-producing cells, including ILC2s, had a survival advantage after sepsis along with decreased morphologic evidence of tissue injury and reduced IL-10 levels in the peritoneal fluid. Administration of a suppressor of tumorigenicity 2 (IL-33R) receptor-blocking antibody led to a transient survival advantage. Taken together, these findings suggest that ILC2s may play an unappreciated role in mediating the inflammatory response in both mice and humans; further, modulating ILC2 response in vivo may allow development of immunomodulatory strategies directed against sepsis.

Thymic Stromal Lymphopoietin Improves Survival and Reduces Inflammation in Sepsis

The mechanisms that contribute to homeostasis of the immune system in sepsis are largely unknown. One study suggests a potential detrimental role for thymic stromal lymphopoietin (TSLP) in sepsis; however, the immune-regulatory effects of TSLP on myeloid cells within the intestinal microenvironment suggest the contrary. Our objective was to clarify TSLP's role in sepsis. Cecal ligation and puncture was performed in mice with total or myeloid-specific deficiency in the TSLP receptor (TSLPR). Survival was monitored closely, peritoneal fluids and plasma were analyzed for markers of inflammation, and myeloid cell numbers and their ability to produce inflammatory mediators was determined. The interaction of TSLP with TSLPR in myeloid cells contributed to mouse survival after septic peritonitis. Mice with TSLPR deficiency in myeloid cells displayed excessive local and systemic inflammation levels (e.g., increased inflammatory cell and cytokine levels) relative to control mice. Moreover, hepatic injury was exacerbated in mice with TSLPR deficiency in their myeloid cells. However, the enhanced inflammatory response did not affect the ability of these mice to clear bacteria. Resident neutrophils and macrophages from septic mice with TSLPR deficiency exhibited an increased ability to produce proinflammatory cytokines. Collectively, our findings suggest that the effects of TSLP on myeloid cells are crucial in reducing the multiple organ failure that is associated with systemic inflammation, which highlights the significance of this cytokine in modulating the host response to infection and in reducing the risks of sepsis development.

A TSLP-complement axis mediates neutrophil killing of methicillin-resistant Staphylococcus aureus

Community-acquired Staphylococcus aureus infections often present as serious skin infections in otherwise healthy individuals and have become a worldwide epidemic problem fueled by the emergence of strains with antibiotic resistance, such as methicillin-resistant S. aureus (MRSA). The cytokine thymic stromal lymphopoietin (TSLP) is highly expressed in the skin and in other barrier surfaces and plays a deleterious role by promoting T helper cell type 2 (TH2) responses during allergic diseases; however, its role in host defense against bacterial infections has not been well elucidated. We describe a previously unrecognized non-TH2 role for TSLP in enhancing neutrophil killing of MRSA during an in vivo skin infection. Specifically, we demonstrate that TSLP acts directly on both mouse and human neutrophils to augment control of MRSA. Additionally, we show that TSLP also enhances killing of Streptococcus pyogenes, another clinically important cause of human skin infections. Unexpectedly, TSLP mechanistically mediates its antibacterial effect by directly engaging the complement C5 system to modulate production of reactive oxygen species by neutrophils. Thus, TSLP increases MRSA killing in a neutrophil- and complement-dependent manner, revealing a key connection between TSLP and the innate complement system, with potentially important therapeutic implications for control of MRSA infection.

Papain-Based Vaccination Modulates Schistosoma mansoni Infection-Induced Cytokine Signals

We have previously shown that immunization of outbred rodents with cysteine peptidases-based vaccine elicited type 2-biased immune responses associated with consistent and reproducible protection against challenge Schistosoma mansoni. We herein start to elucidate the molecular basis of C57BL/6 mouse resistance to S. mansoni following treatment with the cysteine peptidase, papain. We evaluated the early cytokine signals delivered by epidermal, dermal, and draining lymph node cells of naïve, and S. mansoni -infected mice treated 1 day earlier with 0 or 50 μg papain, or immunized twice with papain only (10 μg/mouse), papain-free recombinant S. mansoni glyceraldehyde 3-phosphate dehydrogenase and 2-Cys peroxiredoxin peptide (10 and 15 μg/mouse, respectively = antigen Mix), or papain-adjuvanted antigen Mix. Schistosoma mansoni infection induced epidermal and lymph node cells to release type 1, type 2 and type 17 cytokines, known to counteract each other. Expectedly, humoral immune responses were negligible until patency. Papain pretreatment or papain-based vaccination diminished or shut off S. mansoni infection early induction of type 1, type 17 and type 2 cytokines except for thymic stromal lymphopoietin and programmed the immune system towards a polarized type 2 immune milieu, associated with highly significant (P < 0.005 - <0.0001) resistance to S. mansoni infection.

Positive fungal quantitative PCR and Th17 cytokine detection in bronchoalveolar lavage fluids: Complementary biomarkers of hypersensitivity pneumonitis?

BACKGROUND

Interstitial lung disease (ILD) is a large group of diseases, including hypersensitivity pneumonitis (HP), idiopathic pulmonary fibrosis (IPF) and sarcoidosis.

OBJECTIVE

In this study, we aimed to identify bronchoalveolar lavage fluid (BALF) biomarkers which could be contributive for HP diagnosis.

METHODS

We analyzed 39 BALF samples from 12 ILD patients with sarcoidosis, 11 with IPF and 16 with HP. We determined the levels of 10 cytokines and carried out quantitative PCR for 10 microorganisms involved in farm-associated or domestic forms of HP.

RESULTS

IL-8, IL-6, TNFα, IL-17 and IL-23 levels were significantly higher in BALF samples from HP patients (p<0.05, one-way Kruskal-Wallis analysis). QPCR tests for Eurotium amstelodami and Wallemia sebi were positively significantly more frequently for HP patients (p<0.05, one-way Kruskal-Wallis).

CONCLUSION

The biomarkers identified here can be detected in BALF, which could be routinely obtained as complementary analysis in ILD diagnosis.