Stimulation of glucocorticoid-induced tumor necrosis factor receptor family-related protein ligand (GITRL) induces inflammatory activation of microglia in culture

First report on genome wide association study in western Indian population reveals host genetic factors for COVID-19 severity and outcome

Different human races across the globe responded in a different way to the SARS-CoV-2 infection leading to different disease severity. Therefore, it is anticipated that host genetic factors have a straight association with the COVID-19. We identified a total 6, 7, and 6 genomic loci for deceased-recovered, asymptomatic-recovered, and deceased-asymptomatic group comparison, respectively. Unfavourable alleles of the markers nearby the genes which are associated with lung and heart diseases such as Tumor necrosis factor superfamily (TNFSF4&18), showed noteworthy association with the disease severity and outcome for the COVID-19 patients in the western Indian population. The markers found with significant association with disease prognosis or recovery are of value in determining the individual's response to SARS-CoV-2 infection and can be used for the risk prediction in COVID-19. Besides, GWAS study in other populations from India may help to strengthen the outcome of this study.

Cell-to-Cell Interactions Mediating Functional Recovery after Stroke

Ischemic damage in brain tissue triggers a cascade of molecular and structural plastic changes, thus influencing a wide range of cell-to-cell interactions. Understanding and manipulating this scenario of intercellular connections is the Holy Grail for post-stroke neurorehabilitation. Here, we discuss the main findings in the literature related to post-stroke alterations in cell-to-cell interactions, which may be either detrimental or supportive for functional recovery. We consider both neural and non-neural cells, starting from astrocytes and reactive astrogliosis and moving to the roles of the oligodendrocytes in the support of vulnerable neurons and sprouting inhibition. We discuss the controversial role of microglia in neural inflammation after injury and we conclude with the description of post-stroke alterations in pyramidal and GABAergic cells interactions. For all of these sections, we review not only the spontaneous evolution in cellular interactions after ischemic injury, but also the experimental strategies which have targeted these interactions and that are inspiring novel therapeutic strategies for clinical application.

Blockade of GITRL/GITR signaling pathway attenuates house dust mite-induced allergic asthma in mice through inhibition of MAPKs and NF-κB signaling

GITRL/GITR signaling pathway plays an important role in allergy, inflammation, transplantation and autoimmunity. However, its role in asthma remains unclear. Thus, the present study aimed to investigate changes in this pathway and observe the therapeutic effect of its blocking on asthma. By using house dust mite-induced asthma model, changes of GITRL/GITR and its downstream molecules MAPKs (e.g., p38 MAPK, JNK and Erk) and NF-κB were observed. After that, GITRL in lung of mice was knocked down by recombinant adeno-associated virus to observe the impact on its downstream molecules and assess the therapeutic effect on asthma. These results showed that GITRL/GITR and its downstream molecules MAPKs/NF-κB were activated in asthmatic mice. This activation was suppressed after GITRL knockdown, and allergic airway inflammation and airway hyperresponsiveness were alleviated. These results demonstrate that GITRL/GITR-MAPKs/NF-κB signaling pathway participates in the pathogenesis of asthma. Blockade of GITRL/GITR signaling pathway exhibits protective effects in a mouse model of house dust mite-induced allergic asthma.

Identification of a Novel Antisepsis Pathway: Sectm1a Enhances Macrophage Phagocytosis of Bacteria through Activating GITR

The inability to effectively control invading bacteria or other pathogens is a major cause of multiple organ dysfunction and death in sepsis. As the first-line defense of the immune system, macrophages play a crucial role in the removal of pathogens during sepsis. In this study, we define secreted and transmembrane 1A (Sectm1a) as a novel ligand of glucocorticoid-induced TNFR (GITR) that greatly boosts macrophage phagocytosis and bactericidal capacity. Using a global Sectm1a knockout (KO) mouse model, we observed that Sectm1a deficiency significantly suppressed phagocytosis and bactericidal activity in both recruited macrophages and tissue-resident macrophages, which consequently aggravated bacterial burden in the blood and multiple organs and further increased systemic inflammation, leading to multiple organ injury and increased mortality during polymicrobial sepsis. By contrast, treatment of septic mice with recombinant Sectm1a protein (rSectm1a) not only promoted macrophage phagocytosis and bactericidal activity but also significantly improved survival outcome. Mechanistically, we identified that Sectm1a could bind to GITR in the surface of macrophages and thereby activate its downstream PI3K-Akt pathway. Accordingly, rSectm1a-mediated phagocytosis and bacterial killing were abolished in macrophages by either KO of GITR or pharmacological inhibition of the PI3K-Akt pathway. In addition, rSectm1a-induced therapeutic effects on sepsis injury were negated in GITR KO mice. Taken together, these results uncover that Sectm1a may represent a novel target for drug development to control bacterial dissemination during sepsis or other infectious diseases.

Harnessing the Complete Repertoire of Conventional Dendritic Cell Functions for Cancer Immunotherapy

The onset of checkpoint inhibition revolutionized the treatment of cancer. However, studies from the last decade suggested that the sole enhancement of T cell functionality might not suffice to fight malignancies in all individuals. Dendritic cells (DCs) are not only part of the innate immune system, but also generals of adaptive immunity and they orchestrate the de novo induction of tolerogenic and immunogenic T cell responses. Thus, combinatorial approaches addressing DCs and T cells in parallel represent an attractive strategy to achieve higher response rates across patients. However, this requires profound knowledge about the dynamic interplay of DCs, T cells, other immune and tumor cells. Here, we summarize the DC subsets present in mice and men and highlight conserved and divergent characteristics between different subsets and species. Thereby, we supply a resource of the molecular players involved in key functional features of DCs ranging from their sentinel function, the translation of the sensed environment at the DC:T cell interface to the resulting specialized T cell effector modules, as well as the influence of the tumor microenvironment on the DC function. As of today, mostly monocyte derived dendritic cells (moDCs) are used in autologous cell therapies after tumor antigen loading. While showing encouraging results in a fraction of patients, the overall clinical response rate is still not optimal. By disentangling the general aspects of DC biology, we provide rationales for the design of next generation DC vaccines enabling to exploit and manipulate the described pathways for the purpose of cancer immunotherapy in vivo. Finally, we discuss how DC-based vaccines might synergize with checkpoint inhibition in the treatment of malignant diseases.

Biological role of GITR/GITRL in attributes and immune responses of macrophage

Glucocorticoid-induced tumor necrosis factor receptor family-related protein ligand (GITRL), a member of the tumor necrosis factor superfamily, is expressed in APCs and acts as a costimulatory molecule in the immune system. Although the glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR)/GITRL system has been modulated to promote or decrease T cell-related responses in multiple diseases, studies in macrophages are limited. To address this issue, we compared the expression of GITRL in various types of macrophages and analyzed whether GITRL can affect the fundamental properties and major functions of these cells. Our results demonstrated that M1 polarized macrophages had the highest GITRL levels. Furthermore, GITRL overexpression skewed macrophage polarization toward the M1 phenotype, accelerating proliferation and migration and regulating phagocytosis and killing function. Moreover, GITRL-silenced cells showed a loss of these functions, further confirming its vital role. We also developed an acute peritonitis mouse model, in which macrophages were driven to differentiate into a proinflammatory phenotype with GITRL up-regulation, triggering a positive feedback loop. Our results provide molecular insight into how the GITR/GITRL system modulates innate immune responses, suggesting that manipulation of the GITR/GITRL system to treat diseases depends not only on T cell regulation but also on macrophage participation.

Seasonal adaptations of the hypothalamo-neurohypophyseal system of the dromedary camel

The “ship” of the Arabian and North African deserts, the one-humped dromedary camel (Camelus dromedarius) has a remarkable capacity to survive in conditions of extreme heat without needing to drink water. One of the ways that this is achieved is through the actions of the antidiuretic hormone arginine vasopressin (AVP), which is made in a specialised part of the brain called the hypothalamo-neurohypophyseal system (HNS), but exerts its effects at the level of the kidney to provoke water conservation. Interestingly, our electron microscopy studies have shown that the ultrastructure of the dromedary HNS changes according to season, suggesting that in the arid conditions of summer the HNS is in an activated state, in preparation for the likely prospect of water deprivation. Based on our dromedary genome sequence, we have carried out an RNAseq analysis of the dromedary HNS in summer and winter. Amongst the 171 transcripts found to be significantly differentially regulated (>2 fold change, p value <0.05) there is a significant over-representation of neuropeptide encoding genes, including that encoding AVP, the expression of which appeared to increase in summer. Identification of neuropeptides in the HNS and analysis of neuropeptide profiles in extracts from individual camels using mass spectrometry indicates that overall AVP peptide levels decreased in the HNS during summer compared to winter, perhaps due to increased release during periods of dehydration in the dry season.

Reverse Signaling of Tumor Necrosis Factor Superfamily Proteins in Macrophages and Microglia: Superfamily Portrait in the Neuroimmune Interface

The tumor necrosis factor (TNF) superfamily (TNFSF) is a protein superfamily of type II transmembrane proteins commonly containing the TNF homology domain. The superfamily contains more than 20 protein members, which can be released from the cell membrane by proteolytic cleavage. Members of the TNFSF function as cytokines and regulate diverse biological processes, including immune responses, proliferation, differentiation, apoptosis, and embryogenesis, by binding to TNFSF receptors. Many TNFSF proteins are also known to be responsible for the regulation of innate immunity and inflammation. Both receptor-mediated forward signaling and ligand-mediated reverse signaling play important roles in these processes. In this review, we discuss the functional expression and roles of various reverse signaling molecules and pathways of TNFSF members in macrophages and microglia in the central nervous system (CNS). A thorough understanding of the roles of TNFSF ligands and receptors in the activation of macrophages and microglia may improve the treatment of inflammatory diseases in the brain and periphery. In particular, TNFSF reverse signaling in microglia can be exploited to gain further insights into the functions of the neuroimmune interface in physiological and pathological processes in the CNS.

Genetically modified hematopoietic stem/progenitor cells that produce IL-10-secreting regulatory T cells

Random amino acid copolymers used in the treatment of multiple sclerosis in man or experimental autoimmune encephalomyelitis (EAE) in mice [poly(Y,E,A,K)_n, known as Copaxone, and poly(Y,F,A,K)_n] function at least in part by generation of IL-10-secreting regulatory T cells that mediate bystander immunosuppression. The mechanism through which these copolymers induce Tregs is unknown. To investigate this question, four previously described Vα3.2 Vβ14 T cell receptor (TCR) cDNAs, the dominant clonotype generated in splenocytes after immunization of SJL mice, that differed only in their CDR3 sequences were utilized to generate retrogenic mice. The high-level production of IL-10 as well as IL-5 and small amounts of the related cytokines IL-4 and IL-13 by CD4⁺ T cells isolated from the splenocytes of these mice strongly suggests that the TCR itself encodes information for specific cytokine secretion. The proliferation and production of IL-10 by these Tregs was costimulated by activation of glucocorticoid-induced TNF receptor (GITR) (expressed at high levels by these cells) through its ligand GITRL. A mechanism for generation of cells with this specificity is proposed. Moreover, retrogenic mice expressing these Tregs were protected from induction of EAE by the appropriate autoantigen.

Inflammatory CNS disease caused by immune checkpoint inhibitors: status and perspectives

Cancer treatment strategies based on immune stimulation have recently entered the clinical arena, with unprecedented success. Immune checkpoint inhibitors (ICIs) work by indiscriminately promoting immune responses, which target tumour-associated antigens or tumour-specific mutations. However, the augmented immune response, most notably the T cell response, can cause either direct neurotoxicity or, more commonly, indirect neurotoxic effects through systemic or local inflammatory mechanisms or autoimmune mechanisms. Consequently, patients treated with ICIs are susceptible to CNS disease, including paraneoplastic neurological syndromes, encephalitis, multiple sclerosis and hypophysitis. In this Opinion article, we introduce the mechanisms of action of ICIs and review their adverse effects on the CNS. We highlight the importance of early detection of these neurotoxic effects, which should be distinguished from brain metastasis, and the need for early detection of neurotoxicity. It is crucial that physicians are well informed of these neurological adverse effects, given the anticipated increase in the use of immunotherapies to treat cancer.

CD8+ T cells: GITR matters

As many members of the tumor necrosis factor receptor superfamily, glucocorticoid-induced TNFR-related gene (GITR) plays multiple roles mostly in the cells of immune system. CD8⁺ T cells are key players in the immunity against viruses and tumors, and GITR has been demonstrated to be an essential molecule for these cells to mount an immune response. The aim of this paper is to focus on GITR function in CD8⁺ cells, paying particular attention to numerous and recent studies that suggest its crucial role in mouse disease models.

Glucocorticoid-induced TNF receptor-triggered T cells are key modulators for survival/death of neural stem/progenitor cells induced by ischemic stroke

Increasing evidences show that immune response affects the reparative mechanisms in injured brain. Recently, we have demonstrated that CD4(+)T cells serve as negative modulators in neurogenesis after stroke, but the mechanistic detail remains unclear. Glucocorticoid-induced tumor necrosis factor (TNF) receptor (GITR), a multifaceted regulator of immunity belonging to the TNF receptor superfamily, is expressed on activated CD4(+)T cells. Herein, we show, by using a murine model of cortical infarction, that GITR triggering on CD4(+)T cells increases poststroke inflammation and decreases the number of neural stem/progenitor cells induced by ischemia (iNSPCs). CD4(+)GITR(+)T cells were preferentially accumulated at the postischemic cortex, and mice treated with GITR-stimulating antibody augmented poststroke inflammatory responses with enhanced apoptosis of iNSPCs. In contrast, blocking the GITR-GITR ligand (GITRL) interaction by GITR-Fc fusion protein abrogated inflammation and suppressed apoptosis of iNSPCs. Moreover, GITR-stimulated T cells caused apoptosis of the iNSPCs, and administration of GITR-stimulated T cells to poststroke severe combined immunodeficient mice significantly reduced iNSPC number compared with that of non-stimulated T cells. These observations indicate that among the CD4(+)T cells, GITR(+)CD4(+)T cells are major deteriorating modulators of poststroke neurogenesis. This suggests that blockade of the GITR-GITRL interaction may be a novel immune-based therapy in stroke.

Dexamethasone attenuates lipopolysaccharide-induced liver injury by downregulating glucocorticoid-induced tumor necrosis factor receptor ligand in Kupffer cells

AIM

  Glucocorticoid-induced tumor necrosis factor receptor ligand (GITRL) plays pro-inflammatory roles in immune response. Thus, our aim was to assess if dexamethasone attenuates lipopolysaccharide (LPS)-induced liver injury by affecting GITRL in Kupffer cells (KC).

METHODS

  A BALB/c mouse model of liver injury was established by i.p. injecting with LPS (10 mg/kg) co-treated with or without dexamethasone (3 mg/kg). Blood and liver samples were obtained for analysis of liver morphology, GITRL expression, hepatocellular function and cytokine levels at 24 h after injection. KC were isolated and challenged by LPS (1 µg/mL), with or without dexamethasone (10 µM) co-treatment, or with GITRL siRNA pre-transfection. The GITRL expression and cytokine levels were assayed at 24 h after challenge.

RESULTS

  Dexamethasone treatment significantly improved the survival rate of endotoxemic mice (P < 0.05), whereas serum alanine aminotransferase, aspartate aminotransferase, tumor necrosis factor (TNF)-α, interleukin (IL)-6 and γ-interferon levels were significantly decreased (P < 0.05, respectively). Concurrently, LPS-induced hepatic tissue injury was attenuated as indicated by morphological analysis; and expression of GITRL in liver tissue and KC was downregulated (P < 0.05). Consistent with these in vivo experiments, inhibited expression of GITRL, TNF-α and IL-6 caused by dexamethasone treatment were also observed in LPS-stimulated KC. The GITRL, TNF-α and IL-6 expression was also significantly inhibited by GITRL gene silencing.

CONCLUSION

  The TNF-α and IL-6 expression of LPS-stimulated KC was inhibited by GITRL gene silencing. Dexamethasone attenuates LPS-induced liver injury, at least proportionately, by downregulating GITRL in KC.

Autoimmune therapies targeting costimulation and emerging trends in multivalent therapeutics

Proteins participating in immunological signaling have emerged as important targets for controlling the immune response. A multitude of receptor-ligand pairs that regulate signaling pathways of the immune response have been identified. In the complex milieu of immune signaling, therapeutic agents targeting mediators of cellular signaling often either activate an inflammatory immune response or induce tolerance. This review is primarily focused on therapeutics that inhibit the inflammatory immune response by targeting membrane-bound proteins regulating costimulation or mediating immune-cell adhesion. Many of these signals participate in larger, organized structures such as the immunological synapse. Receptor clustering and arrangement into organized structures is also reviewed and emerging trends implicating a potential role for multivalent therapeutics is posited.

Glucocorticoid-induced TNFR-related (GITR) protein and its ligand in antitumor immunity: functional role and therapeutic modulation

The ability of the tumor necrosis factor receptor (TNFR) family member GITR to modulate immune responses has been the subject of multiple studies. Initially thought to be critically involved in governing functions of regulatory T cells, GITR and its ligand GITRL have meanwhile been found to modulate the reactivity of various different cell types and to influence a broad variety of immunological conditions including the immune response against tumors. Not only GITR, but also GITRL is capable of transducing signals, and the consequences of GITR-GITRL interaction may vary among different effector cell types, differ upon signal transduction via the receptor, the ligand, or both, depend on the level of an ongoing immune response, and even differ among mice and men. In this paper, we address available data on GITR and its ligand in immune responses and discuss the role and potential therapeutic modulation of this molecule system in antitumor immunity.