Lipoxin A₄ modulates adaptive immunity by decreasing memory B-cell responses via an ALX/FPR2-dependent mechanism

Resolvin D1 inhibits T follicular helper cell expansion in systemic lupus erythematosus

OBJECTIVE

Resolvin D1 (RvD1) is one of the specialized pro-resolving lipid mediators, which control inflammation resolution and regulate immune responses. Previous research showed that RvD1 could block the progression of systemic lupus erythematosus (SLE). However, the detailed mechanism remains to be fully understood.

METHOD

Plasma RvD1 levels, and proportions of T follicular helper cells (Tfh cells) were measured in SLE patients and healthy controls. Plasma RvD1 levels and proportions of Tfh cells were quantitated in an MRL/lpr mouse model of lupus treated with RvD1. Naïve CD4+ T cells were purified from MRL/lpr mice to study the effect of RvD1 on Tfh cell differentiation in vitro.

RESULTS

In patients, there were significant negative correlations between plasma RvD1 levels and Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score, as well as between plasma RvD1 and anti-double-stranded DNA antibody levels, and numbers of peripheral Tfh cells and plasma cells. In MRL/lpr mice, the expected amelioration of disease phenotype and inflammatory response with RvD1 treatment correlated with decreased percentages of Tfh cells and plasma cells. In addition, the differentiation and proliferation of Tfh cells were markedly suppressed by RvD1 in vitro.

CONCLUSION

RvD1 may control SLE progression through the suppression of Tfh cell differentiation and subsequent inhibition of B-cell responses.

A signaling network map of Lipoxin (LXA4): an anti-inflammatory molecule

Lipoxins (LXs) are a class of endogenous bioactive lipid mediators that are involved in the regulation of inflammation. They exert immunomodulatory effects by regulating the behaviour of various immune cells, including neutrophils, macrophages, and T and B cells, by promoting the clearance of apoptotic neutrophils. This helps to dampen inflammation and promote tissue repair. LXs regulate the expression of many inflammatory genes by modulating the levels of transcription factors, such as nuclear factor κB (NF-κB), activator protein-1 (AP-1), nerve growth factor-regulated factor 1A binding protein 1 (NGF), and peroxisome proliferator activated receptor γ (PPAR-γ), which are elevated in various diseases, such as respiratory tract diseases, renal diseases, cancer, neurodegenerative diseases, and viral infections. Lipoxin-mediated signaling is involved in chronic inflammation, cancer, diabetes-associated kidney disease, lung injury, liver injury, endometriosis, respiratory tract diseases, neurodegenerative diseases, chronic cerebral hypoperfusion, and retinal degeneration. In this study, we systematically investigated the intricate network of lipoxin signaling by analyzing the relevant literature. The resulting map comprised 467 molecules categorized as activation/inhibition, enzyme catalysis, gene and protein expression, molecular associations, and translocation events. This map serves as a valuable resource for understanding the complexity of lipoxin signaling and its impact on various cellular functions.

Cellular forgetting, desensitisation, stress and ageing in signalling networks. When do cells refuse to learn more?

Recent findings show that single, non-neuronal cells are also able to learn signalling responses developing cellular memory. In cellular learning nodes of signalling networks strengthen their interactions e.g. by the conformational memory of intrinsically disordered proteins, protein translocation, miRNAs, lncRNAs, chromatin memory and signalling cascades. This can be described by a generalized, unicellular Hebbian learning process, where those signalling connections, which participate in learning, become stronger. Here we review those scenarios, where cellular signalling is not only repeated in a few times (when learning occurs), but becomes too frequent, too large, or too complex and overloads the cell. This leads to desensitisation of signalling networks by decoupling signalling components, receptor internalization, and consequent downregulation. These molecular processes are examples of anti-Hebbian learning and 'forgetting' of signalling networks. Stress can be perceived as signalling overload inducing the desensitisation of signalling pathways. Ageing occurs by the summative effects of cumulative stress downregulating signalling. We propose that cellular learning desensitisation, stress and ageing may be placed along the same axis of more and more intensive (prolonged or repeated) signalling. We discuss how cells might discriminate between repeated and unexpected signals, and highlight the Hebbian and anti-Hebbian mechanisms behind the fold-change detection in the NF-κB signalling pathway. We list drug design methods using Hebbian learning (such as chemically-induced proximity) and clinical treatment modalities inducing (cancer, drug allergies) desensitisation or avoiding drug-induced desensitisation. A better discrimination between cellular learning, desensitisation and stress may open novel directions in drug design, e.g. helping to overcome drug resistance.

Single-cell RNA sequencing reveals the immune microenvironment landscape of osteosarcoma before and after chemotherapy

Chemotherapy, a primary treatment for osteosarcoma (OS), has limited knowledge regarding its impact on tumor immune microenvironment (TIME). Here, tissues from 6 chemotherapy-naive OS patients underwent single-cell RNA sequencing (scRNA-seq) and were analyzed alongside public dataset (GSE152048) containing 7 post-chemotherapy OS tissues. CD45+ (PTPRC+) cells were used for cell clustering and annotation. Changes in immune cell composition pre- and post-chemotherapy were characterized. Totally, 28,636 high-quality CD45+ (PTPRC+) cells were extracted. Following chemotherapy, the proportions of regulatory T cells (Tregs) and activated CD8 T cells decreased, while CD8 effector T cells increased. GO analysis indicated that differentially expressed genes (DEGs) in T cells were associated with cell activation, adaptive immune response, and immune response to tumor cells. Furthermore, the proportions of plasma cells increased, while naive B cells decreased. B cell surface receptors expression was upregulated, and GO analysis revealed DEGs of B cells were mainly enriched in B cell-mediated immunity and B cell activation. Moreover, M2 polarization of macrophages was suppressed post-chemotherapy. Overall, this study elucidates chemotherapy remodels the OS TIME landscape, triggering immune heterogeneity and enhancing anti-tumor properties.

Disrupted balance between pro-inflammatory lipid mediators and anti-inflammatory specialized pro-resolving mediators is linked to hyperinflammation in patients with alcoholic hepatitis

Background

Chronic excessive alcohol consumption leads to a spectrum of alcohol-associated liver diseases (ALD), including alcoholic hepatitis (AH). AH is characterized by intense systemic and liver inflammation, posing significant risks of health complications and mortality. While inflammation is a crucial defense mechanism against injury and infection, its timely resolution is essential to prevent tissue damage and restore tissue homeostasis. The resolution of inflammation is an actively regulated process, primarily governed by specialized pro-resolving mediators (SPMs), lipid metabolites derived from ω-6 and ω-3 poly-unsaturated fatty acids (PUFAs). We investigated the balance between pro-inflammatory lipid mediators (PLMs) and SPMs in the ω-6 and ω-3 PUFA metabolic pathways and examined the impact of alcohol abstinence on rectifying the dysregulated biosynthesis of PLMs and SPMs in AH patients.

Methods

LC-MS/MS and ELISA were used to quantify levels of bioactive lipid mediators (LMs) and their precursors in the plasma samples from 58 AH patients, 29 heavy drinkers without overt liver diseases (HDCs), and 35 healthy controls (HCs). Subsequently, we assessed correlations of altered LMs with clinical parameters and various markers of inflammatory cascade andmicrobial translocation. Furthermore, we conducted a longitudinal study to track changes in levels of LMs over 6- and 12-month follow-ups in AH patients who underwent alcohol abstinence.

Results

AH patients exhibited significantly higher plasma levels of ω-6 PLMs (PGD 2 and LTB 4 ) and SPM RvE1 compared to HDCs and/or HCs. Conversely, key SPMs such as LXA4, RvD1, and several precursors in the ω-3 pathway were significantly downregulated in AH patients. Some of these altered LMs were found to correlate with AH disease severity, clinical parameters, and various inflammatory cytokines. In particular, the LTB4/LXA4 ratio was substantially elevated in AH patients relative to HDCs and HCs. This altered ratio displayed a positive correlation with the MELD score, suggesting its potential utility as an indicator of disease severity in AH patients. Importantly, the majority of dysregulated LMs, particularly PLMs, were normalized following alcohol abstinence.

Conclusion

Our study reveals significant dysregulation in the levels of PLM metabolites and anti-inflammatory SPMs in both ω-6 and ω-3 PUFA pathways in AH patients. This disrupted biosynthesis, characterized by an overabundance of PLMs and a deficiency in SPMs, is linked to the heightened inflammation observed in AH patients. Importantly, our findings suggest an important role of alcohol abstinence in restoring the balance of these LMs and the potential therapeutic benefits of SPM supplements in alleviating the inflammatory cascade in AH patients.

Resolution of inflammation in oral diseases

The resolution of inflammation is an essential endogenous process that protects host tissues from an exaggerated chronic inflammatory response. Multiple interactions between host cells and resident oral microbiome regulate the protective functions that lead to inflammation in the oral cavity. Failure of appropriate regulation of inflammation can lead to chronic inflammatory diseases that result from an imbalance between pro-inflammatory and pro-resolution mediators. Thus, failure of the host to resolve inflammation can be considered an essential pathological mechanism for progression from the late stages of acute inflammation to a chronic inflammatory response. Specialized pro-resolving mediators (SPMs), which are essential polyunsaturated fatty acid (PUFA)-derived autacoid mediators, aid in regulating the endogenous inflammation resolving process by stimulating immune cell-mediated clearance of apoptotic polymorphonuclear neutrophils, cellular debris, and microbes, restricting further neutrophil tissue infiltration, and counter-regulating pro-inflammatory cytokine production. The SPM superfamily contains four specialized lipid mediator families: lipoxins, resolvins, protectins, and maresins that can activate resolution pathways. Understanding the crosstalk between resolution signals in the tissue response to injury has therapeutic application potential for preventing, maintaining, and regenerating chronically damaged tissues. Here, we discuss the fundamental concepts of resolution as an active biochemical process, novel concepts demonstrating the role of resolution mediators in tissue regeneration in periodontal and pulpal diseases, and future directions for therapeutic applications with particular emphasis on periodontal therapy.

Formyl peptide receptors in bone research

PURPOSE/AIM OF THE STUDY

The formyl peptide receptor (FPR) participates in the immune response, with roles in infection and inflammation. In this review article, we summarize the current literature on these roles before discussing the function of FPRs in the pathogenesis of musculoskeletal disorders including osteoarthritis (OA), degenerative disc disease (DDD), and rheumatoid arthritis (RA). Additionally, we discuss the potential diagnostic and therapeutic roles of FPRs in these domains.

METHODS

PubMed and Ovid MEDLINE searches were performed from 1965 through March 2022. Keywords included "FPR, tissue expression, inflammation, infection, musculoskeletal disorder, bone, rheumatoid arthritis, osteoarthritis, degenerative disc disease, mitochondria."

RESULTS

Sixty-nine studies were included in this review article. FPRs appear to be ubiquitous in the pathogenesis, diagnosis, and treatment of common musculoskeletal disorders. They can potentially be utilized for the earlier diagnosis of OA and DDD. They may be employed with mesenchymal stem cells (MSCs) to reverse OA and DDD pathologies. With anti-inflammatory, anti-osteolytic, and pro-angiogenic functions, they may broaden treatment options in RA.

CONCLUSIONS

FPRs appear to be heavily involved in the pathogenesis of common musculoskeletal conditions, including arthritis, degenerative disc disease, and rheumatoid arthritis. Furthermore, they demonstrate much promise in the diagnosis and treatment of these conditions. Their roles should continue to be explored.

Lipoxin and glycation in SREBP signaling: Insight into diabetic cardiomyopathy and associated lipotoxicity

Diabetes and cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Diabetes increases cardiovascular risk through hyperglycemia and atherosclerosis. Chronic hyperglycemia accelerates glycation reaction, which forms advanced glycation end products (AGEs). Additionally, hyperglycemia with enhanced levels of cholesterol, native and oxidized low-density lipoproteins, free fatty acids, and oxidative stress induces lipotoxicity. Accelerated glycation and disturbed lipid metabolism are characteristic features of diabetic heart failure. SREBP signaling plays a significant role in lipid and glucose homeostasis. AGEs increase lipotoxicity in diabetic cardiomyopathy by inhibiting SREBP signaling. While anti-inflammatory lipid mediators, lipoxins resolve inflammation caused by lipotoxicity by upregulating the PPARγ expression and regulating CD36. PPARγ connects the bridge between glycation and lipoxin in SREBP signaling. A summary of treatment modalities against diabetic cardiomyopathy is given in brief. This review indicates the novel therapeutic approach in the crosstalk between glycation and lipoxin in SREBP signaling.

Lipoxin Mimetics and the Resolution of Inflammation

Inflammation and its timely resolution are critical to ensure effective host defense and appropriate tissue repair after injury and or infection. Chronic, unresolved inflammation typifies many prevalent pathologies. The key mediators that initiate and drive the inflammatory response are well defined and targeted by conventional anti-inflammatory therapeutics. More recently, there is a growing appreciation that specific mediators, including arachidonate-derived lipoxins, are generated in self-limiting inflammatory responses to promote the resolution of inflammation and endogenous repair mechanisms without compromising host defense. We discuss the proresolving biological actions of lipoxins and recent efforts to harness their therapeutic potential through the development of novel, potent lipoxin mimetics generated via efficient, modular stereoselective synthetic pathways. We consider the evidence that lipoxin mimetics may have applications in limiting inflammation and reversing fibrosis and the underlying mechanisms.

Formyl peptide receptors are involved in CTX-induced impairment of lymphocyte functions

Crotoxin (CTX) is a neurotoxin that is isolated from the venom of Crotalus durissus terrificus, which displays immunomodulatory, anti-inflammatory, and anti-tumoral effects. Previous research has demonstrated that CTX promotes the adherence of leukocytes to the endothelial cells in blood microcirculation and the high endothelial venules of lymph nodes, which reduces the number of blood cells and lymphocytes. Studies have also shown that these effects are mediated by lipoxygenase-derived mediators. However, the exact lipoxygenase-derived eicosanoid involved in the CTX effect on lymphocytes is yet to be characterized. As CTX stimulates lipoxin-derived mediators from macrophages and lymphocyte effector functions could be modulated by activating formyl peptide receptors, we aimed to investigate whether these receptors were involved in CTX-induced redistribution and functions of lymphocytes in rats. We used male Wistar rats treated with CTX to demonstrate that Boc2 (butoxycarbonyl-Phe-Leu-Phe-Leu-Phe), an antagonist of formyl peptide receptors, prevented CTX-induced decrease in the number of circulating lymphocytes and increased the expression of the lymphocyte adhesion molecule LFA1. CTX reduced the T and B lymphocyte functions, such as lymphocyte proliferation in response to the mitogen Concanavalin A and antibody production in response to BSA immunization, respectively, which was prevented by the administration of Boc2. Importantly, mesenteric lymph node lymphocytes from CTX-treated rats showed an increased release of 15-epi-LXA₄. These results indicate that formyl peptide receptors mediate CTX-induced redistribution of lymphocytes and that 15-epi-LXA₄ is a key mediator of the immunosuppressive effects of CTX.

The role of oxylipins in NSAID-exacerbated respiratory disease (N-ERD)

Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyp formation, adult-onset asthma, and hypersensitivity to all cyclooxygenase-1 (COX-1) inhibitors. Oxygenated lipids are collectively known as oxylipins and are polyunsaturated fatty acids (PUFA) oxidation products. The most extensively researched oxylipins being the eicosanoids formed from arachidonic acid (AA). There are four major classes of eicosanoids including leukotrienes, prostaglandins, thromboxanes, and lipoxins. In N-ERD, the underlying inflammatory process of the upper and lower respiratory systems begins and occurs independently of NSAID consumption and is due to the overproduction of cysteinyl leukotrienes. Leukotriene mediators all induce edema, bronchoconstriction, and airway mucous secretion. Thromboxane A2 is a potent bronchoconstrictor and induces endothelial adhesion molecule expression. Elevated Prostaglandin D2 metabolites lead to vasoconstriction, additionally impaired up-regulation of prostaglandin E2 leads to symptoms seen in N-ERD as it is essential for maintaining homeostasis of inflammatory responses in the airway and has bronchoprotective and anti-inflammatory effects. A characteristic feature of N-ERD is diminished lipoxin levels, this decreased capacity to form endogenous mediators with anti-inflammatory properties could facilitate local inflammatory response and expose bronchial smooth muscle to relatively unopposed actions of broncho-constricting substances. Treatment options, such as leukotriene modifying agents, aspirin desensitization, biologic agents and ESS, appear to influence eicosanoid pathways, however more studies need to be done to further understand the role of oxylipins. Besides AA-derived eicosanoids, other oxylipins may also pay a role but have not been sufficiently studied. Identifying pathogenic N-ERD mechanism is likely to define more effective treatment targets.

Annexin A1 upregulates hematoma resolution via the FPR2/p-ERK(1/2)/DUSP1/CD36 signaling pathway after germinal matrix hemorrhage

Germinal matrix hemorrhage (GMH) is one of the leading causes of morbidity and mortality in preterm infants in the United States, with little progress made in its clinical management. Blood clots disrupting normal cerebrospinal fluid circulation and absorption after germinal matrix hemorrhage are key contributors towards post-hemorrhagic hydrocephalus development. n-formyl peptide receptor 2 (FPR2), a G-protein-coupled receptor, has been associated with the activation of p-ERK1/2, which in turn promotes the transcription of the DUSP1 gene, which may play a role in CD36 signaling. CD36 scavenger, a transmembrane glycoprotein, plays an essential role in microglia phagocytic blood clot clearance after GMH. FPR2's role in blood clot clearance after hemorrhagic stroke is unknown. We hypothesize that FPR2 activation by FPR2 agonist Annexin A1 (AnxA1) will enhance hematoma resolution via the upregulation of the CD36 signaling pathway, thereby improving short- and long-term neurological outcomes. Bacterial collagenase (0.3 U) was infused intraparenchymally into the right hemispheric ganglionic eminence in P7 rat pups to induce GMH. AnxA1 and FPR2 Inhibitor (Boc2) were given at 1-h post-GMH via intranasal administration. FPR2 CRISPR was given 48-h prior to GMH induction. Short-term neurological deficits were assessed using negative geotaxis test. Hematoma volume was assessed using hemoglobin assay. Protein expression was assessed using western blots. Long-term neurocognitive deficits and motor coordination were assessed using Morris water maze, rotarod, and foot fault tests. We have demonstrated that AnxA1 treatment enhances hematoma resolution and improved short and long-term outcomes. Lastly, FPR2 agonist AnxA1 treatment resulted in the upregulation of the FPR2/p-ERK(1/2)/DUSP1/CD36 signaling pathway.

Resolution of inflammation via RvD1/FPR2 signaling mitigates Nox2 activation and ferroptosis of macrophages in experimental abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) formation is characterized by inflammation, leukocyte infiltration, and vascular remodeling. Resolvin D1 (RvD1) is derived from ω-3 polyunsaturated fatty acids and is involved in the resolution phase of chronic inflammatory diseases. The aim of this study was to decipher the protective role of RvD1 via formyl peptide receptor 2 (FPR2) receptor signaling in attenuating abdominal aortic aneurysms (AAA). The elastase-treatment model of AAA in C57BL/6 (WT) mice and human AAA tissue was used to confirm our hypotheses. Elastase-treated FPR2-/- mice had a significant increase in aortic diameter, proinflammatory cytokine production, immune cell infiltration (macrophages and neutrophils), elastic fiber disruption, and decrease in smooth muscle cell α-actin expression compared to elastase-treated WT mice. RvD1 treatment attenuated AAA formation, aortic inflammation, and vascular remodeling in WT mice, but not in FPR2-/- mice. Importantly, human AAA tissue demonstrated significantly decreased FPR2 mRNA expression compared to non-aneurysm human aortas. Mechanistically, RvD1/FPR2 signaling mitigated p47phox phosphorylation and prevented hallmarks of ferroptosis, such as lipid peroxidation and Nrf2 translocation, thereby attenuating HMGB1 secretion. Collectively, this study demonstrates RvD1-mediated immunomodulation of FPR2 signaling on macrophages to mitigate ferroptosis and HMGB1 release, leading to resolution of aortic inflammation and remodeling during AAA pathogenesis.

Enriched Marine Oil Supplement Increases Specific Plasma Specialized Pro-Resolving Mediators in Adults with Obesity

BACKGROUND

Specialized pro-resolving mediators (SPMs), synthesized from PUFAs, resolve inflammation and return damaged tissue to homeostasis. Thus, increasing metabolites of the SPM biosynthetic pathway may have potential health benefits for select clinical populations, such as subjects with obesity who display dysregulation of SPM metabolism. However, the concentrations of SPMs and their metabolic intermediates in humans with obesity remains unclear.

OBJECTIVES

The primary objective of this study was to determine if a marine oil supplement increased specific metabolites of the SPM biosynthetic pathway in adults with obesity. The second objective was to determine if the supplement changed the relative abundance of key immune cell populations. Finally, given the critical role of antibodies in inflammation, we determined if ex vivo CD19 + B-cell antibody production was modified by marine oil intervention.

METHODS

Twenty-three subjects [median age: 56 y; BMI (in kg/m2): 33.1] consumed 2 g/d of a marine oil supplement for 28-30 d. The supplement was particularly enriched with 18-hydroxyeicosapentaenoic (HEPE), 14-hydroxydocosahexaenoic acid (14-HDHA), and 17-HDHA. Blood was collected pre- and postsupplementation for plasma mass spectrometry oxylipin and fatty acid analyses, flow cytometry, and B-cell isolation. Paired t-tests and Wilcoxon tests were used for statistical analyses.

RESULTS

Relative to preintervention, the supplement increased 6 different HEPEs and HDHAs accompanied by changes in plasma PUFAs. Resolvin E1 and docosapentaenoic acid-derived maresin 1 concentrations were increased 3.5- and 4.7-fold upon intervention, respectively. The supplement did not increase the concentration of D-series resolvins and had no effect on the abundance of immune cells. Ex vivo B-cell IgG but not IgM concentrations were lowered postsupplementation.

CONCLUSIONS

A marine oil supplement increased select SPMs and their metabolic intermediates in adults with obesity. Additional studies are needed to determine if increased concentrations of specific SPMs control the resolution of inflammation in humans with obesity. This trial was registered at clinicaltrials.gov as NCT04701138.

Activities and Molecular Mechanisms of Diterpenes, Diterpenoids, and Their Derivatives in Rheumatoid Arthritis

Diterpenes and their derivatives have many biological activities, including anti-inflammatory and immunomodulatory effects. To date, several diterpenes, diterpenoids, and their laboratory-derived products have been demonstrated for antiarthritic activities. This study summarizes the literature about diterpenes and their derivatives acting against rheumatoid arthritis (RA) depending on the database reports until 31 August 2021. For this, we have conducted an extensive search in databases such as PubMed, Science Direct, Google Scholar, and Clinicaltrials.gov using specific relevant keywords. The search yielded 2708 published records, among which 48 have been included in this study. The findings offer several potential diterpenes and their derivatives as anti-RA in various test models. Among the diterpenes and their derivatives, andrographolide, triptolide, and tanshinone IIA have been found to exhibit anti-RA activity through diverse pathways. In addition, some important derivatives of triptolide and tanshinone IIA have also been shown to have anti-RA effects. Overall, findings suggest that these substances could reduce arthritis score, downregulate oxidative, proinflammatory, and inflammatory biomarkers, modulate various arthritis pathways, and improve joint destruction and clinical arthritic conditions, signs, symptoms, and physical functions in humans and numerous experimental animals, mainly through cytokine and chemokine as well as several physiological protein interaction pathways. Taken all together, diterpenes, diterpenoids, and their derivatives may be promising tools for RA management.

Specialized pro-resolving mediators as modulators of immune responses

Specialized pro-resolving mediators (SPMs) are endogenous small molecules produced mainly from dietary omega-3 polyunsaturated fatty acids by both structural cells and cells of the active and innate immune systems. Specialized pro-resolving mediators have been shown to both limit acute inflammation and promote resolution and return to homeostasis following infection or injury. There is growing evidence that chronic immune disorders are characterized by deficiencies in resolution and SPMs have significant potential as novel therapeutics to prevent and treat chronic inflammation and immune system disorders. This review focuses on important breakthroughs in understanding how SPMs are produced by, and act on, cells of the adaptive immune system, specifically macrophages, B cells and T cells. We also highlight recent evidence demonstrating the potential of SPMs as novel therapeutic agents in topics including immunization, autoimmune disease and transplantation.

Regulation of T-Cell Immune Responses by Pro-Resolving Lipid Mediators

Both the initiation and the resolution of inflammatory responses are governed by the sequential activation, migration, and control/suppression of immune cells at the site of injury. Bioactive lipids play a major role in the fine-tuning of this dynamic process in a timely manner. During inflammation and its resolution, polymorphonuclear cells (PMNs) and macrophages switch from producing pro-inflammatory prostaglandins and leukotrienes to specialized pro-resolving lipid mediators (SPMs), namely, lipoxins, resolvins, protectins, and maresins, which are operative at the local level to limit further inflammation and tissue injury and restore homeostasis. Accumulating evidences expand now the role and actions of these lipid mediators from innate to adaptive immunity. In particular, SPMs have been shown to contribute to the control of chronic inflammation, and alterations in their production and/or function have been associated with the persistence of several pathological conditions, including autoimmunity, in human and experimental models. In this review, we focus on the impact of pro-resolving lipids on T cells through their ability to modulate T-cell responses. In particular, the effects of the different families of SPMs to restrain effector T-cell functions while promoting regulatory T cells will be reviewed, along with the underlying mechanisms. Furthermore, the emerging concept of SPMs as new biological markers for disease diagnostic and progression and as putative therapeutic tools to regulate the development and magnitude of inflammatory and autoimmune diseases is discussed.

Role of Specialized Pro-Resolving Mediators in Modifying Host Defense and Decreasing Bacterial Virulence

Bacterial infection activates the innate immune system as part of the host’s defense against invading pathogens. Host response to bacterial pathogens includes leukocyte activation, inflammatory mediator release, phagocytosis, and killing of bacteria. An appropriate host response requires resolution. The resolution phase involves attenuation of neutrophil migration, neutrophil apoptosis, macrophage recruitment, increased phagocytosis, efferocytosis of apoptotic neutrophils, and tissue repair. Specialized Pro-resolving Mediators (SPMs) are bioactive fatty acids that were shown to be highly effective in promoting resolution of infectious inflammation and survival in several models of infection. In this review, we provide insight into the role of SPMs in active host defense mechanisms for bacterial clearance including a new mechanism of action in which an SPM acts directly to reduce bacterial virulence.

Changes in B Cell Pool of Patients With Multibacillary Leprosy: Diminished Memory B Cell and Enhanced Mature B in Peripheral Blood

Despite being treatable, leprosy still represents a major public health problem, and many mechanisms that drive leprosy immunopathogenesis still need to be elucidated. B cells play important roles in immune defense, being classified in different subgroups that present distinct roles in the immune response. Here, the profile of B cell subpopulations in peripheral blood of patients with paucibacillary (TT/BT), multibacillary (LL/BL) and erythema nodosum leprosum was analyzed. B cell subpopulations (memory, transition, plasmablasts, and mature B cells) and levels of IgG were analyzed by flow cytometry and ELISA, respectively. It was observed that Mycobacterium leprae infection can alter the proportions of B cell subpopulations (increase of mature and decrease of memory B cells) in patients affected by leprosy. This modulation is associated with an increase in total IgG and the patient's clinical condition. Circulating B cells may be acting in the modulation of the immune response in patients with various forms of leprosy, which may reflect the patient's ability to respond to M. leprae.

Marginating transitional B cells modulate neutrophils in the lung during inflammation and pneumonia

Pulmonary innate immunity is required for host defense; however, excessive neutrophil inflammation can cause life-threatening acute lung injury. B lymphocytes can be regulatory, yet little is known about peripheral transitional IgM+ B cells in terms of regulatory properties. Using single-cell RNA sequencing, we discovered eight IgM+ B cell subsets with unique gene regulatory networks in the lung circulation dominated by transitional type 1 B and type 2 B (T2B) cells. Lung intravital confocal microscopy revealed that T2B cells marginate in the pulmonary capillaries via CD49e and require CXCL13 and CXCR5. During lung inflammation, marginated T2B cells dampened excessive neutrophil vascular inflammation via the specialized proresolving molecule lipoxin A4 (LXA4). Exogenous CXCL13 dampened excessive neutrophilic inflammation by increasing marginated B cells, and LXA4 recapitulated neutrophil regulation in B cell-deficient mice during inflammation and fungal pneumonia. Thus, the lung microvasculature is enriched in multiple IgM+ B cell subsets with marginating capillary T2B cells that dampen neutrophil responses.

Lipoxins and synthetic lipoxin mimetics: Therapeutic potential in renal diseases

Inflammation and its timely resolution are critical to ensuring effective host defence and appropriate tissue repair after injury. Unresolved inflammation typifies many renal pathologies. The key drivers of the inflammatory response are well defined and targeted by conventional anti-inflammatory therapeutics. However, these are associated with undesirable side effects including immune suppression. More recently, there is growing appreciation that specialized lipid mediators [SPMs] including lipoxins promote the resolution of inflammation and endogenous repair mechanisms without compromising host defence. We discuss the pro-resolving bioactions of lipoxins and recent work that aims to harness their therapeutic potential in the context of kidney disease.

Promising Therapeutic Targets for Treatment of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic poly-articular chronic autoimmune joint disease that mainly damages the hands and feet, which affects 0.5% to 1.0% of the population worldwide. With the sustained development of disease-modifying antirheumatic drugs (DMARDs), significant success has been achieved for preventing and relieving disease activity in RA patients. Unfortunately, some patients still show limited response to DMARDs, which puts forward new requirements for special targets and novel therapies. Understanding the pathogenetic roles of the various molecules in RA could facilitate discovery of potential therapeutic targets and approaches. In this review, both existing and emerging targets, including the proteins, small molecular metabolites, and epigenetic regulators related to RA, are discussed, with a focus on the mechanisms that result in inflammation and the development of new drugs for blocking the various modulators in RA.

Aspirin Actions in Treatment of NSAID-Exacerbated Respiratory Disease

Non-steroidal Anti-inflammatory drugs (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyposis, chronic rhinosinusitis, adult-onset asthma and hypersensitive reactions to cyclooxygenase-1 (COX-1) inhibitors. Among the available treatments for this disease, a combination of endoscopic sinus surgery followed by aspirin desensitization and aspirin maintenance therapy has been an effective approach. Studies have shown that long-term aspirin maintenance therapy can reduce the rate of nasal polyp recurrence in patients with N-ERD. However, the exact mechanism by which aspirin can both trigger and suppress airway disease in N-ERD remains poorly understood. In this review, we summarize current knowledge of aspirin effects in N-ERD, cardiovascular disease, and cancer, and consider potential mechanistic pathways accounting for the effects of aspirin in N-ERD.

Specialized Pro-Resolving Lipid Mediators in Neonatal Cardiovascular Physiology and Diseases

Cardiovascular disease remains a leading cause of mortality worldwide. Unresolved inflammation plays a critical role in cardiovascular diseases development. Specialized Pro-Resolving Mediators (SPMs), derived from long chain polyunsaturated fatty acids (LCPUFAs), enhances the host defense, by resolving the inflammation and tissue repair. In addition, SPMs also have anti-inflammatory properties. These physiological effects depend on the availability of LCPUFAs precursors and cellular metabolic balance. Most of the studies have focused on the impact of SPMs in adult cardiovascular health and diseases. In this review, we discuss LCPUFAs metabolism, SPMs, and their potential effect on cardiovascular health and diseases primarily focusing in neonates. A better understanding of the role of these SPMs in cardiovascular health and diseases in neonates could lead to the development of novel therapeutic approaches in cardiovascular dysfunction.

Resolvin D1 Attenuates the Organ Injury Associated With Experimental Hemorrhagic Shock

OBJECTIVE

To evaluate the potential changes in the plasma levels of resolvin D1 (RvD1) in patients with trauma and hemorrhage. Having found that trauma results in a profound reduction in plasma RvD1 in patients, we have then investigated the effects of RvD1 on the organ injury and dysfunction associated with hemorrhagic shock (HS) in the rat.

BACKGROUND

HS is a common cause of death in trauma due to excessive systemic inflammation and multiple organ failure. RvD1 is a member of the resolvin family of pro-resolution mediators.

METHODS

Blood samples were drawn from critically injured patients (n = 27, ACITII-prospective observational cohort study) within 2 hours of injury for targeted liquid chromatography tandem mass spectrometry. HS rats (removal of blood to reduce arterial pressure to 30 ± 2 mm Hg, 90 minutes, followed by resuscitation) were treated with RvD1 (0.3 or 1 μg/kg intravenous (i.v.)) or vehicle (n = 7). Parameters of organ injury and dysfunction were determined.

RESULTS

Plasma levels of RvD1 (mg/dL) were reduced in patients with trauma+HS (0.17 ± 0.08) when compared with healthy volunteers (0.76 ± 0.25) and trauma patients (0.62 ± 0.20). In rats with HS, RvD1 attenuated the kidney dysfunction, liver injury, and tissue ischemia. RvD1 also reduced activation of the nuclear factor (NF)-κB pathway and reduced the expression of pro-inflammatory proteins such as inducible nitric oxide synthase, tumor necrosis factor-α, interleukin-1β, and interleukin-6.

CONCLUSION

Plasma RvD1 is reduced in patients with trauma-HS. In rats with HS, administration of synthetic RvD1 on resuscitation attenuated the multiple organ failure associated with HS by a mechanism that involves inhibition of the activation of NF-κB.

Specialized pro-resolving lipid mediators in endodontics: a narrative review

Endodontics is the branch of dentistry concerned with the morphology, physiology, and pathology of the human dental pulp and periradicular tissues. Human dental pulp is a highly dynamic tissue equipped with a network of resident immunocompetent cells that play major roles in the defense against pathogens and during tissue injury. However, the efficiency of these mechanisms during dental pulp inflammation (pulpitis) varies due to anatomical and physiological restrictions. Uncontrolled, excessive, or unresolved inflammation can lead to pulp tissue necrosis and subsequent bone infections called apical periodontitis. In most cases, pulpitis treatment consists of total pulp removal. Although this strategy has a good success rate, this treatment has some drawbacks (lack of defense mechanisms, loss of healing capacities, incomplete formation of the root in young patients). In a sizeable number of clinical situations, the decision to perform pulp extirpation and endodontic treatment is justifiable by the lack of therapeutic tools that could otherwise limit the immune/inflammatory process. In the past few decades, many studies have demonstrated that the resolution of acute inflammation is necessary to avoid the development of chronic inflammation and to promote repair or regeneration. This active process is orchestrated by Specialized Pro-resolving lipid Mediators (SPMs), including lipoxins, resolvins, protectins and maresins. Interestingly, SPMs do not have direct anti-inflammatory effects by inhibiting or directly blocking this process but can actively reduce neutrophil infiltration into inflamed tissues, enhance efferocytosis and bacterial phagocytosis by monocytes and macrophages and simultaneously inhibit inflammatory cytokine production. Experimental clinical application of SPMs has shown promising result in a wide range of inflammatory diseases, such as renal fibrosis, cerebral ischemia, marginal periodontitis, and cancer; the potential of SPMs in endodontic therapy has recently been explored. In this review, our objective was to analyze the involvement and potential use of SPMs in endodontic therapies with an emphasis on SPM delivery systems to effectively administer SPMs into the dental pulp space.

High serum IgG subclass concentrations in children with e-waste Pb and Cd exposure

Immunoglobulin G (IgG) is the predominant component of the humoral immune system. Epidemiological studies have shown that lead (Pb) or cadmium (Cd) exposure is associated with changes in human IgG levels, and alteration of IgG subclass production can be induced by differential modulation of Th1 and Th2 cytokines caused by Pb or Cd exposure. However, no study has focused on the adverse effects of Pb and Cd co-exposure on IgG subclass production by regulating Th1/Th2 cytokines in children living in electronic waste (e-waste) areas. This study aims to analyze the associations among Pb and Cd in blood, Th1/Th2 cytokines, and IgG subclasses in serum from children. A total of 181 healthy, 2- to 7-year-old children were examined. Of them, 104 were from Guiyu (e-waste exposed group), and the rest were from Haojiang (reference group) in China. Pb and Cd levels in whole blood, cytokines, and IgG subclasses in serum were determined. Exposed children had higher levels of blood Pb and Cd, serum IgG1, IgG1 + IgG2, serum Th1 cytokine interferon-γ (IFN-γ) and lower levels of the Th2 cytokine interleukin (IL)-13. Increased blood Pb levels were positively associated with serum levels of IFN-γ, and negatively associated with serum levels of IL-13. Adjusted linear regression analysis showed that serum levels of IL-13 were negatively associated with serum levels of IgG1 and IgG1 + IgG2. Mediation models indicated that IL-13 had significant mediating effects on the relationships between blood Pb levels and serum IgG1, as well as between blood Pb levels and serum IgG1 + IgG2. Increased blood Cd levels were positively associated with serum levels of IgG1. Our results show heavy metal (particularly Pb) exposure may affect IgG subclass production by regulating Th1/Th2 cytokines in exposed children, thus providing new evidence for a relationship between humoral immune function and environmental exposure.

Untangling Local Pro-Inflammatory, Reparative, and Regulatory Damage-Associated Molecular-Patterns (DAMPs) Pathways to Improve Transplant Outcomes

Detrimental inflammatory responses after solid organ transplantation are initiated when immune cells sense pathogen-associated molecular patterns (PAMPs) and certain damage-associated molecular patterns (DAMPs) released or exposed during transplant-associated processes, such as ischemia/reperfusion injury (IRI), surgical trauma, and recipient conditioning. These inflammatory responses initiate and propagate anti-alloantigen (AlloAg) responses and targeting DAMPs and PAMPs, or the signaling cascades they activate, reduce alloimmunity, and contribute to improved outcomes after allogeneic solid organ transplantation in experimental studies. However, DAMPs have also been implicated in initiating essential anti-inflammatory and reparative functions of specific immune cells, particularly Treg and macrophages. Interestingly, DAMP signaling is also involved in local and systemic homeostasis. Herein, we describe the emerging literature defining how poor outcomes after transplantation may result, not from just an over-abundance of DAMP-driven inflammation, but instead an inadequate presence of a subset of DAMPs or related molecules needed to repair tissue successfully or re-establish tissue homeostasis. Adverse outcomes may also arise when these homeostatic or reparative signals become dysregulated or hijacked by alloreactive immune cells in transplant niches. A complete understanding of the critical pathways controlling tissue repair and homeostasis, and how alloimmune responses or transplant-related processes disrupt these will lead to new immunotherapeutics that can prevent or reverse the tissue pathology leading to lost grafts due to chronic rejection.

Application of specialized pro-resolving mediators in periodontitis and peri-implantitis: a review

Scaling and root planning is a key element in the mechanical therapy used for the eradication of biofilm, which is the major etiological factor for periodontitis and peri‐implantitis. However, periodontitis is also a host mediated disease, therefore, removal of the biofilm without adjunctive therapy may not achieve the desired clinical outcome due to persistent activation of the innate and adaptive immune cells. Most recently, even the resident cells of the periodontium, including periodontal ligament fibroblasts, have been shown to produce several inflammatory factors in response to bacterial challenge. With increased understanding of the pathophysiology of periodontitis, more research is focusing on opposing excessive inflammation with specialized pro‐resolving mediators (SPMs). This review article covers the major limitations of current standards of care for periodontitis and peri‐implantitis, and it highlights recent advances and prospects of SPMs in the context of tissue reconstruction and regeneration. Here, we focus primarily on the role of SPMs in restoring tissue homeostasis after periodontal infection.

Role of polyunsaturated fatty acids in ischemic stroke - A perspective of specialized pro-resolving mediators

Polyunsaturated fatty acids (PUFAs) have been proposed as beneficial for cardiovascular health. However, results from both epidemiological studies and clinical trials have been inconsistent, whereas most of the animal studies showed promising benefits of PUFAs in the prevention and treatment of ischemic stroke. In recent years, it has become clear that PUFAs are metabolized into various types of bioactive derivatives, including the specialized pro-resolving mediators (SPMs). SPMs exert multiple biofunctions, such as to limit excessive inflammatory responses, regulate lipid metabolism and immune cell functions, decrease production of pro-inflammatory factors, increase anti-inflammatory mediators, as well as to promote tissue repair and homeostasis. Inflammation has been recognised as a key contributor to the pathophysiology of acute ischemic stroke. Owing to their potent pro-resolving actions, SPMs are potential for development of novel anti-stroke therapy. In this review, we will summarize current knowledge of epidemiological studies, basic research and clinical trials concerning PUFAs in stroke prevention and treatment, with special attention to SPMs as the unsung heroes behind PUFAs.

Resolution-Based Therapies: The Potential of Lipoxins to Treat Human Diseases

Inflammation is an a physiological response instead an essential response of the organism to injury and its adequate resolution is essential to restore homeostasis. However, defective resolution can be the precursor of severe forms of chronic inflammation and fibrosis. Nowadays, it is known that an excessive inflammatory response underlies the most prevalent human pathologies worldwide. Therefore, great biomedical research efforts have been driven toward discovering new strategies to promote the resolution of inflammation with fewer side-effects and more specificity than the available anti-inflammatory treatments. In this line, the use of endogenous specialized pro-resolving mediators (SPMs) has gained a prominent interest. Among the different SPMs described, lipoxins stand out as one of the most studied and their deficiency has been widely associated with a wide range of pathologies. In this review, we examined the current knowledge on the therapeutic potential of lipoxins to treat diseases characterized by a severe inflammatory background affecting main physiological systems, paying special attention to the signaling pathways involved. Altogether, we provide an updated overview of the evidence suggesting that increasing endogenously generated lipoxins may emerge as a new therapeutic approach to prevent and treat many of the most prevalent diseases underpinned by an increased inflammatory response.

Hormonal Dysregulation and Unbalanced Specialized Pro-Resolving Mediator Biosynthesis Contribute toward Impaired B Cell Outcomes in Obesity

Diet-induced obesity is associated with impaired B-cell-driven humoral immunity, which coincides with chronic inflammation and has consequences for responses to infections and vaccinations. Key nutritional, cellular, and molecular mechanisms by which obesity may impair aspects of humoral immunity such as B cell development, class switch recombination, and formation of long-lived antibody secreting cells are reviewed. A key theme to emerge is the central role of white adipose tissue on the formation and function of pro-inflammatory B cell subsets that exacerbate insulin resistance. The underlying role of select hormones such as leptin is highlighted, which may be driving the formation of pro-inflammatory B cells in the absence of antigen stimulation. This review also extensively covers the regulatory role of lipid metabolites such as prostaglandins and specialized pro-resolving mediators (SPMs) that are synthesized from polyunsaturated fatty acids. Notably, SPM biosynthesis is impaired in obesity and contributes toward impaired antibody production. Future directions for research, including avenues for therapeutic intervention, are included.

Role of specialized pro-resolving lipid mediators and their receptors in virus infection: a promising therapeutic strategy for SARS-CoV-2 cytokine storm

Unexpected viral infections outbreaks, significantly affect human health, leading to increased mortality and life disruption. Among them is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which emerged as a deadly pandemic, calling for intense research efforts on its pathogenicity mechanism and development of therapeutic strategies. In the SARS-CoV-2 cytokine storm, systemic inflammation has been associated with severe illness and mortality. Recent studies have demonstrated special pro-resolving lipids mediators (SPMs) lipoxins, resolvins, maresins, and protectins as potential therapeutic options for abnormal viral-triggered inflammation. Pro-resolving lipids mediators have shown great promise for the treatment of Herpes simplex virus, respiratory syncytial virus, human immunodeficiency virus, and hepatitis C virus. Based on this, studies are being conducted on their therapeutic effects in SARS-CoV-2 infection. In this review, we discussed SPMs and reviewed evidence from recent studies on SPMs as therapeutic options for viral infections, including SARS-CoV2. Based on our analysis of the previous study, we argue that SPMs are a potential treatment for SARS-CoV-2 infection and other viral infections. We expect further research on how SPMs modulate viral-triggered inflammation through G-protein-coupled receptors (GPCRs), and chemical stability and druggability of SPMs.

The roles of small-molecule inflammatory mediators in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation and joint destruction. Although great progress has been made in the treatment of RA with antagonists of pro-inflammatory cytokines such as TNF-α, IL-6 and IL-1, the disease remains refractory in some patients. Previous studies have found that small-molecule inflammatory mediators, such as prostaglandins, leukotrienes, reactive oxygen species, nitric oxide, lipoxins and platelet-activating factor, play a significant role in the development of RA. Such compounds help to induce, maintain or reduce inflammation and could therefore be potential therapeutic targets. In this review, we describe the roles of various classes of small-molecule inflammatory mediators in RA and discuss the effects of some drugs that modulate their activity. Many drugs targeting these mediators have demonstrated good efficacy in mouse models of RA but not in patients. However, it is clear that many small-molecule inflammatory mediators play key roles in the pathogenesis of RA, and a better understanding of the underlying molecular pathways may assist in the development of targeted therapies that are efficacious in RA patients.

Learning of Signaling Networks: Molecular Mechanisms

Molecular processes of neuronal learning have been well described. However, learning mechanisms of non-neuronal cells are not yet fully understood at the molecular level. Here, we discuss molecular mechanisms of cellular learning, including conformational memory of intrinsically disordered proteins (IDPs) and prions, signaling cascades, protein translocation, RNAs [miRNA and long noncoding RNA (lncRNA)], and chromatin memory. We hypothesize that these processes constitute the learning of signaling networks and correspond to a generalized Hebbian learning process of single, non-neuronal cells, and we discuss how cellular learning may open novel directions in drug design and inspire new artificial intelligence methods.

New Advances in Targeting the Resolution of Inflammation: Implications for Specialized Pro-Resolving Mediator GPCR Drug Discovery

Chronic inflammation is a component of numerous diseases including autoimmune, metabolic, neurodegenerative, and cancer. The discovery and characterization of specialized pro-resolving mediators (SPMs) critical to the resolution of inflammation, and their cognate G protein-coupled receptors (GPCRs) has led to a significant increase in the understanding of this physiological process. Approximately 20 ligands, including lipoxins, resolvins, maresins, and protectins, and 6 receptors (FPR2/ALX, GPR32, GPR18, chemerin₁, BLT₁, and GPR37) have been identified highlighting the complex and multilayered nature of resolution. Therapeutic efforts in targeting these receptors have proved challenging, with very few ligands apparently progressing through to preclinical or clinical development. To date, some knowledge gaps remain in the understanding of how the activation of these receptors, and their downstream signaling, results in efficient resolution via apoptosis, phagocytosis, and efferocytosis of polymorphonuclear leukocytes (mainly neutrophils) and macrophages. SPMs bind and activate multiple receptors (ligand poly-pharmacology), while most receptors are activated by multiple ligands (receptor pleiotropy). In addition, allosteric binding sites have been identified signifying the capacity of more than one ligand to bind simultaneously. These fundamental characteristics of SPM receptors enable alternative targeting strategies to be considered, including biased signaling and allosteric modulation. This review describes those ligands and receptors involved in the resolution of inflammation, and highlights the most recent clinical trial results. Furthermore, we describe alternative mechanisms by which these SPM receptors could be targeted, paving the way for the identification of new therapeutics, perhaps with greater efficacy and fidelity.

Therapeutic Potential of Lipoxin A4 in Chronic Inflammation: Focus on Cardiometabolic Disease

Several studies have shown that failure to resolve inflammation may contribute to the progression of many chronic inflammatory disorders. It has been suggested targeting the resolution of inflammation might be a novel therapeutic approach for chronic inflammatory diseases, including inflammatory bowel disease, diabetic complications, and cardiometabolic disease. Lipoxins [LXs] are a class of endogenously generated mediators that promote the resolution of inflammation. Biological actions of LXs include inhibition of neutrophil infiltration, promotion of macrophage polarization, increase of macrophage efferocytosis, and restoration of tissue homeostasis. Recently, several studies have demonstrated that LXs and synthetic analogues protect tissues from acute and chronic inflammation. The mechanism includes down-regulation of pro-inflammatory cytokines and chemokines (e.g., interleukin-1β and tumor necrosis factor-α), inhibition of the activation of the master pro-inflammatory pathway (e.g., nuclear factor κ-light-chain-enhancer of activated B cells pathway) and increased release of the pro-resolving cytokines (e.g., interleukin-10). Three generations of LXs analogues are well described in the literature, and more recently a fourth generation has been generated that appears to show enhanced potency. In this review, we will briefly discuss the potential therapeutic opportunity provided by lipoxin A₄ as a novel approach to treat chronic inflammatory disorders, focusing on cardiometabolic disease and the current drug development in this area.

Lack of resolution sensor drives age-related cardiometabolic and cardiorenal defects and impedes inflammation-resolution in heart failure

Objective

Recently, we observed that the specialized proresolving mediator (SPM) entity resolvin D1 activates lipoxin A₄/formyl peptide receptor 2 (ALX/FPR2), which facilitates cardiac healing and persistent inflammation is a hallmark of impaired cardiac repair in aging. Splenic leukocyte-directed SPMs are essential for the safe clearance of inflammation and cardiac repair after injury; however, the target of SPMs remains undefined in cardiac healing and repair.

Methods

To define the mechanistic basis of ALX/FPR2 as a resolvin D1 target, ALX/FPR2-null mice were examined extensively. The systolic-diastolic heart function was assessed using echocardiography, leukocytes were phenotyped using flow cytometry, and SPMs were quantitated using mass spectrometry. The presence of cardiorenal syndrome was validated using histology and renal markers.

Results

Lack of ALX/FPR2 led to the development of spontaneous obesity and diastolic dysfunction with reduced survival with aging. After cardiac injury, ALX/FPR2^−/− mice showed lower expression of lipoxygenases (−5, −12, −15) and a reduction in SPMs in the infarcted left ventricle and spleen, indicating nonresolving inflammation. Reduced SPM levels in the infarcted heart and spleen are suggestive of impaired cross-talk between the injured heart and splenic leukocytes, which are required for the resolution of inflammation. In contrast, cyclooxygenases (−1 and −2) were over amplified in the infarcted heart. Together, these results suggest interorgan signaling in which the spleen acts as both an SPM biosynthesizer and supplier in acute heart failure. ALX/FPR2 dysfunction magnified obesogenic cardiomyopathy and renal inflammation (↑NGAL, ↑TNF-α, ↑CCL2, ↑IL-1β) with elevated plasma creatinine levels in aging mice. At the cellular level, ALX/FPR2^−/− mice showed impairment of macrophage phagocytic function ex-vivo with expansion of neutrophils after myocardial infarction.

Conclusions

Lack of ALX/FPR2 induced obesity, reduced the life span, amplified leukocyte dysfunction, and facilitated profound interorgan nonresolving inflammation. Our study shows the integrative and indispensable role of ALX/FPR2 in lipid metabolism, cardiac inflammation–resolution processes, obesogenic aging, and renal homeostasis.

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Lack of resolution sensor (ALX/FPR2) led to spontaneous, age-related obesity.

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Absence of ALX/FPR2 triggered obesogenic cardiomyopathy and renal inflammation.

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Deficiency of ALX/FPR2 reduced SPMs in the infarcted heart after cardiac injury.

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ALX/FPR2 dysfunction impaired macrophage function and amplified inflammation.

Spontaneous remission of advanced progressive poorly differentiated non-small cell lung cancer: a case report and review of literature

BACKGROUND

Spontaneous remission (SR) of cancer is a very rare phenomenon of unknown mechanism. In particular, SR of non-small cell lung cancer (NSCLC) has been scarcely reported. We present the case of a 74-year-old woman with advanced, poorly differentiated NSCLC (highly expressing programmed death ligand-1 [PD-L1]) that progressed despite multiple lines of chemotherapy but then spontaneously remitted.

CASE PRESENTATION

The patient presented with hemoptysis and was diagnosed with stage IIIA poorly differentiated NSCLC via bronchoscopic biopsy. She had an unremarkable medical history and moderate performance status. The initial treatment plan was surgery after neoadjuvant chemotherapy. Despite conventional chemotherapy, follow-up chest computed tomography (CT) showed gradual tumor progression and she decided against further treatment after fifth-line chemotherapy. However, the size of lung mass was markedly decreased on follow-up chest CT one year after ceasing chemotherapy. Also, follow-up positron emission tomography images showed decreased metabolic activity in the lung mass and a percutaneous biopsy specimen from the diminished lung mass revealed no viable tumor cells. A diagnosis of SR of NSCLC was confirmed, and the patient was without tumor progression on follow-up nine months later. Later, PD-L1 immunostaining revealed high positivity (> 99%) in initial tumor cells.

CONCLUSION

Our case showing SR of poorly advanced NSCLC refractory to multiple lines of chemotherapy suggested the association between immunity and tumor regression.

Frontline Science: A reduction in DHA-derived mediators in male obesity contributes toward defects in select B cell subsets and circulating antibody

Obesity dysregulates B cell populations, which contributes toward poor immunological outcomes. We previously reported that differing B cell subsets are lowered in the bone marrow of obese male mice. Here, we focused on how lipid metabolites synthesized from docosahexaenoic acid (DHA) known as specialized pro-resolving lipid mediators (SPMs) influence specific B cell populations in obese male mice. Metabololipidomics revealed that splenic SPM precursors 14-hydroxydocosahexaenoic acid (14-HDHA), 17-hydroxydocosahexaenoic acid (17-HDHA), and downstream protectin DX (PDX) were decreased in obese male C57BL/6J mice. Simultaneous administration of these mediators to obese mice rescued major decrements in bone marrow B cells, modest impairments in the spleen, and circulating IgG2c, which is pro-inflammatory in obesity. In vitro studies with B cells, flow cytometry experiments with ALOX5^-/- mice, and lipidomic analyses revealed the lowering of 14-HDHA/17-HDHA/PDX and dysregulation of B cell populations in obesity was driven indirectly via B cell extrinsic mechanisms. Notably, the lowering of lipid mediators was associated with an increase in the abundance of n-6 polyunsaturated fatty acids, which have a high affinity for SPM-generating enzymes. Subsequent experiments revealed female obese mice generally maintained the levels of SPM precursors, B cell subsets, and antibody levels. Finally, obese human females had increased circulating plasma cells accompanied by ex vivo B cell TNFα and IL-10 secretion. Collectively, the data demonstrate that DHA-derived mediators of the SPM pathway control the number of B cell subsets and pro-inflammatory antibody levels in obese male but not female mice through a defect that is extrinsic to B cells.

Role of the lipoxin A4 receptor in the development of neutrophil extracellular traps in Leishmania infantum infection

BACKGROUND

Neutrophils play an immunomodulatory role through the release of neutrophil extracellular traps (NETs). NETs are released in response to Leishmania infection, but the mechanism of NET extrusion has not been elucidated. The lipoxin A4 receptor on neutrophils is crucial for the inflammatory response and immune regulation of many diseases, including Leishmania infection. Therefore, in the present study, we tried to explore whether Leishmania infantum promastigotes stimulate neutrophil activation and NET release via activating the lipoxin A4 receptor.

RESULTS

Leishmania infantum promastigotes stimulated neutrophil activity, but blocking of the lipoxin A4 receptor with its antagonist Boc prior to L. infantum stimulation abrogated these effects. Neutrophils showed citrullinated histone H3 expression and simultaneous NET extrusion on L. infantum stimulation, but a decline in both was observed on blocking of the lipoxin A4 receptor. Moreover, differentiated HL-60 cells with lipoxin A4 receptor silencing showed a decrease in citrullinated histone H3 expression as compared to the unsilenced HL-60 samples on stimulation with promastigotes.

CONCLUSIONS

Leishmania infantum promastigotes altered the characteristics of neutrophils and induced NET extrusion by activating the lipoxin A4 receptor. The lipoxin A4 receptor may have potential as a therapeutic target in relation to NET extrusion in the treatment of leishmaniasis, but its mechanisms of action need to be explored in more depth.

Specialized Proresolving Mediators in Innate and Adaptive Immune Responses in Airway Diseases

Airborne pathogens and environmental stimuli evoke immune responses in the lung. It is critical to health that these responses be controlled to prevent tissue damage and the compromise of organ function. Resolution of inflammation is a dynamic process that is coordinated by biochemical and cellular mechanisms. Recently, specialized proresolving mediators (SPMs) have been identified in resolution exudates. These molecules orchestrate anti-inflammatory and proresolving actions that are cell type specific. In this review, we highlight SPM biosynthesis, the influence of SPMs on the innate and adaptive immune responses in the lung, as well as recent insights from SPMs on inflammatory disease pathophysiology. Uncovering these mediators and cellular mechanisms for resolution is providing new windows into physiology and disease pathogenesis.

Eicosanoid and Specialized Proresolving Mediator Regulation of Lymphoid Cells

Eicosanoids and specialized proresolving mediators (SPMs) regulate leukocyte function and inflammation. They are ideally positioned at the interface of the innate and adaptive immune responses when lymphocytes interact with leukocytes. Receptors for leukotriene B₄ (LTB₄), prostaglandin E₂ (PGE₂), and SPMs are expressed on lymphocytes. Evidence points toward an essential role of these lipid mediators (LMs) in direct regulation of lymphocyte functions. SPMs, which include lipoxins, demonstrate comprehensive protective actions with lymphocytes. LTB₄ and PGE₂ regulation of lymphocytes is diverse and depends on the interaction of lymphocytes with other cells. Importantly, both LTB₄ and PGE₂ are essential regulators of T cell antitumor activity. These LMs are attractive therapeutic targets to control dysregulated innate and adaptive immune responses, promote lymphocyte antitumor activity, and prevent tumor immune evasion.

Lipoxin B4 Enhances Human Memory B Cell Antibody Production via Upregulating Cyclooxygenase-2 Expression

Vaccination has been the most effective way to prevent or reduce infectious diseases; examples include the eradication of smallpox and attenuation of tetanus and measles. However, there is a large segment of the population that responds poorly to vaccines, in part because they are immunocompromised because of disease, age, or pharmacologic therapy and are unable to generate long-term protection. Specialized proresolving mediators are endogenously produced lipids that have potent proresolving and anti-inflammatory activities. Lipoxin B₄ (LXB₄) is a member of the lipoxin family, with its proresolving effects shown in allergic airway inflammation. However, its effects on the adaptive immune system, especially on human B cells, are not known. In this study, we investigated the effects of LXB₄ on human B cells using cells from healthy donors and donors vaccinated against influenza virus in vitro. LXB₄ promoted IgG Ab production in memory B cells and also increased the number of IgG-secreting B cells. LXB₄ enhanced expression of two key transcription factors involved in plasma cell differentiation, BLIMP1 and XBP1. Interestingly, LXB₄ increased expression of cyclooxygenase-2 (COX2), an enzyme that is required for efficient B cell Ab production. The effects of LXB₄ are at least partially COX2-dependent as COX2 inhibitors attenuated LXB₄-stimulated BLIMP1 and Xpb-1 expression as well as IgG production. Thus, our study reveals for the first time, to our knowledge, that LXB₄ boosts memory B cell activation through COX2 and suggests that LXB₄ can serve as a new vaccine adjuvant.

Key roles for lipid mediators in the adaptive immune response

Chronic inflammation is an underlying feature of many diseases, including chronic obstructive pulmonary disease, rheumatoid arthritis, asthma, and multiple sclerosis. There is an increasing appreciation of the dysregulation of adaptive immunity in chronic inflammatory and allergic diseases. The discovery of specialized pro-resolving lipid mediators (SPMs) that actively promote the resolution of inflammation has opened new avenues for the treatment of chronic inflammatory diseases. Much work has been done focusing on the impact of SPMs on innate immune cells. However, much less is known about the influence of SPMs on the development of antigen-specific adaptive immune responses. This Review highlights the important breakthroughs concerning the effects of SPMs on the key cell types involved in the development of adaptive immunity, namely dendritic cells, T cells, and B cells.

Lipoxin A4 Attenuates the Inflammatory Response in Stem Cells of the Apical Papilla via ALX/FPR2

Similar to the onset phase of inflammation, its resolution is a process that unfolds in a manner that is coordinated and regulated by a panel of mediators. Lipoxin A4 (LXA₄) has been implicated as an anti-inflammatory, pro-resolving mediator. We hypothesized that LXA₄ attenuates or prevents an inflammatory response via the immunosuppressive activity of Stem Cells of the Apical Papilla (SCAP). Here, we report for the first time in vitro that in a SCAP population, lipoxin receptor ALX/FPR2 was constitutively expressed and upregulated after stimulation with lipopolysaccharide and/or TNF-α. Moreover, LXA₄ significantly enhanced proliferation, migration, and wound healing capacity of SCAP through the activation of its receptor, ALX/FPR2. Cytokine, chemokine and growth factor secretion by SCAP was inhibited in a dose dependent manner by LXA₄. Finally, LXA₄ enhanced immunomodulatory properties of SCAP towards Peripheral Blood Mononuclear Cells. These findings provide the first evidence that the LXA₄-ALX/FPR2 axis in SCAP regulates inflammatory mediators and enhances immunomodulatory properties. Such features of SCAP may also support the role of these cells in the resolution phase of inflammation and suggest a novel molecular target for ALX/FPR2 receptor to enhance a stem cell-mediated pro-resolving pathway.

Formyl peptide receptor activation inhibits the expansion of effector T cells and synovial fibroblasts and attenuates joint injury in models of rheumatoid arthritis

The effects of formyl peptide receptors (FPRs) on effector T cells and inflammation-causing tissue-resident cells are not well known. Here, we explored the effect of FPR activation on efferent T cell responses in models of rheumatoid arthritis (RA) and on the expansion of fibroblast-like synoviocytes (FLS). Compound 43 (Cpd43; FPR1/2 agonist) was administered to mice with collagen-induced arthritis (CIA) or antigen-induced arthritis (AIA) after disease onset. Joint inflammation/damage and immunity were assessed. FLS were cultured with Cpd43 to test its effects on cell apoptosis and proliferation. To explore the effects of endogenous FPR2 ligands on FLS proliferation, FLS FPR2 was blocked or Annexin A1 (AnxA1) expression silenced. Cpd43 reduced arthritis severity in both models. In CIA, Cpd43 decreased CD4 T cell proliferation and survival and increased the production of the protective cytokine, IFNγ, in lymph nodes. In AIA, Cpd43 increased CD4 apoptosis and production of the anti-inflammatory IL-4, while augmenting the proportion of splenic regulatory T cells and their expression of IL-2Rα. In both models, Cpd43 increased CD4 IL-17A production, without affecting humoral immunity. FPR2 inhibitors reversed Cpd43-mediated effects on AIA and T cell immunity. Cpd43 decreased TNF-induced FLS proliferation and augmented FLS apoptosis in association with intracellular FPR2 accumulation, while endogenous AnxA1 and FPR2 reduced FLS proliferation via the ERK and NFκB pathways. Overall, FPR activation inhibits the expansion of arthritogenic effector CD4 T cells and FLS, and reduces joint injury in experimental arthritis. This suggests the therapeutic potential of FPR ligation for the treatment of RA.

The G-Protein-Coupled Receptor ALX/Fpr2 Regulates Adaptive Immune Responses in Mouse Submandibular Glands

Lipoxin receptor (ALX)/N-formyl peptide receptor (FPR)-2 is a G-protein-coupled receptor that has multiple binding partners, including the endogenous lipid mediators resolvin D1, lipoxin A₄, and the Ca²⁺-dependent phospholipid-binding protein annexin A1. Previous studies have demonstrated that resolvin D1 activates ALX/Fpr2 to resolve salivary gland inflammation in the NOD/ShiLtJ mouse model of Sjögren syndrome. Moreover, mice lacking the ALX/Fpr2 display an exacerbated salivary gland inflammation in response to lipopolysaccharide. Additionally, activation of ALX/Fpr2 has been shown to be important for regulating antibody production in B cells. These previous studies indicate that ALX/Fpr2 promotes resolution of salivary gland inflammation while modulating adaptive immunity, suggesting the need for investigation of the role of ALX/Fpr2 in regulating antibody production and secretory function in mouse salivary glands. Our results indicate that aging female knockout mice lacking ALX/Fpr2 display a significant reduction in saliva flow rates and weight loss, an increased expression of autoimmune-associated genes, an up-regulation of autoantibody production, and increased CD20-positive B-cell population. Although not all effects were noted among the male knockout mice, the results nonetheless indicate that ALX/Fpr2 is clearly involved in the adaptive immunity and secretory function in salivary glands, with further investigation warranted to determine the cause(s) of these between-sex differences.