Lipid mediators foster the differentiation of T follicular helper cells

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.

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.

Annexin A1 as a Regulator of Immune Response in Cancer

Annexin A1 is a 37 kDa phospholipid-binding protein that is expressed in many tissues and cell types, including leukocytes, lymphocytes and epithelial cells. Although Annexin A1 has been extensively studied for its anti-inflammatory activity, it has been shown that, in the cancer context, its activity switches from anti-inflammatory to pro-inflammatory. Remarkably, Annexin A1 shows pro-invasive and pro-tumoral properties in several cancers either by eliciting autocrine signaling in cancer cells or by inducing a favorable tumor microenvironment. Indeed, the signaling of the N-terminal peptide of AnxA1 has been described to promote the switching of macrophages to the pro-tumoral M2 phenotype. Moreover, AnxA1 has been described to prevent the induction of antigen-specific cytotoxic T cell response and to play an essential role in the induction of regulatory T lymphocytes. In this way, Annexin A1 inhibits the anti-tumor immunity and supports the formation of an immunosuppressed tumor microenvironment that promotes tumor growth and metastasis. For these reasons, in this review we aim to describe the role of Annexin A1 in the establishment of the tumor microenvironment, focusing on the immunosuppressive and immunomodulatory activities of Annexin A1 and on its interaction with the epidermal growth factor receptor.

PLA2G4A promotes right-sided colorectal cancer progression by inducing CD39+γδ Treg polarization

The γδ T cell is a promising candidate cell in tumor immunotherapy. However, γδ T cells polarize to CD39⁺γδ Tregs upon colorectal cancer (CRC) induction, and the underlying mechanism remains unclear. Here, we show that the frequency of CD39⁺γδ Tregs, which positively correlated with poor prognosis, was significantly higher in right-sided CRC (RSCRC) than in the left-sided CRC (LSCRC). Interestingly, CD39⁺γδ Tregs from RSCRC showed stronger immunosuppressive phenotype and function than LSCRC. Furthermore, the quantitative mass spectrometry data show that CD39⁺γδ Treg polarization was related to the abnormal activation of the Phospholipase a2-IVa/Arachidonic acid (PLA2G4A/AA) metabolic pathway in RSCRC. Using an in vitro coculture system and an orthotopic murine model of CRC, we show that the overexpression of Pla2g4a in CT26 cells induced CD39⁺γδ Tregs, inhibiting the antitumor immune response. Finally, we found that the overall survival of the PLA2G4A^hi group was significantly shortened compared with PLA2G4A^lo RSCRC, while the survival of LSCRC showed the opposite. Collectively, RSCRC with abnormal PLA2G4A expression educates γδ T cells into CD39⁺γδ Tregs to promote tumor progression and metastasis. Our work highlights the interaction between cancer cells and immune cells by distinguishing the primary tumor site and deepens the understanding of the tumor microenvironment and immunosuppression.

Integration of metabolomics, genomics, and immune phenotypes reveals the causal roles of metabolites in disease

BACKGROUND

Recent studies highlight the role of metabolites in immune diseases, but it remains unknown how much of this effect is driven by genetic and non-genetic host factors.

RESULT

We systematically investigate circulating metabolites in a cohort of 500 healthy subjects (500FG) in whom immune function and activity are deeply measured and whose genetics are profiled. Our data reveal that several major metabolic pathways, including the alanine/glutamate pathway and the arachidonic acid pathway, have a strong impact on cytokine production in response to ex vivo stimulation. We also examine the genetic regulation of metabolites associated with immune phenotypes through genome-wide association analysis and identify 29 significant loci, including eight novel independent loci. Of these, one locus (rs174584-FADS2) associated with arachidonic acid metabolism is causally associated with Crohn's disease, suggesting it is a potential therapeutic target.

CONCLUSION

This study provides a comprehensive map of the integration between the blood metabolome and immune phenotypes, reveals novel genetic factors that regulate blood metabolite concentrations, and proposes an integrative approach for identifying new disease treatment targets.

The N-Formyl Peptide Receptors and Rheumatoid Arthritis: A Dangerous Liaison or Confusing Relationship?

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by a progressive symmetric inflammation of the joints resulting in bone erosion and cartilage destruction with a progressive loss of function and joint deformity. An increased number of findings support the role of innate immunity in RA: many innate immune mechanisms are responsible for producing several cytokines and chemokines involved in RA pathogenesis, such as Tumor Necrosis Factor (TNF)-α, interleukin (IL)-6, and IL-1. Pattern recognition receptors (PRRs) play a crucial role in modulating the activity of the innate arm of the immune response. We focused our attention over the years on the expression and functions of a specific class of PRR, namely formyl peptide receptors (FPRs), which exert a key function in both sustaining and resolving the inflammatory response, depending on the context and/or the agonist. We performed a broad review of the data available in the literature on the role of FPRs and their ligands in RA. Furthermore, we queried a publicly available database collecting data from 90 RA patients with different clinic features to evaluate the possible association between FPRs and clinic-pathologic parameters of RA patients.

Resolvin E1 Regulates Th17 Function and T Cell Activation

Resolvin E1 (RvE1) is a specialized pro-resolving lipid mediator derived from eicosapentaenoic acid and plays a critical role in resolving inflammation and tissue homeostasis. T_h17 cells are a distinct group of T helper (T_h) cells with tissue-destructive functions in autoimmune and chronic inflammatory diseases via the secretion of IL-17. Dendritic cell (DC)-mediated antigen presentation regulates the T_h17-induced progression of inflammation and tissue destruction. In this study, we hypothesized that the RvE1 would restore homeostatic balance and inflammation by targeting the T_h17 function. We designed three experiments to investigate the impact of RvE1 on different phases of T_h17 response and the potential role of DCs: First CD4⁺ T cells were induced by IL-6/TGF_β to measure the effect of RvE1 on T_h17 differentiation in an inflammatory milieu. Second, we measured the impact of RvE1 on DC-stimulated T_h17 differentiation in a co-culture model. Third, we measured the effect of RvE1 on DC maturation. RvE1 blocked the CD25, CCR6 and IL-17 expression; IL-17, IL-21, IL-10, and IL-2 production, suggesting inhibition of T cell activation, T_h17 stimulation and chemoattraction. RvE1 also suppressed the activation of DCs by limiting their pro-inflammatory cytokine production. Our findings collectively demonstrated that the RvE1 targeted the T_h17 activation and the DC function as a potential mechanism for inflammatory resolution and acquired immune response.

Characterizing an siRNA-Containing Lipid-Nanoparticle Prepared by a Microfluidic Reactor: Small-Angle X-ray Scattering and Cryotransmission Electron Microscopic Studies

A new cationic-lipid/siRNA particle that was designed to deliver siRNA was investigated by the combination of small-angle X-ray scattering (SAXS), asymmetric field flow fractionation coupled with multiangle light scattering, and cryotransmission electron microscopy (cryo-TEM). The particle was prepared through two-step mixing using a microfluidic technique. In the first step, siRNA was premixed with a cationic lipid in an EtOH-rich solution. In the second step, the premixed solution was mixed with other lipids, followed by solvent exchange with water. SAXS showed formation of a siRNA/cationic lipid pair in the first step, and this pair consisted of the major part of the core in the final particle. The relationship between the hydrodynamic radius and the radius of gyration indicated the formation of a densely packed core and PEG-rich shell, confirming a well-known core-shell model. SAXS and cryo-TEM showed that the ordering of the core structure enhanced as the siRNA content increased.

Sleep Apnea and Skin

Purpose of the Review

Skin disease is associated with obstructive sleep apnea (OSA) both epidemiologically and mechanistically. In this review we highlight conditions which have a well-established link to obstructive sleep apnea, such as psoriasis and atopic dermatitis.

Recent findings

We describe putative mechanistic links between OSA and skin disease involving inflammatory pathways, obesity, mechanical upper airways obstruction, and hypoxia. In the context of these mechanisms we describe specific skin conditions, and other conditions which are associated with both skin manifestations (including hair/nail findings) and OSA. The risks/ benefits of CPAP in the context of skin disease are also reviewed.

Summary

We conclude that further research is needed to understand the mechanisms behind the associations between OSA and skin disease. Given the frequent co-occurrence of OSA and skin conditions, there would be great benefit for OSA clinical trials to consider improvement in skin disease as an outcome measure.

A novel role for lipoxin A4 in driving a lymph node-eye axis that controls autoimmunity to the neuroretina

The eicosanoid lipoxin A4 (LXA4) has emerging roles in lymphocyte-driven diseases. We identified reduced LXA4 levels in posterior segment uveitis patients and investigated the role of LXA4 in the pathogenesis of experimental autoimmune uveitis (EAU). Immunization for EAU with a retinal self-antigen caused selective downregulation of LXA4 in lymph nodes draining the site of immunization, while at the same time amplifying LXA4 in the inflamed target tissue. T cell effector function, migration and glycolytic responses were amplified in LXA4-deficient mice, which correlated with more severe pathology, whereas LXA4 treatment attenuated disease. In vivo deletion or supplementation of LXA4 identified modulation of CC-chemokine receptor 7 (CCR7) and sphingosine 1- phosphate receptor-1 (S1PR1) expression and glucose metabolism in CD4+ T cells as potential mechanisms for LXA4 regulation of T cell effector function and trafficking. Our results demonstrate the intrinsic lymph node LXA4 pathway as a significant checkpoint in the development and severity of adaptive immunity.

Metabolomic analysis reveals metabolic alterations of human peripheral blood lymphocytes by perfluorooctanoic acid

Perfluorooctanoic acid (PFOA) is a dispersive persistent organic pollutant in the environment. Accumulating reports suggest that PFOA is toxic to human lymphocytes; however, the toxicological effects of PFOA on these cells remain largely unclear. In this study, ultra-performance liquid chromatography (UPLC)-based metabolomic analysis was employed to identify metabolites in human peripheral blood lymphocytes and to assess the metabolic alterations caused by PFOA exposure. Our comparative metabolomic analysis results demonstrated that PFOA treatment could increase the level of organic acids and reduce the level of lipid molecules. Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation further highlighted the fact that the PFOA treatment interfered with the metabolism of amino acids, carbohydrates and lipids, which may lead to disruption of the immune system.

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.

Serum leukotriene B4 levels, tonsillar hypertrophy and sleep-disordered breathing in childhood

OBJECTIVES

In children with snoring, increased production of leukotriene B₄ (LTB₄) may promote tonsillar hypertrophy and sleep-disordered breathing (SDB) or conversely SDB may enhance LTB₄ synthesis. We explored whether: i) high LTB₄ serum levels predict tonsillar hypertrophy; and ii) SDB severity correlates with LTB₄ serum concentration.

METHODS

Normal-weight children with SDB or controls underwent polysomnography and measurement of LTB₄ serum concentration. Tonsillar hypertrophy was the main outcome measure and high LTB₄ serum level (>75 t h percentile value in controls) was the primary explanatory variable. Odds ratio (OR) and the corresponding 95% confidence intervals (CI) for tonsillar hypertrophy in children with versus without high LTB₄ level were calculated. The control subgroup and subgroups of subjects with increasing SDB severity were compared regarding LTB₄ concentration by Kruskal-Wallis test. Spearman's correlation co-efficient was applied to assess the association of LTB₄ concentration with SDB severity.

RESULTS

A total of 104 children with SDB and mean obstructive apnea-hypopnea index-AHI of 4.8 ± 5.3 episodes/h (primary snoring: n = 19; mild SDB: n = 49; moderate/severe SDB: n = 36) and 13 controls (no snoring; AHI: 0.4 ± 0.2 episodes/h) were recruited. The four study subgroups were similar regarding LTB₄ serum concentration (P = 0.64). High LTB₄ (>170.3 pg/mL) was a significant predictor of tonsillar hypertrophy after adjustment for age and gender (OR 3.0 [1.2-7.2]; P = 0.01). There was no association between AHI or desaturation index and LTB₄ serum concentration (r = -0.08; P = 0.37 and r = -0.1; P = 0.30, respectively).

CONCLUSION

No association was identified between SDB severity and LTB₄ levels, but high LTB₄ concentration predicted tonsillar hypertrophy.

Intracellular formyl peptide receptor regulates naïve CD4 T cell migration

We found that formyl peptide receptor (FPR) 1 and FPR3 were expressed intracellularly and/or the nucleus of naïve CD4 T cell. Activation of naïve CD4 T cells with synthetic intracellular agonists dTAT-WKYMVm and CTP-WKYMVm for FPR members stimulated CD4 T cell migration via pertussis toxin-sensitive manner. Knockdown of FPR1, but not knockdown of FPR3, blocked dTAT-WKYMVm-induced naïve CD4 T cell migration. Stimulation of naïve CD4 T cells with dTAT-WKYMVm elicited the activation of ERK, p38 MAPK, and Akt. Activation of CD4 T cells with anti-CD3 and anti-CD28 antibodies caused surface expression of FPR1 and FPR3, but not FPR2. CD4 T cells isolated from sepsis patients expressed the three members of FPR family on their cell surface. Taken together, our results suggest that intracellular FPR in naïve CD4 T cells and surface FPRs in activated CD4 T cells might regulate immune responses by regulating CD4 T cell activity.

Regulation of inflammation by members of the formyl-peptide receptor family

Inflammation is associated with a variety of diseases. The hallmark of inflammation is leukocyte infiltration at disease sites in response to pathogen- or damage-associated chemotactic molecular patterns (PAMPs and MAMPs), which are recognized by a superfamily of seven transmembrane, Gi-protein-coupled receptors (GPCRs) on cell surface. Chemotactic GPCRs are composed of two major subfamilies: the classical GPCRs and chemokine GPCRs. Formyl-peptide receptors (FPRs) belong to the classical chemotactic GPCR subfamily with unique properties that are increasingly appreciated for their expression on diverse host cell types and the capacity to interact with a plethora of chemotactic PAMPs and MAMPs. Three FPRs have been identified in human: FPR1-FPR3, with putative corresponding mouse counterparts. FPR expression was initially described in myeloid cells but subsequently in many non-hematopoietic cells including cancer cells. Accumulating evidence demonstrates that FPRs possess multiple functions in addition to controlling inflammation, and participate in the processes of many pathophysiologic conditions. They are not only critical mediators of myeloid cell trafficking, but are also implicated in tissue repair, angiogenesis and protection against inflammation-associated tumorigenesis. A series recent discoveries have greatly expanded the scope of FPRs in host defense which uncovered the essential participation of FPRs in step-wise trafficking of myeloid cells including neutrophils and dendritic cells (DCs) in host responses to bacterial infection, tissue injury and wound healing. Also of great interest is the FPRs are exploited by malignant cancer cells for their growth, invasion and metastasis. In this article, we review the current understanding of FPRs concerning their expression in a vast array of cell types, their involvement in guiding leukocyte trafficking in pathophysiological conditions, and their capacity to promote the differentiation of immune cells, their participation in tumor-associated inflammation and cancer progression. The close association of FPRs with human diseases and cancer indicates their potential as targets for the development of therapeutics.

High frequency of Bob1lo T follicular helper cells in florid reactive follicular hyperplasia

Florid reactive follicular hyperplasia (FRFH), which is characterized by large germinal centers (GCs) within normal lymphoid follicles, is often observed in benign lesions of lymph nodes and other tissues. Because of the histologic similarity of FRFH to tumorous lesions such as follicular lymphoma, careful pathological examination is required to evaluate such lesions; however, little is known about the mechanism underlying the development of FRFH. In this study, we investigated T follicular helper (Tfh) cells in hyperplastic tonsils of patients with obstructive sleep apnea syndrome (OSA), which frequently exhibits typical FRFH. When we analyzed tonsils of OSA and recurrent tonsillitis (RT) as a control, tonsils of OSA were found to harbor Tfh cells with a nearly 3-fold higher ratio in total CD4⁺ T cells than that in tonsils of RT. Further analysis showed that, in comparison to Tfh cells of RT tonsils, Tfh cells of OSA tonsils were relatively tolerant to CD3-mediated activation-induced cell death (AICD) and also expressed lower levels of a Bob1 transcription coactivator and IL-4, which fosters the development of GC-B cells. Given that Bob1 controls the proliferative activity in response to CD3 stimulation and has been suggested to have a role in the production of IL-4 in Tfh cells, the unique structure of FRFH is possibly associated with the function of Bob1^lo Tfh cells.

Emotional exhaustion-induced latent autoimmune diabetes in adults in a young lady: A CARE-compliant case report

RATIONALE

Latent autoimmune diabetes in adults (LADA) refers to an autoimmune disorder characterized with detectable islets antibodies in the early diagnosis and increased autoimmune beta-cell failure progression. Notably, this kind of diabetes seems to be confused with other phenotypic diabetes.

PATIENT CONCERNS

A young woman suffered an emotional exhaustion-induced LADA, showing asthenia, polydipsia, polyuria, and visible weight loss. The patient emotionally ended a 14-year romantic relationship, leading to the emotional flooding.

DIAGNOSES

The data from physical examination and laboratory tests exhibited as follows: glutamic acid decarboxylase antibody (GADA) = 63.83 U/mL, the fasting blood glucose (FBG) = 13.3 mmol/L, and glycated haemoglobin (HbA1c) = 10.9%. According to levels of GADA, the patient was diagnosed as LADA.

INTERVENTIONS

The patient was clinically treated with insulin for 3-month. Then, running, diet-control, and emotional treatment were combined, such as the patient started a new relationship.

OUTCOMES

An emotional recovery initiated from a new romantic relationship and a baby, showing normal levels of GAD65 (27.007 IU/mL) and FBG (5.46) mmol/L.

LESSONS

The emotional exhaustion might play a significant role in induction of LADA. It is important that individuals should maintain optimism, cheer, and a positive attitude.

Formyl Peptide Receptors in Cellular Differentiation and Inflammatory Diseases

Formyl peptide receptors (FPRs) are a family of classical chemoattractant receptors. Although FPRs are mainly expressed in phagocytic innate immune cells including monocytes/macrophages and neutrophils, recent reports demonstrated that additional different cell types such as T-lymphocytes and several non-immune cells also express functional FPRs. FPRs were first reported as a specific receptor to detect bacteria-derived N-formyl peptides. However, accumulating evidence has shown that FPRs can recognize various ligands derived from pathogens, mitochondria, and host. This review summarizes studies on some interesting endogenous agonists for FPRs. Here, we discuss functional roles of FPRs and their ligands concerning the regulation of cellular differentiation focusing on myeloid lineage cells. Accumulating evidence also suggests that FPRs may contribute to the control of inflammatory diseases. Here, we briefly review the current understanding of the functional role of FPRs and their ligands in inflammatory disorders in some animal disease models. J. Cell. Biochem. 118: 1300-1307, 2017. © 2017 Wiley Periodicals, Inc.