IL-33-mediated protection against experimental cerebral malaria is linked to induction of type 2 innate lymphoid cells, M2 macrophages and regulatory T cells

Group2 innate lymphoid cells ameliorate renal fibrosis and dysfunction associated with adenine-induced CKD

Renal fibrosis is a common pathway of chronic kidney disease (CKD) progression involving primary kidney injury and kidney diseases. Group 2 innate lymphoid cells (ILC2s) mediate type 2 immune responses irrespective of antigen presentation and play a reno-protective role in kidney injury and disease. In the present study, we observed a decrease in kidney-resident ILC2s in CKD and found that enrichment of ILC2s in the kidney ameliorates renal fibrosis. In CKD kidney, ILC2s preferentially produced IL-13 over IL-5 in response to IL-33 stimulation, regardless of ST2L expression. Moreover, GATA3 expression was decreased in ILC2s, and T-bet+ ILC1s and RORγt+ ILC3s were increased in CKD kidney. Adoptive transfer of kidney ILC2s into adenine-induced CKD model mouse improved renal function and fibrosis. Renal fibroblasts cultured with IL33-activated kidney ILC2s suppressed myofibroblast trans-differentiation through Acta2 and Fn-1 regulation. These results suggest that kidney ILC2s prevent CKD progression via improvement of renal fibrosis. Our findings also suggest that ILC2s may contribute to the development of new therapeutic agents and strategies for tissue fibroses.

Oral administration of IPI549 protects mice from neuropathology and an overwhelming inflammatory response during experimental cerebral malaria

Infection with Plasmodium falciparum is often deadly when it results in cerebral malaria, which is associated with neuropathology described as an overwhelming inflammatory response and mechanical obstruction of cerebral microvascular. PI3Kγ is a critical component of intracellular signal transduction and plays a central role in regulating cell chemotaxis, migration, and activation. The purpose of this study was to examine the relationship between inhibiting the PI3Kγ pathway and the outcome of experimental cerebral malaria (ECM) in C57BL/6J mice infected with the mouse malaria parasite, Plasmodium berghei ANKA. We observed that oral administration of the PI3Kγ inhibitor IPI549 after infection completely protected mice from ECM. IPI549 treatment significantly dampened the magnitude of inflammatory responses, with reduced production of pro-inflammatory factors, decreased T cell activation, and altered differentiation of antigen-presenting cells. IPI549 treatment protected the infected mice from neuropathology, as assessed by an observed reduction of pathogenic T cells in the brain. Treating the infected mice with IPI549 three days after parasite inoculation improved the murine blood brain barrier (BBB) integrity and helped the mice pass the onset of ECM. Together, these data indicate that oral administration of the PI3Kγ inhibitor IPI549 has a suppressive role in host inflammation and alleviates cerebral pathology, which supports IPI549 as a new malaria treatment option with potential therapeutic implications for cerebral malaria.

Blockage of mechanosensitive Piezo1 channel alleviates the severity of experimental malaria-associated acute lung injury

BACKGROUND

Malaria-associated acute lung injury (MA-ALI) is a well-recognized clinical complication of severe, complicated malaria that is partly driven by sequestrations of infected red blood cells (iRBCs) on lung postcapillary induced impaired blood flow. In earlier studies the mechanosensitive Piezo1 channel emerged as a regulator of mechanical stimuli, but the function and underlying mechanism of Piezo1 impacting MA-ALI severity via sensing the impaired pulmonary blood flow are still not fully elucidated. Thus, the present study aimed to explore the role of Piezo1 in the severity of murine MA-ALI.

METHODS

Here, we utilized a widely accepted murine model of MA-ALI using C57BL/6 mice with Plasmodium berghei ANKA infection and then added a Piezo1 inhibitor (GsMTx4) to the model. The iRBC-stimulated Raw264.7 macrophages in vitro were also targeted with GsMTx4 to further explore the potential mechanism.

RESULTS

Our data showed an elevation in the expression of Piezo1 and number of Piezo1+-CD68+ macrophages in lung tissues of the experimental MA-ALI mice. Compared to the infected control mice, the blockage of Piezo1 with GsMTx4 dramatically improved the survival rate but decreased body weight loss, peripheral blood parasitemia/lung parasite burden, experimental cerebral malaria incidence, total protein concentrations in bronchoalveolar lavage fluid, lung wet/dry weight ratio, vascular leakage, pathological damage, apoptosis and number of CD68+ and CD86+ macrophages in lung tissues. This was accompanied by a dramatic increase in the number of CD206+ macrophages (M2-like subtype), upregulation of anti-inflammatory cytokines (e.g. IL-4 and IL-10) and downregulation of pro-inflammatory cytokines (e.g. TNF-α and IL-1β). In addition, GsMTx4 treatment remarkably decreased pulmonary intracellular iron accumulation, protein level of 4-HNE (an activator of ferroptosis) and the number of CD68+-Piezo1+ and CD68+-4-HNE+ macrophages but significantly increased protein levels of GPX4 (an inhibitor of ferroptosis) in experimental MA-ALI mice. Similarly, in vitro study showed that the administration of GsMTx4 led to a remarkable elevation in the mRNA levels of CD206, IL-4, IL-10 and GPX-4 but to a substantial decline in CD86, TNF-α, IL-1β and 4-HNE in the iRBC-stimulated Raw264.7 cells.

CONCLUSIONS

Our findings indicated that blockage of Piezo1 with GsMTx4 alleviated the severity of experimental MA-ALI in mice partly by triggering pulmonary macrophage M2 polarization and subsequent anti-inflammatory responses but inhibited apoptosis and ferroptosis in lung tissue. Our data suggested that targeting Piezo1 in macrophages could be a promising therapeutic strategy for treating MA-ALI.

Unravelling mysteries at the perivascular space: a new rationale for cerebral malaria pathogenesis

Cerebral malaria (CM) is a severe neurological complication caused by Plasmodium falciparum parasites; it is characterized by the sequestration of infected red blood cells within the cerebral microvasculature. New findings, combined with a better understanding of the central nervous system (CNS) barriers, have provided greater insight into the players and events involved in CM, including site-specific T cell responses in the human brain. Here, we review the updated roles of innate and adaptive immune responses in CM, with a focus on the role of the perivascular macrophage-endothelium unit in antigen presentation, in the vascular and perivascular compartments. We suggest that these events may be pivotal in the development of CM.

Pathogenetic mechanisms and treatment targets in cerebral malaria

Malaria, the most prevalent mosquito-borne infectious disease worldwide, has accompanied humanity for millennia and remains an important public health issue despite advances in its prevention and treatment. Most infections are asymptomatic, but a small percentage of individuals with a heavy parasite burden develop severe malaria, a group of clinical syndromes attributable to organ dysfunction. Cerebral malaria is an infrequent but life-threatening complication of severe malaria that presents as an acute cerebrovascular encephalopathy characterized by unarousable coma. Despite effective antiparasite drug treatment, 20% of patients with cerebral malaria die from this disease, and many survivors of cerebral malaria have neurocognitive impairment. Thus, an important unmet clinical need is to rapidly identify people with malaria who are at risk of developing cerebral malaria and to develop preventive, adjunctive and neuroprotective treatments for cerebral malaria. This Review describes important advances in the understanding of cerebral malaria over the past two decades and discusses how these mechanistic insights could be translated into new therapies.

Group 2 innate lymphoid cells resolve neuroinflammation following cerebral ischaemia

BACKGROUND

Acute brain ischaemia elicits pronounced inflammation, which aggravates neural injury. However, the mechanisms governing the resolution of acute neuroinflammation remain poorly understood. In contrast to regulatory T and B cells, group 2 innate lymphoid cells (ILC2s) are immunoregulatory cells that can be swiftly mobilised without antigen presentation; whether and how these ILC2s participate in central nervous system inflammation following brain ischaemia is still unknown.

METHODS

Leveraging brain tissues from patients who had an ischaemic stroke and a mouse model of focal ischaemia, we characterised the presence and cytokine release of brain-infiltrating ILC2s. The impact of ILC2s on neural injury was evaluated through antibody depletion and ILC2 adoptive transfer experiments. Using Rag2-/-γc-/- mice receiving passive transfer of IL-4-/- ILC2s, we further assessed the contribution of interleukin (IL)-4, produced by ILC2s, in ischaemic brain injury.

RESULTS

We demonstrate that ILC2s accumulate in the areas surrounding the infarct in brain tissues of patients with cerebral ischaemia, as well as in mice subjected to focal cerebral ischaemia. Oligodendrocytes were a major source of IL-33, which contributed to ILC2s mobilisation. Adoptive transfer and expansion of ILC2s reduced brain infarction. Importantly, brain-infiltrating ILC2s reduced the magnitude of stroke injury severity through the production of IL-4.

CONCLUSIONS

Our findings revealed that brain ischaemia mobilises ILC2s to curb neuroinflammation and brain injury, expanding the current understanding of inflammatory networks following stroke.

Administration of soluble gp130Fc disrupts M-1 macrophage polarization, dendritic cell activation, MDSC expansion and Th-17 induction during experimental cerebral malaria

Regulatory effect of IL-6 on various immune cells plays a crucial role during experimental cerebral malaria pathogenesis. IL-6 neutralization can restore distorted ratios of myeloid dendritic cells and plasmacytoid dendritic cells as well as the balance between Th-17 and T-regulatory cells. IL-6 can also influence immune cells through classical and trans IL-6 signalling pathways. As trans IL-6 signalling is reportedly involved during malaria pathogenesis, we focused on studying the effects of trans IL-6 signalling blockade on various immune cell populations and how they regulate ECM progression. Results show that administration of sgp130Fc recombinant chimera protein lowers the parasitemia, increases the survivability of Plasmodium berghei ANKA infected mice, and restores the distorted ratios of M1/M2 macrophage, mDC/pDC, and Th-17/Treg. IL-6 trans signalling blockade has been found to affect both expansion of myeloid derived suppressor cells (MDSCs) and expression of inflammatory markers on them during Plasmodium berghei ANKA infection indicating that trans IL-6 signalling might regulate various immune cells and their function during ECM. In this work for the first time, we delineate the effect of sgp130Fc administration on influencing the immunological changes within the host secondary lymphoid organ during ECM induced by Plasmodium berghei ANKA infection.

IL-33 Orchestrated the Interaction and Immunoregulatory Functions of Alternatively Activated Macrophages and Regulatory T Cells In Vitro

Our group has previously demonstrated elevated serum-soluble ST2 in patients with active systemic lupus erythematosus, suggesting a role of IL-33 in the underlying pathogenesis. However, inconsistent results have been reported on the effect of exogenous IL-33 on murine lupus activity, which may be mediated by concerted actions of various immune cells in vivo. This study aimed to examine the function of IL-33 on macrophage polarization and regulatory T cells (Treg) and their interactive effects in the lupus setting by in vitro coculture experiments of macrophages and T cells that were performed in the presence or absence of IL-33-containing medium. Compared to IL-4-polarized bone marrow-derived macrophages (BMDM) from MRL/MpJ mice, adding IL-33 enhanced mRNA expression of markers of alternatively activated macrophages, including CD206 and Arg1. IL-33 and IL-4 copolarized BMDM produced higher TGF-β but not IL-6 upon inflammatory challenge. These BMDM induced an increase in the Foxp3+CD25+ Treg population in cocultured allogeneic T cells from MRL/MpJ and predisease MRL/lpr mice. These copolarized BMDM also showed an enhanced suppressive effect on T cell proliferation with reduced IFN-γ and IL-17 release but increased TGF-β production. In the presence of TGF-β and IL-2, IL-33 also directly promoted inducible Treg that expressed a high level of CD25 and more sustained Foxp3. Unpolarized BMDM cocultured with these Treg displayed higher phagocytosis. In conclusion, TGF-β was identified as a key cytokine produced by IL-4 and IL-33 copolarized alternatively activated macrophages and the induced Treg, which may contribute to a positive feedback loop potentiating the immunoregulatory functions of IL-33.

Modulation of Neuroinflammation: Advances in Roles and Mechanisms of the IL-33/ST2 Axis Involved in Ischemic Stroke

Interleukin (IL)-33 was initially recognized as a constituent of the IL-1 cytokine family in 2005. It exerts pleiotropic effects by regulating immune responses via its binding to the receptor ST2 (IL-33R). The IL-33/ST2 pathway has been linked to several inflammatory disorders. In human and rodents, the broad expression of IL-33 in spinal cord tissues and brain indicates its central nervous system-specific functions. Growing evidence supports the protective effects of the IL-33/ST2 pathway in ischemic stroke, along with a better understanding of the underlying mechanisms. IL-33 plays a crucial role in the regulation of the release of inflammatory molecules from glial cells in response to neuropathological lesions. Moreover, IL-33/ST2-mediated neuroprotection following cerebral ischemia may be linked to T-cell function, specifically regulatory T cells. Soluble ST2 (sST2) acts as a decoy receptor in the IL-33/ST2 axis, blocking IL-33 signaling through the membrane ST2 receptor. sST2 has also been identified as a potential inflammatory biomarker of ischemic stroke. Targeting sST2 specifically to eliminate its inhibition of the protective IL-33/ST2 pathway in ischemic brain tissues is a promising approach for the treatment of ischemic stroke.

Coenzyme Q10 exhibits anti-inflammatory and immune-modulatory thereby decelerating the occurrence of experimental cerebral malaria

Cerebral Malaria (CM) is associated with the complex neurological syndrome, whose pathology is mediated by severe inflammatory processes following infection with Plasmodium falciparum. Coenzyme-Q10 (Co-Q10) is a potent anti-inflammatory, anti-oxidant, and anti-apoptotic agent with numerous clinical applications. The aim of this study was to elucidate the role of oral administration of Co-Q10 on the initiation or regulation of inflammatory immune response during experimental cerebral malaria (ECM). For this purpose, the pre-clinical effect of Co-Q10 was evaluated in C57BL/6 J mice infected with Plasmodium berghei ANKA (PbA). Treatment with Co-Q10 resulted in the reduction of infiltrating parasite load, greatly improved the survival rate of PbA-infected mice that occurred independent of parasitaemia and prevented PbA-induced disruption of the blood-brain barrier (BBB) integrity. Exposure to Co-Q10 resulted in the reduction of infiltration of effector CD8 + T cells in the brain and secretion of cytolytic Granzyme B molecules. Notably, Co-Q10-treated mice had reduced levels of CD8 +T cell chemokines CXCR3, CCR2, and CCR5 in the brain following PbA-infection. Brain tissue analysis showed a reduction in the levels of inflammatory mediators TNF- α, CCL3, and RANTES in Co-Q10 administered mice. In addition, Co-Q10 modulated the differentiation and maturation of both splenic and brain dendritic cells and cross-presentation (CD8α+DCs) during ECM. Remarkably, Co-Q10 was very effective in decreasing levels of CD86, MHC-II, and CD40 in macrophages associated with ECM pathology. Exposure to Co-Q10 resulted in increased expression levels of Arginase-1 and Ym1/chitinase 3-like 3, which is linked to ECM protection. Furthermore, Co-Q10 supplementation prevented PbA-induced depletion of Arginase and CD206 mannose receptor levels. Co-Q10 abrogated PbA-driven elevation in pro-inflammatory cytokines IL-1β, IL-18, and IL-6 levels. In conclusion, the oral supplementation with Co-Q10 decelerates the occurrence of ECM by preventing lethal inflammatory immune responses and dampening genes associated with inflammation and immune-pathology during ECM, and offers an inimitable opening for developing an anti-inflammatory agent against cerebral malaria.

Macrophages drive KSHV B cell latency

Kaposi's sarcoma herpesvirus (KSHV) establishes lifelong infection and persists in latently infected B cells. Paradoxically, in vitro B cell infection is inefficient, and cells rapidly die, suggesting the absence of necessary factor(s). KSHV epidemiology unexpectedly mirrors that of malaria and certain helminthic infections, while other herpesviruses are ubiquitous. Elevated circulating monocytes are common in these parasitic infections. Here, we show that KSHV infection of monocytes or M-CSF-differentiated (M2) macrophages is highly efficient. Proteomic analyses demonstrate that infection induces macrophage production of B cell chemoattractants and activating factor. We find that KSHV acts with monocytes or M2 macrophages to stimulate B cell survival, proliferation, and plasmablast differentiation. Further, macrophages drive infected plasma cell differentiation and long-term viral latency. In Kenya, where KSHV is endemic, we find elevated monocyte levels in children with malaria. These findings demonstrate a role for mononuclear phagocytes in KSHV B cell latency and suggest that mononuclear phagocyte abundance may underlie KSHV's geographic disparity.

Regulatory Functions of Hypoxia in Host-Parasite Interactions: A Focus on Enteric, Tissue, and Blood Protozoa

Body tissues are subjected to various oxygenic gradients and fluctuations and hence can become transiently hypoxic. Hypoxia-inducible factor (HIF) is the master transcriptional regulator of the cellular hypoxic response and is capable of modulating cellular metabolism, immune responses, epithelial barrier integrity, and local microbiota. Recent reports have characterized the hypoxic response to various infections. However, little is known about the role of HIF activation in the context of protozoan parasitic infections. Growing evidence suggests that tissue and blood protozoa can activate HIF and subsequent HIF target genes in the host, helping or hindering their pathogenicity. In the gut, enteric protozoa are adapted to steep longitudinal and radial oxygen gradients to complete their life cycle, yet the role of HIF during these protozoan infections remains unclear. This review focuses on the hypoxic response to protozoa and its role in the pathophysiology of parasitic infections. We also discuss how hypoxia modulates host immune responses in the context of protozoan infections.

Crosstalk between the gut microbiota and innate lymphoid cells in intestinal mucosal immunity

The human gastrointestinal mucosa is colonized by thousands of microorganisms, which participate in a variety of physiological functions. Intestinal dysbiosis is closely associated with the pathogenesis of several human diseases. Innate lymphoid cells (ILCs), which include NK cells, ILC1s, ILC2s, ILC3s and LTi cells, are a type of innate immune cells. They are enriched in the mucosal tissues of the body, and have recently received extensive attention. The gut microbiota and its metabolites play important roles in various intestinal mucosal diseases, such as inflammatory bowel disease (IBD), allergic disease, and cancer. Therefore, studies on ILCs and their interaction with the gut microbiota have great clinical significance owing to their potential for identifying pharmacotherapy targets for multiple related diseases. This review expounds on the progress in research on ILCs differentiation and development, the biological functions of the intestinal microbiota, and its interaction with ILCs in disease conditions in order to provide novel ideas for disease treatment in the future.

Melatonin ameliorates neurological deficits through MT2/IL-33/ferritin H signaling-mediated inhibition of neuroinflammation and ferroptosis after traumatic brain injury

Although traumatic brain injury (TBI) is a common cause of death and disability worldwide, there is currently a lack of effective therapeutic drugs and targets. To reveal the complex pathophysiologic mechanisms of TBI, we performed transcriptome analysis of the mouse cerebral cortex and immunohistochemical analysis of human cerebral tissues. The genes Mt1, Mt2, Il33, and Fth1 were upregulated post-TBI and enriched in pathways associated with the inflammatory response, oxidative phosphorylation, and ferroptosis. As an agonist of MT1/2, melatonin (MLT) confers anti-oxidant, anti-inflammatory, and anti-ferroptosis effects after TBI. However, whether these upregulated genes and their corresponding pathways are involved in the neuroprotective effect of MLT remains unclear. In this study, interventions to inhibit MT1/2, IL-33, and ferroptosis (i.e., ferritin H (Fth)-KO) were applied post-TBI. The results showed that MLT attenuated TBI-induced cerebral edema and neurological outcomes by inhibiting inflammation and ferroptosis. Mechanistically, MLT mainly suppressed inflammatory responses and ferroptosis via the activation of MT2 and IL-33 pathways. Building on the previous finding that Fth deletion increases susceptibility to ferroptosis post-TBI, we demonstrated that Fth depletion remarkably exacerbated the post-TBI inflammatory response, and abolished the anti-inflammatory effects of MLT both in vivo and in vitro. Furthermore, the post-TBI anti-inflammatory effect of MLT, which occurs by promoting the polarization of CD206⁺ macrophages, was dependent on Fth. Taken together, these results clarified that MLT alleviates inflammation- and ferroptosis-mediated brain edema and neurological deficits by activating the MT2/IL-33/Fth pathway, which provides a novel target and theoretical basis for MLT to treat TBI patients.

Group 2 innate lymphoid cells and their surrounding environment

Since the discovery of group 2 innate lymphoid cells (ILC2s) in 2010, subsequent studies have revealed their developmental pathways, mechanisms of activation and regulation, and immunological roles in tissue homeostasis and tissue-specific diseases in various organs. Although ILC2s are known to express tissue-specific features depending on where they reside, how the surrounding environment affects the functions of ILC2s remains to be fully elucidated. Recent histologic analyses revealed that ILC2s resides in specific perivascular regions in peripheral tissues with their function being controlled by the surrounding cells via cytokines, lipid mediators, neurotransmitters, and cell-cell interactions through surface molecules. This review summarizes the interactions between ILC2s and surrounding cells, including epithelial cells, neurons, immune cells, and mesenchymal cells, with the objective of promoting the development of novel diagnostic and therapeutic methods for ILC2-related diseases.

Interleukin-33 Ameliorates Murine Systemic Lupus Erythematosus and Is Associated with Induction of M2 Macrophage Polarisation and Regulatory T Cells

The innate cytokine IL-33 is increasingly recognised to possess biological effects on various immune cells. We have previously demonstrated elevated serum level of soluble ST2 in patients with active systemic lupus erythematosus suggesting involvement of IL-33 and its receptor in the lupus pathogenesis. This study sought to examine the effect of exogenous IL-33 on disease activity of pre-disease lupus-prone mice and the underlying cellular mechanisms. Recombinant IL-33 was administered to MRL/lpr mice for 6 weeks, whereas control group received phosphate-buffered saline. IL-33-treated mice displayed less proteinuria, renal histological inflammatory changes, and had lower serum levels of pro-inflammatory cytokines including IL-6 and TNF-α. Renal tissue and splenic CD11b+ extracts showed features of M2 polarisation with elevated mRNA expression of Arg1, FIZZI, and reduced iNOS. These mice also had increased IL-13, ST2, Gata3, and Foxp3 mRNA expression in renal and splenic tissues. Kidneys of these mice displayed less CD11b+ infiltration, had downregulated MCP-1, and increased infiltration of Foxp3-expressing cells. Splenic CD4+ T cells showed increased ST2-expressing CD4+Foxp3+ population and reduced IFN-γ+ population. There were no differences in serum anti-dsDNA antibodies and renal C3 and IgG2a deposit in these mice. Exogenous IL-33 was found to ameliorate disease activity in lupus-prone mice with induction of M2 polarisation, Th2 response, and expansion of regulatory T cells. IL-33 likely orchestrated autoregulation of these cells through upregulation of ST2 expression.

Innate Lymphoid Cell Plasticity in Mucosal Infections

Mucosal tissue homeostasis is a dynamic process that involves multiple mechanisms including regulation of innate lymphoid cells (ILCs). ILCs are mostly tissue-resident cells which are critical for tissue homeostasis and immune response against pathogens. ILCs can sense environmental changes and rapidly respond by producing effector cytokines to limit pathogen spread and initiate tissue recovery. However, dysregulation of ILCs can also lead to immunopathology. Accumulating evidence suggests that ILCs are dynamic population that can change their phenotype and functions under rapidly changing tissue microenvironment. However, the significance of ILC plasticity in response to pathogens remains poorly understood. Therefore, in this review, we discuss recent advances in understanding the mechanisms regulating ILC plasticity in response to intestinal, respiratory and genital tract pathogens. Key transcription factors and lineage-guiding cytokines regulate this plasticity. Additionally, we discuss the emerging data on the role of tissue microenvironment, gut microbiota, and hypoxia in ILC plasticity in response to mucosal pathogens. The identification of new pathways and molecular mechanisms that control functions and plasticity of ILCs could uncover more specific and effective therapeutic targets for infectious and autoimmune diseases where ILCs become dysregulated.

HIF-PHD inhibitor regulates the function of group2 innate lymphoid cells and polarization of M2 macrophages

Hypoxia-inducible factor-prolyl hydroxylase (HIF-PHD) inhibitors are therapeutic agents for renal anemia that work through HIF2-mediated upregulation of erythropoietin (EPO) and have also been reported to suppress renal fibrosis. Group 2 innate lymphoid cells (ILC2s) have been proven to be involved in the pathogenesis of fibrosis in various organs, including the kidney. However, the relationship between the HIF pathway, renal fibrosis, and kidney ILC2s remains unclear. In the present study, we found that HIF activation by HIF-PHD inhibitors suppressed type 2 cytokine production from kidney ILC2s. The enhanced HIF pathway downregulated the IL-33 receptor ST2L on ILC2s, and phosphorylation of downstream p38 MAPK was attenuated. M2 macrophages that promote renal fibrosis were polarized by ILC2 supernatants, but reduced cytokine production from ILC2s treated with HIF-PHD inhibitors suppressed this polarization. Our findings suggest that HIF-PHD inhibitors are potential therapeutic agents for renal fibrosis that are mediated by the alteration of ILC2 function.

Knowledge mapping and research trends of IL-33 from 2004 to 2022: a bibliometric analysis

Background

IL-33 has been studied widely but its comprehensive and systematic bibliometric analysis is yet available. The present study is to summarize the research progress of IL-33 through bibliometric analysis.

Methods

The publications related to IL-33 were identified and selected from the Web of Science Core Collection (WoSCC) database on 7 December 2022. The downloaded data was analyzed with bibliometric package in R software. CiteSpace and VOSviewer were used to conduct IL-33 bibliometric and knowledge mapping analysis.

Results

From 1 January 2004 to 7 December 2022, 4711 articles on IL-33 research published in 1009 academic journals by 24652 authors in 483 institutions from 89 countries were identified. The number of articles had grown steadily over this period. The United States of America(USA) and China are the major contributors in the field of research while University of Tokyo and University of Glasgow are the most active institutions. The most prolific journal is Frontiers in Immunology, while the Journal of Immunity is the top 1 co-cited journal. Andrew N. J. Mckenzie published the most significant number of articles and Jochen Schmitz was co-cited most. The major fields of these publications are immunology, cell biology, and biochemistry & molecular biology. After analysis, the high-frequency keywords of IL-33 research related to molecular biology (sST2, IL-1), immunological effects (type 2 immunity, Th2 cells), and diseases (asthma, cancer, cardiovascular diseases). Among these, the involvement of IL-33 in the regulation of type 2 inflammation has strong research potential and is a current research hotspot.

Conclusion

The present study quantifies and identifies the current research status and trends of IL-33 using bibliometric and knowledge mapping analysis. This study may offer the direction of IL-33-related research for scholars.

The IL-33/ST2 Pathway in Cerebral Malaria

Interleukin-33 (IL-33) is an immunomodulatory cytokine which plays critical roles in tissue function and immune-mediated diseases. IL-33 is abundant within the brain and spinal cord tissues where it acts as a key cytokine to coordinate the exchange between the immune and central nervous system (CNS). In this review, we report the recent advances to our knowledge regarding the role of IL-33 and of its receptor ST2 in cerebral malaria, and in particular, we highlight the pivotal role that IL-33/ST2 signaling pathway could play in brain and cerebrospinal barriers permeability. IL-33 serum levels are significantly higher in children with severe Plasmodium falciparum malaria than children without complications or noninfected children. IL-33 levels are correlated with parasite load and strongly decrease with parasite clearance. We postulate that sequestration of infected erythrocytes or merozoites liberation from schizonts could amplify IL-33 production in endothelial cells, contributing either to malaria pathogenesis or recovery.

Dual Immune Regulatory Roles of Interleukin-33 in Pathological Conditions

Interleukin-33 (IL-33), a member of the IL-1 cytokine family and a multifunctional cytokine, plays critical roles in maintaining host homeostasis and in pathological conditions, such as allergy, infectious diseases, and cancer, by acting on multiple types of immune cells and promoting type 1 and 2 immune responses. IL-33 is rapidly released by immune and non-immune cells upon stimulation by stress, acting as an “alarmin” by binding to its receptor, suppression of tumorigenicity 2 (ST2), to trigger downstream signaling pathways and activate inflammatory and immune responses. It has been recognized that IL-33 displays dual-functioning immune regulatory effects in many diseases and has both pro- and anti-tumorigenic effects, likely depending on its primary target cells, IL-33/sST2 expression levels, cellular context, and the cytokine microenvironment. Herein, we summarize our current understanding of the biological functions of IL-33 and its roles in the pathogenesis of various conditions, including inflammatory and autoimmune diseases, infections, cancers, and cases of organ transplantation. We emphasize the nature of context-dependent dual immune regulatory functions of IL-33 in many cells and diseases and review systemic studies to understand the distinct roles of IL-33 in different cells, which is essential to the development of more effective diagnoses and therapeutic approaches for IL-33-related diseases.

Mouse Models for Unravelling Immunology of Blood Stage Malaria

Malaria comprises a spectrum of disease syndromes and the immune system is a major participant in malarial disease. This is particularly true in relation to the immune responses elicited against blood stages of Plasmodium-parasites that are responsible for the pathogenesis of infection. Mouse models of malaria are commonly used to dissect the immune mechanisms underlying disease. While no single mouse model of Plasmodium infection completely recapitulates all the features of malaria in humans, collectively the existing models are invaluable for defining the events that lead to the immunopathogenesis of malaria. Here we review the different mouse models of Plasmodium infection that are available, and highlight some of the main contributions these models have made with regards to identifying immune mechanisms of parasite control and the immunopathogenesis of malaria.

Dual roles of interleukin-33 in cognitive function by regulating central nervous system inflammation

With the advent of an aging society, the incidence of dementia is increasing, resulting in a vast burden on society. It is increasingly acknowledged that neuroinflammation is implicated in various neurological diseases with cognitive dysfunction such as Alzheimer’s disease, multiple sclerosis, ischemic stroke, traumatic brain injury, and central nervous system infections. As an important neuroinflammatory factor, interleukin-33 (IL-33) is highly expressed in various tissues and cells in the mammalian brain, where it plays a role in the pathogenesis of a number of central nervous system conditions. Reams of previous studies have shown that IL-33 has both pro- and anti-inflammatory effects, playing dual roles in the progression of diseases linked to cognitive impairment by regulating the activation and polarization of immune cells, apoptosis, and synaptic plasticity. This article will summarize the current findings on the effects IL-33 exerts on cognitive function by regulating neuroinflammation, and attempt to explore possible therapeutic strategies for cognitive disorders based on the adverse and protective mechanisms of IL-33.

Insights into IL-33 on inflammatory response during in vitro infection by Trypanosoma cruzi

Inflammatory and regulatory cytokines play an important role in the immunopathogenesis of Trypanosoma cruzi infection. Interleukin (IL)-33 is a member of the IL-1 superfamily of cytokines whose expression/production is upregulated following pro-inflammatory stimulation to alert the immune system in response to tissue stress or damage. The aim of this study was to evaluate the inflammatory profile induced in cultured J774 cells stimulated or not with IL-33 (10 ng/mL), with live parasites (1 × 10⁶ metacyclic trypomastigote forms) and/or total antigen, TcAg (100 µg/mL) and with both, IL-33 and TcAg/T. cruzi. The cultures were evaluated at 24 h and 48 h after addition of the stimuli. For this, the supernatants were collected for the measurement of TNF, IL-17, CCL2, and IL-10 by ELISA and of nitrite by the Griess method. TNF, IL-17, and CCL2 concentrations were elevated in the presence of TcAg or live T. cruzi parasites at 24 h, and the addition of IL-33 potentiated these effects at 48 h. In addition, the T. cruzi-amastigote forms reduced in those infected J774 cells stimulated with IL-33 at 48 h. In conclusion, the IL-33 elevated the production of the TNF, IL-17, and CCL2 in cultured J774 cells stimulated with T. cruzi and/or its antigen and reduced the intracellular parasites, providing impetus to new investigations on its potential actions on the parasite-induced inflammation.

Elevated Plasma Soluble ST2 Levels are Associated With Neuronal Injury and Neurocognitive Impairment in Children With Cerebral Malaria

Background

Murine experimental cerebral malaria studies suggest both protective and deleterious central nervous system effects from alterations in the interleukin-33 (IL-33)/ST2 pathway.

Methods

We assessed whether soluble ST2 (sST2) was associated with neuronal injury or cognitive impairment in a cohort of Ugandan children with cerebral malaria (CM, n=224) or severe malarial anemia (SMA, n=193).

Results

Plasma concentrations of sST2 were higher in children with CM than in children with SMA or in asymptomatic community children. Cerebrospinal fluid (CSF) sST2 levels were elevated in children with CM compared with North American children. Elevated plasma and CSF ST2 levels in children with CM correlated with increased endothelial activation and increased plasma and CSF levels of tau, a marker of neuronal injury. In children with CM who were ≥5 years of age at the time of their malaria episode, but not in children <5 years of age, elevated risk factor-adjusted plasma levels of sST2 were associated with worse scores for overall cognitive ability and attention over a 2-year follow-up.

Conclusions

The study findings suggest that sST2 may contribute to neuronal injury and long-term neurocognitive impairment in older children with CM.

An update on cerebral malaria for therapeutic intervention

BACKGROUND

Cerebral malaria is often pronounced as a major life-threatening neurological complication of Plasmodium falciparum infection. The complex pathogenic landscape of the parasite and the associated neurological complications are still not elucidated properly. The growing concerns of drugresistant parasite strains along with the failure of anti-malarial drugs to subdue post-recovery neuro-cognitive dysfunctions in cerebral malaria patients have called for a demand to explore novel biomarkers and therapeutic avenues. Due course of the brain infection journey of the parasite, events such as sequestration of infected RBCs, cytoadherence, inflammation, endothelial activation, and blood-brain barrier disruption are considered critical.

METHODS

In this review, we briefly summarize the diverse pathogenesis of the brain-invading parasite associated with loss of the blood-brain barrier integrity. In addition, we also discuss proteomics, transcriptomics, and bioinformatics strategies to identify an array of new biomarkers and drug candidates.

CONCLUSION

A proper understanding of the parasite biology and mechanism of barrier disruption coupled with emerging state-of-art therapeutic approaches could be helpful to tackle cerebral malaria.

IL-6 dependent expansion of inflammatory MDSCs (CD11b+ Gr-1+) promote Th-17 mediated immune response during experimental cerebral malaria

Myeloid derived suppressor cells (MDSCs) are a group of heterogeneous cell populations that can suppress T cell responses. Various aspects of MDSCs in regulating immune responses in several cancer and infectious diseases have been reported till date. But the role and regulation of MDSCs have not been systematically studied in the context of malaria. This study depicts the phenotypic and functional characteristics of splenic MDSCs and how they regulate Th-17 mediated immune response during Experimental Cerebral Malaria (ECM). Flow cytometric analysis reveals that MDSCs in the spleen and bone marrow expand at 8 dpi during ECM. Among subtypes of MDSCs, PMN-MDSCs show significant expansion in the spleen but M-MDSCs remain unaltered. Functional analysis of sorted MDSCs from spleens of Plasmodium berghei ANKA (PbA) infected mice shows suppressive nature of these cells and high production of Nitric oxide (NO). Besides, MDSCs were also found to express various inflammatory markers during ECM suggesting the M1 type phenotype of these cells. In-vivo depletion of MDSCs by the use of Anti Gr-1 increases mice survival but doesn't significantly alter the parasitemia. Previously, it has been reported that Treg/Th-17 balance in the spleen is skewed towards Th-17 during ECM. Depletion of MDSCs was found to regulate Th-17 percentages to homeostatic levels and subvert various inflammatory changes in the spleen. Among different factors, IL-6 was found to play an important role in the expansion of MDSCs and expression of inflammatory markers on MDSCs in a STAT3-dependent manner. These findings provide a unique insight into the role of IL-6 in the expansion of the MDSC population which causes inflammatory changes and increased Th-17 responses during ECM.

Identification of Key Determinants of Cerebral Malaria Development and Inhibition Pathways

Cerebral malaria (CM), coma caused by Plasmodium falciparum-infected red blood cells (iRBCs), is the deadliest complication of malaria. The mechanisms that lead to CM development are incompletely understood. Here we report on the identification of activation and inhibition pathways leading to mouse CM with supporting evidence from the analysis of human specimens. We find that CM suppression can be induced by vascular injury when sporozoites exit the circulation to infect the liver and that CM suppression is mediated by the release of soluble factors into the circulation. Among these factors is insulin like growth factor 1 (IGF1), administration of which inhibits CM development in mice. IMPORTANCE Liver infection by Plasmodium sporozoites is a required step for infection of the organism. We found that alternate pathways of sporozoite liver infection differentially influence cerebral malaria (CM) development. CM is one of the primary causes of death following malaria infection. To date, CM research has focused on how CM phenotypes develop but no successful therapeutic treatment or prognostic biomarkers are available. Here we show for the first time that sporozoite liver invasion can trigger CM-inhibitory immune responses. Importantly, we identified a number of early-stage prognostic CM inhibitory biomarkers, many of which had never been associated with CM development. Serological markers identified using a mouse model are directly relevant to human CM.

Innate Lymphoid Cells in Response to Intracellular Pathogens: Protection Versus Immunopathology

Innate lymphoid cells (ILCs) are a heterogeneous group of cytokine-producing lymphocytes which are predominantly located at mucosal barrier surfaces, such as skin, lungs, and gastrointestinal tract. ILCs contribute to tissue homeostasis, regulate microbiota-derived signals, and protect against mucosal pathogens. ILCs are classified into five major groups by their developmental origin and distinct cytokine production. A recently emerged intriguing feature of ILCs is their ability to alter their phenotype and function in response to changing local environmental cues such as pathogen invasion. Once the pathogen crosses host barriers, ILCs quickly activate cytokine production to limit the spread of the pathogen. However, the dysregulated ILC responses can lead to tissue inflammation and damage. Furthermore, the interplay between ILCs and other immune cell types shapes the outcome of the immune response. Recent studies highlighted the important role of ILCs for host defense against intracellular pathogens. Here, we review recent advances in understanding the mechanisms controlling protective and pathogenic ILC responses to intracellular pathogens. This knowledge can help develop new ILC-targeted strategies to control infectious diseases and immunopathology.

CISH constrains the tuft-ILC2 circuit to set epithelial and immune tone

Innate lymphoid cells (ILCs) are tissue-resident effectors poised to activate rapidly in response to local signals such as cytokines. To preserve homeostasis, ILCs must employ multiple pathways, including tonic suppressive mechanisms, to regulate their primed state and prevent inappropriate activation and immunopathology. Such mechanisms remain incompletely characterized. Here we show that cytokine-inducible SH2-containing protein (CISH), a suppressor of cytokine signaling (SOCS) family member, is highly and constitutively expressed in type 2 innate lymphoid cells (ILC2s). Mice that lack CISH either globally or conditionally in ILC2s show increased ILC2 expansion and activation, in association with reduced expression of genes inhibiting cell-cycle progression. Augmented proliferation and activation of CISH-deficient ILC2s increases basal and inflammation-induced numbers of intestinal tuft cells and accelerates clearance of the model helminth, Nippostrongylus brasiliensis, but compromises innate control of Salmonella typhimurium. Thus, CISH constrains ILC2 activity both tonically and after perturbation, and contributes to the regulation of immunity in mucosal tissue.

The role of hypoxia-inducible factor 1-alpha in inflammatory bowel disease

Inflammatory bowel disease (IBD) develops as a result of a combination of genetic predisposition, dysbiosis of the gut microbiota, and environmental influences, which is mainly represented by ulcerative colitis (UC) and Crohn's disease (CD). IBDs can result in inflammatory hypoxia by causing intestinal inflammation and vascular damage. The hypoxia-inducible factor 1-alpha (HIF-1α), as a transcription factor, can regulate the cellular adaptation to low oxygen levels and support the development and function of the gut barrier. HIF-αplays its functions through translocating into the nucleus, dimerizing with HIF-1β, and binding to hypoxia-responsive elements of HIF-1 target genes. So far, most studies have addressed the function of HIF-1α in murine models of IBD. In this review, we aim to outline the major roles of HIF-1α in the IBD.

Harnessing the innate and adaptive immune system for tissue repair and regeneration: Considering more than macrophages

Tissue healing and regeneration is a complex, choreographed, spatiotemporal process involving a plethora of cell types, the activity of which is stringently regulated in order for effective tissue repair to ensue post injury. A number of globally prevalent conditions such as heart disease, organ failure, and severe musculoskeletal disorders require new therapeutic strategies to repair damaged or diseased tissue, particularly given an ageing population in which obesity, diabetes, and consequent tissue defects have reached epidemic proportions. This is further compounded by the lack of intrinsic healing and poor regenerative capacity of certain adult tissues. While vast progress has been made in the last decade regarding tissue regenerative strategies to direct self-healing, for example, through implantation of tissue engineered scaffolds, several challenges have hampered the clinical application of these technologies. Control of the immune response is growing as an attractive approach in regenerative medicine and it is becoming increasingly apparent that an in depth understanding of the interplay between cells of the immune system and tissue specific progenitor cells is of paramount importance. Furthermore, the integration of immunology and bioengineering promises to elevate the efficacy of biomaterial-based tissue repair and regeneration. In this review, we highlight the role played by individual immune cell subsets in tissue repair processes and describe new approaches that are being taken to direct appropriate healing outcomes via biomaterial mediated targeting of immune cell activity. STATEMENT OF SIGNIFICANCE: It is becoming increasingly apparent that controlling the immune response is as an attractive approach in regenerative medicine. Here, we propose that an in-depth understanding of immune system and tissue specific progenitor cell interactions may reveal mechanisms by which tissue healing and regeneration takes place, in addition to identifying novel therapeutic targets that could be used to enhance the tissue repair process. To date, most reviews have focused solely on macrophage subsets. This manuscript details the role of other innate and adaptive immune cells such as innate lymphoid cells (ILCs), natural killer (NK) cells and γδT cells (in addition to macrophages) in tissue healing. We also describe new approaches that are being taken to direct appropriate healing outcomes via biomaterial mediated cytokine and drug delivery.

Microglia and astrocyte responses to neuropathogenic protozoan parasites

Cerebral toxoplasmosis and cerebral malaria are two important neurological diseases caused by protozoan parasites. In this review, we discuss recent findings regarding the innate immune responses of microglia and astrocytes to Toxoplasma and Plasmodium infection. In both infections, these tissue-resident glial cells perform a sentinel function mediated by alarmin crosstalk that licenses adaptive type 1 immunity in the central nervous system. Divergent protective or pathogenic effects of type 1 activation of these astrocytes and microglia are revealed depending on the inherent lytic potential of the protozoan parasite.

The Clinical Significance of Serum IL-33 and sST2 Alterations in the Post-Stroke Depression

Introduction

This study was to test whether the serum levels of IL-33 and sST2 are correlated with the development of depression after acute ischemic stroke.

Methods

Patients diagnosed with acute ischemic stroke were selected. This study took the 24-item Hamilton Depression Rating Scale (HAMD) (score ≥20) as the diagnostic criteria for depression. On the 21st day after admission, patients who met the depression diagnostic criteria were included in the depression group, and patients who failed to meet the diagnostic criteria were included in the non-depression group. The serum levels of IL-33, sST2 and hsCRP were measured by enzyme-linked immunosorbent assay (ELISA).

Results

On 1st day after stroke, compared with the non-depression group, there was no significant difference in the serum IL-33, sST2 and hsCRP levels in the depression group; on 21st day after stroke, compared with the non-depression group, the serum IL-33 and hsCRP levels were significantly increased, while the sST2 level was significantly decreased in the depression group. Correlation analysis showed that IL-33 was positively correlated with the depression quantitative score and hsCRP, while sST2 was negatively correlated with the depression quantitative score and hsCRP. Regression analysis showed that IL-33 and sST2 were independent risk factors for the depression after acute ischemic stroke.

Discussion

The abnormal alterations of serum IL-33 and sST2 levels in the stroke patients may serve as one of the risk factors for the occurrence and exacerbation of the depression, and its mechanism may be related to the promotion of inflammatory factor production in vivo.

Therapeutic Opportunities of Interleukin-33 in the Central Nervous System

Interleukin-33 (IL-33), a member of the IL-1 cytokine family, is involved in various diseases. IL-33 exerts its effects via its heterodimeric receptor complex, which comprises suppression of tumorigenicity 2 (ST2) and the IL-1 receptor accessory protein (IL-1RAP). Increasing evidence has demonstrated that IL-33/ST2 signaling plays diverse but crucial roles in the homeostasis of the central nervous system (CNS) and the pathogenesis of CNS diseases, including neurodegenerative diseases, cerebrovascular diseases, infection, trauma, and ischemic stroke. In the current review, we focus on the functional roles and cellular signaling mechanisms of IL-33 in the CNS and evaluate the potential for diagnostic and therapeutic applications.

The IL-33/ST2 pathway is not essential to Th2 stimulation but is key for modulation and survival during chronic infection with Schistosoma mansoni in mice

Morbidity during chronic schistosomiasis has been associated with the induction and modulation of type-2 granulomatous inflammatory response induced by antigens secreted by the eggs, which become trapped in capillary venules of the host tissues, especially in the liver and intestines. IL-33, an alarmin released after cell damage, binds to its ST2 (suppressor of tumorigenicity 2) receptor, expressed in an variety of immune cells, including ILC2 and macrophages, and stimulates the early production of IL-5 and IL-13, which leads to eosinophil infiltration and activation of a Th2 response. However, the role of IL-33/ST2 activation on Schistosoma-induced granuloma formation and modulation is mostly unknown. In the current work, we comparatively evaluated the immune response and granuloma formation in wild-type BALB/c (WT) and BALB/c mice genetically deficient in the IL-33 receptor (ST2^-/-) experimentally infected with Schistosoma mansoni. Mice were infected with 25 or 50 S. mansoni cercariae and followed for up to 14 weeks to assess mortality. Mice from each experimental group were comparatively evaluated for parasite burden, liver immune response, and granuloma appearance during acute and chronic schistosomiasis. Our data showed that the number of circulating worms and eggs retained in the liver and eliminated in the feces was similar in WT and ST2^-/- infected mice, but infected ST2^-/- mice presented an enhanced rate of mortality. Interestingly, the production of type-2 cytokines by soluble egg antigens (SEA)-stimulated spleen cells, the serum concentrations of IL-5 and Immunoglobulin (Ig)-E, and the level of parasite-reactive IgG1 were similar in infected mice of both experimental groups. The concentrations of IL-4, IL-5, IL-13, and IFN-γ in liver homogenate of infected mice also did not differ between the strains at acute schistosomiasis, but there was a significant increase in IL-17 levels in ST2^-/- infected mice at this phase. On the other hand, IL-4, IL-13, IL-10, IL-17, and IFN-γ concentrations were reduced and the ratios of IL-4/IFN-γ and IL-17/IFN-γ were higher in liver homogenate of chronically infected ST2^-/- mice, suggesting unbalanced Th2 and Th17 responses. Moreover, liver granulomas of ST2^-/- mice were larger and disorganized, showing an intense cellular infiltrate, rich in eosinophils and neutrophils. Our results suggest that the absence of the IL-33/ST2 pathway is not essential for the Schistosoma-induced Th2 response, but is necessary to prevent host mortality by modulating granuloma-mediated pathology.

Neural Regulation of Interactions Between Group 2 Innate Lymphoid Cells and Pulmonary Immune Cells

Emerging evidence supports the involvement of nervous system in the regulation of immune responses. Group 2 innate lymphoid cells (ILC2), which function as a crucial bridge between innate and adaptive immunity, are present in large numbers in barrier tissues. Neuropeptides and neurotransmitters have been found to participate in the regulation of ILC2, adding a new dimension to neuroimmunity. However, a comprehensive and detailed overview of the mechanisms of neural regulation of ILC2, associated with previous findings and prospects for future research, is still lacking. In this review, we compile existing information that supports neurons as yet poorly understood regulators of ILC2 in the field of lung innate and adaptive immunity, focusing on neural regulation of the interaction between ILC2 and pulmonary immune cells.

Astrocytes promote a protective immune response to brain Toxoplasma gondii infection via IL-33-ST2 signaling

It is of great interest to understand how invading pathogens are sensed within the brain, a tissue with unique challenges to mounting an immune response. The eukaryotic parasite Toxoplasma gondii colonizes the brain of its hosts, and initiates robust immune cell recruitment, but little is known about pattern recognition of T. gondii within brain tissue. The host damage signal IL-33 is one protein that has been implicated in control of chronic T. gondii infection, but, like many other pattern recognition pathways, IL-33 can signal peripherally, and the specific impact of IL-33 signaling within the brain is unclear. Here, we show that IL-33 is expressed by oligodendrocytes and astrocytes during T. gondii infection, is released locally into the cerebrospinal fluid of T. gondii-infected animals, and is required for control of infection. IL-33 signaling promotes chemokine expression within brain tissue and is required for the recruitment and/or maintenance of blood-derived anti-parasitic immune cells, including proliferating, IFN-γ-expressing T cells and iNOS-expressing monocytes. Importantly, we find that the beneficial effects of IL-33 during chronic infection are not a result of signaling on infiltrating immune cells, but rather on radio-resistant responders, and specifically, astrocytes. Mice with IL-33 receptor-deficient astrocytes fail to mount an adequate adaptive immune response in the CNS to control parasite burden-demonstrating, genetically, that astrocytes can directly respond to IL-33 in vivo. Together, these results indicate a brain-specific mechanism by which IL-33 is released locally, and sensed locally, to engage the peripheral immune system in controlling a pathogen.

Hippocampal interleukin-33 mediates neuroinflammation-induced cognitive impairments

Background

Interleukin (IL)-33 is expressed in a healthy brain and plays a pivotal role in several neuropathologies, as protective or contributing to the development of cerebral diseases associated with cognitive impairments. However, the role of IL-33 in the brain is poorly understood, raising the question of its involvement in immunoregulatory mechanisms.

Methods

We administered recombinant IL-33 (rmIL-33) by intra-hippocampal injection to C57BL/6 J (WT) and IL-1αβ deficient mice. Chronic minocycline administration was performed and cognitive functions were examined trough spatial habituation test. Hippocampal inflammatory responses were investigated by RT-qPCR. The microglia activation was assessed using immunohistological staining and fluorescence-activated cell sorting (FACS).

Results

We showed that IL-33 administration in mice led to a spatial memory performance defect associated with an increase of inflammatory markers in the hippocampus while minocycline administration limited the inflammatory response. Quantitative assessment of glial cell activation in situ demonstrated an increase of proximal intersections per radius in each part of the hippocampus. Moreover, rmIL-33 significantly promoted the outgrowth of microglial processes. Fluorescence-activated cell sorting analysis on isolated microglia, revealed overexpression of IL-1β, 48 h post-rmIL-33 administration. This microglial reactivity was closely related to the onset of cognitive disturbance. Finally, we demonstrated that IL-1αβ deficient mice were resistant to cognitive disorders after intra-hippocampal IL-33 injection.

Conclusion

Thus, hippocampal IL-33 induced an inflammatory state, including IL-1β overexpression by microglia cells, being causative of the cognitive impairment. These results highlight the pathological role for IL-33 in the central nervous system, independently of a specific neuropathological model.

Group 2 Innate Lymphoid Cells Exacerbate Amebic Liver Abscess in Mice

Entamoeba histolytica, a protozoan parasite in the lumen of the human large intestine, occasionally spreads to the liver and induces amebic liver abscesses (ALAs). Upon infection with E. histolytica, high levels of type 2 cytokines are induced in the liver early after infection. However, the sources and functions of these initial type 2 cytokines in ALA formation remain unclear. In this study, we examined the roles of group 2 innate lymphoid cells (ILC2s) in ALA formation. Hepatic ILC2 numbers were significantly increased and they produced robust levels of IL-5. The in vivo transfer of ILC2s into Rag2^−/−common γ chain (γ_c)^−/− KO mice aggravated ALA formation accompanied by eosinophilia and neutrophilia. Furthermore, IL-33-deficient mice and IL-5-neutralized mice had less ALA formations. These results suggest that ILC2s contribute to exacerbating the pathogenesis of ALA by producing early type 2 cytokines and promoting the accumulation of eosinophils and neutrophils in the liver.

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ILC2s exacerbate ALA by promoting the accumulation of eosinophils and neutrophils

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Hepatic ILC2s are increased and the main source of IL-5 in the early phase of ALA

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Hepatic ILC2s localize with IL-33⁺ cells in the inflammatory areas of ALA

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IL-33 is a trigger of ILC2-mediated ALA formation

Type 2 Innate Lymphoid Cells Accumulate in the Brain After Hypoxia-Ischemia but Do Not Contribute to the Development of Preterm Brain Injury

Background

The immune system of human and mouse neonates is relatively immature. However, innate lymphoid cells (ILCs), commonly divided into the subsets ILC1, ILC2, and ILC3, are already present in the placenta and other fetal compartments and exhibit higher activity than what is seen in adulthood. Recent reports have suggested the potential role of ILCs, especially ILC2s, in spontaneous preterm labor, which is associated with brain damage and subsequent long-term neurodevelopmental deficits. Therefore, we hypothesized that ILCs, and especially ILC2s, play a role in preterm brain injury.

Methods

C57Bl/6J mice at postnatal day 6 were subjected to hypoxia-ischemia (HI) insult induced by left carotid artery ligation and subsequent exposure to 10% oxygen in nitrogen. The presence of ILCs and ILC2s in the brain was examined at different time points after HI. The contribution of ILC2s to HI-induced preterm brain damage was explored using a conditionally targeted ILC2-deficient mouse strain (Rorα ^fl/fl IL7r ^Cre ), and gray and white-matter injury were evaluated at 7 days post-HI. The inflammatory response in the injured brain was assessed using immunoassays and immunochemistry staining.

Results

Significant increases in ILCs and ILC2s were observed at 24 h, 3 days, and 7 days post-HI in the injured brain hemisphere compared with the uninjured hemisphere in wild-type mice. ILC2s in the brain were predominantly located in the meninges of the injured ipsilateral hemispheres after HI but not in the brain parenchyma. Overall, we did not observe changes in cytokine/chemokine levels in the brains of Rorα ^fl/fl IL7r ^Cre mice compared with wild type animals apart from IL-13. Gray and white-matter tissue loss in the brain was not affected after HI in Rorα ^fl/fl IL7r ^Cre mice. Correspondingly, we did not find any differences in reactive microglia and astrocyte numbers in the brain in Rorα ^fl/fl IL7r ^Cre mice compared with wild-type mice following HI insult.

Conclusion

After HI, ILCs and ILC2s accumulate in the injured brain hemisphere. However, ILC2s do not contribute to the development of brain damage in this mouse model of preterm brain injury.

Mediterranean Diet: Lipids, Inflammation, and Malaria Infection

The Mediterranean diet (MedDiet) consists of consumption of vegetables and healthy oils and have beneficial effects on metabolic and inflammatory diseases. Our goal here is to discuss the role of fatty acid content in MedDiet, mostly omega-3, omega-6, and omega-9 on malaria. Malaria affects millions of people around the globe. The parasite Plasmodium causes the disease. The metabolic and inflammatory alterations in the severe forms have damaging consequences to the host. The lipid content in the MedDiet holds anti-inflammatory and pro-resolutive features in the host and have detrimental effects on the Plasmodium. The lipids from the diet impact the balance of pro- and anti-inflammation, thus, lipids intake from the diet is critical to parasite elimination and host tissue damage caused by an immune response. Herein, we go into the cellular and molecular mechanisms and targets of the MedDiet fatty acids in the host and the parasite, reviewing potential benefits of the MedDiet, on inflammation, malaria infection progression, and clinical outcome.

Type 2 innate lymphoid cells regulation by regulatory T cells attenuates atherosclerosis

Regulatory T cells (Tregs) have been shown to attenuate the development and progression of atherosclerosis; however, the exact mechanism is still unclear. In our study, Tregs were adoptively transferred into ApoE^-/- mice, and type 2 innate lymphoid cells (ILC2s) were expanded by the IL-2/Jes6-1 complex or depleted by anti-CD90.2 mAb in ApoE^-/-Rag1^-/- mice to study their effects on atherosclerosis. Then, Tregs were cocultured with ILC2s in vitro to analyze ILC2s number and IL-13 production. In vivo, ApoE^-/-Rag1^-/- mice were treated with activated Tregs with or without anti-CD90.2 mAb to explore whether Tregs reduced atherosclerosis through ILC2s. Finally, neutralizing antibodies and Transwell assay were used to investigate how Tregs regulate ILC2s. Our results show that both Tregs and ILC2s reduce atherosclerosis lesions and macrophage infiltration. Moreover, Tregs effectively expanded the number of ILC2s and increased their production of IL-13 in vivo and in vitro. Furthermore, the reductions in plaque size and macrophage infiltration by Tregs were partly reversed by anti-CD90.2 mAb. Mechanistically, our data reveal that IL-10, TGF-β and cell-cell contacts are required for Tregs-ILC2s regulation. These results show that Tregs may play a partial protective role against atherosclerosis by expanding the number of ILC2s and consequently increasing IL-13 production.

Dichotomous Regulation of Acquired Immunity by Innate Lymphoid Cells

The concept of innate lymphoid cells (ILCs) includes both conventional natural killer (NK) cells and helper ILCs, which resemble CD8⁺ killer T cells and CD4⁺ helper T cells in acquired immunity, respectively. Conventional NK cells are migratory cytotoxic cells that find tumor cells or cells infected with microbes. Helper ILCs are localized at peripheral tissue and are responsible for innate helper-cytokine production. Helper ILCs are classified into three subpopulations: T_H1-like ILC1s, T_H2-like ILC2s, and T_H17/T_H22-like ILC3s. Because of the functional similarities between ILCs and T cells, ILCs can serve as an innate component that augments each corresponding type of acquired immunity. However, the physiological functions of ILCs are more plastic and complicated than expected and are affected by environmental cues and types of inflammation. Here, we review recent advances in understanding the interaction between ILCs and acquired immunity, including T- and B-cell responses at various conditions. Immune suppressive activities by ILCs in particular are discussed in comparison to their immune stimulatory effects to gain precise knowledge of ILC biology and the physiological relevance of ILCs in human diseases.

The IL-33/ST2 Axis in Immune Responses Against Parasitic Disease: Potential Therapeutic Applications

Parasitic infections pose a wide and varying threat globally, impacting over 25% of the global population with many more at risk of infection. These infections are comprised of, but not limited to, toxoplasmosis, malaria, leishmaniasis and any one of a wide variety of helminthic infections. While a great deal is understood about the adaptive immune response to each of these parasites, there remains a need to further elucidate the early innate immune response. Interleukin-33 is being revealed as one of the earliest players in the cytokine milieu responding to parasitic invasion, and as such has been given the name "alarmin." A nuclear cytokine, interleukin-33 is housed primarily within epithelial and fibroblastic tissues and is released upon cellular damage or death. Evidence has shown that interleukin-33 seems to play a crucial role in priming the immune system toward a strong T helper type 2 immune response, necessary in the clearance of some parasites, while disease exacerbating in the context of others. With the possibility of being a double-edged sword, a great deal remains to be seen in how interleukin-33 and its receptor ST2 are involved in the immune response different parasites elicit, and how those parasites may manipulate or evade this host mechanism. In this review article we compile the current cutting-edge research into the interleukin-33 response to toxoplasmosis, malaria, leishmania, and helminthic infection. Furthermore, we provide insight into directions interleukin-33 research may take in the future, potential immunotherapeutic applications of interleukin-33 modulation and how a better clarity of early innate immune system responses involving interleukin-33/ST2 signaling may be applied in development of much needed treatment options against parasitic invaders.

Protection of Batf3-deficient mice from experimental cerebral malaria correlates with impaired cytotoxic T-cell responses and immune regulation

Excessive inflammatory immune responses during infections with Plasmodium parasites are responsible for severe complications such as cerebral malaria (CM) that can be studied experimentally in mice. Dendritic cells (DCs) activate cytotoxic CD8+ T-cells and initiate immune responses against the parasites. Batf3-/- mice lack a DC subset, which efficiently induces strong CD8 T-cell responses by cross-presentation of exogenous antigens. Here we show that Batf3-/- mice infected with Plasmodium berghei ANKA (PbA) were protected from experimental CM (ECM), characterized by a stable blood-brain barrier (BBB) and significantly less infiltrated peripheral immune cells in the brain. Importantly, the absence of ECM in Batf3-/- mice correlated with attenuated responses of cytotoxic T-cells, as their parasite-specific lytic activity as well as the production of interferon gamma and granzyme B were significantly decreased. Remarkably, spleens of ECM-protected Batf3-/- mice had elevated levels of regulatory immune cells and interleukin 10. Thus, protection from ECM in PbA-infected Batf3-/- mice was associated with the absence of strong CD8+ T-cell activity and induction of immunoregulatory mediators and cells.

Innate Lymphoid Cells: Regulators of Gut Barrier Function and Immune Homeostasis

Innate lymphoid cells (ILCs), identified in the early years of this century as a new class of leukocyte family unlike the B or T lymphocytes, play a unique role bridging the innate and adaptive immune responses in mucosal immunity. Their origin, differentiation, and activation process and functions have caught global interest. Recently, accumulating evidence supports that ILCs are vital regulators for gastrointestinal mucosal homeostasis through interactions with other structural and stromal cells in gut epithelial barriers. This review will explore the functions of ILCs and other cells in maintaining gut homeostasis and feature the crosstalk between ILCs with other cells and potential pharmacotherapy targeting ILCs applicable in intestinal innate immunity.

Endothelial Protein C Receptor Could Contribute to Experimental Malaria-Associated Acute Respiratory Distress Syndrome

The severity of Plasmodium falciparum malaria is associated with parasite cytoadherence, but there is limited knowledge about the effect of parasite cytoadherence in malaria-associated acute respiratory distress syndrome (ARDS). Our objective was to evaluate the cytoadherence of infected red blood cells (iRBCs) in a murine model of ARDS and to appraise a potential function of endothelial protein C receptor (EPCR) in ARDS pathogenesis. DBA/2 mice infected with P. berghei ANKA were classified as ARDS- or hyperparasitemia- (HP-) developing mice according to respiratory parameters and parasitemia. Lungs, blood, and bronchoalveolar lavage were collected for gene expression or protein analyses. Primary cultures of microvascular lung endothelial cells from DBA/2 mice were analyzed for iRBC interactions. Lungs from ARDS-developing mice showed evidence of iRBC accumulation along with an increase in EPCR and TNF concentrations. Furthermore, TNF increased iRBC adherence in vitro. Dexamethasone-treated infected mice showed low levels of TNF and EPCR mRNA expression and, finally, decreased vascular permeability, thus protecting mice from ARDS. In conclusion, we identified that increased iRBC cytoadherence in the lungs underlies malaria-associated ARDS in DBA/2-infected mice and that inflammation increased cytoadherence capacity, suggesting a participation of EPCR and a conceivable target for drug development.

Negative Association of Interleukin-33 Plasma Levels and Schistosomiasis Infection in a Site of Polyparasitism in Rural Cameroon

Background: This study aimed to investigate the association of plasma levels of IL-33, a mucosal alarmin known to elicit type-2 immunity, with infection and liver fibrosis profiles of school children from an endemic area for Schistosoma mansoni, malaria and hepatitis (B & C) in rural Cameroon.

Methods: A cross-sectional study enrolling schoolchildren from 5 public schools was conducted. Single schistosomiasis, malaria and hepatitis infections or co-infections were assessed by kato katz, microscopy, and rapid diagnostic tests, respectively. Hepatic fibrosis was assessed by ultrasound according to WHO Niamey guidelines and plasma levels of Interleukin 33 were determined by ELISA. All statistics were performed using R studio software.

Principal findings: We found a prevalence of 13.5% (37/275), 18.2% (50/275), and 8% (22/275), respectively for schistosomiasis, malaria and hepatitis (B or C) single infections. Only 7.6% (21/275) of co-infections were reported. Although Plasma IL-33 showed a minimal negative risk for schistosomiasis infection (AOR 0.99; 95% CI 0.97–1.01), S. mansoni infected participants had lower levels of plasma IL-33 (p = 0.003) which decreased significantly as eggs burdens increased (p = 0.01) with a negative Pearson coefficient of r = −0.22. Hepatic fibrosis occurred in 47.3% (130/275) of our study population independently from plasma levels of IL-33 (AOR 1.00; 95% CI 0.99–1.01).

Conclusion/Significance: Our data failed to show an association between plasma IL-33 levels and liver disease but convincingly report on a negative association between plasma IL-33 levels and schistosomiasis infection and egg burden in school children from a polyparasitic schistosomiasis endemic area.