The homeostatic function of Regnase-2 restricts neuroinflammation.

The precise physiological functions and mechanisms regulating RNase Regnase-2 (Reg-2/ZC3H12B/MCPIP2) activity remain enigmatic. We found that Reg-2 actively modulates neuroinflammation in nontransformed cells, including primary astrocytes. Downregulation of Reg-2 in these cells results in increased mRNA levels of proinflammatory cytokines IL-1ß and IL-6. In primary astrocytes, Reg-2 also regulates the mRNA level of Regnase-1 (Reg-1/ZC3H12A/MCPIP1). Reg-2 is expressed at high levels in the healthy brain, but its expression is reduced during neuroinflammation as well as glioblastoma progression. This process is associated with the upregulation of Reg-1. Conversely, overexpression of Reg-2 is accompanied by the downregulation of Reg-1 in glioma cells in a nucleolytic NYN/PIN domain-dependent manner. Interestingly, low levels of Reg-2 and high levels of Reg-1 correlate with poor-glioblastoma patients' prognoses. While Reg-2 restricts the basal levels of proinflammatory cytokines in resting astrocytes, its expression is reduced in IL-1ß-activated astrocytes. Following IL-1ß exposure, Reg-2 is phosphorylated, ubiquitinated, and degraded by proteasomes. Simultaneously, the Reg-2 transcript is destabilized by tristetraprolin (TTP) and Reg-1 through the AREs elements and conservative stem-loop structure present in its 3'UTR. Thus, the peer-control loop, of Reg-1 and Reg-2 opposing each other, exists. The involvement of TTP in Reg-2 mRNA turnover is confirmed by the observation that high TTP levels correlate with the downregulation of the Reg-2 expression in high-grade human gliomas. Additionally, obtained results reveal the importance of Reg-2 in inhibiting human and mouse glioma cell proliferation. Our current studies identify Reg-2 as a critical regulator of homeostasis in the brain.

Yin Yang 1 controls cerebellar astrocyte maturation.

Diverse subpopulations of astrocytes tile different brain regions to accommodate local requirements of neurons and associated neuronal circuits. Nevertheless, molecular mechanisms governing astrocyte diversity remain mostly unknown. We explored the role of a zinc finger transcription factor Yin Yang 1 (YY1) that is expressed in astrocytes. We found that specific deletion of YY1 from astrocytes causes severe motor deficits in mice, induces Bergmann gliosis, and results in simultaneous loss of GFAP expression in velate and fibrous cerebellar astrocytes. Single cell RNA-seq analysis showed that YY1 exerts specific effects on gene expression in subpopulations of cerebellar astrocytes. We found that although YY1 is dispensable for the initial stages of astrocyte development, it regulates subtype-specific gene expression during astrocyte maturation. Moreover, YY1 is continuously needed to maintain mature astrocytes in the adult cerebellum. Our findings suggest that YY1 plays critical roles regulating cerebellar astrocyte maturation during development and maintaining a mature phenotype of astrocytes in the adult cerebellum.

GAA deficiency disrupts distal airway cells in Pompe disease.

Pompe disease is an autosomal recessive glycogen storage disease caused by mutations in the gene that encodes acid alpha-glucosidase (GAA)-an enzyme responsible for hydrolyzing lysosomal glycogen. GAA deficiency results in systemic lysosomal glycogen accumulation and cellular disruption. Glycogen accumulation in skeletal muscles, motor neurons, and airway smooth muscle cells is known to contribute to respiratory insufficiency in Pompe disease. However, the impact of GAA deficiency on the distal alveolar type 1 and type 2 cells (AT1 and AT2) has not been evaluated. AT1 cells rely on lysosomes for cellular homeostasis so that they can maintain a thin barrier for gas exchange, whereas AT2 cells depend on lysosome-like structures (lamellar bodies) for surfactant production. Using a mouse model of Pompe disease, the Gaa-/- mouse, we investigated the consequences of GAA deficiency on AT1 and AT2 cells using histology, pulmonary function and mechanics, and transcriptional analysis. Histological analysis revealed increased accumulation of lysosomal-associated membrane protein 1 (LAMP1) in the Gaa-/- mice lungs. Furthermore, ultrastructural examination showed extensive intracytoplasmic vacuoles enlargement and lamellar body engorgement. Respiratory dysfunction was confirmed using whole body plethysmography and forced oscillometry. Finally, transcriptomic analysis demonstrated dysregulation of surfactant proteins in AT2 cells, specifically reduced levels of surfactant protein D in the Gaa-/- mice. We conclude that GAA enzyme deficiency leads to glycogen accumulation in the distal airway cells that disrupts surfactant homeostasis and contributes to respiratory impairments in Pompe disease.NEW & NOTEWORTHY This research highlights the impact of Pompe disease on distal airway cells. Prior to this work, respiratory insufficiency in Pompe disease was classically attributed to pathology in respiratory muscles and motor neurons. Using the Pompe mouse model, we note significant pathology in alveolar type 1 and 2 cells with reductions in surfactant protein D and disrupted surfactant homeostasis. These novel findings highlight the potential contributions of alveolar pathology to respiratory insufficiency in Pompe disease.

Cellular inhibitor of apoptosis 2 (cIAP2) restricts neuroinflammation during experimental autoimmune encephalomyelitis.

BACKGROUND: Immune activation, neuroinflammation, and cell death are the hallmarks of multiple sclerosis (MS), which is an autoimmune demyelinating disease of the central nervous system (CNS). It is well-documented that the cellular inhibitor of apoptosis 2 (cIAP2) is induced by inflammatory stimuli and regulates adaptive and innate immune responses, cell death, and the production of inflammatory mediators. However, the impact of cIAP2 on neuroinflammation associated with MS and disease severity remains unknown. METHODS: We used experimental autoimmune encephalomyelitis (EAE), a widely used mouse model of MS, to assess the effect of cIAP2 deletion on disease outcomes. We performed a detailed analysis on the histological, cellular, and molecular levels. We generated and examined bone-marrow chimeras to identify the cIAP2-deficient cells that are critical to the disease outcomes. RESULTS: cIAP2-/- mice exhibited increased EAE severity, increased CD4+ T cell infiltration, enhanced proinflammatory cytokine/chemokine expression, and augmented demyelination. This phenotype was driven by cIAP2-deficient non-hematopoietic cells. cIAP2 protected oligodendrocytes from cell death during EAE by limiting proliferation and activation of brain microglia. This protective role was likely exerted by cIAP2-mediated inhibition of the non-canonical NLRP3/caspase-8-dependent myeloid cell activation during EAE. CONCLUSIONS: Our findings suggest that cIAP2 is needed to modulate neuroinflammation, cell death, and survival during EAE. Significantly, our data demonstrate the critical role of cIAP2 in limiting the activation of microglia during EAE, which could be explored for developing MS therapeutics in the future.

RelB controls adaptive responses of astrocytes during sterile inflammation.

In response to brain injury or infections, astrocytes become reactive, undergo striking morphological and functional changes, and secrete and respond to a spectrum of inflammatory mediators. We asked whether reactive astrocytes also display adaptive responses during sterile IL-1ß-induced neuroinflammation, which may limit tissue injury associated with many disorders of the central nervous system. We found that astrocytes display days-to-weeks long specific tolerance of cytokine genes, which is coordinated by NF-κB family member, RelB. However, in contrast to innate immune cells, astrocytic tolerance does not involve epigenetic silencing of the cytokine genes. Establishment of tolerance depends on persistent higher levels of RelB in tolerant astrocytes and its phosphorylation on serine 472. Mechanistically, this phosphorylation prevents efficient removal of RelB from cytokine promoters by IκBα and helps to establish tolerance. Importantly, ablation of RelB from astrocytes in mice abolishes tolerance during experimental neuroinflammation in vivo.

A detrimental role of RelB in mature oligodendrocytes during experimental acute encephalomyelitis.

BACKGROUND: Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system (CNS). It is firmly established that overactivation of the p65 (RelA) nuclear factor kappa B (NF-κB) transcription factor upregulates expression of inflammatory mediators in both immune and non-immune resident CNS cells and promotes inflammation during MS. In contrast to p65, NF-κB family member RelB regulates immune cell development and can limit inflammation. Although RelB expression is induced during inflammation in the CNS, its role in MS remains unknown. METHODS: To examine the role of RelB in non-immune CNS cells, we generated mice with RelB specifically deleted in astrocytes (RelBΔAST), oligodendrocytes (RelBΔOLIGO), or neural progenitor-derived cells (RelBΔNP). We used experimental autoimmune encephalomyelitis (EAE), an accepted mouse model of MS, to assess the effect of RelB deletion on disease outcomes and performed analysis on the histological, cellular, and molecular level. RESULTS: Despite being a negative regulator of inflammation, conditional knockout of RelB in non-immune resident CNS cells surprisingly decreased the severity of EAE. This protective effect was recapitulated by conditional deletion of RelB in oligodendrocytes but not astrocytes. Deletion of RelB in oligodendrocytes reduced disease severity, promoted survival of mature oligodendrocytes, and correlated with increased activation of p65 NF-κB. CONCLUSIONS: These findings suggest that RelB fine tunes inflammation and cell death/survival during EAE. Importantly, our data points out the detrimental role RelB plays in controlling survival of mature oligodendrocytes, which could be explored as a viable option to treat MS in the future.

RelB/p50 complexes regulate cytokine-induced YKL-40 expression.

The secreted protein, YKL-40, has been proposed as a biomarker of a variety of human diseases characterized by ongoing inflammation, including chronic neurologic pathologies such as multiple sclerosis and Alzheimer's disease. However, inflammatory mediators and the molecular mechanism responsible for enhanced expression of YKL-40 remained elusive. Using several mouse models of inflammation, we now show that YKL-40 expression correlated with increased expression of both IL-1 and IL-6. Furthermore, IL-1 together with IL-6 or the IL-6 family cytokine, oncostatin M, synergistically upregulated YKL-40 expression in both primary human and mouse astrocytes in vitro. The robust cytokine-driven expression of YKL-40 in astrocytes required both STAT3 and NF-κB binding elements of the YKL-40 promoter. In addition, YKL-40 expression was enhanced by constitutively active STAT3 and inhibited by dominant-negative IκBα. Surprisingly, cytokine-driven expression of YKL-40 in astrocytes was independent of the p65 subunit of NF-κB and instead required subunits RelB and p50. Mechanistically, we show that IL-1-induced RelB/p50 complex formation was further promoted by oncostatin M and that these complexes directly bound to the YKL-40 promoter. Moreover, we found that expression of RelB was strongly upregulated during inflammation in vivo and by IL-1 in astrocytes in vitro. We propose that IL-1 and the IL-6 family of cytokines regulate YKL-40 expression during sterile inflammation via both STAT3 and RelB/p50 complexes. These results suggest that IL-1 may regulate the expression of specific anti-inflammatory genes in nonlymphoid tissues via the canonical activation of the RelB/p50 complexes.

ORMDL proteins regulate ceramide levels during sterile inflammation.

The bioactive sphingolipid metabolite, ceramide, regulates physiological processes important for inflammation and elevated levels of ceramide have been implicated in IL-1-mediated events. Although much has been learned about ceramide generation by activation of sphingomyelinases in response to IL-1, the contribution of the de novo pathway is not completely understood. Because yeast ORM1 and ORM2 proteins negatively regulate ceramide levels through inhibition of serine palmitoyltransferase, the first committed step in ceramide biosynthesis, we examined the functions of individual mammalian ORM orthologs, ORM (yeast)-like (ORMDL)1-3, in regulation of ceramide levels. In HepG2 liver cells, downregulation of ORMDL3 markedly increased the ceramide precursors, dihydrosphingosine and dihydroceramide, primarily from de novo biosynthesis based on [U-(13)C]palmitate incorporation into base-labeled and dual-labeled dihydroceramides, whereas downregulation of each isoform increased dihydroceramides [(13)C]labeled in only the amide-linked fatty acid. IL-1 and the IL-6 family cytokine, oncostatin M, increased dihydroceramide and ceramide levels in HepG2 cells and concomitantly decreased ORMDL proteins. Moreover, during irritant-induced sterile inflammation in mice leading to induction of the acute-phase response, which is dependent on IL-1, expression of ORMDL proteins in the liver was strongly downregulated and accompanied by increased ceramide levels in the liver and accumulation in the blood. Together, our results suggest that ORMDLs may be involved in regulation of ceramides during IL-1-mediated sterile inflammation.

Sphingosine-1-phosphate inhibits IL-1-induced expression of C-C motif ligand 5 via c-Fos-dependent suppression of IFN-ß amplification loop.

The neuroinflammation associated with multiple sclerosis involves activation of astrocytes that secrete and respond to inflammatory mediators such as IL-1. IL-1 stimulates expression of many chemokines, including C-C motif ligand (CCL) 5, that recruit immune cells, but it also stimulates sphingosine kinase-1, an enzyme that generates sphingosine-1-phosphate (S1P), a bioactive lipid mediator essential for inflammation. We found that whereas S1P promotes IL-1-induced expression of IL-6, it inhibits IL-1-induced CCL5 expression in astrocytes. This inhibition is mediated by the S1P receptor (S1PR)-2 via an inhibitory G-dependent mechanism. Consistent with this surprising finding, infiltration of macrophages into sites of inflammation increased significantly in S1PR2(-/-) animals. However, activation of NF-κB, IFN regulatory factor-1, and MAPKs, all of which regulate CCL5 expression in response to IL-1, was not diminished by the S1P in astrocytes. Instead, S1PR2 stimulated inositol 1,4,5-trisphosphate-dependent Ca(++) release and Elk-1 phosphorylation and enhanced c-Fos expression. In our study, IL-1 induced the IFNß production that supports CCL5 expression. An intriguing finding was that S1P induced c-Fos-inhibited CCL5 directly and also indirectly through inhibition of the IFN-ß amplification loop. We propose that in addition to S1PR1, which promotes inflammation, S1PR2 mediates opposing inhibitory functions that limit CCL5 expression and diminish the recruitment of immune cells.

Respiratory pathology in the TDP-43 transgenic mouse model of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in death within 2-5 years of diagnosis. Respiratory failure is the most common cause of death in ALS. Mutations in the transactive response DNA binding protein 43 (TDP-43) encoded by the TARDBP gene are associated with abnormal cellular aggregates in neurons of patients with both familial and sporadic ALS. The role of these abnormal aggregates on breathing is unclear. Since respiratory failure is a major cause of death in ALS, we sought to determine the role of TDP-43 mutations on the respiratory motor unit in the Prp-hTDP-43A315T mouse model - a model that expresses human TDP-43 containing the A315T mutation. We assessed breathing using whole-body plethysmography, and investigated neuropathology in hypoglossal and phrenic respiratory motor units. Postmortem studies included quantification of hypoglossal and putative phrenic motor neurons, activated microglia and astrocytes in respiratory control centers, and assessment of hypoglossal and phrenic nerves of TDP43A315T mice. The male TDP43A315T mice display an early onset of rapid progression of disease, and premature death (less than 15 weeks) compared to control mice and compared to female TDP43A315T mice who die between 20 and 35 weeks of age. The TDP43A315T mice have progressive and profound breathing deficits at baseline and during a respiratory challenge. Histologically, hypoglossal and putative phrenic motor neurons of TDP43A315T mice are decreased and have increased microglial and astrocyte activation, indicating pronounced neurodegeneration and neuroinflammation. Further, there is axonopathy and demyelination in the hypoglossal and phrenic nerve of TDP43A315T mice. Thus, the TDP-43A315T mice have significant respiratory pathology and neuropathology, which makes them a useful translatable model for the study of novel therapies on breathing in ALS.

Respiratory characterization of a humanized Duchenne muscular dystrophy mouse model.

Duchenne muscular dystrophy (DMD) is the most common X-linked disease. DMD is caused by a lack of dystrophin, a critical structural protein in striated muscle. Dystrophin deficiency leads to inflammation, fibrosis, and muscle atrophy. Boys with DMD have progressive muscle weakness within the diaphragm that results in respiratory failure in the 2nd or 3rd decade of life. The most common DMD mouse model - the mdx mouse - is not sufficient for evaluating genetic medicines that specifically target the human DMD (hDMD) gene sequence. Therefore, a novel transgenic mouse carrying the hDMD gene with an exon 52 deletion was created (hDMDΔ52;mdx). We characterized the respiratory function and pathology in this model using whole body plethysmography, histology, and immunohistochemistry. At 6-months-old, hDMDΔ52;mdx mice have reduced maximal respiration, neuromuscular junction pathology, and fibrosis throughout the diaphragm, which worsens at 12-months-old. In conclusion, the hDMDΔ52;mdx exhibits moderate respiratory pathology, and serves as a relevant animal model to study the impact of novel genetic therapies, including gene editing, on respiratory function.

Respiratory neuropathology in spinocerebellar ataxia type 7.

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant neurological disorder caused by deleterious CAG repeat expansion in the coding region of the ataxin 7 gene (polyQ-ataxin-7). Infantile-onset SCA7 leads to severe clinical manifestation of respiratory distress, but the exact cause of respiratory impairment remains unclear. Using the infantile-SCA7 mouse model, the SCA7266Q/5Q mouse, we examined the impact of pathological polyQ-ataxin-7 on hypoglossal (XII) and phrenic motor units. We identified the transcript profile of the medulla and cervical spinal cord and investigated the XII and phrenic nerves and the neuromuscular junctions in the diaphragm and tongue. SCA7266Q/5Q astrocytes showed significant intranuclear inclusions of ataxin-7 in the XII and putative phrenic motor nuclei. Transcriptomic analysis revealed dysregulation of genes involved in amino acid and neurotransmitter transport and myelination. Additionally, SCA7266Q/5Q mice demonstrated blunted efferent output of the XII nerve and demyelination in both XII and phrenic nerves. Finally, there was an increased number of neuromuscular junction clusters with higher expression of synaptic markers in SCA7266Q/5Q mice compared with WT controls. These preclinical findings elucidate the underlying pathophysiology responsible for impaired glial cell function and death leading to dysphagia, aspiration, and respiratory failure in infantile SCA7.

Neuro-respiratory pathology in spinocerebellar ataxia.

The spinocerebellar ataxias (SCA) are a heterogeneous group of neurodegenerative disorders with an autosomal dominant inheritance. Symptoms include poor coordination and balance, peripheral neuropathy, impaired vision, incontinence, respiratory insufficiency, dysphagia, and dysarthria. Although many patients with SCA have respiratory-related complications, the exact mechanism and extent of this pathology remain unclear. This review aims to provide an update on the recent clinical and preclinical scientific findings on neuropathology causing respiratory insufficiency in SCA.

What's new and what's next for gene therapy in Pompe disease?

INTRODUCTION: Pompe disease is an autosomal recessive disorder caused by a deficiency of acid-α-glucosidase (GAA), an enzyme responsible for hydrolyzing lysosomal glycogen. A lack of GAA leads to accumulation of glycogen in the lysosomes of cardiac, skeletal, and smooth muscle cells, as well as in the central and peripheral nervous system. Enzyme replacement therapy has been the standard of care for 15 years and slows disease progression, particularly in the heart, and improves survival. However, there are limitations of ERT success, which gene therapy can overcome. AREAS COVERED: Gene therapy offers several advantages including prolonged and consistent GAA expression and correction of skeletal muscle as well as the critical CNS pathology. We provide a systematic review of the preclinical and clinical outcomes of adeno-associated viral mediated gene therapy and alternative gene therapy strategies, highlighting what has been successful. EXPERT OPINION: Although the preclinical and clinical studies so far have been promising, barriers exist that need to be addressed in gene therapy for Pompe disease. New strategies including novel capsids for better targeting, optimized DNA vectors, and adjuctive therapies will allow for a lower dose, and ameliorate the immune response.

Respiratory dysfunction in a mouse model of spinocerebellar ataxia type 7.

Spinocerebellar ataxia type 7 (SCA7) is an autosomal-dominant neurodegenerative disorder caused by a CAG repeat expansion in the coding region of the ataxin-7 gene. Infantile-onset SCA7 patients display extremely large repeat expansions (>200 CAGs) and exhibit progressive ataxia, dysarthria, dysphagia and retinal degeneration. Severe hypotonia, aspiration pneumonia and respiratory failure often contribute to death in affected infants. To better understand the features of respiratory and upper airway dysfunction in SCA7, we examined breathing and putative phrenic and hypoglossal neuropathology in a knock-in mouse model of early-onset SCA7 carrying an expanded allele with 266 CAG repeats. Whole-body plethysmography was used to measure awake spontaneously breathing SCA7-266Q knock-in mice at baseline in normoxia and during a hypercapnic/hypoxic respiratory challenge at 4 and 8 weeks, before and after the onset of disease. Postmortem studies included quantification of putative phrenic and hypoglossal motor neurons and microglia, and analysis of ataxin-7 aggregation at end stage. SCA7-266Q mice had profound breathing deficits during a respiratory challenge, exhibiting reduced respiratory output and a greater percentage of time in apnea. Histologically, putative phrenic and hypoglossal motor neurons of SCA7 mice exhibited a reduction in number accompanied by increased microglial activation, indicating neurodegeneration and neuroinflammation. Furthermore, intranuclear ataxin-7 accumulation was observed in cells neighboring putative phrenic and hypoglossal motor neurons in SCA7 mice. These findings reveal the importance of phrenic and hypoglossal motor neuron pathology associated with respiratory failure and upper airway dysfunction, which are observed in infantile-onset SCA7 patients and likely contribute to their early death.

Respiratory pathology in the Optn-/- mouse model of Amyotrophic Lateral Sclerosis.

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder that results in death due to respiratory failure. Many genetic defects are associated with ALS; one such defect is a mutation in the gene encoding optineurin (OPTN). Using an optineurin null mouse (Optn-/-), we sought to characterize the impact of optineurin deficiency on respiratory neurodegeneration. Respiratory function was assessed at 6 and 12 mo of age using whole body plethysmography at baseline during normoxia (FiO2: 0.21; N2 balance) and during a respiratory challenge with hypoxia and hypercapnia (FiCO2: 0.07, FiO2: 0.10; N2 balance). Histological analyses to assess motor neuron viability and respiratory nerve integrity were performed in the medulla, cervical spinal cord, hypoglossal nerve, and phrenic nerve. Minute ventilation, peak inspiratory flow, and peak expiratory flow are significantly reduced during a respiratory challenge in 6 mo Optn-/-mice. By 12 mo, tidal volume is also significantly reduced in Optn-/- mice. Furthermore, 12mo Optn-/- mice exhibit hypoglossal motor neuron loss, phrenic and hypoglossal dysmyelination, and accumulated mitochondria in the hypoglossal nerve axons. Overall, these data indicate that Optn-/- mice display neurodegenerative respiratory dysfunction and are a useful model to study the impact of novel therapies on respiratory function for optineurin-deficient ALS patients.

Pattern Recognition Receptors in Multiple Sclerosis and Its Animal Models.

Pattern recognition receptors (PRRs) coordinate the innate immune response and have a significant role in the development of multiple sclerosis (MS). Accumulating evidence has identified both pathogenic and protective functions of PRR signaling in MS and its animal model, experimental autoimmune encephalomyelitis (EAE). Additionally, evidence for PRR signaling in non-immune cells and PRR responses to host-derived endogenous ligands has also revealed new pathways controlling the development of CNS autoimmunity. Many PRRs remain uncharacterized in MS and EAE, and understanding the distinct triggers and functions of PRR signaling in CNS autoimmunity requires further investigation. In this brief review, we discuss the diverse pathogenic and protective functions of PRRs in MS and EAE, and highlight major avenues for future research.

RelB acts as a molecular switch driving chronic inflammation in glioblastoma multiforme.

Glioblastoma multiforme (GBM) is a primary brain tumor characterized by extensive necrosis and immunosuppressive inflammation. The mechanisms by which this inflammation develops and persists in GBM remain elusive. We identified two cytokines interleukin-1ß (IL-1) and oncostatin M (OSM) that strongly negatively correlate with patient survival. We found that these cytokines activate RelB/p50 complexes by a canonical NF-κB pathway, which surprisingly drives expression of proinflammatory cytokines in GBM cells, but leads to their inhibition in non-transformed astrocytes. We discovered that one allele of the gene encoding deacetylase Sirtuin 1 (SIRT1), needed for repression of cytokine genes, is deleted in 80% of GBM tumors. Furthermore, RelB specifically interacts with a transcription factor Yin Yang 1 (YY1) in GBM cells and activates GBM-specific gene expression programs. As a result, GBM cells continuously secrete proinflammatory cytokines and factors attracting/activating glioma-associated microglia/macrophages and thus, promote a feedforward inflammatory loop.