K63-linked polyubiquitination of transcription factor IRF1 is essential for IL-1-induced production of chemokines CXCL10 and CCL5.

Although interleukin 1 (IL-1) induces expression of the transcription factor IRF1 (interferon-regulatory factor 1), the roles of IRF1 in immune and inflammatory responses and mechanisms of its activation remain elusive. Here we found that IRF1 was essential for IL-1-induced expression of the chemokines CXCL10 and CCL5, which recruit mononuclear cells into sites of sterile inflammation. Newly synthesized IRF1 acquired Lys63 (K63)-linked polyubiquitination mediated by the apoptosis inhibitor cIAP2 that was enhanced by the bioactive lipid S1P. In response to IL-1, cIAP2 and the sphingosine kinase SphK1 (the enzyme that generates S1P) formed a complex with IRF1, which led to its activation. Thus, IL-1 triggered a hitherto unknown signaling cascade that controlled the induction of IRF1-dependent genes that encode molecules important for sterile inflammation.

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.

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.

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.

Exploring the impact of tertiary lymphoid structures maturity in NSCLC: insights from TLS scoring.

Tertiary Lymphoid Structures (TLS) are lymphoid structures commonly associated with improved survival of cancer patients and response to immunotherapies. However, conflicting reports underscore the need to consider TLS heterogeneity and multiple features such as TLS size, composition, and maturation status, when assessing their functional impact. With the aim of gaining insights into TLS biology and evaluating the prognostic impact of TLS maturity in Non-Small Cell Lung Carcinoma (NSCLC), we developed a multiplex immunofluorescent (mIF) panel including T cell (CD3, CD8), B cell (CD20), Follicular Dendritic cell (FDC) (CD21, CD23) and mature dendritic cell (DC-LAMP) markers. We deployed this panel across a cohort of primary tumor resections from NSCLC patients (N=406) and established a mIF image analysis workstream to specifically detect TLS structures and evaluate the density of each cell phenotype. We assessed the prognostic significance of TLS size, number, and composition, to develop a TLS scoring system representative of TLS biology within a tumor. TLS relative area, (total TLS area divided by the total tumor area), was the most prognostic TLS feature (C-index: 0.54, p = 0.04). CD21 positivity was a marker driving the favorable prognostic impact, where CD21+ CD23- B cells (C-index: 0.57, p = 0.04) and CD21+ CD23- FDC (C-index: 0.58, p = 0.01) were the only prognostic cell phenotypes in TLS. Combining the three most robust prognostic TLS features: TLS relative area, the density of B cells, and FDC CD21+ CD23- we generated a TLS scoring system that demonstrated strong prognostic value in NSCLC when considering the effect of age, sex, histology, and smoking status. This TLS Score also demonstrated significant association with Immunoscore, EGFR mutational status and gene expression-based B-cell and TLS signature scores. It was not correlated with PD-L1 status in tumor cells or immune cells. In conclusion, we generated a prognostic TLS Score representative of the TLS heterogeneity and maturity undergoing within NSCLC tissues. This score could be used as a tool to explore how TLS presence and maturity impact the organization of the tumor microenvironment and support the discovery of spatial biomarker surrogates of TLS maturity, that could be used in the clinic.

The ATR inhibitor ceralasertib potentiates cancer checkpoint immunotherapy by regulating the tumor microenvironment.

The Ataxia telangiectasia and Rad3-related (ATR) inhibitor ceralasertib in combination with the PD-L1 antibody durvalumab demonstrated encouraging clinical benefit in melanoma and lung cancer patients who progressed on immunotherapy. Here we show that modelling of intermittent ceralasertib treatment in mouse tumor models reveals CD8+ T-cell dependent antitumor activity, which is separate from the effects on tumor cells. Ceralasertib suppresses proliferating CD8+ T-cells on treatment which is rapidly reversed off-treatment. Ceralasertib causes up-regulation of type I interferon (IFNI) pathway in cancer patients and in tumor-bearing mice. IFNI is experimentally found to be a major mediator of antitumor activity of ceralasertib in combination with PD-L1 antibody. Improvement of T-cell function after ceralasertib treatment is linked to changes in myeloid cells in the tumor microenvironment. IFNI also promotes anti-proliferative effects of ceralasertib on tumor cells. Here, we report that broad immunomodulatory changes following intermittent ATR inhibition underpins the clinical therapeutic benefit and indicates its wider impact on antitumor immunity.

Targeting microglia-mediated neurotoxicity: the potential of NOX2 inhibitors.

Microglia are key sentinels of central nervous system health, and their dysfunction has been widely implicated in the progressive nature of neurodegenerative diseases. While microglia can produce a host of factors that are toxic to neighboring neurons, NOX2 has been implicated as a common and essential mechanism of microglia-mediated neurotoxicity. Accumulating evidence indicates that activation of the NOX2 enzyme complex in microglia is neurotoxic, both through the production of extracellular reactive oxygen species that damage neighboring neurons as well as the initiation of redox signaling in microglia that amplifies the pro-inflammatory response. More specifically, evidence supports that NOX2 redox signaling enhances microglial sensitivity to pro-inflammatory stimuli, and amplifies the production of neurotoxic cytokines, to promote chronic and neurotoxic microglial activation. Here, we describe the evidence denoting the role of NOX2 in microglia-mediated neurotoxicity with an emphasis on Alzheimer's and Parkinson's disease, describe available inhibitors that have been tested, and detail evidence of the neuroprotective and therapeutic potential of targeting this enzyme complex to regulate microglia.

Neoadjuvant Durvalumab Alone or Combined with Novel Immuno-Oncology Agents in Resectable Lung Cancer: The Phase II NeoCOAST Platform Trial.

Neoadjuvant chemoimmunotherapy improves pathologic complete response rate and event-free survival in patients with resectable non-small cell lung cancer (NSCLC) versus chemotherapy alone. NeoCOAST was the first randomized, multidrug platform trial to examine novel neoadjuvant immuno-oncology combinations for patients with resectable NSCLC, using major pathologic response (MPR) rate as the primary endpoint. Eighty-three patients received a single cycle of treatment: 26 received durvalumab (anti-PD-L1) monotherapy, 21 received durvalumab plus oleclumab (anti-CD73), 20 received durvalumab plus monalizumab (anti-NKG2A), and 16 received durvalumab plus danvatirsen (anti-STAT3 antisense oligonucleotide). MPR rates were higher for patients in the combination arms versus durvalumab alone. Safety profiles for the combinations were similar to those of durvalumab alone. Multiplatform immune profiling suggested that improved MPR rates in the durvalumab plus oleclumab and durvalumab plus monalizumab arms were associated with enhanced effector immune infiltration of tumors, interferon responses and markers of tertiary lymphoid structure formation, and systemic functional immune cell activation. SIGNIFICANCE: A neoadjuvant platform trial can rapidly generate clinical and translational data using candidate surrogate endpoints like MPR. In NeoCOAST, patients with resectable NSCLC had improved MPR rates after durvalumab plus oleclumab or monalizumab versus durvalumab alone and tumoral transcriptomic signatures indicative of augmented immune cell activation and function. See related commentary by Cooper and Yu, p. 2306. This article is featured in Selected Articles from This Issue, p. 2293.

Air pollution & the brain: Subchronic diesel exhaust exposure causes neuroinflammation and elevates early markers of neurodegenerative disease.

BACKGROUND: Increasing evidence links diverse forms of air pollution to neuroinflammation and neuropathology in both human and animal models, but the effects of long-term exposures are poorly understood. OBJECTIVE: We explored the central nervous system consequences of subchronic exposure to diesel exhaust (DE) and addressed the minimum levels necessary to elicit neuroinflammation and markers of early neuropathology. METHODS: Male Fischer 344 rats were exposed to DE (992, 311, 100, 35 and 0 µg PM/m³) by inhalation over 6 months. RESULTS: DE exposure resulted in elevated levels of TNFα at high concentrations in all regions tested, with the exception of the cerebellum. The midbrain region was the most sensitive, where exposures as low as 100 µg PM/m³ significantly increased brain TNFα levels. However, this sensitivity to DE was not conferred to all markers of neuroinflammation, as the midbrain showed no increase in IL-6 expression at any concentration tested, an increase in IL-1ß at only high concentrations, and a decrease in MIP-1α expression, supporting that compensatory mechanisms may occur with subchronic exposure. Aß42 levels were the highest in the frontal lobe of mice exposed to 992 µg PM/m³ and tau [pS199] levels were elevated at the higher DE concentrations (992 and 311 µg PM/m³) in both the temporal lobe and frontal lobe, indicating that proteins linked to preclinical Alzheimer's disease were affected. α Synuclein levels were elevated in the midbrain in response to the 992 µg PM/m³ exposure, supporting that air pollution may be associated with early Parkinson's disease-like pathology. CONCLUSIONS: Together, the data support that the midbrain may be more sensitive to the neuroinflammatory effects of subchronic air pollution exposure. However, the DE-induced elevation of proteins associated with neurodegenerative diseases was limited to only the higher exposures, suggesting that air pollution-induced neuroinflammation may precede preclinical markers of neurodegenerative disease in the midbrain.

Characterization of the immune microenvironment of NSCLC by multispectral analysis of multiplex immunofluorescence images.

Multiplex immunofluorescence (MIF) staining of tumor sections combined with computational pathology quantifies phenotypic variants of tumor and immune cells and assesses their spatial relationships. Here, we discuss a MIF panel composed of cytokeratin, PD-L1, PD1, CD8, CD68, and Ki67 applied to non-small cell lung cancer (NSCLC) to demonstrate key components of the immune response to this cancer. We also describe a method of whole-slide multiplex imaging and digital multispectral image analysis. Key aspects of marker labeling and digital tissue and cellular classification are highlighted. We then illustrate how digital analysis can measure the spatial relationships among important cell types. This approach is presented in the context of a multidisciplinary team of scientists who together can optimize the combined methods to increase the impact of the study findings. Recommendations are provided to assist others to apply similar methods to further understand the immune response to NSCLC.

The Society for Immunotherapy of Cancer statement on best practices for multiplex immunohistochemistry (IHC) and immunofluorescence (IF) staining and validation.

OBJECTIVES: The interaction between the immune system and tumor cells is an important feature for the prognosis and treatment of cancer. Multiplex immunohistochemistry (mIHC) and multiplex immunofluorescence (mIF) analyses are emerging technologies that can be used to help quantify immune cell subsets, their functional state, and their spatial arrangement within the tumor microenvironment. METHODS: The Society for Immunotherapy of Cancer (SITC) convened a task force of pathologists and laboratory leaders from academic centers as well as experts from pharmaceutical and diagnostic companies to develop best practice guidelines for the optimization and validation of mIHC/mIF assays across platforms. RESULTS: Representative outputs and the advantages and disadvantages of mIHC/mIF approaches, such as multiplexed chromogenic IHC, multiplexed immunohistochemical consecutive staining on single slide, mIF (including multispectral approaches), tissue-based mass spectrometry, and digital spatial profiling are discussed. CONCLUSIONS: mIHC/mIF technologies are becoming standard tools for biomarker studies and are likely to enter routine clinical practice in the near future. Careful assay optimization and validation will help ensure outputs are robust and comparable across laboratories as well as potentially across mIHC/mIF platforms. Quantitative image analysis of mIHC/mIF output and data management considerations will be addressed in a complementary manuscript from this task force.

Automated Multiplex Immunofluorescence Panel for Immuno-oncology Studies on Formalin-fixed Carcinoma Tissue Specimens.

Continued developments in immuno-oncology require an increased understanding of the mechanisms of cancer immunology. The immunoprofiling analysis of tissue samples from formalin-fixed, paraffin-embedded (FFPE) biopsies has become a key tool for understanding the complexity of tumor immunology and discovering novel predictive biomarkers for cancer immunotherapy. Immunoprofiling analysis of tissues requires the evaluation of combined markers, including inflammatory cell subpopulations and immune checkpoints, in the tumor microenvironment. The advent of novel multiplex immunohistochemical methods allows for a more efficient multiparametric analysis of single tissue sections than does standard monoplex immunohistochemistry (IHC). One commercially available multiplex immunofluorescence (IF) method is based on tyramide-signal amplification and, combined with multispectral microscopic analysis, allows for a better signal separation of diverse markers in tissue. This methodology is compatible with the use of unconjugated primary antibodies that have been optimized for standard IHC on FFPE tissue samples. Herein we describe in detail an automated protocol that allows multiplex IF labeling of carcinoma tissue samples with a six-marker multiplex antibody panel comprising PD-L1, PD-1, CD68, CD8, Ki-67, and AE1/AE3 cytokeratins with 4',6-diamidino-2-phenylindole as a nuclear cell counterstain. The multiplex panel protocol is optimized in an automated IHC stainer for a staining time that is shorter than that of the manual protocol and can be directly applied and adapted by any laboratory investigator for immuno-oncology studies on human FFPE tissue samples. Also described are several controls and tools, including a drop-control method for fine quality control of a new multiplex IF panel, that are useful for the optimization and validation of the technique.

Atypical microglial response to biodiesel exhaust in healthy and hypertensive rats.

Accumulating evidence suggests a deleterious role for urban air pollution in central nervous system (CNS) diseases and neurodevelopmental disorders. Microglia, the resident innate immune cells and sentinels in the brain, are a common source of neuroinflammation and are implicated in air pollution-induced CNS effects. While renewable energy, such as soy-based biofuel, is of increasing public interest, there is little information on how soy biofuel may affect the brain, especially in people with preexisting disease conditions. To address this, male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats were exposed to 100% Soy-based Biodiesel Exhaust (100SBDE; 0, 50, 150 and 500µg/m3) by inhalation, 4h/day for 4 weeks (5 days/week). Ionized calcium-binding adapter molecule-1 (IBA-1) staining of microglia in the substantia nigra revealed significant changes in morphology with 100SBDE exposure in rats from both genotypes, where SHR were less sensitive. Aconitase activity was inhibited in the frontal cortex and cerebellum of WKY rats exposed to 100SBDE. No consistent changes occurred in pro-inflammatory cytokine expression, nitrated protein, or arginase1 expression in brain regions from either rat strain exposed to 100SBDE. However, while IBA-1 mRNA expression was not modified, CX3CR1 mRNA expression was lower in the striatum of 100SBDE exposed rats regardless of genotype, suggesting a downregulation of the fractalkine receptor on microglia in this brain region. Together, these data indicate that while microglia are detecting and responding to 100SBDE exposure with changes in morphology, there is reduced expression of CX3CR1 regardless of genetic background and the activation response is atypical without traditional inflammatory markers of M1 or M2 activation in the brain.

Potent suppression of arginase 1 expression in murine macrophages by low dose endotoxin.

Macrophages can respond to diverse signals and adopt multiple phenotypes. Although interleukin-4 (IL-4) is shown to potently induce the expression of arginase 1 and contribute to differentiation of macrophages to the anti-inflammatory M2 phenotype, other modulators may potentiate or reduce the effect of IL-4. In this report, we focus on the combinatorial effects of IL-4 with all-trans retinoic acid (ATRA) and lipopolysaccharide (LPS). ATRA has been shown to contribute to the resolution of inflammation, however it has not been linked to arginase 1 expression in macrophages. We demonstrate that although ATRA alone has no effect on the expression or activities of arginase 1, ATRA can dramatically potentiate the induction of arginase 1 by IL-4. On the other hand, high doses of LPS, such as those seen in septic shock, can induce the expression of both M1 and M2 mediators in macrophages. The effects of subclinical doses of LPS, which are prevalent in humans with adverse health conditions, on macrophage differentiation are not well studied. We demonstrate that low dose LPS can effectively suppress the expression of arginase 1 induced by IL-4 and ATRA. Mechanistically, we report that the interleukin-1 receptor-associated kinase 1 (IRAK-1) and Toll-interacting-protein (Tollip) are involved in the suppressive effect of low dose LPS. Our study reveals dynamic modulation of arginase 1 expression in macrophages by competing agonists, and bears relevance for potential intervention of chronic diseases.

Chronic apocynin treatment attenuates beta amyloid plaque size and microglial number in hAPP(751)(SL) mice.

BACKGROUND: NADPH oxidase is implicated in neurotoxic microglial activation and the progressive nature of Alzheimer's Disease (AD). Here, we test the ability of two NADPH oxidase inhibitors, apocynin and dextromethorphan (DM), to reduce learning deficits and neuropathology in transgenic mice overexpressing human amyloid precursor protein with the Swedish and London mutations (hAPP(751)(SL)). METHODS: Four month old hAPP(751)(SL) mice were treated daily with saline, 15 mg/kg DM, 7.5 mg/kg DM, or 10 mg/kg apocynin by gavage for four months. RESULTS: Only hAPP(751)(SL) mice treated with apocynin showed reduced plaque size and a reduction in the number of cortical microglia, when compared to the saline treated group. Analysis of whole brain homogenates from all treatments tested (saline, DM, and apocynin) demonstrated low levels of TNFα, protein nitration, lipid peroxidation, and NADPH oxidase activation, indicating a low level of neuroinflammation and oxidative stress in hAPP(751)(SL) mice at 8 months of age that was not significantly affected by any drug treatment. Despite in vitro analyses demonstrating that apocynin and DM ameliorate Aß-induced extracellular superoxide production and neurotoxicity, both DM and apocynin failed to significantly affect learning and memory tasks or synaptic density in hAPP(751)(SL) mice. To discern how apocynin was affecting plaque levels (plaque load) and microglial number in vivo, in vitro analysis of microglia was performed, revealing no apocynin effects on beta-amyloid (Aß) phagocytosis, microglial proliferation, or microglial survival. CONCLUSIONS: Together, this study suggests that while hAPP(751)(SL) mice show increases in microglial number and plaque load, they fail to exhibit elevated markers of neuroinflammation consistent with AD at 8 months of age, which may be a limitation of this animal model. Despite absence of clear neuroinflammation, apocynin was still able to reduce both plaque size and microglial number, suggesting that apocynin may have additional therapeutic effects independent of anti-inflammatory characteristics.

Diesel exhaust activates and primes microglia: air pollution, neuroinflammation, and regulation of dopaminergic neurotoxicity.

BACKGROUND: Air pollution is linked to central nervous system disease, but the mechanisms responsible are poorly understood. OBJECTIVES: Here, we sought to address the brain-region-specific effects of diesel exhaust (DE) and key cellular mechanisms underlying DE-induced microglia activation, neuroinflammation, and dopaminergic (DA) neurotoxicity. METHODS: Rats were exposed to DE (2.0, 0.5, and 0 mg/m3) by inhalation over 4 weeks or as a single intratracheal administration of DE particles (DEP; 20 mg/kg). Primary neuron-glia cultures and the HAPI (highly aggressively proliferating immortalized) microglial cell line were used to explore cellular mechanisms. RESULTS: Rats exposed to DE by inhalation demonstrated elevated levels of whole-brain IL-6 (interleukin-6) protein, nitrated proteins, and IBA-1 (ionized calcium-binding adaptor molecule 1) protein (microglial marker), indicating generalized neuroinflammation. Analysis by brain region revealed that DE increased TNFα (tumor necrosis factor-α), IL-1ß, IL-6, MIP-1α (macrophage inflammatory protein-1α) RAGE (receptor for advanced glycation end products), fractalkine, and the IBA-1 microglial marker in most regions tested, with the midbrain showing the greatest DE response. Intratracheal administration of DEP increased microglial IBA-1 staining in the substantia nigra and elevated both serum and whole-brain TNFα at 6 hr posttreatment. Although DEP alone failed to cause the production of cytokines and chemokines, DEP (5 µg/mL) pretreatment followed by lipopolysaccharide (2.5 ng/mL) in vitro synergistically amplified nitric oxide production, TNFα release, and DA neurotoxicity. Pretreatment with fractalkine (50 pg/mL) in vitro ameliorated DEP (50 µg/mL)-induced microglial hydrogen peroxide production and DA neurotoxicity. CONCLUSIONS: Together, these findings reveal complex, interacting mechanisms responsible for how air pollution may cause neuroinflammation and DA neurotoxicity.