Single-cell RNA sequencing reveals the evolution of the immune landscape during perihematomal edema progression after intracerebral hemorrhage.

BACKGROUND: Perihematomal edema (PHE) after post-intracerebral hemorrhage (ICH) has complex pathophysiological mechanisms that are poorly understood. The complicated immune response in the post-ICH brain constitutes a crucial component of PHE pathophysiology. In this study, we aimed to characterize the transcriptional profiles of immune cell populations in human PHE tissue and explore the microscopic differences between different types of immune cells. METHODS: 9 patients with basal ganglia intracerebral hemorrhage (hematoma volume 50-100 ml) were enrolled in this study. A multi-stage profile was developed, comprising Group1 (n = 3, 0-6 h post-ICH, G1), Group2 (n = 3, 6-24 h post-ICH, G2), and Group3 (n = 3, 24-48 h post-ICH, G3). A minimal quantity of edematous tissue surrounding the hematoma was preserved during hematoma evacuation. Single cell RNA sequencing (scRNA-seq) was used to map immune cell populations within comprehensively resected PHE samples collected from patients at different stages after ICH. RESULTS: We established, for the first time, a comprehensive landscape of diverse immune cell populations in human PHE tissue at a single-cell level. Our study identified 12 microglia subsets and 5 neutrophil subsets in human PHE tissue. What's more, we discovered that the secreted phosphoprotein-1 (SPP1) pathway served as the basis for self-communication between microglia subclusters during the progression of PHE. Additionally, we traced the trajectory branches of different neutrophil subtypes. Finally, we also demonstrated that microglia-produced osteopontin (OPN) could regulate the immune environment in PHE tissue by interacting with CD44-positive cells. CONCLUSIONS: As a result of our research, we have gained valuable insight into the immune-microenvironment within PHE tissue, which could potentially be used to develop novel treatment modalities for ICH.

Osteoimmunology of Fracture Healing.

PURPOSE OF REVIEW: The purpose of this review is to summarize what is known in the literature about the role inflammation plays during bone fracture healing. Bone fracture healing progresses through four distinct yet overlapping phases: formation of the hematoma, development of the cartilaginous callus, development of the bony callus, and finally remodeling of the fracture callus. Throughout this process, inflammation plays a critical role in robust bone fracture healing. RECENT FINDINGS: At the onset of injury, vessel and matrix disruption lead to the generation of an inflammatory response: inflammatory cells are recruited to the injury site where they differentiate, activate, and/or polarize to secrete cytokines for the purposes of cell signaling and cell recruitment. This process is altered by age and by sex. Bone fracture healing is heavily influenced by the presence of inflammatory cells and cytokines within the healing tissue.

Immune changes in peripheral blood and hematoma of patients with intracerebral hemorrhage.

Immunologic changes in the hematoma of patients with intracerebral hemorrhage (ICH) and the contribution of these changes to prognosis are unknown. We collected the blood samples and hematoma fluid from 35 patients with acute ICH (<30 hours from symptom onset) and 55 age-matched healthy controls. Using flow cytometry and ELISA, we found that the percentages of granulocytes, regulatory T cells, helper T (Th) 17 cells, and dendritic cells were higher in the peripheral blood of patients with ICH than in healthy controls, whereas the percentages of lymphocytes, M1-like macrophages, and M2-like macrophages were lower. Levels of IL-6, IL-17, IL-23, TNF-α, IL-4, IL-10, and TGF-ß were higher in the peripheral blood of patients with ICH. The absolute counts of white blood cells, lymphocytes, monocytes, and granulocytes in the hematoma tended to be greater at 12-30 hours than they were within 12 hours after ICH, but the percentage of Th cells decreased in peripheral blood. Increased levels of IL-10 in the serum and hematoma, and a reduction in M1-like macrophages in hematoma were independently associated with favorable outcome on day 90. These results indicate that immunocytes present in the hematoma may participate in the acute-phase inflammatory response after ICH.

Increased Expression of T Cell Immunoglobulin and Mucin Domain 3 on CD14+ Monocytes Is Associated with Systemic Inflammatory Reaction and Brain Injury in Patients with Spontaneous Intracerebral Hemorrhage.

OBJECTIVE: To study the expression of T cell immunoglobulin and mucin domain 3 (Tim-3) on peripheral blood immunocytes, and the relationship between Tim-3 and the systemic inflammatory response or brain injury in patients with intracerebral hemorrhage (ICH). METHODS: According to the volume of hematoma at 12 hours after onset of ICH, 60 newly diagnosed patients with ICH were divided into the small (volume of hematoma <30 mL, 30 cases) and large (volume of hematoma ≥30 mL, 30 cases) ICH groups. The expression of Tim-3 on peripheral blood immunocytes was analyzed by flow cytometry. Real-time reverse transcriptase polymerase chain reaction was used to detect Tim-3 mRNA on peripheral blood mononuclear cells (PBMCs). Meanwhile, tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), and S-100B protein were measured by enzyme-linked immunosorbent assay. Glasgow outcome scale (GOS) score at Day 30 was used to estimate prognosis of patients. RESULTS: The leukocyte count, neutrophil count, monocyte count, TNF-α, IL-1ß, and S-100B protein increased remarkably after ICH. However, all of them in the large ICH group increased more obviously, and there were significant differences when compared with those in the small ICH group (P < .01). The expression of Tim-3 mRNA on PBMCs in the large ICH group increased remarkably, peaked at Day 3, and was positively associated with the concentrations of TNF-α, IL-1ß, and S-100B protein (P < .01). Tim-3 was predominantly expressed itself on CD14+ monocytes. There was a negative correlation between GOS score and Tim-3 mRNA, TNF-α, IL-1ß, or S-100B protein. CONCLUSIONS: The expression of Tim-3 on CD14 + monocytes involves in systemic inflammatory reaction after ICH and may be a novel treatment target.

Neutrophil-Lymphocyte Ratio and Perihematomal Edema Growth in Intracerebral Hemorrhage.

BACKGROUND AND PURPOSE: Although preclinical studies have shown inflammation to mediate perihematomal edema (PHE) after intracerebral hemorrhage, clinical data are lacking. Leukocyte count, often used to gauge serum inflammation, has been correlated with poor outcome but its relationship with PHE remains unknown. Our aim was to test the hypothesis that leukocyte count is associated with PHE growth. METHODS: We included patients with intracerebral hemorrhage admitted to a tertiary-care stroke center between 2011 and 2015. The primary outcome was absolute PHE growth during 24 hours, calculated using semiautomated planimetry. Linear regression models were constructed to study the relationship between absolute and differential leukocyte counts (monocyte count and neutrophil-lymphocyte ratio) and 24-hour PHE growth. RESULTS: A total of 153 patients were included. Median hematoma and PHE volumes at baseline were 14.4 (interquartile range, 6.3-36.3) and 14.0 (interquartile range, 5.9-27.8), respectively. In linear regression analysis adjusted for demographics and intracerebral hemorrhage characteristics, absolute leukocyte count was not associated with PHE growth (ß, 0.07; standard error, 0.15; P=0.09). In secondary analyses, neutrophil-lymphocyte ratio was correlated with PHE growth (ß, 0.22; standard error, 0.08; P=0.005). CONCLUSIONS: Higher neutrophil-lymphocyte ratio is independently associated with PHE growth. This suggests that PHE growth can be predicted using differential leukocyte counts on admission.

Adoptive Regulatory T-cell Therapy Attenuates Perihematomal Inflammation in a Mouse Model of Experimental Intracerebral Hemorrhage.

The CD4+CD25+ regulatory T cells (Tregs), an innate immunomodulator, suppress cerebral inflammation and maintain immune homeostasis in multiple central nervous system injury, but its role in intracerebral hemorrhage (ICH) has not been fully characterized. This study investigated the effect of Tregs on brain injury using the mouse ICH model, which is established by autologous blood infusion. The results showed that tail intravenous injection of Tregs significantly reduced brain water content and Evans blue dye extravasation of perihematoma at day (1, 3 and 7), and improved short- and long-term neurological deficits following ICH in mouse model. Tregs treatment reduced the content of pro-inflammatory cytokines interleukin (IL)-1ß, IL-6, tumor necrosis factor-α, and malondialdehyde, while increasing the superoxide dismutase (SOD) enzymatic activity at day (1, 3 and 7) following ICH. Furthermore, Tregs treatment obviously reduced the number of NF-κB+, IL-6+, TUNEL+ and active caspase-3+ cells at day 3 after ICH. These results indicate that adoptive transfer of Tregs may provide neuroprotection following ICH in mouse models.

A Pronounced Inflammatory Activity Characterizes the Early Fracture Healing Phase in Immunologically Restricted Patients.

Immunologically restricted patients such as those with autoimmune diseases or malignancies often suffer from delayed or insufficient fracture healing. In human fracture hematomas and the surrounding bone marrow obtained from immunologically restricted patients, we analyzed the initial inflammatory phase on cellular and humoral level via flow cytometry and multiplex suspension array. Compared with controls, we demonstrated higher numbers of immune cells like monocytes/macrophages, natural killer T (NKT) cells, and activated T helper cells within the fracture hematomas and/or the surrounding bone marrow. Also, several pro-inflammatory cytokines such as Interleukin (IL)-6 and Tumor necrosis factor α (TNFα), chemokines (e.g., Eotaxin and RANTES), pro-angiogenic factors (e.g., IL-8 and Macrophage migration inhibitory factor: MIF), and regulatory cytokines (e.g., IL-10) were found at higher levels within the fracture hematomas and/or the surrounding bone marrow of immunologically restricted patients when compared to controls. We conclude here that the inflammatory activity on cellular and humoral levels at fracture sites of immunologically restricted patients considerably exceeds that of control patients. The initial inflammatory phase profoundly differs between these patient groups and is probably one of the reasons for prolonged or insufficient fracture healing often occurring within immunologically restricted patients.

Neutrophils contribute to fracture healing by synthesizing fibronectin+ extracellular matrix rapidly after injury.

The role of inflammatory cells in bone regeneration remains unclear. We hypothesize that leukocytes contribute to fracture healing by rapidly synthesizing an "emergency extracellular matrix (ECM)" before stromal cells infiltrate the fracture hematoma (FH) and synthesize the eventual collagenous bone tissue. 53 human FHs were isolated at different time points after injury, ranging from day 0 until day 23 after trauma and stained using (immuno)histochemistry. FHs isolated within 48 h after injury contained fibronectin(+) ECM, which increased over time. Neutrophils within the early FHs stained positive for cellular fibronectin and neutrophil derived particles were visible within the fibronectin(+) ECM. Stromal cells appeared at day 5 after injury or later and collagen type I birefringent fibrils could be identified during the second week after injury. Our study suggests that neutrophils contribute to bone regeneration by synthesizing an "emergency ECM" before stromal cells infiltrate the FH and synthesize the eventual bone tissue.

Cardiac Mass, Aortic Intramural Hematoma, and IgG4-related Disease: A Case Report.

As a designated entity within medicine, immunoglobulin G4 (IgG4)-related disease is relatively new. It is immune-mediated origin, characterized by a tendency for formation of tumefactive lesions, the infiltration of IgG4-positive plasma cells, and frequent but not invariable elevations of IgG4 levels in the serum. IgG4-related cardiac mass accompanying aortic intramural hematoma is an extremely rare clinical presentation. Herein we present the case of a patient who was admitted to our department complaining of severe chest pain. Computed tomographic angiography examination revealed a cardiac mass accompanying an aortic intramural hematoma. He underwent a surgical resection of the cardiac mass and a replacement of the ascending aorta with Hemashield Platinum graft and made an uneventful recovery. A diagnosis of an IgG4-related disease was made based on laboratory results and pathological examination. Corticosteroids were administered postoperatively. This case shows that the heart itself can also be a potential site for IgG4-related disease.

Intraventricular Bleeding and Hematoma Size as Predictors of Infection Development in Intracerebral Hemorrhage: A Prospective Cohort Study.

BACKGROUND: Acute intracerebral hemorrhage (ICH) is associated with increased susceptibility to bacterial infection. The physiopathology of this phenomenon is not very clear. We conducted a prospective observational study investigating the correlation and independent predictors of infections in patients with ICH. PATIENTS AND METHODS: Patients admitted between April 1997 and June 2013 with ICH diagnosis were evaluated for inclusion and exclusion criteria. RESULTS: Two hundred twenty-two patients were included in this study. Ninety four patients (42.6%) presented with an infection during hospitalization being more common than pneumonia (30%) and urinary tract infections (14%). Intraventricular hemorrhage (IVH) (95% confidence interval [CI], 62.7% versus 39.3%; P < .001) and higher ICH score (95% CI, 2.31% versus 1.67%; P = .0014) were more common in patients who had infections. We found the following risk factors for having an infection in patients with ICH: IVH (odds ratio [OR] 2.3; 95% IC, 1.3-4.1), each point of ICH score (OR 1.3; 95% CI, 1.1-1.6), and having a hematoma volume larger than 30 cc (OR 2.0; 95% CI, 1.1-3.5). The localization of the hematoma was not found to be relevant. CONCLUSIONS: ICH score, size of the hematoma, and presence of IVH are independent risk factors for having an infection after ICH.

Local inflammation in fracture hematoma: results from a combined trauma model in pigs.

Background. Previous studies showed significant interaction between the local and systemic inflammatory response after severe trauma in small animal models. The purpose of this study was to establish a new combined trauma model in pigs to investigate fracture-associated local inflammation and gain information about the early inflammatory stages after polytrauma. Material and Methods. Combined trauma consisted of tibial fracture, lung contusion, liver laceration, and controlled hemorrhage. Animals were mechanically ventilated and under ICU-monitoring for 48 h. Blood and fracture hematoma samples were collected during the time course of the study. Local and systemic levels of serum cytokines and diverse alarmins were measured by ELISA kit. Results. A statistical significant difference in the systemic serum values of IL-6 and HMGB1 was observed when compared to the sham. Moreover, there was a statistical significant difference in the serum values of the fracture hematoma of IL-6, IL-8, IL-10, and HMGB1 when compared to the systemic inflammatory response. However a decrease of local proinflammatory concentrations was observed while anti-inflammatory mediators increased. Conclusion. Our data showed a time-dependent activation of the local and systemic inflammatory response. Indeed it is the first study focusing on the local and systemic inflammatory response to multiple-trauma in a large animal model.

Hematoma-inspired alginate/platelet releasate/CaPO4 composite: initiation of the inflammatory-mediated response associated with fracture repair in vitro and ex vivo injection delivery.

A clinical need continues for consistent bone remodeling within problematic sites such as those of fracture nonunion, avascular necrosis, or irregular bone formations. In attempt to address such needs, a biomaterial system is proposed to induce early inflammatory responses after implantation and to provide later osteoconductive scaffolding for bone regeneration. Biomaterial-induced inflammation would parallel the early stage of hematoma-induced fracture repair and allow scaffold-promoted remodeling of osseous tissue to a healthy state. Initiation of the wound healing cascade by two human concentrated platelet releasate-containing alginate/ß-tricalcium phosphate biocomposites has been studied in vitro using the TIB-71™ RAW264.7 mouse monocyte cell line. Inflammatory responses inherent to the base material were found and could be modulated through incorporation of platelet releasate. Differences in hydrogel wt% (2 vs. 8 %) and/or calcium phosphate granule vol.% (20 vs. 10 %) allowed for tuning the response associated with platelet releasate-associated growth factor elution. Tunability from completely suppressing the inflammatory response to augmenting the response was observed through varied elution profiles of both releasate-derived bioagents and impurities inherent to alginate. A 2.5-fold upregulation of inducible-nitric oxide synthase gene expression followed by a tenfold increase in nitrite media levels was induced by inclusion of releasate within the 8 wt%/10 vol.% formulation and was comparable to an endotoxin positive control. Whereas, near complete elimination of inflammation was seen when releasate was included within the 2 wt%/20 vol.% formulation. These in vitro results suggested tunable interactions between the multiple platelet releasate-derived bioagents and the biocomposites for enhancing hematoma-like fracture repair. Additionally, minimally invasive delivery for in situ curing of the implant system via injection was demonstrated in rat tail vertebrae using microcomputed tomography.

Human early fracture hematoma is characterized by inflammation and hypoxia.

BACKGROUND: An effective immune system, especially during the inflammatory phase, putatively influences the quality and likelihood of bone healing. If and how this is reflected within the initial fracture hematoma is unclear. QUESTIONS/PURPOSES: We therefore asked the following questions: (1) Does the local expression in fracture hematoma of genes involved in adaptation to hypoxia, migration, angiogenesis, and osteogenesis vary as compared to the peripheral blood? (2) Do these changes occur time dependently? (3) Is the gene expression during fracture hematoma formation altered by irradiation? METHODS: Cells from fracture hematoma of 20 patients and hematomas formed in 40 patients after THA (20 without and 20 with preoperative radiation) were isolated and RNA was extracted to analyze the influence of oxygen deprivation during fracture healing on mRNA expression of genes (HIF1A, LDHA, and PGK1) involved in immunoregulation (IL6, IL8, CXCR4), angiogenesis (VEGF, IL8), and osteogenesis (SPP1, RUNX2) by quantitative PCR. RESULTS: We observed locally increased LDHA gene expression in fracture hematoma cells (6-72 h post fracture) reflecting the adaptation to hypoxia. IL6, IL8, and VEGF upregulation indicated hypoxia-mediated inflammation and angiogenesis; increased CXCR4 expression reflected immigration of immune cells. Osteogenic differentiation was reflected in the increased expression of the SPP1 and RUNX2 genes. The increased expression of the LDHA, VEGF, IL8, SPP1 and RUNX2 genes occurred time dependently. Irradiation suppressed HIF1A, IL6, IL8, CXCR4, and RUNX2 gene expression. CONCLUSIONS: Our data suggest cells in the fracture hematoma (1) adapt to hypoxia and (2) promote inflammation in fracture healing at the mRNA level, indicating early involvement of the immune system. CLINICAL RELEVANCE: The initial fracture hematoma is important for the onset of angiogenesis, chemotaxis, and osteogenesis.

[Long-term response to rituximab in a patient with acquired hemophilia]. / Respuesta a largo plazo con rituximab en una paciente con hemofilia adquirida.

A 28 year-old female without history of previous disease. In the seventh month of her first pregnancy she developed hemorrhagic tendency that worsened in the early postpartum period. Activated partial thromboplastin time was 110 sec (control=35.8 sec) with negative tests for lupus anticoagulant. Factor VIII was <1% and a factor VIII inhibitor titer was 84 Bethesda Units/mL (BU). Initial therapy included methylprednisolone, prednisone, and cyclophosphamide. After two weeks of treatment, clinical conditions of the patient improved slightly and she was discharged. Outpatient therapy included azathioprine, and prednisone for a period of 22 months but in-hospital management was several times required. We initiated rituximab 375 mg/m2/week/4 weeks. A clinical improvement and increased levels of factors VIII and XI were observed 10 weeks later and factor VIII inhibitor decreased to undetectable levels. After a 82-month follow-up period (since the first rituximab infusion), she is asymptomatic and factor VIII and factor XI plasma levels are 70% and 94%, respectively FVIII inhibitor level is still undetectable. Rituximab seems an alternative for the treatment of acquired hemophilia refractory to standard treatment.

Early detection of complications in pancreas transplants by microdialysis catheters, an observational feasibility study.

BACKGROUND: Despite advances in immunosuppression and surgical technique, pancreas transplantation is encumbered with a high rate of complication and graft losses. Particularly, venous graft thrombi occur relatively frequently and are rarely detected before the transplant is irreversibly damaged. METHODS: To detect complications early, when the grafts are potentially salvageable, we placed microdialysis catheters anteriorly and posteriorly to the graft in a cohort of 34 consecutive patients. Glucose, lactate, pyruvate, and glycerol were measured at the bedside every 1-2 hours. RESULTS: Nine patients with graft venous thrombosis had significant lactate and lactate-to-pyruvate-ratio increases without concomitant rise in blood glucose or clinical symptoms. The median lactate in these patients was significantly higher in both catheters compared to non-events (n = 15). Out of the nine thrombi, four grafts underwent successful angiographic extraction, one did not require intervention and four grafts were irreversibly damaged and explanted. Four patients with enteric anastomosis leakages had significantly higher glycerol measurements compared to non-events. As with the venous thrombi, lactate and lactate-to-pyruvate ratio were also increased in six patients with graft surrounding hematomas. CONCLUSIONS: Bedside monitoring with microdialysis catheters is a promising surveillance modality of pancreatic grafts, but differentiating between the various pathologies proves challenging.

CD47 Blocking Antibody Accelerates Hematoma Clearance After Intracerebral Hemorrhage in Aged Rats.

Both experimental studies and surgical clinical trials suggest that hematoma clearance is a therapeutic target in intracerebral hemorrhage (ICH). We have investigated effects of CD47, a "don't eat me" signal expressed on erythrocytes, on hematoma resolution after ICH in young mice. This study expands those findings by examining the effects on a CD47 blocking antibody in aged rats. First, male Fischer 344 rats (18 months old) received an intracaudate injection of 50 µL autologous whole blood or saline. Hematoma features of magnetic resonance imaging (MRI) and neurological deficits were evaluated within 3 days. Second, rats had an intracaudate co-injection of 50 µL autologous blood with either CD47 blocking antibody or IgG. MRI was used to quantify hematoma/iron volume, hemolysis, brain swelling, and atrophy at different time points, behavioral tests to assess neurological deficits, and immunohistochemistry to assess brain injury and neuroinflammation. The CD47 blocking antibody significantly promoted hematoma clearance, attenuated brain swelling, hemolysis, and neuronal loss and increased the number of phagocytic macrophages in and around hematoma 3 days after ICH. Moreover, CD47 blockade reduced neuronal loss, brain atrophy, and neurobehavioral deficits at day 28. These results indicate that a CD47 blocking antibody can accelerate hematoma clearance and alleviate short- and long-term brain injury after ICH in aged rats and that it might be a therapeutic strategy for ICH.

Time Course of Immune Response and Immunomodulation During Normal and Delayed Healing of Musculoskeletal Wounds.

Single trauma injuries or isolated fractures are often manageable and generally heal without complications. In contrast, high-energy trauma results in multi/poly-trauma injury patterns presenting imbalanced pro- and anti- inflammatory responses often leading to immune dysfunction. These injuries often exhibit delayed healing, leading to fibrosis of injury sites and delayed healing of fractures depending on the intensity of the compounding traumas. Immune dysfunction is accompanied by a temporal shift in the innate and adaptive immune cells distribution, triggered by the overwhelming release of an arsenal of inflammatory mediators such as complements, cytokines and damage associated molecular patterns (DAMPs) from necrotic cells. Recent studies have implicated this dysregulated inflammation in the poor prognosis of polytraumatic injuries, however, interventions focusing on immunomodulating inflammatory cellular composition and activation, if administered incorrectly, can result in immune suppression and unintended outcomes. Immunomodulation therapy is promising but should be conducted with consideration for the spatial and temporal distribution of the immune cells during impaired healing. This review describes the current state of knowledge in the spatiotemporal distribution patterns of immune cells at various stages during musculoskeletal wound healing, with a focus on recent advances in the field of Osteoimmunology, a study of the interface between the immune and skeletal systems, in long bone fractures. The goals of this review are to (1) discuss wound and fracture healing processes of normal and delayed healing in skeletal muscles and long bones; (2) provide a balanced perspective on temporal distributions of immune cells and skeletal cells during healing; and (3) highlight recent therapeutic interventions used to improve fracture healing. This review is intended to promote an understanding of the importance of inflammation during normal and delayed wound and fracture healing. Knowledge gained will be instrumental in developing novel immunomodulatory approaches for impaired healing.

Immunological therapeutics in acute aortic syndrome.

Acute aortic syndrome is a group of interlinked conditions with common presenting symptoms, including aortic dissection, penetrating atherosclerotic ulcer, and intramural hematoma. Pharmacological management of acute aortic syndrome is a growing area, with key themes to address the underlying inflammatory pathways believed to be the cause. Research into interleukins, matrix metalloproteinases, and granulocyte macrophage colony-stimulating factor are just some of the many immunological properties being investigated and translated into medical therapies. Stem cell experiments may indicate further advances in the pathologies of acute aortic syndrome. The study of pharmacogenomics to improve treatment across different genomes is also a novel area outlined in this paper.

Remote ischemic post-conditioning promotes hematoma resolution via AMPK-dependent immune regulation.

Spontaneous intracerebral hemorrhage (ICH) produces the highest acute mortality and worst outcomes of all stroke subtypes. Hematoma volume is an independent determinant of ICH patient outcomes, making clot resolution a primary goal of clinical management. Herein, remote-limb ischemic post-conditioning (RIC), the repetitive inflation-deflation of a blood pressure cuff on a limb, accelerated hematoma resolution and improved neurological outcomes after ICH in mice. Parabiosis studies revealed RIC accelerated clot resolution via a humoral-mediated mechanism. Whereas RIC increased anti-inflammatory macrophage activation, myeloid cell depletion eliminated the beneficial effects of RIC after ICH. Myeloid-specific inactivation of the metabolic regulator, AMPKα1, attenuated RIC-induced anti-inflammatory macrophage polarization and delayed hematoma resolution, providing a molecular link between RIC and immune activation. Finally, chimera studies implicated myeloid CD36 expression in RIC-mediated neurological recovery after ICH. Thus, RIC, a clinically well-tolerated therapy, noninvasively modulates innate immune responses to improve ICH outcomes. Moreover, immunometabolic changes may provide pharmacodynamic blood biomarkers to clinically monitor the therapeutic efficacy of RIC.