Peripheral Myeloid Cells Research Articles

P14.09 Early Expansion of M-MDSCs and High Plasma TSLP levels as Predictors of Primary Resistance to PD1 Inhibitors in Metastatic NSCLC

Elevation of peripheral myeloid cell populations has been associated with poor response to PD-1 inhibitors in metastatic non-small cell lung cancer (mNSCLC). The mechanisms underlying this relationship remain poorly understood. Thymic stromal lymphopoietin (TSLP), a cytokine involved in T-cell maturation, has been implicated in a complex feedback loop leading to expansion of myeloid populations and tumor growth. We hypothesized that TSLP levels directly correlate with the expansion of myeloid derived suppressor cell (MDSC) populations and sought to explore their association with response to PD-1 inhibitors in mNSCLC.

Single-cell RNA sequencing reveals functional heterogeneity of glioma-associated brain macrophages

Microglia are resident myeloid cells in the central nervous system (CNS) that control homeostasis and protect CNS from damage and infections. Microglia and peripheral myeloid cells accumulate and adapt tumor supporting roles in human glioblastomas that show prevalence in men. Cell heterogeneity and functional phenotypes of myeloid subpopulations in gliomas remain elusive. Here we show single-cell RNA sequencing (scRNA-seq) of CD11b+ myeloid cells in naïve and GL261 glioma-bearing mice that reveal distinct profiles of microglia, infiltrating monocytes/macrophages and CNS border-associated macrophages. We demonstrate an unforeseen molecular heterogeneity among myeloid cells in naïve and glioma-bearing brains, validate selected marker proteins and show distinct spatial distribution of identified subsets in experimental gliomas. We find higher expression of MHCII encoding genes in glioma-activated male microglia, which was corroborated in bulk and scRNA-seq data from human diffuse gliomas. Our data suggest that sex-specific gene expression in glioma-activated microglia may be relevant to the incidence and outcomes of glioma patients.

The Role of PTX3 in Mineralization Processes and Aging-Related Bone Diseases

The Long Pentraxin 3 (PTX3) is a multifunctional glycoprotein released by peripheral blood leukocytes and myeloid dendritic cells in response to primary pro-inflammatory stimuli, that acts as a non-redundant component of the humoral arm of innate immunity. In addition to the primary role in the acute inflammatory response, PTX3 seems to be involved in other physiological and pathological processes. Indeed, PTX3 seems to play a pivotal role in the deposition and remodeling of bone matrix during the mineralization process, promoting osteoblasts differentiation and activity. Recently, PTX3 was seen to be involved in the ectopic calcifications’ formation in breast cancer disease. In this regard, it has been observed that breast cancer tumors characterized by high expression of PTX3 and high amount of Breast Osteoblast Like Cells (BOLCs) showed several Hydroxyapatite (HA) microcalcifications, suggesting a likely role for PTX3 in differentiation and osteoblastic activity in both bone and extra-bone sites. Furthermore, given its involvement in bone metabolism, several studies agree with the definition of PTX3 as a molecule significantly involved in the pathogenesis of age-related bone diseases, such as osteoporosis, both in mice and humans. Recent results suggest that genetic and epigenetic mechanisms acting on PTX3 gene are also involved in the progression of these diseases. Based on these evidences, the aim of our systemic review was to offer an overview of the variety of biological processes in which PTX3 is involved, focusing on bone mineralization, both in a physiological and pathological context.

Temporally distinct myeloid cell responses mediate damage and repair after cerebrovascular injury.

Cerebrovascular injuries can cause severe edema and inflammation that adversely affect human health. Here, we observed recanalization after successful endovascular thrombectomy for acute large vessel occlusion was associated with cerebral edema and poor clinical outcomes in patients who experienced hemorrhagic transformation. To understand this process, we developed a cerebrovascular injury model using transcranial ultrasound that enabled spatiotemporal evaluation of resident and peripheral myeloid cells. We discovered that injurious and reparative responses diverged based on time and cellular origin. Resident microglia initially stabilized damaged vessels in a purinergic receptor-dependent manner, which was followed by influx of myelomonocytic cells that caused severe edema. Prolonged blockade of myeloid cell recruitment with anti-adhesion molecule therapy prevented severe edema but also promoted neuronal destruction and fibrosis by interfering with vascular repair later orchestrated by pro-inflammatory monocytes and pro-angiogenic repair-associated microglia (RAM). These data demonstrate how temporally distinct myeloid cell responses can contain, exacerbate, and ultimately repair a cerebrovascular injury.

Dendritic cell responses to Plasmodium falciparum in a malaria-endemic setting

BackgroundPlasmodium falciparum causes the majority of malaria cases worldwide and children in sub-Saharan Africa are the most vulnerable group affected. Non-sterile clinical immunity that protects from symptoms develops slowly and is relatively short-lived. Moreover, current malaria vaccine candidates fail to induce durable high-level protection in endemic settings, possibly due to the immunomodulatory effects of the malaria parasite itself. Because dendritic cells play a crucial role in initiating immune responses, the aim of this study was to better understand the impact of cumulative malaria exposure as well as concurrent P. falciparum infection on dendritic cell phenotype and function.MethodsIn this cross-sectional study, the phenotype and function of dendritic cells freshly isolated from peripheral blood samples of Malian adults with a lifelong history of malaria exposure who were either uninfected (n = 27) or asymptomatically infected with P. falciparum (n = 8) was assessed. Additionally, plasma cytokine and chemokine levels were measured in these adults and in Malian children (n = 19) with acute symptomatic malaria.ResultsWith the exception of lower plasmacytoid dendritic cell frequencies in asymptomatically infected Malian adults, peripheral blood dendritic cell subset frequencies and HLA-DR surface expression did not differ by infection status. Peripheral blood myeloid dendritic cells of uninfected Malian adults responded to in vitro stimulation with P. falciparum blood-stage parasites by up-regulating the costimulatory molecules HLA-DR, CD80, CD86 and CD40 and secreting IL-10, CXCL9 and CXCL10. In contrast, myeloid dendritic cells of asymptomatically infected Malian adults exhibited no significant responses above the uninfected red blood cell control. IL-10 and CXCL9 plasma levels were elevated in both asymptomatic adults and children with acute malaria.ConclusionsThe findings of this study indicate that myeloid dendritic cells of uninfected adults with a lifelong history of malaria exposure are able to up-regulate co-stimulatory molecules and produce cytokines. Whether mDCs of malaria-exposed individuals are efficient antigen-presenting cells capable of mounting an appropriate immune response remains to be determined. The data also highlights IL-10 and CXCL9 as important factors in both asymptomatic and acute malaria and add to the understanding of asymptomatic P. falciparum infections in malaria-endemic areas.

Calcium Pyrophosphate Dihydrate Crystals Increase the Granulocyte/Monocyte Progenitor (GMP) and Enhance Granulocyte and Monocyte Differentiation In Vivo.

Calcium pyrophosphate dihydrate (CPPD) crystals are formed locally within the joints, leading to pseudogout. Although the mobilization of local granulocytes can be observed in joints where pseudogout has manifested, the mechanism of this activity remains poorly understood. In this study, CPPD crystals were administered to mice, and the dynamics of splenic and peripheral blood myeloid cells were analyzed. As a result, levels of both granulocytes and monocytes were found to increase following CPPD crystal administration in a concentration-dependent manner, with a concomitant decrease in lymphocytes in the peripheral blood. In contrast, the levels of other cells, such as dendritic cell subsets, T-cells, and B-cells, remained unchanged in the spleen, following CPPD crystal administration. Furthermore, an increase in granulocytes/monocyte progenitors (GMPs) and a decrease in megakaryocyte/erythrocyte progenitors (MEPs) were also observed in the bone marrow. In addition, CPPD administration induced production of IL-1β, which acts on hematopoietic stem cells and hematopoietic progenitors and promotes myeloid cell differentiation and expansion. These results suggest that CPPD crystals act as a “danger signal” to induce IL-1β production, resulting in changes in course of hematopoietic progenitor cell differentiation and in increased granulocyte/monocyte levels, and contributing to the development of gout.

Immovable Object Meets Unstoppable Force? Dialogue Between Resident and Peripheral Myeloid Cells in the Inflamed Brain.

Inflammation of the brain parenchyma is characteristic of neurodegenerative, autoimmune, and neuroinflammatory diseases. During this process, microglia, which populate the embryonic brain and become a permanent sentinel myeloid population, are inexorably joined by peripherally derived monocytes, recruited by the central nervous system. These cells can quickly adopt a morphology and immunophenotype similar to microglia. Both microglia and monocytes have been implicated in inducing, enhancing, and/or maintaining immune-mediated pathology and thus disease progression in a number of neuropathologies. For many years, experimental and analytical systems have failed to differentiate resident microglia from peripherally derived myeloid cells accurately. This has impeded our understanding of their precise functions in, and contributions to, these diseases, and hampered the development of novel treatments that could target specific cell subsets. Over the past decade, microglia have been investigated more intensively in the context of neuroimmunological research, fostering the development of more precise experimental systems. In light of our rapidly growing understanding of these cells, we discuss the differential origins of microglia and peripherally derived myeloid cells in the inflamed brain, with an analysis of the problems resolving these cell types phenotypically and morphologically, and highlight recent developments enabling more precise identification.

Peripheral Myeloid Cell EP2 Activation Contributes to the Deleterious Consequences of Status Epilepticus.

A multidimensional inflammatory response ensues after status epilepticus (SE), driven partly by cyclooxygenase-2-mediated activation of prostaglandin EP2 receptors. The inflammatory response is typified by astrocytosis, microgliosis, erosion of the blood-brain barrier (BBB), formation of inflammatory cytokines, and brain infiltration of blood-borne monocytes. Our previous studies have shown that inhibition of monocyte brain invasion or systemic administration of an EP2 receptor antagonist relieves multiple deleterious consequences of SE. Here we identify those effects of EP2 antagonism that are reproduced by conditional ablation of EP2 receptors in immune myeloid cells and show that systemic EP2 antagonism blocks monocyte brain entry in male mice. The induction of hippocampal IL-6 after pilocarpine SE was nearly abolished in EP2 conditional KO mice. Serum albumin levels in the cortex, a measure of BBB breakdown, were significantly higher after SE in EP2-sufficient mice but not in EP2 conditional KOs. EP2 deficiency in innate immune cells accelerated the recovery from sickness behaviors following SE. Surprisingly, neurodegeneration was not alleviated in myeloid conditional KOs. Systemic EP2 antagonism prevented monocyte brain infiltration and provided broader rescue of SE-induced effects than myeloid EP2 ablation, including neuroprotection and broader suppression of inflammatory mediators. Reporter expression indicated that the cellular target of CD11b-driven Cre was circulating myeloid cells but, unexpectedly, not microglia. These findings indicate that activation of EP2 receptors on immune myeloid cells drives substantial deficits in behavior and disrupts the BBB after SE. The benefits of systemic EP2 antagonism can be attributed, in part, to blocking brain recruitment of blood-borne monocytes.SIGNIFICANCE STATEMENT Unabated seizures reduce quality of life, promote the development of epilepsy, and can be fatal. We previously identified activation of prostaglandin EP2 receptors as a driver of undesirable consequences of seizures. However, the relevant EP2-expressing cell types remain unclear. Here we identify peripheral innate immune cells as a driver of the EP2-related negative consequences of seizures. Removal of EP2 from peripheral immune cells was beneficial, abolishing production of a key inflammatory cytokine, accelerating weight regain, and limiting behavioral deficits. These findings provide evidence that EP2 engagement on peripheral immune and brain endothelia contributes to the deleterious effects of SE, and will assist in the development of beneficial therapies to enhance quality of life in individuals who suffer prolonged seizures.

Knockout of microglial P38A mapk in a mouse model of Alzheimer’s disease

AbstractBackgroundThe p38a MAPK signaling pathway is a well‐established regulator of neuroinflammation, and pharmacological inhibitors of this pathway can protect against cognitive impairment in animal models of Alzheimer’s disease (AD). This protection by p38a inhibitors might be mediated via protective effects on neurons, anti‐inflammatory effects on glia, or some combination thereof. To assess whether reduction of p38‐dependent microglial proinflammatory responses is beneficial in this context, we generated AD model mice with microglial knockout (KO) of p38a.MethodThe APPswe/PS1dE9 (MMRRC #34832) mouse AD model was crossed with p38afl/fl mice (Jax #031129) to generate AD model mice homozygous for the floxed p38a allele. These were subsequently crossed with CX3CR1CreERT2 mice (Jax #020940) that express a tamoxifen‐inducible promoter allowing for removal of p38a from microglia. This breeding scheme generated four groups of mice, used in a 2 x 2 study design: WT and AD mice with floxed p38a, with or without a copy of the myeloid‐specific Cre allele. All mice were placed on tamoxifen diet (400 ppm) for 4 weeks beginning at 5 months of age, near the beginning of amyloid plaque deposition in this AD model. After administration of tamoxifen, mice were returned to normal chow for several months, allowing turnover of peripheral myeloid cells. Mice underwent behavioral testing in open field and novel spatial recognition y‐maze (8 months of age), and radial arm water maze (11 months of age). Microglial isolation via fluorescence‐activated cellular sorting and subsequent RNAseq analysis was performed on a subset of 4 mice per group.ResultsMicroglial p38a KO had no effect on the hyperlocomotive phenotype associated with amyloid overexpression in this model; however, p38a KO increased errors in the RAWM test of spatial learning and memory in the AD model but not WT mice.ConclusionsThe p38a signaling pathway in microglia is important in restricting amyloid‐associated cognitive decline. We are currently characterizing the effects of microglial p38 KO on amyloid pathology, neuroinflammation, and microglial gene expression.

Somatic Mutations in a Single Residue of UBA1 Cause Vexas, a Severe Adult-Onset Rheumatic Disease Associated with Myeloid Dysplasia

Introduction: Identifying the causes of adult-onset rheumatic diseases remains a challenge, and limits diagnosis, prognosis, and targeted treatment. We hypothesized that mutations in genes regulating the post-translational modification ubiquitin, previously implicated in two autoinflammatory diseases, may define new rheumatic disorders. Methods: We analyzed peripheral blood exome sequence data from 2,560 individuals with inflammation-related diagnoses for deleterious mutations in >800 ubiquitin-related genes. After discovering three patients with novel UBA1 mutations, we identified additional cases based on clinical similarities through screening multiple independent cohorts. Clinical evaluation of all patients combined with Sanger sequencing, digital droplet PCR, immunoblotting, immunohistochemistry, flow cytometry, and transcriptome/cytokine profiling were performed. CRISPR/Cas9 edited zebrafish provided an in vivo model to assess UBA1 gene function. Results: Twenty-eight adult males were identified with somatic mutations at methionine 41 in UBA1, an X-linked gene, encoding the major E1 enzyme that initiates ubiquitylation. Methionine 41 is highly conserved in UBA1, and these mutations were not observed in exome sequences from over 80,000 healthy controls. Among affected individuals, mutations were found in more than half of hematopoietic stem cells, exclusively in peripheral blood myeloid cells, and not in lymphocytes or fibroblasts. The variant allele fraction of UBA1 p.Met41 mutations in peripheral blood ranged from 20-95%. Patients developed an often fatal, treatment-refractory inflammatory syndrome in late adulthood, with fever, neutrophilic cutaneous and pulmonary inflammation, chondritis, and vasculitis and some individuals met clinical criteria for relapsing polychondritis, Sweet syndrome, polyarteritis nodosa, or giant cell arteritis. In addition, the majority of subjects developed myelodysplastic bone marrow with cytopenias, characteristic vacuoles in myeloid and erythroid precursors cells, progressive bone marrow failure and thromboembolic disease, and some fulfilled clinical criteria for myelodysplastic syndrome or plasma cell dyscrasia. Transformation into MDS with excess blasts or acute myeloid leukemia did not occur in any case. Mutations at p.Met41, the initiation start site of the canonical cytoplasmic isoform, caused loss of this protein and expression of a novel, catalytically impaired isoform initiated at p.Met67. Mutant peripheral blood cells exhibited decreased ubiquitylation and activated innate immune pathways. Knockout of the zebrafish cytoplasmic UBA1 isoform homologue, but not the nuclear isoform, caused systemic inflammation. These results identify somatic mutations in UBA1 as the cause, and not the consequence, of this inflammatory disease. Conclusions: We have defined a novel disorder, VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic), which connects seemingly unrelated adult-onset inflammatory and hematologic diseases. Our work also reveals somatic mutations in a hematopoietic stem cell as a cause of adult-onset rheumatic syndromes that overlap with hematologic conditions. Identification of UBA1 mutations as a cause of these diseases has important implications for classification, prognosis, and treatment of patients, and for the role of somatic mutations of hematopoietic origin in multi-organ pathophysiology. Figure Disclosures Young: Novartis: Research Funding.

Conditional Ablation of Myeloid TNF Improves Functional Outcome and Decreases Lesion Size after Spinal Cord Injury in Mice.

Spinal cord injury (SCI) is a devastating condition consisting of an instant primary mechanical injury followed by a secondary injury that progresses for weeks to months. The cytokine tumor necrosis factor (TNF) plays an important role in the pathophysiology of SCI. We investigated the effect of myeloid TNF ablation (peripheral myeloid cells (macrophages and neutrophils) and microglia) versus central myeloid TNF ablation (microglia) in a SCI contusion model. We show that TNF ablation in macrophages and neutrophils leads to reduced lesion volume and improved functional outcome after SCI. In contrast, TNF ablation in microglia only or TNF deficiency in all cells had no effect. TNF levels tended to be decreased 3 h post-SCI in mice with peripheral myeloid TNF ablation and was significantly decreased 3 days after SCI. Leukocyte and microglia populations and all other cytokines (IL-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12, and IFNγ) and chemokines (CCL2, CCL5, and CXCL1) investigated, in addition to TNFR1 and TNFR2, were comparable between genotypes. Analysis of post-SCI signaling cascades demonstrated that the MAPK kinase SAPK/JNK decreased and neuronal Bcl-XL levels increased post-SCI in mice with ablation of TNF in peripheral myeloid cells. These findings demonstrate that peripheral myeloid cell-derived TNF is pathogenic in SCI.

Hepatobiliary malignancies have distinct peripheral myeloid-derived suppressor cell signatures and tumor myeloid cell profiles

Myeloid-derived suppressor cells (MDSCs) are immunosuppressive cells that are increased in patients with numerous malignancies including viral-derived hepatocellular carcinoma (HCC). Here, we report an elevation of MDSCs in the peripheral blood of patients with other hepatobiliary malignancies including non-viral HCC, neuroendocrine tumors (NET), and colorectal carcinoma with liver metastases (CRLM), but not cholangiocarcinoma (CCA). The investigation of myeloid cell infiltration in HCC, NET and intrahepatic CCA tumors further established that the frequency of antigen-presenting cells was limited compared to benign lesions, suggesting that primary and metastatic hepatobiliary cancers have distinct peripheral and tumoral myeloid signatures. Bioinformatics analysis of The Cancer Genome Atlas dataset demonstrated that a high MDSC score in HCC patients is associated with poor disease outcome. Given our observation that MDSCs are increased in non-CCA malignant liver cancers, these cells may represent suitable targets for effective immunotherapy approaches.

Deciphering the heterogeneity of myeloid cells during neuroinflammation in the single-cell era.

Multiple sclerosis (MS) is a disabling neuroinflammatory disease, which is little understood and lacks a sufficient therapeutic regimen. Myeloid cells have repeatedly shown to play a pivotal role in the disease progression. During homeostasis, only the CNS‐resident microglia and CNS‐associated macrophages are present in the CNS. Neuroinflammation causes peripheral immune cells to infiltrate the CNS contributing to disease progression and neurological sequelae. The differential involvement of the diverse peripheral and resident myeloid cell subsets to the disease pathogenesis and outcome are highly debated and difficult to assess. However, novel technological advances (new mouse models, single‐cell RNA‐Sequencing, and CYTOF) have improved the depth of immune profiling, which allows the characterization of distinct myeloid subsets. This review provides an overview of current knowledge on the phenotypes and roles of these different myeloid subsets in neuroinflammatory disease and their therapeutic relevance.

Interaction of microglia with infiltrating immune cells in the different phases of stroke.

Stroke, in association with its complications, is one of the leading causes of mortality and morbidity worldwide. Cerebral ischemia triggers an inflammatory response in the brain that is controlled by the activation of resident microglia as well as the infiltration of peripheral myeloid and lymphoid cells into the brain parenchyma. This inflammation has been shown to have both beneficial and detrimental effects on stroke outcome. The focus of this review lies on the functions of myeloid cells and their interaction with infiltrating lymphocytes in different phases of stroke. A detailed and time‐specific understanding of the contribution of different immune cell subsets during the course of cerebral ischemia is crucial to specifically promote beneficial and inhibit detrimental effects of inflammation on stroke outcome.

Modifying macrophages at the periphery has the capacity to change microglial reactivity and to extend ALS survival.

Microglia and peripheral macrophages have both been implicated in amyotrophic lateral sclerosis (ALS), although their respective roles have yet to be determined. We now show that macrophages along peripheral motor neuron axons in mouse models and patients with ALS react to neurodegeneration. In ALS mice, peripheral myeloid cell infiltration into the spinal cord was limited and depended on disease duration. Targeted gene modulation of the reactive oxygen species pathway in peripheral myeloid cells of ALS mice, using cell replacement, reduced both peripheral macrophage and microglial activation, delayed symptoms and increased survival. Transcriptomics revealed that sciatic nerve macrophages and microglia reacted differently to neurodegeneration, with abrupt temporal changes in macrophages and progressive, unidirectional activation in microglia. Modifying peripheral macrophages suppressed proinflammatory microglial responses, with a shift toward neuronal support. Thus, modifying macrophages at the periphery has the capacity to influence disease progression and may be of therapeutic value for ALS.

Parallels between retinal and brain pathology and response to immunotherapy in old, late-stage Alzheimer's disease mouse models.

Despite growing evidence for the characteristic signs of Alzheimer's disease (AD) in the neurosensory retina, our understanding of retina–brain relationships, especially at advanced disease stages and in response to therapy, is lacking. In transgenic models of AD (APPSWE/PS1∆E9; ADtg mice), glatiramer acetate (GA) immunomodulation alleviates disease progression in pre‐ and early‐symptomatic disease stages. Here, we explored the link between retinal and cerebral AD‐related biomarkers, including response to GA immunization, in cohorts of old, late‐stage ADtg mice. This aged model is considered more clinically relevant to the age‐dependent disease. Levels of synaptotoxic amyloid β‐protein (Aβ)1–42, angiopathic Aβ1–40, non‐amyloidogenic Aβ1–38, and Aβ42/Aβ40 ratios tightly correlated between paired retinas derived from oculus sinister (OS) and oculus dexter (OD) eyes, and between left and right posterior brain hemispheres. We identified lateralization of Aβ burden, with one‐side dominance within paired retinal and brain tissues. Importantly, OS and OD retinal Aβ levels correlated with their cerebral counterparts, with stronger contralateral correlations and following GA immunization. Moreover, immunomodulation in old ADtg mice brought about reductions in cerebral vascular and parenchymal Aβ deposits, especially of large, dense‐core plaques, and alleviation of microgliosis and astrocytosis. Immunization further enhanced cerebral recruitment of peripheral myeloid cells and synaptic preservation. Mass spectrometry analysis identified new parallels in retino‐cerebral AD‐related pathology and response to GA immunization, including restoration of homeostatic glutamine synthetase expression. Overall, our results illustrate the viability of immunomodulation‐guided CNS repair in old AD model mice, while shedding light onto similar retino‐cerebral responses to intervention, providing incentives to explore retinal AD biomarkers.

Potential for Targeting Myeloid Cells in Controlling CNS Inflammation.

Multiple Sclerosis (MS) is characterized by immune cell infiltration to the central nervous system (CNS) as well as loss of myelin. Characterization of the cells in lesions of MS patients revealed an important accumulation of myeloid cells such as macrophages and dendritic cells (DCs). Data from the experimental autoimmune encephalomyelitis (EAE) model of MS supports the importance of peripheral myeloid cells in the disease pathology. However, the majority of MS therapies focus on lymphocytes. As we will discuss in this review, multiple strategies are now in place to target myeloid cells in clinical trials. These strategies have emerged from data in both human and mouse studies. We discuss strategies targeting myeloid cell migration, growth factors and cytokines, biological functions (with a focus on miRNAs), and immunological activities (with a focus on nanoparticles).

Effects of long-term and brain-wide colonization of peripheral bone marrow-derived myeloid cells in the CNS

BackgroundMicroglia, the primary resident myeloid cells of the brain, play critical roles in immune defense by maintaining tissue homeostasis and responding to injury or disease. However, microglial activation and dysfunction has been implicated in a number of central nervous system (CNS) disorders, thus developing tools to manipulate and replace these myeloid cells in the CNS is of therapeutic interest.MethodsUsing whole body irradiation, bone marrow transplant, and colony-stimulating factor 1 receptor inhibition, we achieve long-term and brain-wide (~ 80%) engraftment and colonization of peripheral bone marrow-derived myeloid cells (i.e., monocytes) in the brain parenchyma and evaluated the long-term effects of their colonization in the CNS.ResultsHere, we identify a monocyte signature that includes an upregulation in Ccr1, Ms4a6b, Ms4a6c, Ms4a7, Apobec1, Lyz2, Mrc1, Tmem221, Tlr8, Lilrb4a, Msr1, Nnt, and Wdfy1 and a downregulation of Siglech, Slc2a5, and Ccl21a/b. We demonstrate that irradiation and long-term (~ 6 months) engraftment of the CNS by monocytes induces brain region-dependent alterations in transcription profiles, astrocytes, neuronal structures, including synaptic components, and cognition. Although our results show that microglial replacement with peripherally derived myeloid cells is feasible and that irradiation-induced changes can be reversed by the replacement of microglia with monocytes in the hippocampus, we also observe that brain-wide engraftment of peripheral myeloid cells (relying on irradiation) can result in cognitive and synaptic deficits.ConclusionsThese findings provide insight into better understanding the role and complexity of myeloid cells in the brain, including their regulation of other CNS cells and functional outcomes.

Intestinal Immune Homeostasis and Inflammatory Bowel Disease: A Perspective on Intracellular Response Mechanisms

The pathogenesis of inflammatory bowel disease (IBD) involves perturbation of intestinal immune homeostasis in genetically susceptible individuals. A mutual interplay between intestinal epithelial cells (IECs) and gut resident microbes maintains a homeostatic environment across the gut. An idiopathic gastrointestinal (GI) complication triggers aberrant physiological stress in the epithelium and peripheral myeloid cells, leading to a chronic inflammatory condition. Indeed, events in the endoplasmic reticulum (ER) and mitochondria contribute to orchestrating intracellular mechanisms such as the unfolded protein response (UPR) and oxidative stress, respectively, to resolve aberrant cellular stress. This review highlights the signaling cascades encrypted within ER and mitochondria in IECs and/or myeloid cells to dissipate chronic stress in maintaining intestinal homeostasis.

Gasdermin-D-dependent IL-1\u03b1 release from microglia promotes protective immunity during chronic Toxoplasma gondii infection

Microglia, resident immune cells of the CNS, are thought to defend against infections. Toxoplasma gondii is an opportunistic infection that can cause severe neurological disease. Here we report that during T. gondii infection a strong NF-κB and inflammatory cytokine transcriptional signature is overrepresented in blood-derived macrophages versus microglia. Interestingly, IL-1α is enriched in microglia and IL-1β in macrophages. We find that mice lacking IL-1R1 or IL-1α, but not IL-1β, have impaired parasite control and immune cell infiltration within the brain. Further, we show that microglia, not peripheral myeloid cells, release IL-1α ex vivo. Finally, we show that ex vivo IL-1α release is gasdermin-D dependent, and that gasdermin-D and caspase-1/11 deficient mice show deficits in brain inflammation and parasite control. These results demonstrate that microglia and macrophages are differently equipped to propagate inflammation, and that in chronic T. gondii infection, microglia can release the alarmin IL-1α, promoting neuroinflammation and parasite control.