Oxidized phospholipid inhibition of toll-like receptor (TLR) signaling is restricted to TLR2 and TLR4: roles for CD14, LPS-binding protein, and MD2 as targets for specificity of inhibition

Impact of oxidized phosphatidylcholine supplementation on the lipidome of RAW264.7 macrophages

Oxidized phospholipids (OxPLs) have emerged as critical damage-associated molecular patterns (DAMPs) and modulators of numerous biological processes, including inflammation, playing a significant role in health and disease. Despite their recognized influence on macrophage polarization, the precise mechanisms by which distinct OxPL species shape macrophage behavior remains poorly understood. The present study investigates the impact of two oxidized phosphatidylcholines (OxPC): omega 3 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphatidylcholine (OxPC22:6), and omega 6 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphatidylcholine (OxPC18:2), on the lipidomic profile of RAW264.7 macrophages, through an LC-MS lipidomic analysis. Our findings demonstrate that the OxPCs under study modulate macrophage lipidome differently, highlighting the significance of the sn-2 acyl chain composition for their biological function. When administered alone, neither of the OxPCs induced a pro-inflammatory phenotype in macrophages. OxPC22:6 appears to induce a preparatory pro-inflammatory state in macrophages, improving their subsequent inflammatory responses, while OxPC18:2 seems to induce a resting state on macrophages. Under LPS stimulation, both OxPCs were found to selectively attenuate certain LPS-driven lipidomic changes (PC.O, PC.P, PI.P, PE.P) while amplifying others (DG, Cer, LPC, PE.O, PI.O, TG, PC, PI) and introducing unique alterations to the macrophage lipidome (SM, PE, LPE). Core lipidomic changes, crucial for macrophages' LPS response, were identified, with sustained elevation of TG, DG, Cer, PC, LPC, and PI.O and reduction of PE.O, PI, and CAR. These observations suggest that, in the presence of LPS, mainly OxPC22:6 amplifies the pro-inflammatory lipidomic signature of macrophages. Further research is needed to clarify whether the observed lipidomic adaptations improve, impair, or inhibit macrophages' inflammatory capacities and response.

LPS binding caspase activation and recruitment domains (CARDs) are bipartite lipid binding modules

Caspase-11 is an innate immune pattern recognition receptor (PRR) that detects cytosolic bacterial lipopolysaccharides (LPS) through its caspase activation and recruitment domain (CARD). Caspase-11 also detects eukaryotic (i.e., self) lipids. This observation raises the question of whether common or distinct mechanisms govern caspase interactions with self- and nonself-lipids. In this study, using biochemical, computational, and cell-based assays, we report that the caspase-11 CARD functions as a bipartite lipid-binding module. Distinct regions within the CARD bind to phosphate groups and long acyl chains of self- and nonself-lipids. Self-lipid binding capability is conserved across numerous caspase-11 homologs and orthologs. The symmetry in self- and nonself-lipid detection mechanisms enabled us to engineer an LPS-binding domain de novo, using an ancestral CARD-like domain present in the fish Amphilophus citrinellus. These findings offer insights into the molecular basis of LPS recognition by caspase-11 and highlight the fundamental and likely inseparable relationship between self and nonself discrimination.

Class B Scavenger Receptor CD36 as a Potential Therapeutic Target in Inflammation Induced by Danger-Associated Molecular Patterns

The class B scavenger receptor CD36 is known to bind and mediate the transport of lipid-related ligands and it functions as a pattern recognition receptor (PRR) for a variety of pathogens, including bacteria and viruses. In this study, we assessed CD36's role as a PRR mediating pro-inflammatory effects of several known Danger-Associated Molecular Patterns (DAMPs) used either as a single preparation or as a combination of DAMPs in the form of total cell/skeletal muscle tissue lysates. Our data demonstrated that multiple DAMPs, including HMGB1, HSPs, histone H3, SAA, and oxPAPC, as well as cell/tissue lysate preparations, induced substantially higher (~7-10-fold) IL-8 cytokine responses in HEK293 cells overexpressing CD36 compared to control WT cells. At the same time, DAMP-induced secretion of IL-6 in bone marrow-derived macrophages (BMDM) from CD36-/- mice was markedly (~2-3 times) reduced, as compared to macrophages from normal mice. Synthetic amphipathic helical peptides (SAHPs), known CD36 ligands, efficiently blocked CD36-dependent inflammatory responses induced by both cell and tissue lysates, HMGB1 and histone H3 in CD36+ cells. IP injection of total cellular lysate preparation induced inflammatory responses that were assessed by the expression of liver and lung pro-inflammatory markers, including IL-6, TNF-α, CD68, and CXCL1, and was reduced by ~50% in CD36-deficient mice compared to normal mice. Our findings demonstrate that CD36 is a PRR contributing to the innate immune response via mediating DAMP-induced inflammatory signaling and highlight the importance of this receptor as a potential therapeutic target in DAMP-associated inflammatory conditions.

LPS binding caspase activation and recruitment domains (CARDs) are bipartite lipid binding modules

Caspase-11 is an innate immune pattern recognition receptor (PRR) that detects cytosolic bacterial lipopolysaccharides (LPS) through its caspase activation and recruitment domain (CARD), triggering inflammatory cell death known as pyroptosis. Caspase-11 also detects eukaryotic (i.e. self) lipids. This observation raises the question of whether common or distinct mechanisms govern the interactions with self and nonself lipids. In this study, using biochemical, computational, and cell-based assays, we report that the caspase-11 CARD functions as a bipartite lipid-binding module. Distinct regions within the CARD bind to phosphate groups and long acyl chains of self and nonself lipids. Self-lipid binding capability is conserved across numerous caspase-11 homologs and orthologs. The symmetry in self and nonself lipid detection mechanisms enabled us to engineer an LPS-binding domain de novo, using an ancestral CARD-like domain present in the fish Amphilophus citrinellus. These findings offer critical insights into the molecular basis of LPS recognition by caspase-11 and highlight the fundamental and likely inseparable relationship between self and nonself discrimination.

The non-enzymatic oxidation of phosphatidylethanolamine and phosphatidylserine and their intriguing roles in inflammation dynamics and diseases

Phosphatidylethanolamine (PE) and phosphatidylserine (PS), along with phosphatidylcholine (PC), are key phospholipids (PL) in cell membranes and lipoproteins, prone to oxidative modifications. Their oxidized forms, OxPE and OxPS, play significant roles in inflammation and immune response. This review explores their structural oxidative changes under non-enzymatic conditions and their roles in physiological and pathological contexts, influencing inflammation, and immunity. Specific oxidations of PE and PS significantly alter their physicochemical properties, leading to enhanced biological functions, reduced activity, or inactivation. OxPE may show pro-inflammatory actions, similar to well-documented OxPC, while the OxPS pro-inflammatory effects are less noted. However, OxPS and OxPE have also shown an antagonistic effect against lipopolysaccharides (LPS), suggesting a protective role against exacerbated immune responses, similar to OxPC. Further research is needed to deepen our understanding of these less-studied OxPL classes. The role of OxPE and OxPS in disease pathogenesis remains largely unexplored, with limited studies linking them to Alzheimer's disease, diabetes, rheumatoid arthritis, traumatic brain injury, and skin inflammation. These findings highlight the potential of OxPE and OxPS as biomarkers for disease diagnosis, monitoring, and therapeutic targeting.

Analysis of oxidized glucosylceramide and its effects on altering gene expressions of inflammation induced by LPS in intestinal tract cell models

Glucosylceramide (GlcCer) belongs to sphingolipids and is found naturally in plant foods and other sources that humans consume daily. Our previous studies demonstrated that GlcCer prevents inflammatory bowel disease both in vitro and in vivo, whose patients are increasing alarmingly. Although some lipids are vulnerable to oxidation which changes their structure and activities, it is unknown whether oxidative modification of GlcCer affects its activity. In this research, we oxidized GlcCer in the presence of a photosensitizer, analyzed the oxide by mass spectrometric techniques, and examined its anti-inflammatory activity in lipopolysaccharide (LPS)-treated differentiated Caco-2 cells as in vitro model of intestinal inflammation. The results showed that GlcCer is indeed oxidized, producing GlcCer hydroperoxide (GlcCerOOH) as a primary oxidation product. We also found that oxidized GlcCer preserves beneficial functions of GlcCer, suppressing inflammatory-related gene expressions. These findings suggested that GlcCerOOH may perform as an LPS recognition antagonist to discourage inflammation rather than induce inflammation.

Host-derived oxidized phospholipids initiate effector-triggered immunity fostering lethality upon microbial encounter

Macrophages detect invading microorganisms via pattern recognition receptors that recognize pathogen-associated molecular patterns, or via sensing the activity of virulence factors that initiates effector-triggered immunity (ETI). Tissue damage that follows pathogen encounter leads to the release of host-derived factors that participate to inflammation. How these self-derived molecules are sensed by macrophages and their impact on immunity remain poorly understood. Here we demonstrate that, in mice and humans, host-derived oxidized phospholipids (oxPLs) are formed upon microbial encounter. oxPL blockade restricts inflammation and prevents the death of the host, without affecting pathogen burden. Mechanistically, oxPLs bind and inhibit AKT, a master regulator of immunity and metabolism. AKT inhibition potentiates the methionine cycle, and epigenetically dampens Il10, a pluripotent anti-inflammatory cytokine. Overall, we found that host-derived inflammatory cues act as "self" virulence factors that initiate ETI and that their activity can be targeted to protect the host against excessive inflammation upon microbial encounter.

SARS-CoV-2 activates the TLR4/MyD88 pathway in human macrophages: A possible correlation with strong pro-inflammatory responses in severe COVID-19

Background

Toll-like receptors (TLRs) play a pivotal role in the immunologic response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Exaggerated inflammatory response of innate immune cells, however, may drive morbidity and death in Coronavirus disease 19 (COVID-19).

Objective

We investigated the engagement of SARS-CoV-2 with TLR4 in order to better understand how to tackle hyperinflammation in COVID-19.

Methods

We combined RNA-sequencing data of human lung tissue and of bronchoalveolar lavage fluid cells derived from COVID-19 patients with functional studies in human macrophages using SARS-CoV-2 spike proteins and viable SARS-CoV-2. Pharmacological inhibitors as well as gene editing with CRISPR/Cas9 were used to delineate the signalling pathways involved.

Results

We found TLR4 to be the most abundantly upregulated TLR in human lung tissue irrespective of the underlying pathology. Accordingly, bronchoalveolar lavage fluid cells from patients with severe COVID-19 showed an NF-κB-pathway dominated immune response, whereas they were mostly defined by type I interferon signalling in moderate COVID-19. Mechanistically, we found the Spike ectodomain, but not receptor binding domain monomer to induce TLR4-dependent inflammation in human macrophages. By using pharmacological inhibitors as well as CRISPR/Cas9 deleted macrophages, we identify SARS-CoV-2 to engage canonical TLR4-MyD88 signalling. Importantly, we demonstrate that TLR4 blockage prevents exaggerated inflammatory responses in human macrophages infected with different SARS-CoV-2 variants, including immune escape variants B.1.1.7.-E484K and B.1.1.529 (omicron).

Conclusion

Our study critically extends the current knowledge on TLR-mediated hyperinflammatory responses to SARS-CoV-2 in human macrophages, paving the way for novel approaches to tackle severe COVID-19.

Take-home message

Our study combining human lung transcriptomics with functional studies in human macrophages clearly supports the design and development of TLR4 - directed therapeutics to mitigate hyperinflammation in severe COVID-19.

Antimyeloperoxidase antibodies modulate inflammatory responses and activate profibrotic pathways in human monocytes

Antimyeloperoxidase (anti-MPO) and antiproteinase 3 (anti-PR3) antibodies are found in anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV). We investigated the effect of both anti-MPO and anti-PR3 IgG on human monocytes. Peripheral blood monocytes were cultured under a range of conditions that included TLR agonists, anti-MPO IgG and anti-PR3 IgG with appropriate controls. Experiments included whole transcriptome profiling and an assessment of the role of Fc receptors. When monocytes were stimulated with LPS or R848, anti-MPO but not anti-PR3 IgG, caused a reduction in IL-10 secretion and had a profound effect on cell-surface marker expression. Anti-MPO but not anti-PR3 IgG enhanced monocyte survival in the absence of TLR stimulation. These effects depended on the Fc receptor CD32a. With TLR stimulation, the effect of anti-MPO but not anti-PR3 IgG on the transcriptional response at 6 h was variable, but we identified a core set of transcripts likely to be important. Without TLR stimulation, there was a robust effect of anti-MPO but not anti-PR3 IgG on the transcriptional response at 24 h, and there was a highly significant enrichment of genes encoding extracellular matrix and extracellular matrix-associated proteins. Analysis with nCounter confirmed many of the differentially expressed transcripts and supported a role for CD32a. These data show that anti-MPO, but not anti-PR3 IgG, from patients with AAV has wide-ranging effects on monocytes which depend on CD32a. The activation of a profibrotic transcriptional response by anti-MPO but not anti-PR3 IgG may give insights into the differences in disease phenotype.

Elevated Galectin-3 Is Associated with Aging, Multiple Sclerosis, and Oxidized Phosphatidylcholine-Induced Neurodegeneration

Aging is a significant risk factor associated with the progression of CNS neurodegenerative diseases including multiple sclerosis (MS). Microglia, the resident macrophages of the CNS parenchyma, are a major population of immune cells that accumulate in MS lesions. While they normally regulate tissue homeostasis and facilitate the clearance of neurotoxic molecules including oxidized phosphatidylcholines (OxPCs), their transcriptome and neuroprotective functions are reprogrammed by aging. Thus, determining the factors that instigate aging associated microglia dysfunction can lead to new insights for promoting CNS repair and for halting MS disease progression. Through single-cell RNA sequencing (scRNAseq), we identified Lgals3, which encodes for galectin-3 (Gal3), as an age upregulated gene by microglia responding to OxPC. Consistently, excess Gal3 accumulated in OxPC and lysolecithin-induced focal spinal cord white matter (SCWM) lesions of middle-aged mice compared with young mice. Gal3 was also elevated in mouse experimental autoimmune encephalomyelitis (EAE) lesions and more importantly in MS brain lesions from two male and one female individuals. While Gal3 delivery alone into the mouse spinal cord did not induce damage, its co-delivery with OxPC increased cleaved caspase 3 and IL-1β within white matter lesions and exacerbated OxPC-induced injury. Conversely, OxPC-mediated neurodegeneration was reduced in Gal3-/- mice compared with Gal3+/+ mice. Thus, Gal3 is associated with increased neuroinflammation and neurodegeneration and its overexpression by microglia/macrophages may be detrimental for lesions within the aging CNS.SIGNIFICANCE STATEMENT Aging accelerates the progression of neurodegenerative diseases such as multiple sclerosis (MS). Understanding the molecular mechanisms of aging that increases the susceptibility of the CNS to damage could lead to new strategies to manage MS progression. Here, we highlight that microglia/macrophage-associated galectin-3 (Gal3) was upregulated with age exacerbated neurodegeneration in the mouse spinal cord white matter (SCWM) and in MS lesions. More importantly, co-injection of Gal3 with oxidized phosphatidylcholines (OxPCs), which are neurotoxic lipids found in MS lesions, caused greater neurodegeneration compared with injection of OxPC alone, whereas genetic loss of Gal3 reduced OxPC damage. These results demonstrate that Gal3 overexpression is detrimental to CNS lesions and suggest its deposition in MS lesions may contribute to neurodegeneration.

Neuronal ApoE4 in Alzheimer's disease and potential therapeutic targets

The most prevalent genetic risk factor for Alzheimer's disease (AD) is Apolipoprotein E (ApoE), a gene located on chromosome 19 that encodes three alleles (e2, e3, and e4) that give rise to the ApoE subtypes E2, E3, and E4, respectively. E2 and E4 have been linked to increased plasma triglyceride concentrations and are known to play a critical role in lipoprotein metabolism. The prominent pathological features of AD mainly include senile plaques formed by amyloid β (Aβ₄₂) aggregation and neuronal fibrous tangles (NFTs), and the deposited plaques are mainly composed of Aβ hyperphosphorylation and truncated head. In the central nervous system, the ApoE protein is primarily derived from astrocytes, but ApoE is also produced when neurons are stressed or affected by certain stress, injury, and aging conditions. ApoE4 in neurons induces Aβ and tau protein pathologies, leading to neuroinflammation and neuronal damage, impairing learning and memory functions. However, how neuronal ApoE4 mediates AD pathology remains unclear. Recent studies have shown that neuronal ApoE4 may lead to greater neurotoxicity, which increases the risk of AD development. This review focuses on the pathophysiology of neuronal ApoE4 and explains how neuronal ApoE4 mediates Aβ deposition, pathological mechanisms of tau protein hyperphosphorylation, and potential therapeutic targets.

OxPAPC stabilizes liquid-ordered domains in biomimetic membranes

Long-chain polyunsaturated fatty acids (PUFAs) are prone to nonenzymatic oxidation in response to differing environmental stressors and endogenous cellular sources. There is increasing evidence that phospholipids containing oxidized PUFA acyl chains control the inflammatory response. However, the underlying mechanism(s) of action by which oxidized PUFAs exert their functional effects remain unclear. Herein, we tested the hypothesis that replacement of 1-palmitoyl-2-arachidonyl-phosphatidylcholine (PAPC) with oxidized 1-palmitoyl-2-arachidonyl-phosphatidylcholine (oxPAPC) regulates membrane architecture. Specifically, with solid-state 2H NMR of biomimetic membranes, we investigated how substituting oxPAPC for PAPC modulates the molecular organization of liquid-ordered (Lo) domains. 2H NMR spectra for bilayer mixtures of 1,2-dipalmitoylphosphatidylcholine-d62 (an analog of DPPC deuterated throughout sn-1 and -2 chains) and cholesterol to which PAPC or oxPAPC was added revealed that replacing PAPC with oxPAPC disrupted molecular organization, indicating that oxPAPC does not mix favorably in a tightly packed Lo phase. Furthermore, unlike PAPC, adding oxPAPC stabilized 1,2-dipalmitoylphosphatidylcholine-d6-rich/cholesterol-rich Lo domains formed in mixtures with 1,2-dioleoylphosphatidylcholine while decreasing the molecular order within 1,2-dioleoylphosphatidylcholine-rich liquid-disordered regions of the membrane. Collectively, these results suggest a mechanism in which oxPAPC stabilizes Lo domains-by disordering the surrounding liquid-disordered region. Changes in the structure, and thereby functionality, of Lo domains may underly regulation of plasma membrane-based inflammatory signaling by oxPAPC.

Compartmentalized regulation of lipid signaling in oxidative stress and inflammation: Plasmalogens, oxidized lipids and ferroptosis as new paradigms of bioactive lipid research

Perturbations in lipid homeostasis combined with conditions favoring oxidative stress constitute a hallmark of the inflammatory response. In this review we focus on the most recent results concerning lipid signaling in various oxidative stress-mediated responses and inflammation. These include phagocytosis and ferroptosis. The best characterized event, common to these responses, is the synthesis of oxygenated metabolites of arachidonic acid and other polyunsaturated fatty acids. Major developments in this area have highlighted the importance of compartmentalization of the enzymes and lipid substrates in shaping the appropriate response. In parallel, other relevant lipid metabolic pathways are also activated and, until recently, there has been a general lack of knowledge on the enzyme regulation and molecular mechanisms operating in these pathways. Specifically, data accumulated in recent years on the regulation and biological significance of plasmalogens and oxidized phospholipids have expanded our knowledge on the involvement of lipid metabolism in the progression of disease and the return to homeostasis. These recent major developments have helped to establish the concept of membrane phospholipids as cellular repositories for the compartmentalized production of bioactive lipids involved in cellular regulation. Importantly, an enzyme classically described as being involved in regulating the homeostatic turnover of phospholipids, namely the group VIA Ca²⁺-independent phospholipase A₂ (iPLA₂β), has taken center stage in oxidative stress and inflammation research owing to its key involvement in regulating metabolic and ferroptotic signals arising from membrane phospholipids. Understanding the role of iPLA₂β in ferroptosis and metabolism not only broadens our knowledge of disease but also opens possible new horizons for this enzyme as a target for therapeutic intervention.

Current Understanding on the Role of Lipids in Macrophages and Associated Diseases

Lipid metabolism is the major intracellular mechanism driving a variety of cellular functions such as energy storage, hormone regulation and cell division. Lipids, being a primary component of the cell membrane, play a pivotal role in the survival of macrophages. Lipids are crucial for a variety of macrophage functions including phagocytosis, energy balance and ageing. However, functions of lipids in macrophages vary based on the site the macrophages are residing at. Lipid-loaded macrophages have recently been emerging as a hallmark for several diseases. This review discusses the significance of lipids in adipose tissue macrophages, tumor-associated macrophages, microglia and peritoneal macrophages. Accumulation of macrophages with impaired lipid metabolism is often characteristically observed in several metabolic disorders. Stress signals differentially regulate lipid metabolism. While conditions such as hypoxia result in accumulation of lipids in macrophages, stress signals such as nutrient deprivation initiate lipolysis and clearance of lipids. Understanding the biology of lipid accumulation in macrophages requires the development of potentially active modulators of lipid metabolism.

TLR4 Blockade Using Docosahexaenoic Acid Restores Vulnerability of Drug-Tolerant Tumor Cells and Prevents Breast Cancer Metastasis and Postsurgical Relapse

Nonmutational mechanisms were recently discovered leading to reversible drug tolerance. Despite the rapid elimination of a majority of tumor cells, a small subpopulation of "'drug-tolerant"' cells remain viable with lethal drug exposure, which may further lead to resistance or tumor relapse. Several signaling pathways are involved in the local or systemic inflammatory responses contributing to drug-induced phenotypic switch. Here, we report that Toll-like receptor 4 (TLR4)-interacting lipid docosahexaenoic acid (DHA) restores the cytotoxic effect of doxorubicin (DOX) in the lipopolysaccharide-treated breast tumor cell line 4T1, preventing the phenotypic switch to drug-tolerant cells, which significantly reduces primary tumor growth and lung metastasis in both 4T1 orthotopic and experimental metastasis models. Importantly, DHA in combination with DOX delays and inhibits tumor recurrence following surgical removal of the primary tumor. Furthermore, the coencapsulation of DHA and DOX in a nanoemulsion significantly prolongs the survival of mice in the postsurgical 4T1 tumor relapse model with significantly reduced systemic toxicity. The synergistic antitumor, antimetastasis, and antirecurrence effects of DHA + DOX combination are likely mediated by attenuating TLR4 activation, thus sensitizing tumor cells to standard chemotherapy.

Biting the hand that feeds: Metabolic determinants of cell fate during infection

Metabolic shifts can occur in cells of the innate immune system in response to microbial infection. Whether these metabolic shifts benefit host defense and propagation of an immune response appears to be context dependent. In an arms race, host-adapted microbes and mammalian cells vie for control of biosynthetic machinery, organelles, and metabolites. Herein, we discuss the intersection of host metabolism and cell-intrinsic immunity with implications for cell fate during infection. Sensation of microbial ligands in isolation results in host metabolic shifts that imbues normal innate immune function, such as cytokine secretion. However, living microbes have an arsenal of effectors and strategies to subvert cell-intrinsic immune responses by manipulating host metabolism. Consequently, host metabolism is monitored as an indicator of invasion or manipulation by a pathogen, primarily through the actions of guard proteins and inflammasome pathways. In this review, we frame initiation of cell-intrinsic immunity in the context of host metabolism to include a physiologic "Goldilocks zone" of allowable shifts with guard circuits monitoring wide perturbations away from this zone for the initiation of innate immune responses. Through comparison of studies with purified microbial ligands, dead microbes, and live pathogens we may begin to understand how shifts in metabolism determine the outcome of host-pathogen interactions.

Probiotic supplementation and systemic inflammation in relapsing-remitting multiple sclerosis: A randomized, double-blind, placebo-controlled trial

Background

Multiple sclerosis (MS) is a complex inflammatory disease in which demyelination occurs in the central nervous system affecting approximately 2.5 million people worldwide. Intestinal microbiome changes play an important role in the etiology of chronic diseases.

Objective

This study aimed to investigate the effect of probiotic supplementation on systemic inflammation in patients with MS.

Methods

A 12-week double-blind clinical trial study was designed and seventy patients with MS were randomly divided into two groups receiving probiotics and placebo. Patients in the intervention group received two capsules containing multi-strain probiotics daily and patients in the control group received the same amount of placebo. Factors associated with systemic inflammation were assessed at the beginning and end of the study.

Results

Sixty-five patients were included in the final analysis. There was no significant difference between the two groups in terms of baseline variables except for the duration of the disease (P > 0.05). At the end of the study, probiotic supplementation compared to the placebo caused a significant reduction in the serum levels of CRP (-0.93 ± 1.62 vs. 0.05 ± 1.74, P = 0.03), TNF-α (-2.09 ± 1.88 vs. 0.48 ± 2.53, P = 0.015) and IFN-γ (-13.18 ± 7.33 vs. -1.93 ± 5.99, P < 0.001). Also, we found a significant increase in the FOXP3 and TGF-β levels in the intervention group (P < 0.05).

Conclusion

The results of our study showed that supplementation with probiotics can have beneficial effects on serum levels of some factors associated with systemic inflammation.

Clinical trial registration

[http://www.irct.ir], identifier [IRCT20181210041 918N1].

Systemic and Ocular Anti-Inflammatory Mechanisms of Green Tea Extract on Endotoxin-Induced Ocular Inflammation

Introduction

Green tea extract (GTE) alleviated ocular inflammations in endotoxin-induced uveitis (EIU) rat model induced by lipopolysaccharide (LPS) but the underlying mechanism is unclear.

Objectives

To investigate the systematic and local mechanisms of the alleviation by untargeted metabolomics using liquid chromatography-tandem mass spectrometry.

Methods

Sprague-Dawley rats were divided into control group, LPS treatment group, and LPS treatment group treated with GTE two hours after LPS injection. The eyes were monitored by slip lamp and electroretinography examination after 24 hours. The plasma and retina were collected for metabolomics analysis.

Results

In LPS treated rats, the iris showed hyperemia. Plasma prostaglandins, arachidonic acids, corticosteroid metabolites, and bile acid metabolites increased. In the retina, histamine antagonists, corticosteroids, membrane phospholipids, free antioxidants, and sugars also increased but fatty acid metabolites, N-acetylglucosamine-6-sulphate, pyrocatechol, and adipic acid decreased. After GTE treatment, the a- and b- waves of electroretinography increased by 13%. Plasma phosphorylcholine lipids increased but plasma prostaglandin E1, cholanic metabolites, and glutarylglycine decreased. In the retina, tetranor-PGAM, pantothenic derivatives, 2-ethylacylcarinitine, and kynuramine levels decreased but anti-oxidative seleno-peptide level increased. Only phospholipids, fatty acids, and arachidonic acid metabolites in plasma and in the retina had significant correlation (p < 0.05, r > 0.4 or r < -0.4).

Conclusions

The results showed GTE indirectly induced systemic phosphorylcholine lipids to suppress inflammatory responses, hepatic damage, and respiratory mitochondrial stress in EIU rats induced by LPS. Phospholipids may be a therapeutic target of GTE for anterior chamber inflammation.

Targeting oxidized phospholipids by AAV-based gene therapy in mice with established hepatic steatosis prevents progression to fibrosis

Oxidized phosphatidylcholines (OxPCs) are implicated in chronic tissue damage. Hyperlipidemic LDL-R--deficient mice transgenic for an OxPC-recognizing IgM fragment (scFv-E06) are protected against nonalcoholic fatty liver disease (NAFLD). To examine the effect of OxPC elimination at different stages of NAFLD progression, we used cre-dependent, adeno-associated virus serotype 8-mediated expression of the single-chain variable fragment of E06 (AAV8-scFv-E06) in hepatocytes of albumin-cre mice. AAV8-induced expression of scFv-E06 at the start of FPC diet protected mice from developing hepatic steatosis. Independently, expression of scFv-E06 in mice with established steatosis prevented the progression to hepatic fibrosis. Mass spectrometry-based oxophospho-lipidomics identified individual OxPC species that were reduced by scFv-E06 expression. In vitro, identified OxPC species dysregulated mitochondrial metabolism and gene expression in hepatocytes and hepatic stellate cells. We demonstrate that individual OxPC species independently affect disease initiation and progression from hepatic steatosis to steatohepatitis, and that AAV-mediated expression of scFv-E06 is an effective therapeutic intervention.

Innate immune detection of lipid oxidation as a threat assessment strategy

Oxidized phospholipids that result from tissue injury operate as immunomodulatory signals that, depending on the context, lead to proinflammatory or anti-inflammatory responses. In this Perspective, we posit that cells of the innate immune system use the presence of oxidized lipids as a generic indicator of threat to the host. Similarly to how pathogen-associated molecular patterns represent general indicators of microbial encounters, oxidized lipids may be the most common molecular feature of an injured tissue. Therefore, microbial detection in the absence of oxidized lipids may indicate encounters with avirulent microorganisms. By contrast, microbial detection and detection of oxidized lipids would indicate encounters with replicating microorganisms, thereby inducing a heightened inflammatory and defensive response. Here we review recent studies supporting this idea. We focus on the biology of oxidized phosphocholines, which have emerged as context-dependent regulators of immunity. We highlight emerging functions of oxidized phosphocholines in dendritic cells and macrophages that drive unique inflammasome and migratory activities and hypermetabolic states. We describe how these lipids hyperactivate dendritic cells to stimulate antitumour CD8+ T cell immunity and discuss the potential implications of the newly described activities of oxidized phosphocholines in host defence.

Acute iron oxide nanoparticles exposure induced murine eosinophilic airway inflammation via TLR2 and TLR4 signaling

Iron oxide nanoparticles (Fe₂ O₃ NPs) is the main component of air pollution particles in urban rail transit environment. People are more exposed to Fe₂ O₃ NPs, however, the studies on relationship between Fe₂ O₃ NPs and respiratory health are limited. In the present study, acute airway inflammation caused by Fe₂ O₃ NPs and its possible mechanism were investigated. BALB/c mice were intratracheally challenged with different concentrations of Fe₂ O₃ NPs. Fe₂ O₃ NPs induced bronchial epithelial barrier function damage, infiltration of neutrophils and lymphocytes into the airway submucosa, secretion of mucus in the airway epithelium and elevated expression of eosinophil major basic protein (EMBP) in lungs. Compared with the control group, Fe₂ O₃ NPs increased eosinophils by 20 times in bronchoalveolar lavage fluid (BALF), and markedly increased eosinophils related cytokines and chemokines, including interleukin (IL) -5, IL-33, thymic stromal lymphopoietin (TSLP), monocyte chemotactic protein (MCP)-3, eotaxin, tumor necrosis factor (TNF)-α, keratinocyte chemoattractant (KC). Furthermore, Fe₂ O₃ NPs up-regulated levels of IL-5, MCP-3, eotaxin, and KC in serum. In vitro studies showed that Fe₂ O₃ NPs increased the genes and proteins expression of Toll-like receptors (TLR)-2, TLR4, TNF receptor associated factor 6 (TRAF6), myeloid differentiation factor 88 (MyD88), nuclear factor (NF)-κB, and TNF-α in RAW267.4 cells. The downstream inflammatory cytokine protein expression and release such as TNF-α was significantly decreased after using TLR2/TLR4 inhibitor OxPAPC, but not MyD88 inhibitor ST2825. These results suggest that TLR2 and TLR4 played important role in Fe₂ O₃ NPs inducing acute eosinophilic airway inflammation in the murine lung.

Polyene Phosphatidylcholine Interacting with TLR-2 Prevents the Synovial Inflammation via Inactivation of MAPK and NF-κB Pathways

Rheumatoid arthritis (RA) is a chronic autoimmune joint disease that causes cartilage and bone damage or even disability, seriously endangering human health. Chronic synovial inflammation has been shown to play a vital role in disease sustainability. Therefore, downregulation of synovial inflammation is considered to be an effective discipline for RA therapy. Polyene phosphatidylcholine (PPC) is a hepatoprotective agent, which was observed to inhibit inflammation in macrophages and prevent collagen-induced arthritis (CIA) of rats in our previous study. However, the underlying mechanism remains unclear. The present study further reported that PPC can inhibit synovial inflammation. In lipopolysaccharide (LPS)-stimulated primary synovial fibroblasts (SFs) of mice, PPC significantly decreased pro-inflammatory cytokines production while increasing anti-inflammatory cytokines level. In this process, PPC downregulated the expression of TLR-2 and their downstream signaling molecules such as MyD88, p-ERK1/2, p-JNK1/2, and p-P38 in MAPK pathway and p-IκBα and NF-κB-p65 in NF-κB pathway. Moreover, the inhibitory effect of PPC on the above molecules and cytokines was weakened after pre-treatment with TLR-2 agonist Pam3CSK4. In addition, PPC lost its anti-inflammatory effect and its suppressing capability on MAPK and NF-κB pathways in TLR-2^-/- primary SFs after exposure to LPS. Collectively, this study demonstrated that PPC can alleviate synovial inflammation through TLR-2-mediated MAPK and NF-κB pathways, which can be proposed to be a potential drug candidate for RA prevention.

5-Dodecanolide, a Compound Isolated from Pig Lard, Presents Powerful Anti-Inflammatory Properties

BACKGROUND

Pork lard (PL) is traditionally used as an anti-inflammatory agent. We propose to demonstrate the anti-inflammatory properties of PL, and elucidate which compounds could be responsible for the anti-inflammatory effects.

METHODS

The anti-inflammatory effects of PL were tested in a rat model of zymosan-induced hind paw inflammation. Further, the hydroalcoholic extract from PL was obtained, the composition analyzed, and the anti-inflammatory activity of the extracts and isolated components assayed using immune cells stimulated with lipopolysaccharide (LPS).

RESULTS

Applying the ointment on the inflamed rat feet reduced the foot diameter, foot weight, and activities of antioxidant enzymes and inflammatory markers of circulating neutrophils. The main components of the hydroalcoholic extract were 5-dodecanolide, oleamide, hexadecanoic acid, 9-octadecenoic acid, hexadecanamide, and resolvin D1.

CONCLUSIONS

PL reduces the immune response in an animal model stimulated with zymosan. Hydroalcoholic PL extract and its components (5-Dodecanolide, Oleamide, and Resolvin D1) exerted an anti-inflammatory effect on LPS-stimulated neutrophils and peripheral mononuclear cells reducing the capability to produce TNFα, as well as the activities of antioxidant and pro-inflammatory enzymes. These effects are attributable to 5-dodecanolide, although the effects of this compound alone do not reach the magnitude of the anti-inflammatory effects observed by the complete hydroalcoholic extract.

A highly conserved host lipase deacylates oxidized phospholipids and ameliorates acute lung injury in mice

Oxidized phospholipids have diverse biological activities, many of which can be pathological, yet how they are inactivated in vivo is not fully understood. Here, we present evidence that a highly conserved host lipase, acyloxyacyl hydrolase (AOAH), can play a significant role in reducing the pro-inflammatory activities of two prominent products of phospholipid oxidation, 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine. AOAH removed the sn-2 and sn-1 acyl chains from both lipids and reduced their ability to induce macrophage inflammasome activation and cell death in vitro and acute lung injury in mice. In addition to transforming Gram-negative bacterial lipopolysaccharide from stimulus to inhibitor, its most studied activity, AOAH can inactivate these important danger-associated molecular pattern molecules and reduce tissue inflammation and injury.

The soluble cytoplasmic tail of CD45 regulates T-cell activation via TLR4 signaling

The soluble cytoplasmic tail of CD45 (ct-CD45) is a cleavage fragment of CD45, that is generated during the activation of human phagocytes. Upon release to the extracellular space, ct-CD45 binds to human T cells and inhibits their activation in vitro. Here, we studied the potential role of TLR4 as a receptor for ct-CD45. Treatment of Jurkat TLR4/CD14 reporter cells with ct-CD45 induced the upregulation of the reporter gene NFκB-eGFP and could be blocked by inhibitors of TLR4 signaling. Conversely, ct-CD45 did not promote the NFκB-controlled eGFP induction in reporter cells expressing TLR1, TLR2, and TLR6 transgenes and did not lead to the activation of the transcription factors NFκB, AP-1, and NFAT in a Jurkat reporter cell line expressing endogenous TLR5. Moreover, ct-CD45 binds to recombinant TLR4 in an in vitro assay and this association was reduced in the presence of oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine. Blockade of TLR4 with mAb HTA125 partially reversed the ct-CD45-mediated inhibition of T-cell proliferation. Interestingly, targeting of TLR4 with mAb W7C11 also suppressed T-cell proliferation. In summary, the results of this study demonstrate that ct-CD45 acts via a noncanonical TLR4 activation pathway on T cells, which modulates TCR signaling.

Oxidized phospholipids on alkyl-amide scaffold demonstrate anti-endotoxin and endothelial barrier-protective properties

Oxidized phospholipids (OxPLs) containing enzymatically or non-enzymatically oxidized fatty acids (oxylipins) are increasingly recognized as lipid mediators involved in pathogenesis of diseases. Further understanding of structure-activity relationship and molecular mechanisms activated by OxPLs is hampered by the complexity of synthesis of individual molecular species. Although dozens of individual free oxylipins are commercially available, their attachment to the phospholipid scaffold requires relatively harsh conditions during activation of carboxy-group, which may lead to decomposition of unstable oxylipins. Furthermore, additional protection-deprotection steps are required for oxylipins containing hydroxy-groups. In this work we describe synthesis of OxPLs containing oxylipins bound at the sn-2-position via an amide-bond that is characteristic of sphingophospholipids. Activation of oxylipins and attachment to the phospholipid scaffold are performed under mild conditions and characterized by high yield. Hydroxy-groups of oxylipins do not interfere with reactions and therefore no protection/deprotection steps are needed. In order to prevent oxylipin migration, a fatty acid residue at the sn-1 was bound through an alkyl bond, which is a common bond present in a large proportion of naturally occurring phospholipids. An additional advantage of combining alkyl and amide bonds in a single phospholipid molecule is that both types of bonds are phospholipase A1/A2-resistant, which may be expected to improve biological stability of OxPLs and thus simplify analysis of their effects. As proof of principle, several alkyl-amide oxidized phosphatidylcholines (OxPCs) containing either linear or prostane ring oxylipins have been synthesized. Importantly, we show here that alkyl-amide-OxPCs demonstrated biological activities similar to those of di-acyl-OxPCs. Alkyl-amide-OxPCs inhibited pro-inflammatory action of LPS and increased endothelial cellular barrier in vitro and in mouse models. The effects of alkyl-amide and di-acyl-OxPCs developed in a similar range of concentrations. We hypothesize that alkyl-amide-OxPLs may become a useful tool for deeper analysis of the structure-activity relationship of OxPLs.

Progresses on three pattern recognition receptor families (TLRs, RLRs and NLRs) in teleost

Pattern recognition receptors (PRRs) are a class of immune sensors that play crucial roles in detecting and responding to the conserved patterns of microorganisms. To date, many PRRs, such as TLRs, RLRs and NLRs, as well as their downstream molecules have been identified and characterized in teleost, while their ligands and immunoregulatory mechanisms remain largely unknown. In the present review, we described and discussed the main members of TLR/RLR/NLR families, including their expression profiles, signaling transductions and functions in teleost. And some splicing isoforms from TLR/RLR/NLR families were also addressed, which play synergistic and/or antagonistic roles in response to pathogen infections in teleost. TLRs sense different pathogens by forming homodimer and/or heterodimer. Beyond, functions of TLRs can also be affected by migrating. And some endolysosomal TLRs undergo proteolytic cleavage and in a pH-dependent mechanism to attain a mature functional form that mediate ligand recognition and downstream signaling. Until now, more than 80 members in TLR/RLR/NLR families have been identified in teleost, while only TLR5, TLR9, TLR19, TLR21, TLR22, MDA5, LGP2, NOD1 and NOD2 have direct evidence of ligand recognition in teleost. Meanwhile, new ligands as well as signaling pathways do occur during evolution of teleost. This review summarizes progresses on the TLRs/RLRs/NLRs in teleost. We attempt to insight into the ligands recognition and signaling transmission of TLRs/RLRs/NLRs in teleost.

Oxidized Phosphatidylcholines Induce Multiple Functional Defects in Airway Epithelial Cells

Oxidative stress is a hallmark of numerous airway diseases, contributing to extensive cell and tissue damage. Cell membranes and the airway mucosal lining are rich in phospholipids that are particularly susceptible to oxidative attack, producing bioactive molecules including oxidized phosphatidylcholines (OxPC). With the recent discovery of elevated OxPC in asthmatic patients after allergen challenge, we hypothesized that OxPC directly contribute to disease by inducing airway epithelial cell dysfunction. We found that OxPC induced concentration-dependent cell stress and loss of viability in BEAS-2B and Calu-3 cell lines and primary human epithelial cells. These responses corresponded with significant epithelial barrier dysfunction, which was further compounded when combining OxPC with an epithelial wound. OxPC inhibited DNA synthesis and migration required to re-establish barrier function, but cells recovered if OxPC were washed off soon after treatment. OxPC induced generation of reactive oxygen species, lipid peroxidation and mitochondrial dysfunction, raising the possibility that OxPC cause pathological lipid metabolism in a self-propagating cycle. The oxidative stress induced by OxPC could not be abrogated by putative OxPC receptor blockers, but partial recovery of barrier function, proliferation and lipid peroxidation could be achieved with the antioxidant n-acetyl cysteine. In summary, we have identified OxPC as a group of bioactive molecules that significantly impair multiple facets of epithelial cell function, consistent with pathological features of asthma. Further characterisation of the mechanisms by which OxPC affect epithelial cells could yield new insights into how oxidative stress contributes to the pathogenesis of airway disease.

Effect of Probiotic Consumption on Immune Response in Athletes: A Meta-analysis

The possible effect of probiotic interventions on immunological markers in athletes is inconclusive. Therefore, to synthesize and quantitatively analyze the existing evidence on this topic, systematic literature searches of online databases PubMed, Scopus, Cochrane Library, and ISI Web of Sciences was carried out up to February 2021 to find all randomized controlled trials (RCTs) concerning the immunological effects of probiotics in athletes. In the random-effects model, weighted mean difference (WMD) and 95% confidence interval (CI) explained the net effect. The authors assessed the likelihood of publication bias via Egger's and Begg's statistics. A total of 13 RCTs (836 participants) were retrieved. Probiotic consumption reduced lymphocyte T cytotoxic count significantly (WMD=-0.08 cells×10⁹/L; 95% CI: -0.15 to -0.01; p=0.022) with evidence of moderate heterogeneity (I ²⁼59.1%, p=0.044) and monocyte count when intervention duration was ≤ 4 weeks (WMD=-0.08 cells×10⁹/L; 95% CI: -0.16 to -0.001; I ²⁼0.0%). Furthermore, leukocyte count was significantly elevated (WMD=0.48 cells×10⁹/L; 95% CI: 0.02 to 0.93; I ²⁼0.0%) when multi-strain probiotics were used. Probiotic supplements may improve immunological markers, including lymphocyte T cytotoxic, monocyte, and leukocyte in athletes. Further randomized controlled trials using diverse strains of probiotics and consistent outcome measures are necessary to allow for evidence-based recommendations.

Oxidized phospholipids affect small intestine neuromuscular transmission and serotonergic pathways in juvenile mice

BACKGROUND

Oxidized phospholipid derivatives (OxPAPCs) act as bacterial lipopolysaccharide (LPS)-like damage-associated molecular patterns. OxPAPCs dose-dependently exert pro- or anti-inflammatory effects by interacting with several cellular receptors, mainly Toll-like receptors 2 and 4. It is currently unknown whether OxPAPCs may affect enteric nervous system (ENS) functional and structural integrity.

METHODS

Juvenile (3 weeks old) male C57Bl/6 mice were treated intraperitoneally with OxPAPCs, twice daily for 3 days. Changes in small intestinal contractility were evaluated by isometric neuromuscular responses to receptor and non-receptor-mediated stimuli. Alterations in ENS integrity and serotonergic pathways were assessed by real-time PCR and confocal immunofluorescence microscopy in longitudinal muscle-myenteric plexus whole-mount preparations (LMMPs). Tissue levels of serotonin (5-HT), tryptophan, and kynurenine were measured by HPLC coupled to UV/fluorescent detection.

KEY RESULTS

OxPAPC treatment induced enteric gliosis, loss of myenteric plexus neurons, and excitatory hypercontractility, and reduced nitrergic neurotransmission with no changes in nNOS⁺ neurons. Interestingly, these changes were associated with a higher functional response to 5-HT, altered immunoreactivity of 5-HT receptors and serotonin transporter (SERT) together with a marked decrease in 5-HT levels, shifting tryptophan metabolism toward kynurenine production.

CONCLUSIONS AND INFERENCES

OxPAPC treatment disrupted structural and functional integrity of the ENS, affecting serotoninergic tone and 5-HT tissue levels toward a higher kynurenine content during adolescence, suggesting that changes in intestinal lipid metabolism toward oxidation can affect serotoninergic pathways, potentially increasing the risk of developing functional gastrointestinal disorders during critical stages of development.

Cyclopentenone Prostaglandins and Structurally Related Oxidized Lipid Species Instigate and Share Distinct Pro- and Anti-inflammatory Pathways

Oxidized lipids play a critical role in a variety of diseases with two faces: pro- and anti-inflammatory. The molecular mechanisms of this Janus-faced activity remain largely unknown. Here, we have identified that cyclopentenone-containing prostaglandins such as 15d-PGJ2 and structurally related oxidized phospholipid species possess a dual and opposing bioactivity in inflammation, depending on their concentration. Exposure of dendritic cells (DCs)/macrophages to low concentrations of such lipids before Toll-like receptor (TLR) stimulation instigates an anti-inflammatory response mediated by nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent inhibition of nuclear factor κB (NF-κB) activation and downstream targets. By contrast, high concentrations of such lipids upon TLR activation of DCs/macrophages result in inflammatory apoptosis characterized by mitochondrial depolarization and caspase-8-mediated interleukin (IL)-1β maturation independently of Nrf2 and the classical inflammasome pathway. These results uncover unexpected pro- and anti-inflammatory activities of physiologically relevant lipid species generated by enzymatic and non-enzymatic oxidation dependent on their concentration, a phenomenon known as hormesis.

Direct Targets and Subsequent Pathways for Molecular Hydrogen to Exert Multiple Functions: Focusing on Interventions in Radical Reactions

Molecular hydrogen (H₂) was long regarded as non-functional in mammalian cells. We overturned the concept by demonstrating that H₂ exhibits antioxidant effects and protects cells against oxidative stress. Subsequently, it has been revealed that H₂ has multiple functions in addition to antioxidant effects, including antiinflammatory, anti-allergic functions, and as cell death and autophagy regulation. Additionally, H₂ stimulates energy metabolism. As H₂ does not readily react with most biomolecules without a catalyst, it is essential to identify the primary targets with which H₂ reacts or interacts directly. As a first event, H₂ may react directly with strong oxidants, such as hydroxyl radicals (•OH) in vivo. This review addresses the key issues related to this in vivo reaction. •OH may have a physiological role because it triggers a free radical chain reaction and may be involved in the regulation of Ca2+- or mitochondrial ATP-dependent K+-channeling. In the subsequent pathway, H₂ suppressed a free radical chain reaction, leading to decreases in lipid peroxide and its end products. Derived from the peroxides, 4-hydroxy-2-nonenal functions as a mediator that up-regulates multiple functional PGC-1α. As the other direct target in vitro and in vivo, H₂ intervenes in the free radical chain reaction to modify oxidized phospholipids, which may act as an antagonist of Ca2+-channels. The resulting suppression of Ca2+-signaling inactivates multiple functional NFAT and CREB transcription factors, which may explain H₂ multi-functionality. This review also addresses the involvement of NFAT in the beneficial role of H₂ in COVID-19, Alzheimer's disease and advanced cancer. We discuss some unsolved issues of H₂ action on lipopolysaccharide signaling, MAPK and NF-κB pathways and the Nrf2 paradox. Finally, as a novel idea for the direct targeting of H2, this review introduces the possibility that H₂ causes structural changes in proteins via hydrate water changes.

Novel Mechanisms of Ozone-Induced Pulmonary Inflammation and Resolution, and the Potential Protective Role of Scavenger Receptor BI

INTRODUCTION

Increases in ambient levels of ozone (O3), a criteria air pollutant, have been associated with increased susceptibility and exacerbations of chronic pulmonary diseases through lung injury and inflammation. O3 induces pulmonary inflammation, in part by generating damage-associated molecular patterns (DAMPs), which are recognized by pattern recognition receptors (PRRs), such as toll-like receptors (TLRs) and scavenger receptors (SRs). This inflammatory response is mediated in part by alveolar macrophages (AMs), which highly express PRRs, including scavenger receptor BI (SR-BI). Once pulmonary inflammation has been induced, an active process of resolution occurs in order to prevent secondary necrosis and to restore tissue homeostasis. The processes known to promote the resolution of inflammation include the clearance by macrophages of apoptotic cells, known as efferocytosis, and the production of specialized pro-resolving mediators (SPMs). Impaired efferocytosis and production of SPMs have been associated with the pathogenesis of chronic lung diseases; however, these impairments have yet to be linked with exposure to air pollutants.

SPECIFIC AIMS

The primary goals of this study were: Aim 1 - to define the role of SR-BI in O3-derived pulmonary inflammation and resolution of injury; and Aim 2 - to determine if O3 exposure alters pulmonary production of SPMs and processes known to promote the resolution of pulmonary inflammation and injury.

METHODS

To address Aim 1, female wild-type (WT) and SR-BI-deficient, or knock-out (SR-BI KO), mice were exposed to either O3 or filtered air. In one set of experiments mice were instilled with an oxidized phospholipid (oxPL). Bronchoalveolar lavage fluid (BALF) and lung tissue were collected for the analyses of inflammatory and injury markers and oxPL. To estimate efferocytosis, mice were administered apoptotic cells (derived from the Jurkat T cell line) after O3 or filtered air exposure.

To address Aim 2, male WT mice were exposed to either O3 or filtered air, and levels of SPMs were assessed in the lung, as well as markers of inflammation and injury in BALF. In some experiments SPMs were administered before exposure to O3or filtered air, to determine whether SPMs could mitigate inflammatory or resolution responses. Efferocytosis was measured as in Aim 1.

RESULTS

For Aim 1, SR-BI protein levels increased in the lung tissue of mice exposed to O3, compared with mice exposed to filtered air. Compared with WT controls, SR-BI KO mice had a significant increase in the number of neutrophils in their airspace 24 hours post O3 exposure. The oxPL levels increased in the airspace of both WT and SR-BI KO mice after O3 exposure, compared with filtered air controls. Four hours after instillation of an oxPL, SR-BI KO mice had an increase in BALF neutrophils and total protein, and a nonsignificant increase in macrophages compared with WT controls. O3 exposure decreased efferocytosis in both WT and SR-BI KO female mice.

For Aim 2, mice given SPM supplementation before O3 exposure showed significantly increased AM efferocytosis when compared with the O3exposure control mice and also showed some mitigation of the effects of O3 on inflammation and injury. Several SPMs and their precursors were measured in lung tissue using reverse-phase high performance liquid chromatography (HPLC) with tandem mass spectrometry (MS/MS). At 24 hours after O3 exposure 14R-hydroxydocosahexaenoic acid (HDHA) and 10,17-dihydroxydocosahexaenoic acid (diHDoHE) were significantly decreased in lung tissue, but at 6 hours after exposure, levels of these SPMs increased.

CONCLUSIONS

Our findings identify novel mechanisms by which O3 may induce pulmonary inflammation and also increase susceptibility to and exacerbations of chronic lung diseases.

Oxidized Phospholipids in Control of Endothelial Barrier Function: Mechanisms and Implication in Lung Injury

Earlier studies investigating the pathogenesis of chronic vascular inflammation associated with atherosclerosis described pro-inflammatory and vascular barrier disruptive effects of lipid oxidation products accumulated in the sites of vascular lesion and atherosclerotic plaque. However, accumulating evidence including studies from our group suggests potent barrier protective and anti-inflammatory properties of certain oxidized phospholipids (OxPLs) in the lung vascular endothelium. Among these OxPLs, oxidized 1-palmitoyl-2-arachdonyl-sn-glycero-3-phosphocholine (OxPAPC) causes sustained enhancement of lung endothelial cell (EC) basal barrier properties and protects against vascular permeability induced by a wide variety of agonists ranging from bacterial pathogens and their cell wall components, endotoxins, thrombin, mechanical insults, and inflammatory cytokines. On the other hand, truncated OxPLs cause acute endothelial barrier disruption and potentiate inflammation. It appears that multiple signaling mechanisms triggering cytoskeletal remodeling are involved in OxPLs-mediated regulation of EC barrier. The promising vascular barrier protective and anti-inflammatory properties exhibited by OxPAPC and its particular components that have been established in the cellular and animal models of sepsis and acute lung injury has prompted consideration of OxPAPC as a prototype therapeutic molecule. In this review, we will summarize signaling and cytoskeletal mechanisms involved in OxPLs-mediated damage, rescue, and restoration of endothelial barrier in various pathophysiological settings and discuss a future potential of OxPAPC in treating lung disorders associated with endothelial barrier dysfunction.

Innate Immune Interference Attenuates Inflammation In Bacillus Endophthalmitis

Purpose

To explore the consequences of innate interference on intraocular inflammatory responses during Bacillus endophthalmitis.

Methods

Bacillus endophthalmitis was induced in mice. Innate immune pathway activation was interfered by injecting S layer protein-deficient (∆slpA) B. thuringiensis or by treating wild-type (WT)-infected mice with a TLR2/4 inhibitor (WT+OxPAPC). At 10 hours postinfection, eyes were harvested and RNA was purified. A NanoString murine inflammation panel was used to compare gene expression in WT-infected, WT+OxPAPC, ∆slpA-infected, and uninfected eyes.

Results

In WT-infected eyes, 56% of genes were significantly upregulated compared to uninfected controls. Compared to WT-infected eyes, the expression of 27% and 50% of genes were significantly reduced in WT+OxPAPC and ∆slpA-infected eyes, respectively. Expression of 61 genes that were upregulated in WT-infected eyes was decreased in WT+OxPAPC and ∆slpA-infected eyes. Innate interference resulted in blunted expression of complement factors (C3, Cfb, and C6) and several innate pathway genes (TLRs 2, 4, 6, and 8, MyD88, Nod2, Nlrp3, NF-κB, STAT3, RelA, RelB, and Ptgs2). Innate interference also reduced the expression of several inflammatory cytokines (CSF2, CSF3, IL-6, IL-1β, IL-1α, TNFα, IL-23α, TGFβ1, and IL-12β) and chemokines (CCL2, CCL3, and CXCLs 1, 2, 3, 5, 9, and 10). All of the aforementioned genes were significantly upregulated in WT-infected eyes.

Conclusions

These results suggest that interfering with innate activation significantly reduced the intraocular inflammatory response in Bacillus endophthalmitis. This positive clinical outcome could be a strategy for anti-inflammatory therapy of an infection typically refractory to corticosteroid treatment.

Oxidation specific epitopes in asthma: New possibilities for treatment

Oxidative stress is an important feature of asthma pathophysiology that is not currently targeted by any of our frontline treatments. Reactive oxygen species, generated during times of heightened oxidative stress, can damage cellular lipids causing the production of oxidation specific epitopes (OSE). OSEs are elevated in chronic inflammatory diseases and promoting their clearance by the body, through pattern recognition receptors and IgM antibodies, prevents and resolves inflammation and tissue damage in animal models. Current research on OSEs in asthma is limited. Although they are present in the lungs of people with asthma during periods of exacerbation or allergen exposure, we do not know if they are linked with disease pathobiology. This article reviews our current understanding of OSEs in asthma and explores whether targeting OSE clearance mechanisms may be a novel therapeutic intervention for asthma.

Pharmacological validation of targets regulating CD14 during macrophage differentiation

The signalling receptor for LPS, CD14, is a key marker of, and facilitator for, pro-inflammatory macrophage function. Pro-inflammatory macrophage differentiation remains a process facilitating a broad array of disease pathologies, and has recently emerged as a potential target against cytokine storm in COVID19. Here, we perform a whole-genome CRISPR screen to identify essential nodes regulating CD14 expression in myeloid cells, using the differentiation of THP-1 cells as a starting point. This strategy uncovers many known pathways required for CD14 expression and regulating macrophage differentiation while additionally providing a list of novel targets either promoting or limiting this process. To speed translation of these results, we have then taken the approach of independently validating hits from the screen using well-curated small molecules. In this manner, we identify pharmacologically tractable hits that can either increase CD14 expression on non-differentiated monocytes or prevent CD14 upregulation during macrophage differentiation. An inhibitor for one of these targets, MAP2K3, translates through to studies on primary human monocytes, where it prevents upregulation of CD14 following M-CSF induced differentiation, and pro-inflammatory cytokine production in response to LPS. Therefore, this screening cascade has rapidly identified pharmacologically tractable nodes regulating a critical disease-relevant process.

The role of oxidized phospholipids in the development of disease

Oxidized phospholipids (OxPLs), complex mixtures of phospholipid oxidation products generated during normal or pathological processes, are increasingly recognized to show bioactive effects on many cellular signalling pathways. There is a growing body of evidence showing that OxPLs play an important role in many diseases, so it is essential to define the specific role of OxPLs in different diseases for the design of disease therapies. In vastly diverse pathological processes, OxPLs act as pro-inflammatory agents and contribute to the progression of many diseases; in addition, they play a role in anti-inflammatory processes, promoting the dissipation of inflammation and inhibiting the progression of some diseases. In addition to participating in the regulation of inflammatory responses, OxPLs affect the occurrence and development of diseases through other pathways, such as apoptosis promotion. In this review, the different and even opposite effects of different OxPL molecular species are discussed. Furthermore, the specific effects of OxPLs in various diseases, as well as the receptor and cellular mechanisms involved, are summarized.

Synergy between 15-lipoxygenase and secreted PLA2 promotes inflammation by formation of TLR4 agonists from extracellular vesicles

Damage-associated endogenous molecules induce innate immune response, thus making sterile inflammation medically relevant. Stress-derived extracellular vesicles (stressEVs) released during oxidative stress conditions were previously found to activate Toll-like receptor 4 (TLR4), resulting in expression of a different pattern of immune response proteins in comparison to lipopolysaccharide (LPS), underlying the differences between pathogen-induced and sterile inflammation. Here we report that synergistic activities of 15-lipoxygenase (15-LO) and secreted phospholipase A₂ (sPLA₂) are needed for the formation of TLR4 agonists, which were identified as lysophospholipids (lysoPLs) with oxidized unsaturated acyl chain. Hydroxy, hydroperoxy, and keto products of 2-arachidonoyl-lysoPI oxidation by 15-LO were identified by mass spectrometry (MS), and they activated the same gene pattern as stressEVs. Extracellular PLA₂ activity was detected in the synovial fluid from rheumatoid arthritis and gout patients. Furthermore, injection of sPLA₂ promoted K/BxN serum-induced arthritis in mice, whereby ankle swelling was partially TLR4 dependent. Results confirm the role of oxidized lysoPL of stressEVs in sterile inflammation that promotes chronic diseases. Both 15-LO and sPLA₂ enzymes are induced during inflammation, which opens the opportunity for therapy without compromising innate immunity against pathogens.

Macrophage TLR4 and PAR2 Signaling: Role in Regulating Vascular Inflammatory Injury and Repair

Macrophages play a central role in dictating the tissue response to infection and orchestrating subsequent repair of the damage. In this context, macrophages residing in the lungs continuously sense and discriminate among a wide range of insults to initiate the immune responses important to host-defense. Inflammatory tissue injury also leads to activation of proteases, and thereby the coagulation pathway, to optimize injury and repair post-infection. However, long-lasting inflammatory triggers from macrophages can impair the lung's ability to recover from severe injury, leading to increased lung vascular permeability and neutrophilic injury, hallmarks of Acute Lung Injury (ALI). In this review, we discuss the roles of toll-like receptor 4 (TLR4) and protease activating receptor 2 (PAR2) expressed on the macrophage cell-surface in regulating lung vascular inflammatory signaling.

Trimetazidine Improves the Outcome of EECP Therapy in Patients with Refractory Angina Pectoris

Introduction:

Cardiovascular disease (CAD) associated with death and disability remains a serious medical problem. In some patients the initial clinical coronary artery disease presentation is stable angina pectoris.

Aim:

The aim of the study was to evaluate the effect of EECP therapy with or without trimetazidine (TMZ) in patients with refractory angina via modulating peripheral monocyte expression of Toll like receptor2 (TLR2) and its downstream signaling.

Methods:

This is a double-blind randomized prospective study in which 88 stable refractory angina patients allocated into two groups, Enhanced External Counter Pulsation (EECP) group: included 44 patients with stable refractory angina, and were treated with EECP-Therapy. TMZ-EECP group: included 44 patients with stable refractory angina, we gave TMZ 35 mg twice daily in addition to EECP-Therapy.

Results:

TLR2 expression in peripheral monocyte investigated by flow cytometry and 8-iso-prostaglandin F2β (8-iso-PGF2 β), interleukin1β (IL-1β), heat shock protein 60 (HSP60) and monocytes chemoattractant protein-1(MCP-1) were also measured before the EECP-therapy and before giving TMZ to patients, and after 35 hours of EECP treatment (7 consecutive weeks). Inhibition in TLR2 expression in peripheral monocyte was observed among the EECP group (P<0.05). Inflammatory cytokine MCP-1 was remarkably decreased in both study groups but (heat shock protein 60 (HSP60), MCP-1 and interleukin-1β (IL-1β)) significantly decreased levels were observed among the TMZ-EECP group (P<0.05). Also, the oxidative stress biomarker 8-iso-prostaglandin F2β (8-iso-PGF2β) was decreased in both study groups but significantly decreased levels were observed among the TMZ-EECP group (P<0.05). TMZ and EECP therapy in patients with stable refractory angina remarkably decreased the inflammatory markers HSP60, MCP-1 and IL-1β in serum levels also the decreased levels were found in serum levels of oxidative stress marker 8-iso-PGF2β serum level.

Conclusion:

EECP-therapy decreased the expression of TLR2 on peripheral monocytes in patients with chronic stable refractory angina which yield improvement in the quality of patients’ life by decreasing the frequency of angina episodes, decreasing the Short-acting nitrate use and change the exercise tolerance and distance.

Phenotype and Response to PAMPs of Human Monocyte-Derived Foam Cells Obtained by Long-Term Culture in the Presence of oxLDLs

Cholesterol-laden, foam macrophages constitute the most characteristic component of human atherosclerotic plaques. Persistent uptake of oxLDLs results in accumulation of lipid bodies inside the cells and determines their phenotype and subsequent functions. In this work, we describe the phenotype of human monocyte-derived foam cells obtained by differentiation in the constant presence of oxLDLs for 30 days (prolonged-hMDFCs). Although neither the total cellular nor the cell surface expression of Toll-like receptors (TLR) was regulated by oxLDLs, the prolonged-hMDFCs changed dramatically their responsiveness to TLR ligands and inactivated bacteria. Using multiplex technology, we observed an acute decline in cytokine and chemokine production after surface and endosomal TLR stimulation with the exception of TLR2/6 triggering with agonists Pam2CSK4 and MALP-2. We also noted significant reduction of some surface receptors which can have accessory function in recognition of particulate antigens (CD47, CD81, and CD11b). In contrast, the prolonged-hMDFCs responded to inflammasome activation by LPS/nigericin with extensive, necrotic type cell death, which was partially independent of caspase-1. This pyroptosis-like cell death was aggravated by necrostatin-1 and rapamycin. These findings identify a potential contribution of mature foam cells to inflammatory status by increasing the immunogenic cell death burden. The observed cross-talk between foam cell death pathways may lead to recognition of a potential new marker for atherosclerosis disease severity. Overall, our study demonstrates that, in contrast to other cellular models of foam cells, the prolonged-hMDFCs acquire a functional phenotype which may help understanding the role of foam cells in the pathogenesis of atherosclerosis.

MIP-1α Expression Induced by Co-Stimulation of Human Monocytic Cells with Palmitate and TNF-α Involves the TLR4-IRF3 Pathway and Is Amplified by Oxidative Stress

Metabolic inflammation is associated with increased expression of saturated free fatty acids, proinflammatory cytokines, chemokines, and adipose oxidative stress. Macrophage inflammatory protein (MIP)-1α recruits the inflammatory cells such as monocytes, macrophages, and neutrophils in the adipose tissue; however, the mechanisms promoting the MIP-1α expression remain unclear. We hypothesized that MIP-1α co-induced by palmitate and tumor necrosis factor (TNF)-α in monocytic cells/macrophages could be further enhanced in the presence of reactive oxygen species (ROS)-mediated oxidative stress. To investigate this, THP-1 monocytic cells and primary human macrophages were co-stimulated with palmitate and TNF-α and mRNA and protein levels of MIP-1α were measured by using quantitative reverse transcription, polymerase chain reaction (qRT-PCR) and commercial enzyme-linked immunosorbent assays (ELISA), respectively. The cognate receptor of palmitate, toll-like receptor (TLR)-4, was blunted by genetic ablation, neutralization, and chemical inhibition. The involvement of TLR4-downstream pathways, interferon regulatory factor (IRF)-3 or myeloid differentiation (MyD)-88 factor, was determined using IRF3-siRNA or MyD88-deficient cells. Oxidative stress was induced in cells by hydrogen peroxide (H2O2) treatment and ROS induction was measured by dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay. The data show that MIP-1α gene/protein expression was upregulated in cells co-stimulated with palmitate/TNF-α compared to those stimulated with either palmitate or TNF-α (P < 0.05). Further, TLR4-IRF3 pathway was implicated in the cooperative induction of MIP-1α in THP-1 cells, and this cooperativity between palmitate and TNF-α was clathrin-dependent and also required signaling through c-Jun and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Notably, ROS itself induced MIP-1α and could further promote MIP-1α secretion together with palmitate and TNF-α. In conclusion, palmitate and TNF-α co-induce MIP-1α in human monocytic cells via the TLR4-IRF3 pathway and signaling involving c-Jun/NF-κB. Importantly, oxidative stress leads to ROS-driven MIP-1α amplification, which may have significance for metabolic inflammation.

Differential Modulation of the Phospholipidome of Proinflammatory Human Macrophages by the Flavonoids Quercetin, Naringin and Naringenin

The immunomodulatory activity of flavonoids is increasingly appreciated. Macrophage phospholipids (PLs) play crucial roles in cell-mediated inflammatory responses. However, little is known on how these PLs are affected upon flavonoid treatment. In this work, we have used mass-spectrometry-based lipidomics to characterize the changes in the phospholipidome of proinflammatory human-macrophage-like cells (THP-1-derived and LPS+IFN-γ-stimulated) incubated with non-cytotoxic concentrations of three flavonoids: quercetin, naringin and naringenin. One hundred forty-seven PL species belonging to various classes were identified, and their relative abundances were determined. Each flavonoid displayed its own unique signature of induced effects. Quercetin produced the strongest impact, acting both on constitutive PLs (phosphatidylcholines, phosphatidylethanolamines and sphingomyelins) and on minor signaling lipids, such as phosphatidylinositol (PI) and phosphatidylserine (PS) species. Conversely, naringin hardly affected structural PLs, producing changes in signaling molecules that were opposite to those seen in quercetin-treated macrophages. In turn, albeit sharing some effects with quercetin, naringenin did not change PI and PS levels and interfered with a set of phosphatidylcholines distinct from those modulated by quercetin. These results demonstrate that flavonoids bioactivity involves profound and specific remodeling of macrophage phospholipidome, paving the way to future studies on the role of cellular phospholipids in flavonoid-mediated immunomodulatory effects.

Inflammation, Lipid (Per)oxidation, and Redox Regulation

Significance: Inflammation increases during the aging process. It is linked to mitochondrial dysfunction and increased reactive oxygen species (ROS) production. Mitochondrial macromolecules are critical targets of oxidative damage; they contribute to respiratory uncoupling with increased ROS production, redox stress, and a cycle of senescence, cytokine production, and impaired oxidative phosphorylation. Targeting the formation or accumulation of oxidized biomolecules, particularly oxidized lipids, in immune cells and mitochondria could be beneficial for age-related inflammation and comorbidities. Recent Advances: Inflammation is central to age-related decline in health and exhibits a complex relationship with mitochondrial redox state and metabolic function. Improvements in mass spectrometric methods have led to the identification of families of oxidized phospholipids (OxPLs), cholesterols, and fatty acids that increase during inflammation and which modulate nuclear factor erythroid 2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor gamma (PPARγ), activator protein 1 (AP1), and NF-κB redox-sensitive transcription factor activity. Critical Issues: The kinetic and spatial resolution of the modified lipidome has profound and sometimes opposing effects on inflammation, promoting initiation at high concentration and resolution at low concentration of OxPLs. Future Directions: There is an emerging opportunity to prevent or delay age-related inflammation and vascular comorbidity through a resolving (oxy)lipidome that is dependent on improving mitochondrial quality control and restoring redox homeostasis.

Lipids, inflammasomes, metabolism, and disease

Inflammasomes are multi-protein complexes that regulate the cleavage of cysteine protease caspase-1, secretion of inflammatory cytokines, and induction of inflammatory cell death, pyroptosis. Several members of the nod-like receptor family assemble inflammasome in response to specific ligands. An exception to this is the NLRP3 inflammasome which is activated by structurally diverse entities. Recent studies have suggested that NLRP3 might be a sensor of cellular homeostasis, and any perturbation in distinct metabolic pathways results in the activation of this inflammasome. Lipid metabolism is exceedingly important in maintaining cellular homeostasis, and it is recognized that cells and tissues undergo extensive lipid remodeling during activation and disease. Some lipids are involved in instigating chronic inflammatory diseases, and new studies have highlighted critical upstream roles for lipids, particularly cholesterol, in regulating inflammasome activation implying key functions for inflammasomes in diseases with defective lipid metabolism. The focus of this review is to highlight how lipids regulate inflammasome activation and how this leads to the progression of inflammatory diseases. The key roles of cholesterol metabolism in the activation of inflammasomes have been comprehensively discussed. Besides, the roles of oxysterols, fatty acids, phospholipids, and lipid second messengers are also summarized in the context of inflammasomes. The overriding theme is that lipid metabolism has numerous but complex functions in inflammasome activation. A detailed understanding of this area will help us develop therapeutic interventions for diseases where dysregulated lipid metabolism is the underlying cause.

Oxidized Phospholipids in Healthy and Diseased Lung Endothelium

Circulating and cell membrane phospholipids undergo oxidation caused by enzymatic and non-enzymatic mechanisms. As a result, a diverse group of bioactive oxidized phospholipids generated in these conditions have both beneficial and harmful effects on the human body. Increased production of oxidized phospholipid products with deleterious effects is linked to the pathogenesis of various cardiopulmonary disorders such as atherosclerosis, thrombosis, acute lung injury (ALI), and inflammation. It has been determined that the contrasting biological effects of lipid oxidation products are governed by their structural variations. For example, full-length products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine oxidation (OxPAPC) have prominent endothelial barrier protective and anti-inflammatory activities while most of the truncated oxidized phospholipids induce vascular leak and exacerbate inflammation. The extensive studies from our group and other groups have demonstrated a strong potential of OxPAPC in mitigating a wide range of agonist-induced lung injuries and inflammation in pulmonary endothelial cell culture and rodent models of ALI. Concurrently, elevated levels of truncated oxidized phospholipids are present in aged mice lungs that potentiate the inflammatory agents-induced lung injury. On the other hand, increased levels of full length OxPAPC products accelerate ALI recovery by facilitating production of anti-inflammatory lipid mediator, lipoxin A4, and other molecules with anti-inflammatory properties. These findings suggest that OxPAPC-assisted lipid program switch may be a promising therapeutic strategy for treatment of acute inflammatory syndromes. In this review, we will summarize the vascular-protective and deleterious aspects of oxidized phospholipids and discuss their therapeutic potential including engineering of stable analogs of oxidized phospholipids with improved anti-inflammatory and barrier-protective properties.

Bacillus S-Layer-Mediated Innate Interactions During Endophthalmitis

Bacillus endophthalmitis is a severe intraocular infection. Hallmarks of Bacillus endophthalmitis include robust inflammation and rapid loss of vision. We reported that the absence of Bacillus surface layer protein (SLP) significantly blunted endophthalmitis severity. Here, we further investigated SLP in the context of Bacillus-retinal cell interactions and innate immune pathways to explore the mechanisms by which SLP contributes to intraocular inflammation. We compared phenotypes of Wild-type (WT) and SLP deficient (ΔslpA) Bacillus thuringiensis by analyzing bacterial adherence to and phagocytosis by human retinal Muller cells and phagocytosis by mouse neutrophils. Innate immune receptor activation by the Bacillus envelope and purified SLP was analyzed using TLR2/4 reporter cell lines. A synthetic TLR2/4 inhibitor was used as a control for this receptor activation. To induce endophthalmitis, mouse eyes were injected intravitreally with 100 CFU WT or ΔslpA B. thuringiensis. A group of WT infected mice was treated intravitreally with a TLR2/4 inhibitor at 4 h postinfection. At 10 h postinfection, infected eyes were analyzed for viable bacteria, inflammation, and retinal function. We observed that B. thuringiensis SLPs contributed to retinal Muller cell adherence, and protected this pathogen from Muller cell- and neutrophil-mediated phagocytosis. We found that B. thuringiensis envelope activated TLR2 and, surprisingly, TLR4, suggesting the presence of a surface-associated TLR4 agonist in Bacillus. Further investigation showed that purified SLP from B. thuringiensis activated TLR4, as well as TLR2 in vitro. Growth of WT B. thuringiensis was significantly higher and caused greater inflammation in untreated eyes than in eyes treated with the TLR2/4 inhibitor. Retinal function analysis also showed greater retention of A-wave and B-wave function in infected eyes treated with the TLR2/4 inhibitor. The TLR2/4 inhibitor was not antibacterial in vitro, and did not cause inflammation when injected into uninfected eyes. Taken together, these results suggest a potential role for Bacillus SLP in host-bacterial interactions, as well as in endophthalmitis pathogenesis via TLR2- and TLR4-mediated pathways.

The Generation and Identity of Human Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) are cells of myeloid lineage with a potent immunosuppressive capacity. They are present in cancer patients as well as in patients with severe inflammatory conditions and infections. MDSCs exist as two main subtypes, the granulocytic (G-MDSCs) and the monocytic (Mo-MDSCs) type, as defined by their surface phenotype and functions. While the functions of MDSCs have been investigated in depth, the origin of human MDSCs is less characterized and even controversial. In this review, we recapitulate theories on how MDSCs are generated in mice, and whether this knowledge is translatable into human MDSC biology, as well as on problems of defining MDSCs by their immature cell surface phenotype in relation to the plasticity of myeloid cells. Finally, the challenge of pharmacological targeting of MDSCs in the future is envisioned.