Hypoxia attenuates inflammatory mediators production induced by Acanthamoeba via Toll-like receptor 4 signaling in human corneal epithelial cells

Acanthamoeba keratitis (AK) is a vision-threatening corneal infection that is intimately associated with contact lens use which leads to hypoxic conditions on the corneal surface. However, the effect of hypoxia on the Acanthamoeba-induced host inflammatory response of corneal epithelial cells has not been studied. In the present study, we investigated the effect of hypoxia on the Acanthamoeba-induced production of inflammatory mediators interleukin-8 (IL-8) and interferon-β (IFN-β) in human corneal epithelial cells and then evaluated its effects on the Toll-like receptor 4 (TLR4) signaling, including TLR4 and myeloid differentiation primary response gene (88) (MyD88) expression as well as the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and extracellular signal-regulated kinases 1/2 (ERK1/2). We then studied the effect of hypoxia on a TLR4-specific inflammatory response triggered by the TLR4 ligand lipopolysaccharide (LPS). Our data showed that hypoxia significantly decreased the production of IL-8 and IFN-β. Furthermore, hypoxia attenuated Acanthamoeba-triggered TLR4 expression as well as the activation of NF-κB and ERK1/2, indicating that hypoxia abated Acanthamoeba-induced inflammatory responses by affecting TLR4 signaling. Hypoxia also inhibited LPS-induced IL-6 and IL-8 secretion, myeloid differentiation primary response gene (88) MyD88 expression and NF-κB activation, confirming that hypoxia suppressed the LPS-induced inflammatory response by affecting TLR4 signaling. In conclusion, our results demonstrated that hypoxia attenuated the host immune and inflammatory response against Acanthamoeba infection by suppressing TLR4 signaling, indicating that hypoxia might impair the host cell's ability to eliminate the Acanthamoeba invasion and that hypoxia could enhance cell susceptibility to Acanthamoeba infection. These results may explain why contact lens use is one of the most prominent risk factors for AK.     

MyD88 in lung resident cells governs airway inflammatory and pulmonary function responses to organic dust treatment

Inhalation of organic dusts within agriculture environments contributes to the development and/or severity of airway diseases, including asthma and chronic bronchitis. MyD88 KO (knockout) mice are nearly completely protected against the inflammatory and bronchoconstriction effects induced by acute organic dust extract (ODE) treatments. However, the contribution of MyD88 in lung epithelial cell responses remains unclear. In the present study, we first addressed whether ODE-induced changes in epithelial cell responses were MyD88-dependent by quantitating ciliary beat frequency and cell migration following wounding by electric cell-substrate impedance sensing. We demonstrate that the normative ciliary beat slowing response to ODE is delayed in MyD88 KO tracheal epithelial cells as compared to wild type (WT) control. Similarly, the normative ODE-induced slowing of cell migration in response to wound repair was aberrant in MyD88 KO cells. Next, we created MyD88 bone marrow chimera mice to investigate the relative contribution of MyD88-dependent signaling in lung resident (predominately epithelial cells) versus hematopoietic cells. Importantly, we demonstrate that ODE-induced airway hyperresponsiveness is MyD88-dependent in lung resident cells, whereas MyD88 action in hematopoietic cells is mainly responsible for ODE-induced TNF-α release. MyD88 signaling in lung resident and hematopoietic cells are necessary for ODE-induced IL-6 and neutrophil chemoattractant (CXCL1 and CXCL2) release and neutrophil influx. Collectively, these findings underscore an important role for MyD88 in lung resident cells for regulating ciliary motility, wound repair and inflammatory responses to ODE, and moreover, show that airway hyperresponsiveness appears uncoupled from airway inflammatory consequences to organic dust challenge in terms of MyD88 involvement.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0272-9) contains supplementary material, which is available to authorized users.     

Activation of MyD88 signaling upon staphylococcal enterotoxin binding to MHC class II molecules

Ligands binding to Toll-like receptor (TLR), interleukin 1 receptor (IL-1R), or IFN-γR1 are known to trigger MyD88-mediated signaling, which activates pro-inflammatory cytokine responses. Recently we reported that staphylococcal enterotoxins (SEA or SEB), which bind to MHC class II molecules on APCs and cross link T cell receptors, activate MyD88- mediated pro-inflammatory cytokine responses. We also reported that MyD88(-/-) mice were resistant to SE- induced toxic shock and had reduced levels of serum cytokines. In this study, we investigated whether MHC class II- SE interaction by itself is sufficient to activate MyD88 in MHC class II(+) cells and induce downstream pro-inflammatory signaling and production of cytokines such as TNF-α and IL-1β. Here we report that human monocytes treated with SEA, SEB, or anti-MHC class II monoclonal antibodies up regulated MyD88 expression, induced activation of NF-kB, and increased expression of IL-1R1 accessory protein, TNF-α and IL-1β. MyD88 immunoprecipitated from cell extracts after SEB stimulation showed a greater proportion of MyD88 phosphorylation compared to unstimulated cells indicating that MyD88 was a component of intracellular signaling. MyD88 downstream proteins such as IRAK4 and TRAF6 were also up regulated in monocytes after SEB stimulation. In addition to monocytes, primary B cells up regulated MyD88 in response to SEA or SEB stimulation. Importantly, in contrast to primary B cells, MHC class II deficient T2 cells had no change of MyD88 after SEA or SEB stimulation, whereas MHC class II-independent activation of MyD88 was elicited by CpG or LPS. Collectively, these results demonstrate that MHC class II utilizes a MyD88-mediated signaling mechanism when in contact with ligands such as SEs to induce pro-inflammatory cytokines.     

Pellino-1 selectively regulates epithelial cell responses to rhinovirus

Pellino-1 has recently been identified as a regulator of interleukin-1 (IL-1) signaling, but its roles in regulation of responses of human cells to human pathogens are unknown. We investigated the potential roles of Pellino-1 in the airways. We show for the first time that Pellino-1 regulates responses to a human pathogen, rhinovirus minor group serotype 1B (RV-1B). Knockdown of Pellino-1 by small interfering RNA (siRNA) was associated with impaired production of innate immune cytokines such as CXCL8 from human primary bronchial epithelial cells in response to RV-1B, without impairment in production of antiviral interferons (IFN), and without loss of control of viral replication. Pellino-1 actions were likely to be independent of interleukin-1 receptor-associated kinase-1 (IRAK-1) regulation, since Pellino-1 knockdown in primary epithelial cells did not alter responses to IL-1 but did inhibit responses to poly(I·C), a Toll-like receptor 3 (TLR3) activator that does not signal via IRAK-1 to engender a response. These data indicate that Pellino-1 represents a novel target that regulates responses of human airways to human viral pathogens, independently of IRAK signaling. Neutralization of Pellino-1 may therefore provide opportunities to inhibit potentially harmful neutrophilic inflammation of the airways induced by respiratory viruses, without loss of control of the underlying viral infection.     

Nontypeable Haemophilus influenzae-Induced MyD88 Short Expression Is Regulated by Positive IKKβ and CREB Pathways and Negative ERK1/2 Pathway

Airway diseases such as asthma and chronic obstructive pulmonary disease (COPD) are characterized by excessive inflammation and are exacerbated by nontypeable Haemophilus influenzae (NTHi). Airway epithelial cells mount the initial innate immune responses to invading pathogens and thus modulate inflammation. While inflammation is necessary to eliminate a pathogen, excessive inflammation can cause damage to the host tissue. Therefore, the inflammatory response must be tightly regulated and deciphering the signaling pathways involved in this response will enhance our understanding of the regulation of the host inflammatory response. NTHi binds to TLR2 and signal propagation requires the adaptor molecule myeloid differentiation factor 88 (MyD88). An alternative spliced form of MyD88 is called MyD88 short (MyD88s) and has been identified in macrophages and embryonic cell lines as a negative regulator of inflammation. However, the role of MyD88s in NTHi-induced inflammation in airway epithelial cells remains unknown. Here we show that NTHi induces MyD88s expression and MyD88s is a negative regulator of inflammation in airway epithelial cells. We further demonstrate that MyD88s is positively regulated by IKKβ and CREB and negatively regulated by ERK1/2 signaling pathways. Taken together these data indicate that airway inflammation is controlled in a negative feedback manner involving MyD88s and suggest that airway epithelial cells are essential to maintain immune homeostasis.     

TLR2/MyD88/NF-κB pathway, reactive oxygen species, potassium efflux activates NLRP3/ASC inflammasome during respiratory syncytial virus infection

Human respiratory syncytial virus (RSV) constitute highly pathogenic virus that cause severe respiratory diseases in newborn, children, elderly and immuno-compromised individuals. Airway inflammation is a critical regulator of disease outcome in RSV infected hosts. Although "controlled" inflammation is required for virus clearance, aberrant and exaggerated inflammation during RSV infection results in development of inflammatory diseases like pneumonia and bronchiolitis. Interleukin-1β (IL-1β) plays an important role in inflammation by orchestrating the pro-inflammatory response. IL-1β is synthesized as an immature pro-IL-1β form. It is cleaved by activated caspase-1 to yield mature IL-1β that is secreted extracellularly. Activation of caspase-1 is mediated by a multi-protein complex known as the inflammasome. Although RSV infection results in IL-1β release, the mechanism is unknown. Here in, we have characterized the mechanism of IL-1β secretion following RSV infection. Our study revealed that NLRP3/ASC inflammasome activation is crucial for IL-1β production during RSV infection. Further studies illustrated that prior to inflammasome formation; the "first signal" constitutes activation of toll-like receptor-2 (TLR2)/MyD88/NF-κB pathway. TLR2/MyD88/NF-κB signaling is required for pro-IL-1β and NLRP3 gene expression during RSV infection. Following expression of these genes, two "second signals" are essential for triggering inflammasome activation. Intracellular reactive oxygen species (ROS) and potassium (K(+)) efflux due to stimulation of ATP-sensitive ion channel promote inflammasome activation following RSV infection. Thus, our studies have underscored the requirement of TLR2/MyD88/NF-κB pathway (first signal) and ROS/potassium efflux (second signal) for NLRP3/ASC inflammasome formation, leading to caspase-1 activation and subsequent IL-1β release during RSV infection.     

Membrane-tethered MUC1 mucin is phosphorylated by epidermal growth factor receptor in airway epithelial cells and associates with TLR5 to inhibit recruitment of MyD88

MUC1 is a membrane-tethered mucin glycoprotein expressed on the apical surface of mucosal epithelial cells. Previous in vivo and in vitro studies established that MUC1 counterregulates airway inflammation by suppressing TLR signaling. In this article, we elucidate the mechanism by which MUC1 inhibits TLR5 signaling. Overexpression of MUC1 in HEK293 cells dramatically reduced Pseudomonas aeruginosa-stimulated IL-8 expression and decreased the activation of NF-κB and MAPK compared with cells not expressing MUC1. However, overexpression of MUC1 in HEK293 cells did not affect NF-κB or MAPK activation in response to TNF-α. Overexpression of MyD88 abrogated the ability of MUC1 to inhibit NF-κB activation, and MUC1 overexpression inhibited flagellin-induced association of TLR5/MyD88 compared with controls. The MUC1 cytoplasmic tail associated with TLR5 in all cells tested, including HEK293T cells, human lung adenocarcinoma cell line A549 cells, and human and mouse primary airway epithelial cells. Activation of epidermal growth factor receptor tyrosine kinase with TGF-α induced phosphorylation of the MUC1 cytoplasmic tail at the Y46EKV sequence and increased association of MUC1/TLR5. Finally, in vivo experiments demonstrated increased immunofluorescence colocalization of Muc1/TLR5 and Muc1/phosphotyrosine staining patterns in mouse airway epithelium and increased Muc1 tyrosine phosphorylation in mouse lung homogenates following P. aeruginosa infection. In conclusion, epidermal growth factor receptor tyrosine phosphorylates MUC1, leading to an increase in its association with TLR5, thereby competitively and reversibly inhibiting recruitment of MyD88 to TLR5 and downstream signaling events. This unique ability of MUC1 to control TLR5 signaling suggests its potential role in the pathogenesis of chronic inflammatory lung diseases.     

Critical role of constitutive type I interferon response in bronchial epithelial cell to influenza infection

Innate antiviral responses in bronchial epithelial cells (BECs) provide the first line of defense against respiratory viral infection and the effectiveness of this response is critically dependent on the type I interferons (IFNs). However the importance of the antiviral responses in BECs during influenza infection is not well understood. We profiled the innate immune response to infection with H3N2 and H5N1 virus using Calu-3 cells and primary BECs to model proximal airway cells. The susceptibility of BECs to influenza infection was not solely dependent on the sialic acid-bearing glycoprotein, and antiviral responses that occurred after viral endocytosis was more important in limiting viral replication. The early antiviral response and apoptosis correlated with the ability to limit viral replication. Both viruses reduced RIG-I associated antiviral responses and subsequent induction of IFN-β. However it was found that there was constitutive release of IFN-β by BECs and this was critical in inducing late antiviral signaling via type I IFN receptors, and was crucial in limiting viral infection. This study characterizes anti-influenza virus responses in airway epithelial cells and shows that constitutive IFN-β release plays a more important role in initiating protective late IFN-stimulated responses during human influenza infection in bronchial epithelial cells.     

TRIF Mediates Toll-like Receptor 5-induced Signaling in Intestinal Epithelial Cells

Toll-like receptors (TLRs) associate with adaptor molecules (MyD88, Mal/TIRAP, TRAM, and TRIF) to mediate signaling of host-microbial interaction. For instance, TLR4 utilizes the combination of both Mal/TIRAP-MyD88 (MyD88-dependent pathway) and TRAM-TRIF (MyD88-independent pathway). However, TLR5, the specific receptor for flagellin, is known to utilize only MyD88 to elicit inflammatory responses, and an involvement of other adaptor molecules has not been suggested in TLR5-dependent signaling. Here, we found that TRIF is involved in mediating TLR5-induced nuclear factor κB (NFκB) and mitogen-activated protein kinases (MAPKs), specifically JNK1/2 and ERK1/2, activation in intestinal epithelial cells. TLR5 activation by flagellin permits the physical interaction between TLR5 and TRIF in human colonic epithelial cells (NCM460), whereas TLR5 does not interact with TRAM upon flagellin stimulation. Both primary intestinal epithelial cells from TRIF-KO mice and TRIF-silenced NCM460 cells significantly reduced flagellin-induced NFκB (p105 and p65), JNK1/2, and ERK1/2 activation compared with control cells. However, p38 activation by flagellin was preserved in these TRIF-deficient cells. TRIF-KO intestinal epithelial cells exhibited substantially reduced inflammatory cytokine (keratinocyte-derived cytokine, macrophage inflammatory protein 3α, and IL-6) expression upon flagellin, whereas control cells from TRIF-WT mice showed robust cytokine expression by flagellin. Compare with TRIF-WT mice, TRIF-KO mice were resistant to in vivo intestinal inflammatory responses: flagellin-mediated exacerbation of colonic inflammation and dextran sulfate sodium-induced experimental colitis. We conclude that in addition to MyD88, TRIF mediates TLR5-dependent responses and, thereby regulates inflammatory responses elicited by flagellin/TLR5 engagement. Our findings suggest an important role of TRIF in regulating host-microbial communication via TLR5 in the gut epithelium.     

The role of intermediary domain of MyD88 in cell activation and therapeutic inhibition of TLRs

Adaptor MyD88 has a pivotal role in TLR and IL-1R signaling and is involved in mediating excessive inflammation. MyD88 is composed of a death domain and a Toll/IL-1R domain connected by an intermediary domain (INT). The alternatively spliced form of MyD88 lacking the INT prevents signaling through MyD88-dependent TLRs. We designed a peptide from the INT and showed that it inhibits TLR4 activation by LPS when linked to a cell-penetrating peptide. As a new approach for the delivery of signaling-inhibitory peptides, INT peptide acylation also provided efficient cell translocation and inhibition of activation. We determined that INT peptide targets IL-1R-associated kinase 4. Furthermore, MyD88 mutant and molecular modeling refines the MyD88- IL-1R-associated kinase 4 interaction model based on the Myddosome structure. In addition to TLR4, INT peptide also inhibited TLR5, TLR2, TLR9, and IL-1R signaling but not TLR3, which uses Toll/IL-1R domain-containing adapter inducing IFN-β signaling adaptor. Inhibition of signaling in murine and human cells was observed by decreased NF-κB activation, cytokine mRNA synthesis, and phosphorylation of downstream kinases. In the endotoxemic mouse model, INT peptide suppressed production of inflammatory cytokines and improved survival, supporting therapeutic application of INT peptides for the suppression of inflammatory conditions mediated by MyD88.     

MyD88 Intrinsically Regulates CD4 T-Cell Responses

Myeloid differentiation factor 88 (MyD88) is an essential adaptor protein in the Toll-like receptor-mediated innate signaling pathway, as well as in interleukin-1 receptor (IL-1R) and IL-18R signaling. The importance of MyD88 in the regulation of innate immunity to microbial pathogens has been well demonstrated. However, its role in regulating acquired immunity to viral pathogens and neuropathogenesis is not entirely clear. In the present study, we examine the role of MyD88 in the CD4⁺ T-cell response following lymphocytic choriomeningitis virus (LCMV) infection. We demonstrate that wild-type (WT) mice developed a CD4⁺ T-cell-mediated wasting disease after intracranial infection with LCMV. In contrast, MyD88 knockout (KO) mice did not develop wasting disease in response to the same infection. This effect was not the result of MyD88 regulation of IL-1 or IL-18 responses since IL-1R1 KO and IL-18R KO mice were not protected from weight loss. In the absence of MyD88, naïve CD4⁺ T cells failed to differentiate to LCMV-specific CD4 T cells. We demonstrated that MyD88 KO antigen-presenting cells are capable of activating WT CD4⁺ T cells. Importantly, when MyD88 KO CD4⁺ T cells were reconstituted with an MyD88-expressing lentivirus, the rescued CD4⁺ T cells were able to respond to LCMV infection and support IgG2a antibody production. Overall, these studies reveal a previously unknown role of MyD88-dependent signaling in CD4⁺ T cells in the regulation of the virus-specific CD4⁺ T-cell response and in viral infection-induced immunopathology in the central nervous system.     

TLR9 and MyD88 are crucial for the development of protective immunity to malaria

Effective resolution of malaria infection by avoiding pathogenesis requires regulated pro- to anti-inflammatory responses and the development of protective immunity. TLRs are known to be critical for initiating innate immune responses, but their roles in the regulation of immune responses and development of protective immunity to malaria remain poorly understood. In this study, using wild-type, TLR2(-/-), TLR4(-/-), TLR9(-/-), and MyD88(-/-) mice infected with Plasmodium yoelii, we show that TLR9 and MyD88 regulate pro/anti-inflammatory cytokines, Th1/Th2 development, and cellular and humoral responses. Dendritic cells from TLR9(-/-) and MyD88(-/-) mice produced significantly lower levels of proinflammatory cytokines and higher levels of anti-inflammatory cytokines than dendritic cells from wild-type mice. NK and CD8(+) T cells from TLR9(-/-) and MyD88(-/-) mice showed markedly impaired cytotoxic activity. Furthermore, mice deficient in TLR9 and MyD88 showed higher Th2-type and lower Th1-type IgGs. Consequently, TLR9(-/-) and MyD88(-/-) mice exhibited compromised ability to control parasitemia and were susceptible to death. Our data also show that TLR9 and MyD88 distinctively regulate immune responses to malaria infection. TLR9(-/-) but not MyD88(-/-) mice produced significant levels of both pro- and anti-inflammatory cytokines, including IL-1β and IL-18, by other TLRs/inflammasome- and/or IL-1R/IL-18R-mediated signaling. Thus, whereas MyD88(-/-) mice completely lacked cell-mediated immunity, TLR9(-/-) mice showed low levels of cell-mediated immunity and were slightly more resistant to malaria infection than MyD88(-/-) mice. Overall, our findings demonstrate that TLR9 and MyD88 play central roles in the immune regulation and development of protective immunity to malaria, and have implications in understanding immune responses to other pathogens.     

Viral inhibition of IL-1- and neutrophil elastase-induced inflammatory responses in bronchial epithelial cells

Previously, we elucidated the intracellular mechanisms by which neutrophil elastase (NE) up-regulates inflammatory gene expression in bronchial epithelial cells. In this study, we examine the effects of both IL-1 and NE on inflammatory gene expression in 16HBE14o- bronchial epithelial cells and investigate approaches to abrogate these inflammatory responses. IL-1 induced IL-8 protein production in time- and dose-dependent fashions, an important observation given that IL-8 is a potent neutrophil chemoattractant and a key inflammatory mediator. IL-1 and NE were shown to activate the p38 MAPK pathway in 16HBE14o- cells. Western blot analysis demonstrated IL-1R-associated kinase 1 (IRAK-1) degradation in response to stimulation with both IL-1 and NE. In addition, the expression of dominant negative IRAK-1 (IRAK-1delta), IRAK-2delta, or IRAK-4delta inhibited IL-1- and NE-induced NF-kappaB-linked reporter gene expression. Dominant negative versions of the intracellular adaptor proteins MyD88 (MyD88delta) and MyD88 adaptor-like (Mal P/H) abrogated NE-induced NF-kappaB reporter gene expression. In contrast, only MyD88delta was found to inhibit IL-1-induced NF-kappaB reporter activity. We also investigated the vaccinia virus proteins, A46R and A52R, which have been shown to antagonize IL-1 signaling. Transfection with A46R or A52R cDNA inhibited IL-1- and NE-induced NF-kappaB and IL-8R gene expression and IL-8 protein production in primary and transformed bronchial epithelial cells. Furthermore, cytokine array studies demonstrated that IL-1 and NE can up-regulate the expression of IL-6, oncostatin M, epithelial cell-derived neutrophil activating peptide-78, growth-related oncogene family members, vascular endothelial growth factor, and GM-CSF, with induction of these proteins inhibited by the viral proteins. These findings identify vaccinia virus proteins as possible therapeutic agents for the manifestations of several inflammatory lung diseases.     

Serum amyloid A activates the NLRP3 inflammasome and promotes Th17 allergic asthma in mice

IL-1β is a cytokine critical to several inflammatory diseases in which pathogenic Th17 responses are implicated. Activation of the NLRP3 inflammasome by microbial and environmental stimuli can enable the caspase-1-dependent processing and secretion of IL-1β. The acute-phase protein serum amyloid A (SAA) is highly induced during inflammatory responses, wherein it participates in systemic modulation of innate and adaptive immune responses. Elevated levels of IL-1β, SAA, and IL-17 are present in subjects with severe allergic asthma, yet the mechanistic relationship among these mediators has yet to be identified. In this study, we demonstrate that Saa3 is expressed in the lungs of mice exposed to several mixed Th2/Th17-polarizing allergic sensitization regimens. SAA instillation into the lungs elicits robust TLR2-, MyD88-, and IL-1-dependent pulmonary neutrophilic inflammation. Furthermore, SAA drives production of IL-1α, IL-1β, IL-6, IL-23, and PGE(2), causes dendritic cell (DC) maturation, and requires TLR2, MyD88, and the NLRP3 inflammasome for secretion of IL-1β by DCs and macrophages. CD4(+) T cells polyclonally stimulated in the presence of conditioned media from SAA-exposed DCs produced IL-17, and the capacity of polyclonally stimulated splenocytes to secrete IL-17 is dependent upon IL-1, TLR2, and the NLRP3 inflammasome. Additionally, in a model of allergic airway inflammation, administration of SAA to the lungs functions as an adjuvant to sensitize mice to inhaled OVA, resulting in leukocyte influx after Ag challenge and a predominance of IL-17 production from restimulated splenocytes that is dependent upon IL-1R signaling.     

Cutting edge: myeloid differentiation factor 88 is essential for pulmonary host defense against Pseudomonas aeruginosa but not Staphylococcus aureus

Myeloid differentiation factor 88 (MyD88) is an adapter molecule required for signal transduction via Toll-like receptors (TLRs) and receptors of the IL-1 family. Consequently, MyD88-deficient mice are highly susceptible to bacterial infections, including systemic infection with Staphylococcus aureus. To determine the role of MyD88 in innate immunity to bacterial pneumonia, we exposed MyD88-deficient and wild-type mice to aerosolized Pseudomonas aeruginosa or S. aureus. As predicted, MyD88-deficient mice failed to mount an early cytokine or inflammatory response or to control bacterial replication after infection with P. aeruginosa, which resulted in necrotizing pneumonia and death. By contrast, MyD88-deficient mice controlled S. aureus infection despite blunted local cytokine and inflammatory responses. Thus, whereas MyD88-dependent signaling is integral to the initiation of cytokine and inflammatory responses to both pathogens following infection of the lower respiratory tract, MyD88 is essential for innate immunity to P. aeruginosa but not S. aureus.     

Neutrophils require SHP1 to regulate IL-1β production and prevent inflammatory skin disease

The regulation of neutrophil recruitment, activation, and disposal is pivotal for circumscribed inflammation. SHP1(Y208N/Y208N) mutant mice develop severe cutaneous inflammatory disease that is IL-1R dependent. Genetic reduction in neutrophil numbers and neutrophilic responses to infection is sufficient to prevent the spontaneous initiation of this disease. Neutrophils from SHP1(Y208N/Y208N) mice display increased pro-IL-1β production due to altered responses to MyD88-dependent and MyD88-independent signals. The IL-1R-dependent inflammatory disease in SHP1(Y208N/Y208N) mice develops independently of caspase 1 and proteinase 3 and neutrophil elastase. In response to Fas ligand, a caspase 1-independent inducer of IL-1β production, neutrophils from SHP1(Y208N/Y208N) mice produce elevated levels of IL-1β but display reduced caspase 3 and caspase 7 activation. In neutrophils deficient in SHP1, IL-1β induces high levels of pro-IL-1β suggesting the presence of a paracrine IL-1β loop. These data indicate that the neutrophil- and IL-1-dependent disease in SHP1(Y208N/Y208N) mice is a consequence of loss of negative regulation of TLR and IL-1R signaling.