Aged Microglia Research Articles

Cellular senescence in white matter microglia is induced during ageing in mice and exacerbates the neuroinflammatory phenotype

Cellular senescence, a state of irreversible cell-cycle arrest caused by a variety of cellular stresses, is critically involved in age-related tissue dysfunction in various organs. However, the features of cells in the central nervous system that undergo senescence and their role in neural impairment are not well understood as yet. Here, through comprehensive investigations utilising single-cell transcriptome analysis and various mouse models, we show that microglia, particularly in the white matter, undergo cellular senescence in the brain and spinal cord during ageing and in disease models involving demyelination. Microglial senescence is predominantly detected in disease-associated microglia, which appear in ageing and neurodegenerative diseases. We also find that commensal bacteria promote the accumulation of senescent microglia and disease-associated microglia during ageing. Furthermore, knockout of p16INK4a, a key senescence inducer, ameliorates the neuroinflammatory phenotype in damaged spinal cords in mice. These results advance our understanding of the role of cellular senescence in the central nervous system and open up possibilities for the treatment of age-related neural disorders.

Characterizing microglial senescence: Tau as a key player.

The highest risk factor for the development of neurodegenerative diseases like tauopathies is aging. Many physiological decrements underlying aging are linked to cellular senescence. Senescent cells are characterized by an irreversible growth arrest and formation of a senescence-associated secretory phenotype (SASP), a proinflammatory secretome that modifies the cellular microenvironment and contributes to tissue deterioration. Microglia, the innate immune cells in the brain, can enter a senescent state during aging. In addition, senescent microglia have been identified in the brains of tau-transgenic mice and patients suffering from tauopathies. While the contribution of senescent microglia to the development of tauopathies and other neurodegenerative diseases is a growing area of research, the effect of tau on microglial senescence remains elusive. Here, we exposed primary microglia to 5 and 15 nanomolar (nM) of monomeric tau for 18 h, followed by a recovery period of 48 h. Using multiple senescence markers, we found that exposure to 15 nM, but not 5 nM of tau increased levels of cell cycle arrest and a DNA damage marker, induced loss of the nuclear envelope protein lamin B1 and the histone marker H3K9me3, impaired tau clearance and migration, altered the cell morphology and resulted in formation of a SASP. Taken together, we show that exposure to tau can lead to microglial senescence. As senescent cells were shown to negatively impact tau pathologies, this suggests the presence of a vicious circle, which should be further investigated in the future.

The role of signaling crosstalk of microglia in hippocampus on progression of ageing and Alzheimer's disease

Based on single-cell sequencing of the hippocampi of 5× familiar Alzheimer's disease (5× FAD) and wild type mice at 2-, 12-, and 24-month of age, we found an increased percentage of microglia in aging and Alzheimer's disease (AD) mice. Blood brain barrier injury may also have contributed to this increase. Immune regulation by microglia plays a major role in the progression of aging and AD, according to the functions of 41 intersecting differentially expressed genes in microglia. Signaling crosstalk between C−C motif chemokine ligand (CCL) and major histocompatibility complex-1 bridges intercellular communication in the hippocampus during aging and AD. The amyloid precursor protein (APP) and colony stimulating factor (CSF) signals drive 5× FAD to deviate from aging track to AD occurrence among intercellular communication in hippocampus. Microglia are involved in the progression of aging and AD can be divided into 10 functional types. The strength of the interaction among microglial subtypes weakened with aging, and the CCL and CSF signaling pathways were the fundamental bridge of communication among microglial subtypes.

Studying NF-κB signaling during neuroinflammation in Alzheimer’s Diseases in vitrousing hiPSC-derived brain models

Abstract Neuroinflammation is a key pathological driver of various neurological diseases, including Alzheimer’s disease (AD). NF-κB signaling pathway is widely recognized as a hallmark of inflammation and cellular senescence in which aged microglia may undergo cellular senescence partly influenced by NF-κB. Our previous data indicated that ex vivo microglia comprised of two distinct subpopulations distinguished by morphology and motility. Most microglia cells formed a tight cell cluster, termed “clustered microglia”. The rest was a subpopulation of microglia with smaller cell size and high motility, termed “free-roaming microglia”. In microglia from aged animals, the composition of clustered versus free-roaming subsets was shifted toward a higher prevalence of free-roaming microglia where c-Rel is expressed and the canonical NF-κB signaling is more sustained. To study NF-κB signaling in the context of neuroinflammation, we are developing 3D models, using hiPSC neurons derived from healthy donors of various age groups and co-culturing them with primary microglia from knock-in mice in which their endogenous c-Rel was labeled with a fluorescent protein. Moreover, individuals with APOE-e4 genotype have an increased risk of developing AD. To develop 3D brain models for AD, we will use co-culture of microglia and neurons derived from hiPSCs of APOE-e4 carriers. Live cell imaging and biomarker assessment of microglia and neurons activated by Amyloid β (1–42) will uncover important molecular mechanisms associated with age-dependent interactions between neurons from healthy versus AD-risk individuals, and resident macrophages of the young and aged brains.

Study on the Role of an Erythrocyte Membrane-Coated Nanotheranostic System in Targeted Immune Regulation of Alzheimer's Disease.

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases in the elderly population. Despite significant advances in studies of the pathobiology on AD, there is still no effective treatment. Here, an erythrocyte membrane-camouflaged nanodrug delivery system (TR-ZRA) modified with transferrin receptor aptamers that can be targeted across the blood-brain barrier to ameliorate AD immune environment is established. Based on metal-organic framework (Zn-CA), TR-ZRA is loaded with CD22shRNA plasmid to silence the abnormally high expression molecule CD22 in aging microglia. Most importantly, TR-ZRA can enhance the ability of microglia to phagocytose Aβ and alleviate complement activation, which can promote neuronal activity and decrease inflammation level in the AD brain. Moreover, TR-ZRA is also loaded with Aβ aptamers, which allow rapid and low-cost monitoring of Aβ plaques in vitro. After treatment with TR-ZRA, learning, and memory abilities are enhanced in AD mice. In conclusion, the biomimetic delivery nanosystem TR-ZRA in this study provides a promising strategy and novel immune targets for AD therapy.

Microglial priming induced by loss of Mef2C contributes to postoperative cognitive dysfunction in aged mice

Postoperative cognitive dysfunction (POCD) is a common postoperative central nervous system (CNS) complication with a higher occurrence among aged individuals than among young individuals. The aim of this study was to explore the mechanisms by which POCD preferentially affects older individuals. We found here that exploratory laparotomy induced cognitive function decline in aged mice but not in young mice and that this decline was accompanied by inflammatory activation of microglia in the hippocampus. Furthermore, microglial depletion by feeding of a standard diet containing a colony stimulating factor 1 receptor (CSF1R) inhibitor (PLX5622) markedly protected aged mice from POCD. Notably, the expression of myocyte-specific enhancer 2C (Mef2C), an immune checkpoint that limits overactivation of microglia, was downregulated in aged microglia. Knocking down Mef2C induced a microglial priming phenotype in young mice, resulting in postoperative increases in the hippocampal levels of the inflammatory factors IL1-β, IL-6 and TNF-α that could impair cognition; these findings were consistent with the observations in aged mice. In vitro, BV2 cells lacking Mef2C released higher levels of inflammatory cytokines upon stimulation with lipopolysaccharide (LPS, a bacterial toxin) than Mef2C-sufficient cells. Moreover, upregulation of Mef2C in aged mice restrained postoperative microglial activation, attenuating the neuroinflammatory response and cognitive impairment. These results reveal that during aging, loss of Mef2C leads to microglial priming, amplifying postsurgical neuroinflammation and contributing to the vulnerability of elderly patients to POCD. Thus, targeting the immune checkpoint Mef2C in microglia may be a potential strategy for the prevention and treatment of POCD in aged individuals.

Abstract 16: Retinoid X Receptors (RXR) Play Essential Roles In Improving Post-ischemic Stroke Recovery In Aged Brain By Restoring Age-associated Dysfunctions Of Microglia/macrophages

After stroke, microglia and blood macrophages (MΦ) clear dead cells and cellular debris in the infarcted brain through phagocytosis. However, the phagocytic capability of MΦ declines with age. Age-related dysfunctions in MΦ also include reduced secretion of trophic factors, resulting in poor recovery after stroke. Retinoid-X-receptor (RXR) is a pleiotropic transcription factor. Our earlier studies suggest that RXR enhances MΦ phagocytic functions and improves post-stroke recovery in young mice. To assess MΦ dysfunctions with age, microglia were FACS-sorted from the brains of young adults (2-4 mo old) and aged (18-20 mo old) mice for gene expression profiling with qPCR. RXR agonist bexarotene (BEX; 5 mg/kg) or vehicle were IP injected daily for 3d prior to harvest (n=3/group). We found that compared to young adults, aged microglia have reduced expression of trophic factors ( Vegf ) and scavenger receptors ( Cd206 and Cd36 ) and that BEX treatment restored this deficit. Also, in agreement with gene expression profiles, using erythrocytes as targets for phagocytosis, we showed that BEX enhanced the phagocytic ability of MΦ in aged brain. This suggests that RXR activations restore the age-associated dysfunctions in MΦ.To further investigate the role of MΦ RXR activations in recovery after stroke, aged (18-20 months old) myeloid-specific RXRα knockout mice (Mac-RXRα-KO) and littermate control (RXRα-LoxP) of both sexes were subject to 60 min MCA occlusion. To activate RXR, BEX (5 mg/kg) or vehicle control was IP injected 24h after stroke onset and then daily for 7d (n=22/group). Sensorimotor functions were assessed using foot-fault and corner turn tests (d3, 7, 14, 28). The cognitive functions were evaluated via novel object recognition test (d30). We found that BEX significantly improved sensorimotor and cognitive functions in RXRα-LoxP mice. The beneficial effect of BEX was diminished in Mac-RXRα-KO mice, suggesting RXR signaling in MΦ plays essential role in recovery after stroke. Brain histology and serological cytokine profiles will also be discussed. In conclusion, our data show that activating RXR restores age-related dysfunctions in MΦ. More importantly, RXR in MΦ may be a potential target to improve post-stroke recovery in aged brain.

Aging microglia and phagocytosis.

Studies have shown that aging potentially disrupts inter-organelle communication leading to changes in cellular functions. Microglia are a specialized type of macrophage in the central nervous system that are responsible for the phagocytosis of synapses, dead neurons, and other waste materials. In microglia, disrupted communication between the endoplasmic reticulum (ER) and phagosome could compromise phagocytosis. Consequently, such disruption may have implications in the onset and/or development of neurodegenerative diseases. Therefore, we investigated the hypothesis that ER-calcium plays a vital role in microglia phagocytosis relative to phagosome development. We conducted this study using in vitro and in silico analyses of calcium dynamics and actin remodeling in BV2 microglia. Our preliminary data suggest that ER-calcium is localized to the developing phagosome during phagocytosis. This is accompanied by actin remodeling that is co-localized to the same subregions. The spatiotemporal data from these live cell imaging experiments will be analyzed through a computational model to quantify the dynamics of ER-calcium signaling and phagocytosis. The elucidation of these cellular phenomena through this analysis will help create a foundational understanding of inter-organelle communication in microglia phagocytosis.

Microglia in brain aging: An overview of recent basic science and clinical research developments.

Aging is characterized by progressive degeneration of tissues and organs, and it is positively associated with an increased mortality rate. The brain, as one of the most significantly affected organs, experiences age-related changes, including abnormal neuronal activity, dysfunctional calcium homeostasis, dysregulated mitochondrial function, and increased levels of reactive oxygen species. These changes collectively contribute to cognitive deterioration. Aging is also a key risk factor for neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. For many years, neurodegenerative disease investigations have primarily focused on neurons, with less attention given to microglial cells. However, recently, microglial homeostasis has emerged as an important mediator in neurological disease pathogenesis. Here, we provide an overview of brain aging from the perspective of the microglia. In doing so, we present the current knowledge on the correlation between brain aging and the microglia, summarize recent progress of investigations about the microglia in normal aging, Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, and then discuss the correlation between the senescent microglia and the brain, which will culminate with a presentation of the molecular complexity involved in the microglia in brain aging with suggestions for healthy aging.

Bystanders or not? Microglia and lymphocytes in aging and stroke.

As the average age of the world population increases, more people will face debilitating aging-associated conditions, including dementia and stroke. Not only does the incidence of these conditions increase with age, but the recovery afterward is often worse in older patients. Researchers and health professionals must unveil and understand the factors behind age-associated diseases to develop a therapy for older patients. Aging causes profound changes in the immune system including the activation of microglia in the brain. Activated microglia promote T lymphocyte transmigration leading to an increase in neuroinflammation, white matter damage, and cognitive impairment in both older humans and rodents. The presence of T and B lymphocytes is observed in the aged brain and correlates with worse stroke outcomes. Preclinical strategies in stroke target either microglia or the lymphocytes or the communications between them to promote functional recovery in aged subjects. In this review, we examine the role of the microglia and T and B lymphocytes in aging and how they contribute to cognitive impairment. Additionally, we provide an important update on the contribution of these cells and their interactions in preclinical aged stroke.

Microglia in brain aging: An overview of recent basic science and clinical research developments

Microglia in brain aging: An overview of recent basic science and clinical research developments

Naturally-aged microglia exhibit phagocytic dysfunction accompanied by gene expression changes reflective of underlying neurologic disease

Age-associated microglial dysfunction contributes to the accumulation of amyloid-β (Aβ) plaques in Alzheimer’s disease. Although several studies have shown age-related declines in the phagocytic capacity of myeloid cells, relatively few have examined phagocytosis of normally aged microglia. Furthermore, much of the existing data on aging microglial function have been generated in accelerated genetic models of Alzheimer’s disease. Here we found that naturally aged microglia phagocytosed less Aβ over time. To gain a better understanding of such dysfunction, we assessed differences in gene expression between young and old microglia that either did or did not phagocytose Aβ. Young microglia had both phagocytic and neuronal maintenance signatures indicative of normal microglial responses, whereas, old microglia, regardless of phagocytic status, exhibit signs of broad dysfunction reflective of underlying neurologic disease states. We also found downregulation of many phagocytic receptors on old microglia, including TREM2, an Aβ phagocytic receptor. TREM2 protein expression was diminished in old microglia and loss of TREM2+ microglia was correlated with impaired Aβ uptake, suggesting a mechanism for phagocytic dysfunction in old microglia. Combined, our work reveals that normally aged microglia have broad changes in gene expression, including defects in Aβ phagocytosis that likely underlies the progression to neurologic disease.

MICROGLIA AND INFILTRATING T-CELLS ADOPT LONG-TERM, AGE-SPECIFIC, TRANSCRIPTIONAL CHANGES AFTER TRAUMATIC BRAIN INJURY IN MICE.

Aged traumatic brain injury (TBI) patients suffer increased mortality and long-term neurocognitive and neuropsychiatric morbidity compared with younger patients. Microglia, the resident innate immune cells of the brain, are complicit in both. We hypothesized that aged microglia would fail to return to a homeostatic state after TBI and adopt a long-term injury-associated state within aged brains compared with young brains after TBI. Young and aged male C57BL/6 mice underwent TBI via controlled cortical impact versus sham injury and were sacrificed 4 months post-TBI. We used single-cell RNA sequencing to examine age-associated cellular responses after TBI. Brains were harvested, and CD45+ cells were isolated via fluorescence-activated cell sorting. cDNA libraries were prepared using the 10x Genomics Chromium Single Cell 3' Reagent Kit, followed by sequencing on a HiSeq 4,000 instrument and computational analyses. Post-injury, aged mice demonstrated a disparate microglial gene signature and an increase in infiltrating T cells compared with young adult mice. Notably, aged mice post-injury had a subpopulation of age-specific, immune-inflammatory microglia resembling the gene profile of neurodegenerative disease-associated microglia with enriched pathways involved in leukocyte recruitment and brain-derived neurotrophic factor signaling. Meanwhile, post-injury, aged mice demonstrated heterogeneous T-cell infiltration with gene profiles corresponding to CD8 effector memory, CD8 naive-like, CD8 early active T cells, and Th1 cells with enriched pathways, such as macromolecule synthesis. Taken together, our data showed that the aged brain had an age-specific gene signature change in both T-cell infiltrates and microglia, which may contribute to its increased vulnerability to TBI and the long-term sequelae of TBI.

Microglia senescence is related to neuropathic pain-associated comorbidities in the spared nerve injury model.

The increased presence of senescent cells in different neurological diseases suggests the contribution of senescence in the pathophysiology of neurodegenerative disorders. Microglia can adapt to any type of disturbance of the homeostasis of the central nervous system, and its altered activity can lead to permanent and unresolvable damage. The aim of this work was to characterize the behavioural phenotype of spared nerve injury mice and then associate it with senescence-related mechanisms. In this work, we investigated the timing of the onset of anxiety, depression, or memory decline associated with peripheral neuropathic pain and their correlation with the presence of microglial cellular senescence. Spared nerve injury mice showed a persistent pain hypersensitivity from 3 days after surgery. Twenty-eight days after nerve injury, they also developed anxiety, depression, and cognitive impairment. The appearance of these symptoms was coincident to a significant increase of senescence markers, such as β-galactosidase and senescent-associated secretory phenotype, at the microglial level in the spinal cord and hippocampus of spared nerve injury animals. These markers were unaltered at previous time points. In murine immortalized microglial cells (BV2) stimulated with LPS 500 ng/mL for 10 days (4 hours/day) every other day, we observed an increase of β-galactosidase and senescent-associated secretory phenotype appearance, a reduction of cell viability, and an increase of senescence-associated heterochromatin foci. Therefore, present findings could represent an important step to a better understanding of the pathophysiological cellular mechanisms in comorbidities related to neuropathic pain states.

Microglial repopulation alleviates age-related decline of stable wakefulness in mice.

Changes in wake/sleep architecture have been observed in both aged human and animal models, presumably due to various functional decay throughout the aging body particularly in the brain. Microglia have emerged as a modulator for wake/sleep architecture in the adult brain, and displayed distinct morphology and activity in the aging brain. However, the link between microglia and age-related wake/sleep changes remains elusive. In this study, we systematically examined the brain vigilance and microglia morphology in aging mice (3, 6, 12, and 18 months old), and determined how microglia affect the aging-related wake/sleep alterations in mice. We found that from young adult to aged mice there was a clear decline in stable wakefulness at nighttime, and a decrease of microglial processes length in various brain regions involved in wake/sleep regulation. The decreased stable wakefulness can be restored following the time course of microglia depletion and repopulation in the adult brain. Microglia repopulation in the aging brain restored age-related decline in stable wakefulness. Taken together, our findings suggest a link between aged microglia and deteriorated stable wakefulness in aged brains.

Concentration and proteolysis of CX3CL1 may regulate the microglial response to CX3CL1.

Fractalkine (FKN) is a membrane-bound chemokine that can be cleaved by proteases such as ADAM 10, ADAM 17, and cathepsin S to generate soluble fragments. Studies using different forms of the soluble FKN yield conflicting results in vivo. These observations prompted us to investigate the function and pharmacology of two commonly used isoforms of FKN, a human full-length soluble FKN (sFKN), and a human chemokine domain only FKN (cdFKN). Both are prevalent in the literature and are often assumed to be functionally equivalent. We observed that recombinant sFKN and cdFKN exhibit similar potencies in a cell-based cAMP assay, but binding affinity for CX3CR1 was modestly different. There was a 10-fold difference in potency between sFKN and cdFKN when assessing their ability to stimulate β-arrestin recruitment. Interestingly, high concentrations of FKN, regardless of cleavage variant, were ineffective at reducing pro-inflammatory microglial activation and may induce a pro-inflammatory response. This effect was observed in mouse and rat primary microglial cells as well as microglial cell lines. The inflammatory response was exacerbated in aged microglia, which is known to exhibit age-related inflammatory phenotypes. We observed the same effects in Cx3cr1-/- primary microglia and therefore speculate that an alternative FKN receptor may exist. Collectively, these data provide greater insights into the function and pharmacology of these common FKN reagents, which may clarify conflicting reports and urge greater caution in the selection of FKN peptides for use in in vitro and in vivo studies and the interpretation of results obtained using these differing peptides.

Microglial CD74 Expression Is Regulated by TGFβ Signaling.

Simple SummaryIn the present study, we provided evidence that TGFβ signaling regulated the expression of the microglia activation marker CD74. Our data demonstrated that TGFβ1 inhibited LPS-induced upregulation of CD74. Moreover, inhibition of microglial TGFβ signaling in vitro and silencing of TGFβ signaling by deletion of Tgfbr2 in vivo resulted in marked upregulation of microglial CD74.Microglia play important roles during physiological and pathological situations in the CNS. Several reports have described the expression of Cd74 in disease-associated and aged microglia. Here, we demonstrated that TGFβ1 controled the expression of Cd74 in microglia in vitro and in vivo. Using BV2 cells, primary microglia cultures as well as Cx3cr1CreERT2:R26-YFP:Tgfbr2fl/fl in combination with qPCR, flow cytometry, and immunohistochemistry, we were able to provide evidence that TGFβ1 inhibited LPS-induced upregulation of Cd74 in microglia. Interestingly, TGFβ1 alone was able to mediate downregulation of CD74 in vitro. Moreover, silencing of TGFβ signaling in vivo resulted in marked upregulation of CD74, further underlining the importance of microglial TGFβ signaling during regulation of microglia activation. Taken together, our data indicated that CD74 is a marker for activated microglia and further demonstrated that microglial TGFβ signaling is important for regulation of Cd74 expression during microglia activation.

Microglial Activation and Connectivity in Alzheimer Disease and Aging.

Alzheimer disease (AD) is characterized by amyloid β (Aβ) plaques and neurofibrillary tau tangles, but increasing evidence suggests that neuroinflammation also plays a key role, driven by the activation of microglia. Aβ and tau pathology appear to spread along pathways of highly connected brain regions, but it remains elusive whether microglial activation follows a similar distribution pattern. Here, we assess whether connectivity is associated with microglia activation patterns. We included 32 Aβ-positive early AD subjects (18 women, 14 men) and 18 Aβ-negative age-matched healthy controls (10 women, 8 men) from the prospective ActiGliA (Activity of Cerebral Networks, Amyloid and Microglia in Aging and Alzheimer's Disease) study. All participants underwent microglial activation positron emission tomography (PET) with the third-generation mitochondrial 18 kDa translocator protein (TSPO) ligand [18 F]GE-180 and magnetic resonance imaging (MRI) to measure resting-state functional and structural connectivity. We found that inter-regional covariance in TSPO-PET and standardized uptake value ratio was preferentially distributed along functionally highly connected brain regions, with MRI structural connectivity showing a weaker association with microglial activation. AD patients showed increased TSPO-PET tracer uptake bilaterally in the anterior medial temporal lobe compared to controls, and higher TSPO-PET uptake was associated with cognitive impairment and dementia severity in a disease stage-dependent manner. Microglial activation distributes preferentially along highly connected brain regions, similar to tau pathology. These findings support the important role of microglia in neurodegeneration, and we speculate that pathology spreads throughout the brain along vulnerable connectivity pathways. ANN NEUROL 2022;92:768-781.

Alzheimer's Amyloid-β Accelerates Cell Senescence and Suppresses the SIRT1/NRF2 Pathway in Human Microglial Cells.

Microglia play important roles in maintenance of brain homeostasis, while due to some pathological stimuli in aging-related neurodegenerative diseases including Alzheimer's disease, they are malfunctioning. Here, we demonstrated that amyloid-β (Aβ) accelerated cell senescence characterized by the upregulation of p21 and PAI-1 as well as senescence-associated beta-galactosidase (SA-β-gal) in human microglial cells. Consistently, Aβ induced the senescence-associated mitochondrial dysfunctions such as repression of ATP production, oxygen consumption rate (OCR), and mitochondrial membrane potential and enhancement of ROS production. Furthermore, Aβ was found to significantly suppress mRNA expression and protein level of Sirtuin-1 (SIRT1), a key regulator of senescence, and inhibit mRNA expression and translocation of NRF2, a critical transcription factor in inflammatory responses, leading to impairment of phagocytosis. Rescue of SIRT1, as expected, could counteract the pathological effects of Aβ. In summary, our findings revealed that Aβ accelerates human microglial senescence mainly through its suppression of the SIRT1/NRF2 pathway and suggested that genetic and pharmaceutical rescue of SIRT1 may provide a potential alternative treatment.

CD11bhigh B Cells Increase after Stroke and Regulate Microglia.

Recent studies have highlighted the deleterious contributions of B cells to post-stroke recovery and cognitive decline. Different B cell subsets have been proposed on the basis of expression levels of transcription factors (e.g., T-bet) as well as specific surface proteins. CD11b (α-chain of integrin) is expressed by several immune cell types and is involved in regulation of cell motility, phagocytosis, and other essential functions of host immunity. Although B cells express CD11b, the CD11bhigh subset of B cells has not been well characterized, especially in immune dysregulation seen with aging and after stroke. Here, we investigate the role of CD11bhigh B cells in immune responses after stroke in young and aged mice. We evaluated the ability of CD11bhigh B cells to influence pro- and anti-inflammatory phenotypes of young and aged microglia (MG). We hypothesized that CD11bhigh B cells accumulate in the brain and contribute to neuroinflammation in aging and after stroke. We found that CD11bhigh B cells are a heterogeneous subpopulation of B cells predominantly present in naive aged mice. Their frequency increases in the brain after stroke in young and aged mice. Importantly, CD11bhigh B cells regulate MG phenotype and increase MG phagocytosis in both ex vivo and in vivo settings, likely by production of regulatory cytokines (e.g., TNF-α). As both APCs and adaptive immune cells with long-term memory function, B cells are uniquely positioned to regulate acute and chronic phases of the post-stroke immune response, and their influence is subset specific.