Abnormal T cell activation caused by the imbalance of the IL-1/IL-1R antagonist system is responsible for the development of experimental autoimmune encephalomyelitis

Inflammasomes: mechanism of action, role in disease, and therapeutics

The inflammasomes are innate immune system receptors and sensors that regulate the activation of caspase-1 and induce inflammation in response to infectious microbes and molecules derived from host proteins. They have been implicated in a host of inflammatory disorders. Recent developments have greatly enhanced our understanding of the molecular mechanisms by which different inflammasomes are activated. Additionally, increasing evidence in mouse models, supported by human data, strongly implicates an involvement of the inflammasome in the initiation or progression of diseases with a high impact on public health, such as metabolic disorders and neurodegenerative diseases. Finally, recent developments pointing toward promising therapeutics that target inflammasome activity in inflammatory diseases have been reported. This review will focus on these three areas of inflammasome research.

Exacerbation of autoimmune neuroinflammation by dietary sodium is genetically controlled and sex specific

Multiple sclerosis (MS) is a debilitating autoimmune neuroinflammatory disease influenced by genetics and the environment. MS incidence in female subjects has approximately tripled in the last century, suggesting a sex-specific environmental influence. Recent animal and human studies have implicated dietary sodium as a risk factor in MS, whereby high sodium augmented the generation of T helper (Th) 17 cells and exacerbated experimental autoimmune encephalomyelitis (EAE), the principal model of MS. However, whether dietary sodium interacts with sex or genetics remains unknown. Here, we show that high dietary sodium exacerbates EAE in a strain- and sex-specific fashion. In C57BL6/J mice, exposure to a high-salt diet exacerbated disease in both sexes, while in SJL/JCrHsd mice, it did so only in females. In further support of a genetic component, we found that sodium failed to modify EAE course in C57BL6/J mice carrying a 129/Sv-derived interval on chromosome 17. Furthermore, we found that the high-sodium diet did not augment Th17 or Th1 responses, but it did result in increased blood-brain barrier permeability and brain pathology. Our results demonstrate that the effects of dietary sodium on autoimmune neuroinflammation are sex specific, genetically controlled, and CNS mediated.

Exacerbation of autoimmune neuroinflammation by dietary sodium is genetically controlled and sex specific

Multiple sclerosis (MS) is a debilitating autoimmune neuroinflammatory disease influenced by genetics and the environment. MS incidence in female subjects has approximately tripled in the last century, suggesting a sex-specific environmental influence. Recent animal and human studies have implicated dietary sodium as a risk factor in MS, whereby high sodium augmented the generation of T helper (Th) 17 cells and exacerbated experimental autoimmune encephalomyelitis (EAE), the principal model of MS. However, whether dietary sodium interacts with sex or genetics remains unknown. Here, we show that high dietary sodium exacerbates EAE in a strain- and sex-specific fashion. In C57BL6/J mice, exposure to a high-salt diet exacerbated disease in both sexes, while in SJL/JCrHsd mice, it did so only in females. In further support of a genetic component, we found that sodium failed to modify EAE course in C57BL6/J mice carrying a 129/Sv-derived interval on chromosome 17. Furthermore, we found that the high-sodium diet did not augment Th17 or Th1 responses, but it did result in increased blood-brain barrier permeability and brain pathology. Our results demonstrate that the effects of dietary sodium on autoimmune neuroinflammation are sex specific, genetically controlled, and CNS mediated.

VBP15, a novel anti-inflammatory, is effective at reducing the severity of murine experimental autoimmune encephalomyelitis

Multiple sclerosis is a chronic disease of the central nervous system characterized by an autoimmune inflammatory reaction that leads to axonal demyelination and tissue damage. Glucocorticoids, such as prednisolone, are effective in the treatment of multiple sclerosis in large part due to their ability to inhibit pro-inflammatory pathways (e.g., NFκB). However, despite their effectiveness, long-term treatment is limited by adverse side effects. VBP15 is a recently described compound synthesized based on the lazeroid steroidal backbone that shows activity in acute and chronic inflammatory conditions, yet displays a much-reduced side effect profile compared to traditional glucocorticoids. The purpose of this study was to determine the effectiveness of VBP15 in inhibiting inflammation and disease progression in experimental autoimmune encephalomyelitis (EAE), a widely used mouse model of multiple sclerosis. Our data show that VBP15 is effective at reducing both disease onset and severity. In parallel studies, we observed that VBP15 was able to inhibit the production of NFκB-regulated pro-inflammatory transcripts in human macrophages. Furthermore, treatment with prednisolone-but not VBP15-increased expression of genes associated with bone loss and muscle atrophy, suggesting lack of side effects of VBP15. These findings suggest that VBP15 may represent a potentially safer alternative to traditional glucocorticoids in the treatment of multiple sclerosis and other inflammatory diseases.

Systemic inflammation and the brain: novel roles of genetic, molecular, and environmental cues as drivers of neurodegeneration

The nervous and immune systems have evolved in parallel from the early bilaterians, in which innate immunity and a central nervous system (CNS) coexisted for the first time, to jawed vertebrates and the appearance of adaptive immunity. The CNS feeds from, and integrates efferent signals in response to, somatic and autonomic sensory information. The CNS receives input also from the periphery about inflammation and infection. Cytokines, chemokines, and damage-associated soluble mediators of systemic inflammation can also gain access to the CNS via blood flow. In response to systemic inflammation, those soluble mediators can access directly through the circumventricular organs, as well as open the blood–brain barrier. The resulting translocation of inflammatory mediators can interfere with neuronal and glial well-being, leading to a break of balance in brain homeostasis. This in turn results in cognitive and behavioral manifestations commonly present during acute infections – including anorexia, malaise, depression, and decreased physical activity – collectively known as the sickness behavior (SB). While SB manifestations are transient and self-limited, under states of persistent systemic inflammatory response the cognitive and behavioral changes can become permanent. For example, cognitive decline is almost universal in sepsis survivors, and a common finding in patients with systemic lupus erythematosus. Here, we review recent genetic evidence suggesting an association between neurodegenerative disorders and persistent immune activation; clinical and experimental evidence indicating previously unidentified immune-mediated pathways of neurodegeneration; and novel immunomodulatory targets and their potential relevance for neurodegenerative disorders.

Chronic systemic IL-1β exacerbates central neuroinflammation independently of the blood-brain barrier integrity

Peripheral circulating cytokines are involved in immune to brain communication and systemic inflammation is considered a risk factor for flaring up the symptoms in most neurodegenerative diseases. We induced both central inflammatory demyelinating lesion, and systemic inflammation with an interleukin-1β expressing adenovector. The peripheral pro-inflammatory stimulus aggravated the ongoing central lesion independently of the blood-brain barrier (BBB) integrity. This model allows studying the role of specific molecules and cells (neutrophils) from the innate immune system, in the relationship between central and peripheral communication, and on relapsing episodes of demyelinating lesions, along with the role of BBB integrity.

Beyond canonical inflammasomes: emerging pathways in IL-1-mediated autoinflammatory disease

In recent years, non-communicable chronic diseases that are potentiated by sterile inflammation have replaced infectious diseases as the major threat to human health. Sterile inflammation that results from aberrant tissue damage plays pivotal roles in the pathogenesis of numerous acute and chronic inflammatory diseases including atherosclerosis, type 2 diabetes, cancer, obesity, and multiple neurodegenerative diseases. The cellular events and molecular signaling pathways that govern sterile inflammation currently remain poorly defined; however, emerging data suggest central roles for IL-1 in driving autoimmune and inflammatory disease pathogenesis. Improved characterization of the immunological pathways that contribute to sterile inflammation are desperately needed to develop effective therapeutics to treat these devastating diseases. In this review, we discuss recent advances in our understanding of how IL-1 is regulated in response to tissue damage. In particular, we highlight recent studies that describe novel roles for conventional cell death molecules in the regulation of IL-1β production.

IL-17+Foxp3+ T cells: an intermediate differentiation stage between Th17 cells and regulatory T cells

Foxp3(+) Tregs have been known as a major regulator of immune homeostasis through their immunosuppressive function. Th17 lineage is a CD4(+) T cell subset that exerts its function by secreting proinflammatory cytokines and protecting host against microbial infections. The altered ratio between Foxp3(+) Tregs and Th17 cells plays an important role in the pathogenesis of immune-related diseases. Recent mice and human studies have demonstrated that Tregs can be reprogrammed into a novel population, IL-17(+)Foxp3(+) T cells, phenotypically and functionally resembling Th17 cells under the complicated cytokine stimulation. The identification of IL-17(+)Foxp3(+) T cells may provide a new understanding of therapy targeting Tregs and Th17 cells in autoimmune diseases and cancer. Here, we highlight significant data regarding the phenotype profile, origination, differentiation, and the pleiotropic functions of IL-17(+)Foxp3(+) T cells and the reciprocal relationships of these cells to Tregs and Th17 cells. Furthermore, the role of IL-17(+)Foxp3(+) T cells in tumorigenesis and clinical implications in cancer therapy are discussed in this review.

Sex-specific control of central nervous system autoimmunity by p38 mitogen-activated protein kinase signaling in myeloid cells

OBJECTIVE

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS), characterized by a global increasing incidence driven by relapsing-remitting disease in females. Investigators have described p38 mitogen-activated protein kinase (MAPK) as a key regulator of inflammatory responses in autoimmunity, but its role in the sexual dimorphism in MS or MS models remains unexplored.

METHODS

Toward this end, we used experimental autoimmune encephalomyelitis (EAE), the principal animal model of MS, combined with pharmacologic and genetic inhibition of p38 MAPK activity and transcriptomic analyses.

RESULTS

Pharmacologic inhibition of p38 MAPK selectively ameliorated EAE in female mice. Conditional deletion studies demonstrated that p38α signaling in macrophages/myeloid cells, but not T cells or dendritic cells, mediated this sexual dimorphism, which was dependent on the presence of adult sex hormones. Analysis of CNS inflammatory infiltrates showed that female but not male mice lacking p38α in myeloid cells exhibited reduced immune cell activation compared with controls, whereas peripheral T-cell priming was unaffected in both sexes. Transcriptomic analyses of myeloid cells revealed differences in p38α-controlled transcripts comprising female- and male-specific gene modules, with greater p38α dependence of proinflammatory gene expression in females.

INTERPRETATION

Our findings demonstrate a key role for p38α in myeloid cells in CNS autoimmunity and uncover important molecular mechanisms underlying sex differences in disease pathogenesis. Taken together, our results suggest that the p38 MAPK signaling pathway represents a novel target for much needed disease-modifying therapies for MS.

RIP1-driven autoinflammation targets IL-1α independently of inflammasomes and RIP3

The protein-tyrosine phosphatase SHP-1 has critical roles in immune signalling, but how mutations in SHP-1 cause inflammatory disease in humans remains poorly defined. Mice homozygous for the Tyr208Asn amino acid substitution in the carboxy terminus of SHP-1 (referred to as Ptpn6(spin) mice) spontaneously develop a severe inflammatory syndrome that resembles neutrophilic dermatosis in humans and is characterized by persistent footpad swelling and suppurative inflammation. Here we report that receptor-interacting protein 1 (RIP1)-regulated interleukin (IL)-1α production by haematopoietic cells critically mediates chronic inflammatory disease in Ptpn6(spin) mice, whereas inflammasome signalling and IL-1β-mediated events are dispensable. IL-1α was also crucial for exacerbated inflammatory responses and unremitting tissue damage upon footpad microabrasion of Ptpn6(spin) mice. Notably, pharmacological and genetic blockade of the kinase RIP1 protected against wound-induced inflammation and tissue damage in Ptpn6(spin) mice, whereas RIP3 deletion failed to do so. Moreover, RIP1-mediated inflammatory cytokine production was attenuated by NF-κB and ERK inhibition. Together, our results indicate that wound-induced tissue damage and chronic inflammation in Ptpn6(spin) mice are critically dependent on RIP1-mediated IL-1α production, whereas inflammasome signalling and RIP3-mediated necroptosis are dispensable. Thus, we have unravelled a novel inflammatory circuit in which RIP1-mediated IL-1α secretion in response to deregulated SHP-1 activity triggers an inflammatory destructive disease that proceeds independently of inflammasomes and programmed necrosis.

Innate and adaptive effects of inflammasomes on T cell responses

Inflammasomes are protein complexes that form in response to pathogen-derived or host-derived stress signals. Their activation leads to the production of inflammatory cytokines and promotes a pyrogenic cell death process. The massive release of inflammatory mediators that follows inflammasome activation is a key event in alarming innate immune cells. Growing evidence also highlights the role of inflammasome-dependent cytokines in shaping the adaptive immune response, as exemplified by the capacity of IL-1β to support Th17 responses, or by the finding that IL-18 evokes antigen-independent IFN-γ secretion by memory CD8(+) T cells. A deeper understanding of these mechanisms and on how to manipulate this powerful inflammatory system therefore represents an important step forward in the development of improved vaccine strategies.

IL-1R1 is required for dendritic cell-mediated T cell reactivation within the CNS during West Nile virus encephalitis

IL-1R1 signaling drives T cell activation in the CNS via effects on DC activation.

Infections of the central nervous system (CNS) with cytopathic viruses require efficient T cell responses to promote viral clearance, limit immunopathology, and enhance survival. We found that IL-1R1 is critical for effector T cell reactivation and limits inflammation within the CNS during murine West Nile virus (WNV) encephalitis. WNV-infected IL-1R1^−/− mice display intact adaptive immunity in the periphery but succumb to WNV infection caused by loss of virologic control in the CNS with depressed local Th1 cytokine responses, despite parenchymal entry of virus-specific CD8⁺ T cells. Ex vivo analysis of CD4⁺ T cells from WNV-infected CNS of IL-1R1^−/− mice revealed impaired effector responses, whereas CD8⁺ T cells revealed no cell intrinsic defects in response to WNV antigen. WNV-infected, IL-1R1^−/− mice also exhibited decreased activation of CNS CD11c⁺CD11b⁻CD103⁺ and CD11c⁺CD11b⁻CD8α⁺Dec-205⁺ cells with reduced up-regulation of the co-stimulatory molecules CD80, CD86, and CD68. Adoptive transfer of wild-type CD11c-EYFP⁺ cells from WNV-infected CNS into WNV-infected IL-1R1^−/− mice trafficked into the CNS restored T cell functions and improved survival from otherwise lethal infection. These data indicate that IL-1R1 signaling promotes virologic control during WNV infection specifically within the CNS via modulation of CD11c⁺ cell–mediated T cell reactivation at this site.

The role of reactive oxygen species and proinflammatory cytokines in type 1 diabetes pathogenesis

Type 1 diabetes (T1D) is a T cell–mediated autoimmune disease characterized by the destruction of insulin-secreting pancreatic β cells. In humans with T1D and in nonobese diabetic (NOD) mice (a murine model for human T1D), autoreactive T cells cause β-cell destruction, as transfer or deletion of these cells induces or prevents disease, respectively. CD4⁺ and CD8⁺ T cells use distinct effector mechanisms and act at different stages throughout T1D to fuel pancreatic β-cell destruction and disease pathogenesis. While these adaptive immune cells employ distinct mechanisms for β-cell destruction, one central means for enhancing their autoreactivity is by the secretion of proinflammatory cytokines, such as IFN-γ, TNF-α, and IL-1. In addition to their production by diabetogenic T cells, proinflammatory cytokines are induced by reactive oxygen species (ROS) via redox-dependent signaling pathways. Highly reactive molecules, proinflammatory cytokines are produced upon lymphocyte infiltration into pancreatic islets and induce disease pathogenicity by directly killing β cells, which characteristically possess low levels of antioxidant defense enzymes. In addition to β-cell destruction, proinflammatory cytokines are necessary for efficient adaptive immune maturation, and in the context of T1D they exacerbate autoimmunity by intensifying adaptive immune responses. The first half of this review discusses the mechanisms by which autoreactive T cells induce T1D pathogenesis and the importance of ROS for efficient adaptive immune activation, which, in the context of T1D, exacerbates autoimmunity. The second half provides a comprehensive and detailed analysis of (1) the mechanisms by which cytokines such as IL-1 and IFN-γ influence islet insulin secretion and apoptosis and (2) the key free radicals and transcription factors that control these processes.

Induction and regulation of pathogenic Th17 cell responses in schistosomiasis

Schistosomiasis is a major tropical disease caused by trematode helminths in which the host mounts a pathogenic immune response against tissue-trapped parasite eggs. The immunopathology consists of egg antigen-specific CD4 T cell-mediated granulomatous inflammation that varies greatly in magnitude in humans and among mouse strains in an experimental model. New evidence, covered in this review, intimately ties the development of severe pathology to IL-17-producing CD4 T helper (Th17) cells, a finding that adds a new dimension to the traditional CD4 Th1 vs. Th2 cell paradigm. Most examined mouse strains, in fact, develop severe immunopathology with substantial Th17 as well as Th1 and Th2 cell responses; a solely Th2-polarized response is an exception that is only observed in low-pathology strains such as the C57BL/6. The ability to mount pathogenic Th17 cell responses is genetically determined and depends on the production of IL-23 and IL-1β by antigen presenting cells following recognition of egg antigens; analyses of several F2 progenies of (high × low)-pathology strain crosses demonstrated that quantitative trait loci governing IL-17 levels and disease severity vary substantially from cross to cross. Low pathology is dominant, which may explain the low incidence of severe disease in humans; however, coinfection with intestinal nematodes can also dampen pathogenic Th17 cell responses by promoting regulatory mechanisms such as those afforded by alternatively activated macrophages and T regulatory cells. A better understanding of the pathways conducive to severe forms of schistosomiasis and their regulation should lead to interventions similar to those presently used to manage other immune-mediated diseases.

IL-1 family cytokines trigger sterile inflammatory disease

Inflammation plays vital roles in protective responses against pathogens and tissue repair, however, improper resolution of inflammatory networks is centrally involved in the pathogenesis of many acute and chronic diseases. Extensive advances have been made in recent years to define the inflammatory processes that are required for pathogen clearance, however, in comparison, less is known about the regulation of inflammation in sterile settings. Over the past decade non-communicable chronic diseases that are potentiated by sterile inflammation have replaced infectious diseases as the major threat to global human health. Thus, improved understanding of the sterile inflammatory process has emerged as one of the most important areas of biomedical investigation during our time. In this review we highlight the central role that interleukin-1 family cytokines play in sterile inflammatory diseases.

CNS response to a second pro-inflammatory event depends on whether the primary demyelinating lesion is active or resolved

Interleukin-1β (IL-1β) is considered to be one of the most important mediators in the pathogenesis of inflammatory diseases, particularly in neurodegenerative diseases such as multiple sclerosis (MS). MS is a chronic inflammatory disease characterized by demyelination and remyelination events, with unpredictable relapsing and remitting episodes that seldom worsen MS lesions. We proposed to study the effect of a unique component of the inflammatory process, IL-1β, and evaluate its effect in repeated episodes, similar to the relapsing-remitting MS pathology. Using adenoviral vectors, we developed a model of focal demyelination/remyelination triggered by the chronic expression of IL-1β. The long-term expression of IL-1β in the striatum produced blood-brain barrier (BBB) breakdown, demyelination, microglial/macrophage activation, and neutrophil infiltration but no overt neuronal degeneration. This demyelinating process was followed by complete remyelination of the area. This simple model allows us to study demyelination and remyelination independently of the autoimmune and adaptive immune components. Re-exposure to this cytokine when the first inflammatory response was still unresolved generated a lesion with decreased neuroinflammation, demyelination, axonal injury and glial response. However, a second long-term expression of IL-1β when the first lesion was resolved could not be differentiated from the first event. In this study, we demonstrated that the response to a second inflammatory stimulus varies depending on whether the initial lesion is still active or has been resolved. Considering that anti-inflammatory treatments have shown little improvement in MS patients, studies about the behavior of specific components of the inflammatory process should be taken into account to develop new therapeutic tools.

Type I IFN-mediated regulation of IL-1 production in inflammatory disorders

Although contributing to inflammatory responses and to the development of certain autoimmune pathologies, type I interferons (IFNs) are used for the treatment of viral, malignant, and even inflammatory diseases. Interleukin-1 (IL-1) is a strongly pyrogenic cytokine and its importance in the development of several inflammatory diseases is clearly established. While the therapeutic use of IL-1 blocking agents is particularly successful in the treatment of innate-driven inflammatory disorders, IFN treatment has mostly been appreciated in the management of multiple sclerosis. Interestingly, type I IFNs exert multifaceted immunomodulatory effects, including the reduction of IL-1 production, an outcome that could contribute to its efficacy in the treatment of inflammatory diseases. In this review, we summarize the current knowledge on IL-1 and IFN effects in different inflammatory disorders, the influence of IFNs on IL-1 production, and discuss possible therapeutic avenues based on these observations.

Toll-like receptor (TLR) and inflammasome actions in the central nervous system

During the past 10 years, much attention has been focused towards elucidating the impact of Toll-like receptors (TLRs) in central nervous system (CNS) innate immunity. TLR signaling triggers the transcriptional activation of pro-interleukin-1β (pro-IL-1β) and pro-IL-18 that are processed into their active forms by the inflammasome. Recent studies have demonstrated inflammasome involvement during CNS infection, autoimmune disease, and injury. This review will address inflammasome actions within the CNS and how cooperation between TLR and inflammasome signaling may influence disease outcome. In addition, the concept of alternative inflammasome functions independent of IL-1 and IL-18 processing are considered in the context of CNS disease.

Interleukin-1 receptor mediates the interplay between CD4+ T cells and ocular resident cells to promote keratinizing squamous metaplasia in Sjögren's syndrome

Keratinizing squamous metaplasia (SQM) of the ocular mucosal epithelium is a blinding corneal disease characterized by the loss of conjunctival goblet cells (GCs), pathological ocular surface keratinization and tissue recruitment of immune cells. Using the autoimmune regulator (Aire)-deficient mouse as a model for Sjögren's syndrome (SS)-associated SQM, we identified CD4(+) T lymphocytes as the main immune effectors driving SQM and uncovered a pathogenic role for interleukin-1 (IL-1). IL-1, a pleiotropic cytokine family enriched in ocular epithelia, governs tissue homeostasis and mucosal immunity. Here, we used adoptive transfer of autoreactive CD4(+) T cells to dissect the mechanism whereby IL-1 promotes SQM. CD4(+) T cells adoptively transferred from both Aire knockout (KO) and Aire/IL-1 receptor type 1 (IL-1R1) double KO donors conferred SQM to severe-combined immunodeficiency (scid) recipients with functional IL-1R1, but not scid recipients lacking IL-1R1. In the lacrimal gland, IL-1R1 was primarily immunolocalized to ductal epithelium surrounded by CD4(+) T cells. In the eye, IL-1R1 was expressed on local mucosal epithelial and stromal cells, but not on resident antigen-presenting cells or infiltrating immune cells. In both tissues, autoreactive CD4(+) T-cell infiltration was only observed in the presence of IL-1R1-postive resident cells. Moreover, persistent activation of IL-1R1 signaling led to chronic immune-mediated inflammation by retaining CD4(+) T cells in the local microenvironment. Following IL-1R1-dependent infiltration of CD4(+) T cells, we observed SQM hallmarks in local tissues-corneal keratinization, conjunctival GC mucin acidification and epithelial cell hyperplasia throughout the ocular surface mucosa. Proinflammatory IL-1 expression in ocular epithelial cells significantly correlated with reduced tear secretion, while CD4(+) T-cell infiltration of the lacrimal gland predicted the development of ocular SQM. Collectively, data in this study indicated a central role for IL-1 in orchestrating a functional interplay between immune cells and resident cells of SS-targeted tissues in the pathogenesis of SQM.

Emerging strategies for the treatment of multiple sclerosis

Despite extraordinary advances in the field of neuroimmunology, ideal treatment for patients with multiple sclerosis remains an unmet need. Existing treatments are only partially effective in preventing multiple sclerosis relapses, have a limited impact on the accrual of disability, have not been effective in progressive forms of the disease, and treatment remains preventive rather than restorative. This review provides an overview of emerging therapies and targets, and incorporates strategies for two different approaches to multiple sclerosis: prevention, through immune modulation; and repair, through neuroprotection and remyelination. Agents at all stages of development, from late-stage clinical trials of BG-12, teriflunomide, alemtuzumab, daclizumab and anti-CD20 agents, to novel approaches in preclinical testing, are discussed.

Inflammasome-derived IL-1β regulates the production of GM-CSF by CD4(+) T cells and γδ T cells

Recent findings have demonstrated an indispensable role for GM-CSF in the pathogenesis of experimental autoimmune encephalomyelitis. However, the signaling pathways and cell populations that regulate GM-CSF production in vivo remain to be elucidated. Our work demonstrates that IL-1R is required for GM-CSF production after both TCR- and cytokine-induced stimulation of immune cells in vitro. Conventional αβ and γδ T cells were both identified to be potent producers of GM-CSF. Moreover, secretion of GM-CSF was dependent on IL-1R under both IL-12- and IL-23-induced stimulatory conditions. Deficiency in IL-1R conferred significant protection from experimental autoimmune encephalomyelitis, and this correlated with reduced production of GM-CSF and attenuated infiltration of inflammatory cells into the CNS. We also find that GM-CSF production in vivo is not restricted to a defined CD4(+) T cell lineage but is rather heterogeneously expressed in the effector CD4(+) T cell population. In addition, inflammasome-derived IL-1β upstream of IL-1R is a critical regulator of GM-CSF production by T cells during priming, and the adapter protein, MyD88, promotes GM-CSF production in both αβ and γδ T cells. These findings highlight the importance of inflammasome-derived IL-1β and the IL-1R/MyD88 signaling axis in the regulation of GM-CSF production.

The encephalitogenicity of T(H)17 cells is dependent on IL-1- and IL-23-induced production of the cytokine GM-CSF

Interleukin 17 (IL-17)-producing helper T cells (T(H)17 cells) require exposure to IL-23 to become encephalitogenic, but the mechanism by which IL-23 promotes their pathogenicity is not known. Here we found that IL-23 induced production of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) in T(H)17 cells and that GM-CSF had an essential role in their encephalitogenicity. Our findings identify a chief mechanism that underlies the important role of IL-23 in autoimmune diseases. IL-23 induced a positive feedback loop whereby GM-CSF secreted by T(H)17 cells stimulated the production of IL-23 by antigen-presenting cells. Such cross-regulation of IL-23 and GM-CSF explains the similar pattern of resistance to autoimmunity when either of the two cytokines is absent and identifies T(H)17 cells as a crucial source of GM-CSF in autoimmune inflammation.

IL-1 signalling determines the fate of skin grafts expressing non-self protein in keratinocytes

Although IL-1 is a known inflammatory cytokine during pathogen infection, the role of IL-1 in skin graft rejection, particularly where foreign antigen is expressed exclusively in keratinocytes, is less understood. Here, we use a syngeneic skin graft system, where antigens are expressed in epithelial cells via either a keratin 14 or keratin 5 promoter, to explore the role of IL-1 in graft rejection and induction of epithelial antigen-specific effector CD8(+) T-cell function. Keratin 5 ovalbumin (K5mOVA) transgenic skin grafts destined for rejection demonstrated increased expression of IL-1beta and its receptors compared to K14 HPV16 E7 transgenic grafts that do not reject spontaneously. Rejection of OVA grafts lacking the IL-1 receptor (IL-1R1) was delayed and associated with decreased numbers of antigen-specific CD8 T cells. In contrast, K14E7 grafts survived on immunocompetent, syngeneic recipients with decreased graft levels of IL-1beta and IL-1R1 and 2. However, in the absence of the IL-1 receptor antagonist, IL-1Ra, skin grafts were spontaneously rejected and an E7-specific CD8 T-cell response was primed. Thus, expression of the HPV16E7 oncoprotein in epithelial cells prevents IL-1beta-associated skin graft rejection and induction of antigen-specific CD8 T-cell responses. Enhancing IL-1beta signalling, via blocking of the IL-1 receptor antagonist, may represent an alternative strategy for treatment of HPV16E7-associated cancers.

A role of IL-1R1 signaling in the differentiation of Th17 cells and the development of autoimmune diseases

IL-1 cytokine family plays a key role in the innate immune response against pathogen- and danger-associated molecular patterns. More recently, IL-1 receptor type 1 (IL-R1) signaling has been identified as a critical step in the differentiation and commitment of Th17 cells, which mediate the development of autoimmune diseases. Given its significance in the induction of the adoptive immune response, this complex signaling pathway is tightly regulated. Upon binding of IL-1 to IL-1R1, IL-1R accessory protein (AcP) is recruited to form a high affinity IL-1R1-IL-1RAcP heterodimeric receptor, which initiates the downstream signaling cascade. Multiple negative regulators of this pathway, including inhibitory membrane-bound IL-RII, secreted soluble (s)IL-1RI, sIL-RII and sIL-1RAcP, the regulatory IL-1R1 antagonist (IL-1R1a) and the IL-1R1-signlaing-induced single Ig-IL-1R-related (SIGIRR), provide a negative feedback control of this pathway, and suppress excessive IL-1 signaling and Th17 cell differentiation. IL-1R1 signaling induces human Th17 cell differentiation, leading to the expression of IL-1R-associated protein kinase (IRAK)4 and retinoic acid-related orphan nuclear hormone receptor (ROR), Th17 cell lineage transcription factors, which together with signal transducer and activator of the transcription (STAT)3, activate this cell lineage's specific cytokine expression profile, including IL-17A, IL-17F, IL-21 and IL-22. Given the role of IL-1 signaling and Th17 cells in the development of the autoinflammatory and autoimmune diseases, therapeutic strategies inhibiting IL-1R1 signaling are discussed as a novel approach for the treatment of autoimmune diseases and particularly multiple sclerosis (MS).

Interferon-beta is a key regulator of proinflammatory events in experimental autoimmune encephalomyelitis

BACKGROUND

Interferon (IFN)-β is an effective therapy for relapsing-remitting multiple sclerosis, yet its mechanism of action remains ill-defined.

OBJECTIVES

Our objective was to characterize the role of IFN-β in immune regulation in experimental autoimmune encephalomyelitis (EAE).

METHODS

IFN-β(+/+) and IFN-β(-/-) mice were immunized with myelin oligodendrocyte glycoprotein peptide in the presence or absence of IFN-β, to induce EAE. Disease pathogenesis was monitored in the context of incidence, time of onset, clinical score, and immune cell activation in the brains, spleens and lymph nodes of affected mice.

RESULTS

Compared with IFN-β(+/+) mice, IFN-β(-/-) mice exhibited an earlier onset and a more rapid progression of EAE, increased numbers of CD11b(+) leukocytes infiltrating affected brains and an increased percentage of Th17 cells in the central nervous system and draining lymph nodes. IFN-β treatment delayed disease onset and reduced disease severity. Ex vivo experiments revealed that the lack of IFN-β results in enhanced generation of autoreactive T cells, a likely consequence of the absence of IFN-β-regulated events in both the CD4(+) T cells and antigen-presenting dendritic cells. Gene expression analysis of IFN-β-treated bone marrow macrophages (CD11b(+)) identified modulation of genes affecting T cell proliferation and Th17 differentiation.

CONCLUSIONS

We conclude that IFN-β acts to suppress the generation of autoimmune-inducing Th17 cells during the development of disease as well as modulating pro-inflammatory mediators.

Glatiramer acetate triggers PI3Kδ/Akt and MEK/ERK pathways to induce IL-1 receptor antagonist in human monocytes

Glatiramer acetate (GA), an immunomodulator used in multiple sclerosis (MS) therapy, induces the production of secreted IL-1 receptor antagonist (sIL-1Ra), a natural inhibitor of IL-1β, in human monocytes, and in turn enhances sIL-1Ra circulating levels in MS patients. GA is a mixture of peptides with random Glu, Lys, Ala, and Tyr sequences of high polarity and hydrophilic nature that is unlikely to cross the blood-brain barrier. In contrast, sIL-1Ra crosses the blood-brain barrier and, in turn, may mediate GA anti-inflammatory activities within the CNS by counteracting IL-1β activities. Here we identify intracellular signaling pathways induced by GA that control sIL-1Ra expression in human monocytes. By using kinase knockdown and specific inhibitors, we demonstrate that GA induces sIL-1Ra production via the activation of PI3Kδ, Akt, MEK1/2, and ERK1/2, demonstrating that both PI3Kδ/Akt and MEK/ERK pathways rule sIL-1Ra expression in human monocytes. The pathways act in parallel upstream glycogen synthase kinase-3α/β (GSK3α/β), the knockdown of which enhances sIL-1Ra production. Together, our findings demonstrate the existence of signal transduction triggered by GA, further highlighting the mechanisms of action of this drug in MS.

NLRP3 plays a critical role in the development of experimental autoimmune encephalomyelitis by mediating Th1 and Th17 responses

The interplay between innate and adaptive immunity is important in multiple sclerosis (MS). The inflammasome complex, which activates caspase-1 to process pro-IL-1beta and pro-IL-18, is rapidly emerging as a pivotal regulator of innate immunity, with nucleotide-binding domain, leucine-rich repeat containing protein family, pyrin domain containing 3 (NLRP3) (cryopyrin or NALP3) as a prominent player. Although the role of NLRP3 in host response to pathogen associated molecular patterns and danger associated molecular patterns is well documented, its role in autoimmune diseases is less well studied. To investigate the role of NLRP3 protein in MS, we used a mouse model of MS, experimental autoimmune encephalomyelitis (EAE). Nlrp3 expression was elevated in the spinal cords during EAE, and Nlrp3(-/-) mice had a dramatically delayed course and reduced severity of disease. This was accompanied by a significant reduction of the inflammatory infiltrate including macrophages, dendritic cells, CD4, and CD8(+) T cells in the spinal cords of the Nlrp3(-/-) mice, whereas microglial accumulation remained the same. Nlrp3(-/-) mice also displayed improved histology in the spinal cords with reduced destruction of myelin and astrogliosis. Nlrp3(-/-) mice with EAE produced less IL-18, and the disease course was similar to Il18(-/-) mice. Furthermore, Nlrp3(-/-) and Il18(-/-) mice had similarly reduced IFN-gamma and IL-17 production. Thus, NLRP3 plays a critical role in the induction of the EAE, likely through effects on capase-1-dependent cytokines which then influence Th1 and Th17.

IL-1: discoveries, controversies and future directions

Although there has been a great amount of progress in the 25 years since the first reporting of the cDNA for IL-1alpha and IL-1beta, the history of IL-1 goes back to the early 1940s. In fact, the entire field of inflammatory cytokines, TLR and the innate immune response can be found in the story of IL-1. This Viewpoint follows the steps from the identification of the fever-inducing activities of "soluble factors" produced by endotoxin-stimulated leukocytes through to the discovery of cryopyrin and the caspase-1 inflammasome and on to the clinical benefits of anti-IL-1beta-based therapeutics. It also discusses some of the current controversies regarding the activation of the inflammasome. The future of novel anti-inflammatory agents to combat chronic inflammation is based, in part, on the diseases that are uniquely responsive to anti-IL-1beta, which is surely a reason to celebrate the 25th anniversary of the cloning of IL-1alpha and IL-1beta.

The IL-1 family: regulators of immunity

Over recent years it has become increasingly clear that innate immune responses can shape the adaptive immune response. Among the most potent molecules of the innate immune system are the interleukin-1 (IL-1) family members. These evolutionarily ancient cytokines are made by and act on innate immune cells to influence their survival and function. In addition, they act directly on lymphocytes to reinforce certain adaptive immune responses. This Review provides an overview of both the long-established and more recently characterized members of the IL-1 family. In addition to their effects on immune cells, their involvement in human disease and disease models is discussed.

Regulation of IL-17 expression by the developmental pathway of CD4 T cells in the thymus

CD4 T cells selected by MHC class II expressing thymocytes (T-CD4 T cells) have distinct effector functions compared to that of epithelial cell-selected CD4 T cells (E-CD4 T cells). T-CD4 T cells produce both Th1 and Th2 effector cytokines immediately after stimulation and also express IL-4 in addition to IFN-gamma under the Th1 differentiation condition. In the present study, we investigated the capability of T-CD4 T cells to become IL-17-producing cells. We found that T-CD4 T cells express reduced IL-17 under Th17-inducing conditions. T-CD4 T cells express very low levels of receptor for TGF-beta and IL-21 that are essential to induce IL-17 expression. In addition, the induction of RORgammat, a key transcription factor for IL-17 gene expression, was compromised in T-CD4 T cells under Th17 skewing conditions and ectopic expression of RORgammat restored IL-17 expression. The defect of IL-17 and RORgammat expression in T-CD4 T cells is cell intrinsic and not due to effects of a secreted factor. Thus, the developmental pathway of CD4 T cells in the thymus plays a critical role in controlling an immune response by suppressing the generation of the Th17 lineage.

HIV Coreceptors and Their Roles in Leukocyte Trafficking During Neuroinflammatory Diseases

Due to the increasing resistance of HIV-1 to antiretroviral therapies, there has been much emphasis on the discovery and development of alternative therapeutics for HIV-1-infected individuals. The chemokine receptors CXCR4 (Bleul et al. 1996a; Feng et al. 1996; Nagasawa et al. 1996; Oberlin et al. 1996) and CCR5 (Alkhatib et al. 1996; Deng et al. 1996; Dragic et al. 1996) were identified as target molecules from the time their role as coreceptors for HIV-1 entry into leukocytes was first discovered 10 years ago. Initial studies focused on the use of the chemokine ligands, or altered derivatives, of CXCR4 and CCR5 to prevent the entrance of HIV-1 into immune cells (Schols 2006). While these studies showed some initial promise, there was evidence of significant caveats to their use, including selection of alternative coreceptor utilizing strains (Marechal et al. 1999; Mosier et al. 1999) and the potential to cause inflammatory side effects. These data prompted the development and study of small molecule inhibitors of CXCR4 and CCR5, which have also been used to examine the roles of these molecules in a variety of inflammatory and infectious diseases.

IL-1R signaling within the central nervous system regulates CXCL12 expression at the blood-brain barrier and disease severity during experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease of the CNS characterized by disruption of the blood-brain barrier (BBB). This breach in CNS immune privilege allows undeterred trafficking of myelin-specific lymphocytes into the CNS where they induce demyelination. Although the mechanism of BBB compromise is not known, the chemokine CXCL12 has been implicated as a molecular component of the BBB whose pattern of expression is specifically altered during MS and which correlates with disease severity. The inflammatory cytokine IL-1beta has recently been shown to contribute not only to BBB permeability but also to the development of IL-17-driven autoimmune responses. Using experimental autoimmune encephalomyelitis, the rodent model of MS, we demonstrate that IL-1beta mediates pathologic relocation of CXCL12 during the induction phase of the disease, before the development of BBB disruption. We also show that CD4, CD8, and, surprisingly gammadelta T cells are all sources of IL-1beta. In addition, gammadelta T cells are also targets of this cytokine, contributing to IL-1beta-mediated production of IL-17. Finally, we show that the level of CNS IL-1R determines the clinical severity of experimental autoimmune encephalomyelitis. These data suggest that T cell-derived IL-1beta contributes to loss of immune privilege during CNS autoimmunity via pathologic alteration in the expression of CXCL12 at the BBB.

Immunological and inflammatory functions of the interleukin-1 family

More than any other cytokine family, the interleukin (IL)-1 family is closely linked to the innate immune response. This linkage became evident upon the discovery that the cytoplasmic domain of the IL-1 receptor type I is highly homologous to the cytoplasmic domains of all Toll-like receptors (TLRs). Thus, fundamental inflammatory responses such as the induction of cyclooxygenase type 2, increased expression of adhesion molecules, or synthesis of nitric oxide are indistinguishable responses of both IL-1 and TLR ligands. Both families nonspecifically affect antigen recognition and lymphocyte function. IL-1beta is the most studied member of the IL-1 family because of its role in mediating autoinflammatory diseases. Although the TLR and IL-1 families evolved to assist in host defense against infection, unlike the TLR family, the IL-1 family also includes members that suppress inflammation, both specifically within the IL-1 family but also nonspecifically for TLR ligands and the innate immune response.

Immunogenetics of drug-induced skin blistering disorders. Part II: Synthesis

The overall immunopathogenesis relevant to a large series of disorders caused by a drug or its associated hyperimmune condition is discussed based upon examining the genetics of severe drug-induced bullous skin problems (sporadic idiosyncratic adverse events including Stevens–Johnson syndrome and Toxic epidermal necrolysis). New results from an exemplar study on shared precipitating and perpetuating inner causes with other related disease phenotypes including aphtous stomatitis, Behçets, erythema multiforme, Hashimoto’s thyroiditis, pemphigus, periodic fevers, Sweet’s syndrome and drug-induced multisystem hypersensitivity are presented. A call for a collaborative, wider demographic profiling and deeper immunotyping in suggested future work is made.

Alternate splicing of interleukin-1 receptor type II (IL1R2) in vitro correlates with clinical glucocorticoid responsiveness in patients with AIED

Autoimmune Inner Ear Disease (AIED) is poorly characterized clinically, with no definitive laboratory test. All patients suspected of having AIED are given glucocorticoids during periods of acute hearing loss, however, only half initially respond, and still fewer respond over time.

We hypothesized that AIED is a systemic autoimmune disease characterized by dysfunctional peripheral blood mononuclear cells (PBMC) responses to a unique cochlear antigen(s). To test this hypothesis, we examined end-stage AIED patients undergoing cochlear implant surgery and compared autologous perilymph stimulated PBMC from AIED patients to controls. We determined that autologous perilymph from AIED patients was unable to induce expression of a long membrane-bound Interleukin-1 Receptor Type II (mIL1R2) transcript in PBMC as compared with controls, despite similar expression of the short soluble IL1R2 (sIL1R2) transcript (p<0.05). IL1R2 is a molecular decoy that traps interleukin-1β (IL-1β) and does not initiate subsequent signaling events, thereby suppressing an inflammatory response. IL1R2 transcript length is regulated by alternate splicing, and the major inhibitory function is attributed to the full-length mIL1R2. In addition, IL1R2 expression is induced by dexamethasone.

Separately, we prospectively examined patients with newer onset glucocorticoid-responsive AIED. Immediately prior to clinical treatment for acute deterioration of hearing thresholds, their PBMC demonstrated a robust induction of mIL1R2 in PBMC in response to dexamethasone in vitro that correlated with a clinical response to prednisone in vivo (p<0.0001) as measured by hearing restoration. In contrast, clinically steroid unresponsive patients demonstrated high basal levels of mIL1R2 in their PBMC and only minimally augmented expression in response to dexamethasone. Thus, induced expression of mIL1R2 appears to be a protective mechanism in hearing homeostasis and warrants further investigation in a large prospective clinical trial to determine if IL1R2 can be used as a specific biomarker for AIED.

IL-17 promotes progression of cutaneous leishmaniasis in susceptible mice

Resistance to leishmaniasis in C57BL/6 mice depends on Th1/Tc1 cells. BALB/c mice preferentially develop Th2 immunity and succumb to infection. We now assessed the role of IL-17 in cutaneous leishmaniasis. During the course of Leishmania major infection, BALB/c CD4 cells and neutrophils produced increased amounts of IL-17 as compared with cells from C57BL/6 mice. This increase was associated with significantly increased IL-23 release from L. major-infected BALB/c dendritic cells (DC), whereas IL-6 and TGF-beta1 production by BALB/c and C57BL/6 DC were comparable. Interestingly, lesion sizes in infected IL-17-deficient BALB/c mice were dramatically smaller and failed to progress as compared with those in control mice. Similar amounts of IL-4, IL-10, and IFN-gamma were produced by T cells from IL-17-deficient mice and control mice consistent with development of Th2-predominant immunity in all animals. Improved disease outcome was associated with decreased CXCL2-accumulation in lesion sites and decreased neutrophil immigration into lesions of infected IL-17-deficient mice confirming prior observations that enhanced neutrophil recruitment contributes to disease susceptibility in BALB/c mice. This study excludes an important facilitating role for IL-17 in Th1/Th2 development in L. major-infected BALB/c mice, and suggests that IL-23 production by L. major-infected DC maintains IL-17(+) cells that influence disease progression via regulation of neutrophil recruitment.

Glatiramer acetate increases IL-1 receptor antagonist but decreases T cell-induced IL-1beta in human monocytes and multiple sclerosis

Mechanisms of action as well as cellular targets of glatiramer acetate (GA) in multiple sclerosis (MS) are still not entirely understood. IL-1beta is present in CNS-infiltrating macrophages and microglial cells and is an important mediator of inflammation in experimental autoimmune encephalitis (EAE), the MS animal model. A natural inhibitor of IL-1beta, the secreted form of IL-1 receptor antagonist (sIL-1Ra) improves EAE disease course. In this study we examined the effects of GA on the IL-1 system. In vivo, GA treatment enhanced sIL-1Ra blood levels in both EAE mice and patients with MS, whereas IL-1beta levels remained undetectable. In vitro, GA per se induced the transcription and production of sIL-1Ra in isolated human monocytes. Furthermore, in T cell contact-activated monocytes, a mechanism relevant to chronic inflammation, GA strongly diminished the expression of IL-1beta and enhanced that of sIL-1Ra. This contrasts with the effect of GA in monocytes activated upon acute inflammatory conditions. Indeed, in LPS-activated monocytes, IL-1beta and sIL-1Ra production were increased in the presence of GA. These results demonstrate that, in chronic inflammatory conditions, GA enhances circulating sIL-1Ra levels and directly affects monocytes by triggering a bias toward a less inflammatory profile, increasing sIL-1Ra while diminishing IL-1beta production. This study sheds light on a mechanism that is likely to participate in the therapeutic effects of GA in MS.

The roles of IL-17A in inflammatory immune responses and host defense against pathogens

T-helper 17 (Th17) cells are a newly discovered CD4(+) helper T-cell subset that produces interleukin-17A (IL-17A) and IL-17F. IL-17A plays important roles in allergic responses such as delayed-type hypersensitivity, contact hypersensitivity, and allergic airway inflammation. IL-17A promotes inflammation by inducing various proinflammatory cytokines and chemokines, recruiting neutrophils, enhancing antibody production, and activating T cells. IL-17A expression is also augmented in autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. Using mouse models of these diseases, we found that IL-17A plays a central role in their development. IL-6 is required for the development of Th17 cells and tumor necrosis factor functions downstream of IL-17A during the effector phase. IL-1 is important both for developing Th17 cells and eliciting inflammation. Th17 cells, like Th1 and Th2 cells, are involved in host defense against infections, but the contribution of these Th subsets to defense mechanisms differs among pathogens. The roles of IL-17F remain largely unknown. In this review, we introduce how IL-17A/IL-17F are involved in inflammatory immune responses and host defense mechanisms and discuss their relationship with other cytokines in the development of inflammatory and infectious diseases.

Dendritic cell IL-23 and IL-1 production in response to schistosome eggs induces Th17 cells in a mouse strain prone to severe immunopathology

Infection with schistosomes results in a CD4 T cell-mediated inflammatory reaction against parasite eggs that varies greatly in magnitude both in humans as well as in mice. In the murine disease, the severe form of immunopathology correlates with high levels of IL-17. We now report that live schistosome eggs stimulate dendritic cells from high pathology-prone CBA mice to produce IL-12p40, IL-6, and TGF-beta, whereas those from low pathology-prone BL/6 mice only make TGF-beta. Moreover, egg-stimulated dendritic cells plus naive CD4 T cells from CBA mice resulted in increased levels of IL-6, IL-23, IL-1beta, as well as IL-17 and the chemokines CXCL1, CXCL2, and CCL2, whereas similarly treated BL/6 cell cocultures instead expressed higher IL-4, IL-5, IL-10, and the transcription factor Foxp3. Neutralization of IL-23 and IL-1, but not of IL-6 or IL-21, profoundly inhibited egg-induced IL-17 production in the CBA cocultures. Conversely, stimulation with schistosome eggs in the presence of exogenous IL-23 and IL-1beta induced BL/6 cells to make IL-17. These findings identify IL-23 and IL-1 as critical host factors that drive IL-17 production, and suggest that parasite recognition followed by a genetically determined innate proinflammatory response induces the development of Th17 cells and thus controls the outcome of immunopathology in schistosomiasis.

Induction, function and regulation of IL-17-producing T cells

Recent reports have provided convincing evidence that IL-17-producing T cells play a key role in the pathogenesis of organ-specific autoimmune diseases, a function previously attributed exclusively to IFN-gamma-secreting Th1 cells. Furthermore, it appears that IL-17-producing T cells can also function with Th1 cells to mediate protective immunity to pathogens. Although much of the focus has been on IL-17-secreting CD4+ T cells, termed Th17 cells, CD8+ T cells, gammadelta T cells and NKT cells are also capable of secreting IL-17. The differentiation of Th17 cells from naïve T cells appears to involve signals from TGF-beta, IL-6, IL-21, IL-1beta and IL-23. Furthermore, IL-1alpha or IL-1beta in synergy with IL-23 can promote IL-17 secretion from memory T cells. The induction or function of Th17 cells is regulated by cytokines secreted by the other major subtypes of T cells, including IFN-gamma, IL-4, IL-10 and at high concentrations, TGF-beta. The main function of IL-17-secreting T cells is to mediate inflammation, by stimulating production of inflammatory cytokines, such as TNF-alpha, IL-1beta and IL-6, and inflammatory chemokines that promote the recruitment of neutrophils and macrophages.