Silver nanoparticle immunomodulatory potential in absence of direct cytotoxicity in RAW 264.7 macrophages and MPRO 2.1 neutrophils.

Engineered nanomaterials (ENM) are being used in a wide range of consumer products and pharmaceuticals; hence, there is an increasing risk for human exposure and potential adverse outcomes. The immune system, vital in host defense and protection against environmental agents, is typically initiated and executed by innate effector immune cells including macrophages and neutrophils. Previous literature has reported the immune system as a major target of ENM toxicity; however, there is inconsistency regarding the immunotoxicity of ENM. This could be attributed to differences in ENM physicochemical properties, cellular models examined, biocorona formation, etc. Thus, the current study examined the toxicity and immunomodulatory effects of silver nanoparticles (AgNP), one of the most utilized ENM in consumer and medical products, in two key innate immune cell models, e.g. RAW 264.7 cells (macrophages) and differentiated MPRO 2.1 cells (promyelocytes/neutrophils). The results showed that despite a generation of reactive oxygen species, exposure to 20 nm citrate-coated AgNP was not associated with major oxidative damage, inflammatory responses, nor cytotoxicity. Nevertheless, and most importantly, pre-exposure to the AgNP for 24 h enhanced RAW 264.7 cell phagocytic ability as well as the release of inflammatory cytokine interleukin-6 in response to lipopolysaccharide (LPS). In MPRO 2.1 cells, AgNP pre-exposure also resulted in enhanced phagocytic ability; however, these cells manifest reduced cell degranulation (elastase release) and oxidative burst in response to phorbol myristate acetate (PMA). Taken together, these findings indicated to us that exposure to AgNP, despite not being directly (cyto)toxic to these cells, had the potential to alter immune cell responses. The findings underscore the import of assessing immune cell function post-exposure to ENM beyond the standard endpoints such as oxidative stress and cytotoxicity. In addition, these findings further illustrate the importance of understanding the underlying molecular mechanisms of ENM-cellular interactions, particularly in the immune system.

MiR-30a increases MDSC differentiation and immunosuppressive function by targeting SOCS3 in mice with B-cell lymphoma.

Myeloid-derived suppressor cells (MDSCs), including granulocytic (G)-MDSCs and monocytic (M)-MDSCs, play a critical role in tumor-induced T cell tolerance. MDSC immunosuppressive function and differentiation are significantly promoted in patients and B-cell lymphoma model mice. However, the mechanisms regulating these processes remain largely unclear. In the present study, we observed increased microRNA (miR)-30a expression both in G-MDSCs and in M-MDSCs from B cell lymphoma model mice. After transfection with miR-30a mimics, the differentiation and suppressive capacities of MDSCs were significantly increased via up-regulation of arginase-1. Moreover, we showed that the 3'-UTR of suppressor of cytokine signaling 3 (SOCS3) mRNA is a direct target of miR-30a. Decreased SOCS3 expression and activated Janus kinase-signal transducer and activator of transcription 3 signaling promote MDSC differentiation and suppressive activities. These findings provide new insights into the molecular mechanisms underlying MDSC expansion and function during B cell lymphoma development.

The Granulocyte Progenitor Stage Is a Key Target of IRF8-Mediated Regulation of Myeloid-Derived Suppressor Cell Production.

Alterations in myelopoiesis are common across various tumor types, resulting in immature populations termed myeloid-derived suppressor cells (MDSCs). MDSC burden correlates with poorer clinical outcomes, credited to their ability to suppress antitumor immunity. MDSCs consist of two major subsets, monocytic and polymorphonuclear (PMN). Intriguingly, the latter subset predominates in many patients and tumor models, although the mechanisms favoring PMN-MDSC responses remain poorly understood. Ordinarily, lineage-restricted transcription factors regulate myelopoiesis that collectively dictate cell fate. One integral player is IFN regulatory factor (IRF)-8, which promotes monocyte/dendritic cell differentiation while limiting granulocyte development. We recently showed that IRF8 inversely controls MDSC burden in tumor models, particularly the PMN-MDSC subset. However, where IRF8 acts in the pathway of myeloid differentiation to influence PMN-MDSC production has remained unknown. In this study, we showed that: 1) tumor growth was associated with a selective expansion of newly defined IRF8lo granulocyte progenitors (GPs); 2) tumor-derived GPs had an increased ability to form PMN-MDSCs; 3) tumor-derived GPs shared gene expression patterns with IRF8-/- GPs, suggesting that IRF8 loss underlies GP expansion; and 4) enforced IRF8 overexpression in vivo selectively constrained tumor-induced GP expansion. These findings support the hypothesis that PMN-MDSCs result from selective expansion of IRF8lo GPs, and that strategies targeting IRF8 expression may limit their load to improve immunotherapy efficacy.

Functional interleukin-33 receptors are expressed in early progenitor stages of allergy-related granulocytes.

Interleukin-33 (IL-33) induces T helper type 2 (Th2) cytokine production and eosinophilia independently of acquired immunity, leading to innate immunity-mediated allergic inflammation. Allergy-related innate myeloid cells such as eosinophils, basophils and mast cells express the IL-33 receptor (IL-33R), but it is still unknown how IL-33 regulates allergic inflammation involving these cells and their progenitors. Here, we revealed that the functional IL-33R was expressed on eosinophil progenitors (EoPs), basophil progenitors (BaPs) and mast cell progenitors (MCPs). In the presence of IL-33, these progenitors did not expand, but produced a high amount of Th2 and pro-inflammatory cytokines such as IL-9, IL-13, IL-1ß and IL-6. The amount of cytokines produced by these progenitors was greater than that by mature cells. In vivo, IL-33 stimulated the expansion of EoPs, but it was dependent upon the elevated serum IL-5 that is presumably derived from type 2 innate lymphoid cells that express functional IL-33R. These data collectively suggest that EoPs, BaPs and MCPs are not only the sources of allergy-related granulocytes, but can also be sources of allergy-related cytokines in IL-33-induced inflammation. Because such progenitors can differentiate into mature granulocytes at the site of inflammation, they are potential therapeutic targets in IL-33-related allergic diseases.

The LINA Study: Higher Sensitivity of Infant Compared to Maternal Eosinophil/Basophil Progenitors to Indoor Chemical Exposures.

PURPOSE: Enhanced eosinophil/basophil (Eo/B) progenitor cell levels are known to be associated with allergic inflammation and atopy risk. The aim of the present study was to investigate the influence of different indoor exposures on the recruitment and differentiation of Eo/B progenitors in mother-child pairs. METHODS: In 68 mother-child pairs of the LINA study peripheral blood mononuclear cells were used to assess Eo/B colony forming units (CFUs). Information about disease outcomes and indoor exposures was obtained from questionnaires. Indoor concentrations of volatile organic compounds (VOCs) were measured by passive sampling. RESULTS: Infant's Eo/B CFUs were positively associated with exposure to tobacco smoke, disinfectants, or VOCs. In contrast, for maternal Eo/B CFUs, only a few associations were seen. Higher numbers of infant Eo/B CFUs were observed in children with wheezing symptoms within the second year of life. CONCLUSIONS: We demonstrate that infant's hematopoietic cells seem to respond with more sensitivity to environmental exposure compared to maternal cells. At least in infants, an activation of these hematopoietic cells by environmental exposure could contribute to an enhanced risk for the development of respiratory outcomes.

Aspectos inmunológicos de la leucemia mieloblástica aguda / An immunological approach to acute myeloid leukaemia

INTRODUCCIÓN: La leucemia mieloblástica aguda (LMA) constituye la segunda hemopatía maligna en la población pediátrica y una de las principales causas de mortalidad por cáncer infantil. La supervivencia se sitúa alrededor del 60% sin haber mejorado en las últimas décadas, por lo que son necesarios nuevos enfoques terapéuticos. El efecto antileucémico ejercido por los linfocitos y las células natural killer (NK) del sistema inmunológico está bien establecido en el trasplante de células madre hematopoyéticas pero también como estrategia de inmunoterapia adoptiva tras la quimioterapia de consolidación. PACIENTES Y MÉTODOS: De manera retrospectiva, se analizan las características clínicas de los pacientes diagnosticados de LMA en nuestro centro durante el período 1996-2014. Además en 10 leucemias agudas, 5 linfoides y 5 mieloides, se analizaron la intensidad media de fluorescencia de HLA-I, MICA-B, ULBP1-4, ligandos para los receptores de las células NK. RESULTADOS: Un total de 67 pacientes formaron parte de este análisis. La supervivencia libre de eventos con una mediana de seguimiento de 25 meses fue del 62% (IC del 95%, 55-67). Las LMA con menor supervivencia fueron las secundarias, las no M3 y las carentes de marcadores citogenéticos favorables. La probabilidad de recaída fue del 38% (IC del 95%, 31-45). La expresión de HLA-I y ULBP-4 fue significativamente menor en los blastos mieloides que en los linfoides. CONCLUSIONES: Nuestros resultados clínicos son similares a los descritos en la literatura. No se ha modificado significativamente la supervivencia en las últimas décadas y la probabilidad de recaída sigue siendo elevada. Los blastos mieloides podrían ser más susceptibles a las células NK al expresar menos HLA-I, por lo que estrategias de terapia celular podrían ser eficaces tal y como reportan otros grupos

INTRODUCTION: Acute myeloid leukaemia (AML) is the second haematological malignancy in the paediatric population, and one of the leading causes of childhood cancer mortality. Survival is currently around 60%, with no improvement in last decades, suggesting that new therapeutic approaches are needed. The anti-leukaemia effect mediated by the lymphocytes and natural killer (NK) cells of the immune system has been established in haematopoietic stem cell transplantation, and also as adoptive immunotherapy after consolidation chemotherapy schemes. PATIENTS AND METHODS: A retrospective study was conducted on the clinical characteristics of patients diagnosed and treated for AML in our centre during 1996-2014. The mean fluorescence intensities of HLA-I, MICA/B and ULBP1-4, ligands for NK cell receptors, were also analysed in ten new diagnosed leukaemia cases, five myeloid and five lymphoid. RESULTS: A total of 67 patients were used in this analysis. With a median follow up of 25 months, the event-free survival was 62% (95% CI: 55-67). Secondary AML, non-M3 phenotype, and the absence of favourable cytogenetic markers had a lower survival. The probability of relapse was 38% (95% CI: 31-45). The expression of HLA-I and ULBP-4 was significantly lower in myeloid than in lymphoid blast cells. CONCLUSIONS: Our clinical results are similar to those described in the literature. Survival did not significantly change in recent decades, and the likelihood of relapse remains high. Myeloid blasts might be more susceptible to the cytotoxicity of NK cells through their lower expression of HLA-I. NK therapy strategies in minimal disease situation could be effective, as reported by other groups

Elimination of Granulocytic Myeloid-Derived Suppressor Cells in Lupus-Prone Mice Linked to Reactive Oxygen Species-Dependent Extracellular Trap Formation.

OBJECTIVE: Emerging evidence supports a crucial role of myeloid-derived suppressor cells (MDSCs) in the regulation of autoimmune diseases. However, their role in systemic lupus erythematosus (SLE) remains unknown. This study sought to address the role of MDSCs in the pathogenesis of SLE. METHODS: MDSCs from (NZB × NZW)F1 lupus-prone mice were assessed for phenotype by flow cytometry, and the function of MDSCs was analyzed by in vitro T cell proliferation assay and real-time quantitative polymerase chain reaction. Extracellular trap (ET) formation was evaluated by immunofluorescence and confocal microscopy. The production of reactive oxygen species (ROS) by Ly-6G+ cells was determined by fluorescence-activated cell sorting analysis. RESULTS: Expansion of MDSCs was impaired and the function of MDSCs was defective in the lymphoid organs of (NZB × NZW)F1 lupus-prone mice with established disease, in which involvement of predominantly the granulocytic MDSC (G-MDSC) cell subset was observed. More specifically, the results showed that increased elimination of G-MDSCs, driven by the inflammatory milieu of lupus, could be attributed to ET formation, and that cytokines, such as interferon-α (IFNα), IFNγ, and interleukin-6, play a role in this process. Induction of ET release by G-MDSCs was mediated by the production of ROS, since inhibition of ROS generation significantly reduced ET release. CONCLUSION: Collectively, the results of this study reveal that elimination of a crucial regulatory immune cell subset is a feature of the SLE microenvironment. These findings provide new insights into the pathogenetic mechanisms of the disease.

The transcription factor XBP1 is selectively required for eosinophil differentiation.

The transcription factor XBP1 has been linked to the development of highly secretory tissues such as plasma cells and Paneth cells, yet its function in granulocyte maturation has remained unknown. Here we discovered an unexpectedly selective and absolute requirement for XBP1 in eosinophil differentiation without an effect on the survival of basophils or neutrophils. Progenitors of myeloid cells and eosinophils selectively activated the endoribonuclease IRE1α and spliced Xbp1 mRNA without inducing parallel endoplasmic reticulum (ER) stress signaling pathways. Without XBP1, nascent eosinophils exhibited massive defects in the post-translational maturation of key granule proteins required for survival, and these unresolvable structural defects fed back to suppress critical aspects of the transcriptional developmental program. Hence, we present evidence that granulocyte subsets can be distinguished by their differential reliance on secretory-pathway homeostasis.

Impact of Pre-Transplant Anti-T Cell Globulin (ATG) on Immune Recovery after Myeloablative Allogeneic Peripheral Blood Stem Cell Transplantation.

BACKGROUND: Pre-transplant infusion of rabbit anti-T cell globulin (ATG) is increasingly used as prevention of graft-versus-host disease (GVHD) after allogeneic peripheral blood stem cell transplantation (PBSCT). However, the precise impact of pre-transplant ATG on immune recovery after PBSCT is still poorly documented. METHODS: In the current study, we compared immune recovery after myeloablative PBSCT in 65 patients who either received (n = 37) or did not (n = 28) pre-transplant ATG-Fresenius (ATG-F). Detailed phenotypes of circulating T, B, natural killer (NK) and invariant NKT (iNKT) cells were analyzed by multicolor flow cytometry at serial time-points from day 40 to day 365 after transplantation. Thymic function was also assessed by sjTREC quantification. Serious infectious events were collected up to 2 years post-transplantation. RESULTS: Pre-transplant ATG-F had a prolonged (for at least up to 1-year) and selective negative impact on the T-cell pool, while it did not impair the recovery of B, NK nor iNKT cells. Among T cells, ATG-F selectively compromised the recovery of naïve CD4+, central memory CD4+ and naïve CD8+ cells, while it spared effector memory T and regulatory T cells. Levels of sjTRECs were similar in both cohorts at 1-year after PBSCT, suggesting that ATG-F unlikely impaired thymopoiesis at long-term after PBSCT. Finally, the incidence and rate of serious infections were similar in both groups, while ATG-F patients had a lower incidence of grade II-IV acute graft-versus-host disease. CONCLUSIONS: Pre-transplant ATG-F induces long-lasting modulation of the circulating T-cell pool after myeloablative PBSCT, that may participate in preventing graft-versus-host disease without deeply compromising anti-pathogen defenses.

"Tear drops" in the cerebrospinal fluid: Correct by scatter, but pathognomonic by site.

Extramedullary relapse in acute promyelocytic leukemia (APL) is rare, but occurs most commonly in central nervous system (CNS), generally in high-risk cases (total leucocyte count≥10,000/µL, atypical morphology or disseminated intravascular coagulation at presentation), and concomitant with bone marrow (BM) relapse. Here, we describe a case of APL who except for CD56 positivity was low risk but had a CNS relapse without concomitant BM involvement. Diagnosis of isolated CNS relapse was based on characteristic tear-drop pattern for CD45/side scatter plot on flow cytometry, a full compatible immunophenotype and cytomorphology in the cerebrospinal fluid. The case illustrates the value of the latter and the importance of including CD56 in risk assessment of APL.

Monocytic and promyelocytic myeloid-derived suppressor cells may contribute to G-CSF-induced immune tolerance in haplo-identical allogeneic hematopoietic stem cell transplantation.

We investigated the effects of granulocyte colony-stimulating factor (G-CSF) on monocytic (M), promyelocytic (P), and granulocytic (G) myeloid-derived suppressor cells (MDSCs) both in bone marrow and peripheral blood of 20 healthy donors and the association of MDSCs subgroups with acute and chronic graft-versus-host disease (aGvHD/cGvHD) in 62 patients who underwent haplo-identical allogeneic hematopoietic stem cell transplantation (allo-HSCT). Patients who received a higher absolute counts of M-MDSCs or P-MDSCs exhibited lower incidence of grade II-IV aGvHD (P = 0.001; P = 0.031) and extensive cGvHD (P = 0.011; P = 0.021). In the multivariate analysis, absolute counts of MDSCs in allografts emerged as independent factors that reduced the occurrence of grade II-IV aGvHD (M-MDSCs: HR = 0.087, 95% CI = 0.020-0.381, P = 0.001; P-MDSCs: HR = 0.357, 95% CI = 0.139-0.922, P = 0.033) and extensive cGvHD (M-MDSCs: HR = 0.196, 95% CI = 0.043-0.894, P = 0.035; P-MDSCs: HR = 0.257, 95% CI = 0.070-0.942, P = 0.04). Delayed M-MDSC reconstitution was associated with aGvHD onset. The 3-year cumulative incidence of transplant related mortality and relapse, 3-year probability of disease-free survival, and overall survival did not differ significantly between these subgroups. Our results suggested that G-CSF-induced immune tolerance may be mediated by M/P-MDSCs in allo-HSCT.

E-cadherin is a specific marker for erythroid differentiation and has utility, in combination with CD117 and CD34, for enumerating myeloblasts in hematopoietic neoplasms.

OBJECTIVES: E-cadherin, epithelial calcium-dependent cell adhesion protein, has been identified as a marker of immature erythroid precursors in recent years. However, the specificity of E-cadherin in bone marrow specimens for erythroblasts vs myeloblasts or other early hematopoietic precursors in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) has not been fully elucidated. METHODS: We analyzed 105 cases of AML and MDS to evaluate the specificity of E-cadherin. RESULTS: Of 84 cases of AML, including cases with megakaryocytic, erythroid, monocytic, and granulocytic differentiation, all five acute erythroleukemia cases were positive, as well as one case of megakaryoblastic leukemia that showed coexpression of glycophorin A. In addition, we demonstrate that a panel of three markers, E-cadherin, CD117, and CD34, is effective in identifying lineage-specific myeloblasts in cases of MDS where left-shifted erythroid hyperplasia may complicate morphologic assessment of myeloblasts. CONCLUSIONS: In marrow specimens, E-cadherin is a useful marker for erythroid differentation.

Angiotensin-converting enzyme overexpression in myelocytes enhances the immune response.

Angiotensin-converting enzyme (ACE) plays an important role in blood pressure control. ACE also has effects on renal function, reproduction, hematopoiesis, and several aspects of the immune response. ACE 10/10 mice overexpress ACE in monocytic cells; macrophages from ACE 10/10 mice demonstrate increased polarization toward a proinflammatory phenotype. As a result, ACE 10/10 mice have a highly effective immune response following challenge with melanoma, bacterial infection, or Alzheimer disease. As shown in ACE 10/10 mice, enhanced monocytic function greatly contributes to the ability of the immune response to defend against a wide variety of antigenic and non-antigenic challenges.

Eosinophil activities modulate the immune/inflammatory character of allergic respiratory responses in mice.

BACKGROUND: The importance and specific role(s) of eosinophils in modulating the immune/inflammatory phenotype of allergic pulmonary disease remain to be defined. Established animal models assessing the role(s) of eosinophils as contributors and/or causative agents of disease have relied on congenitally deficient mice where the developmental consequences of eosinophil depletion are unknown. METHODS: We developed a novel conditional eosinophil-deficient strain of mice (iPHIL) through a gene knock-in strategy inserting the human diphtheria toxin (DT) receptor (DTR) into the endogenous eosinophil peroxidase genomic locus. RESULTS: Expression of DTR rendered resistant mouse eosinophil progenitors sensitive to DT without affecting any other cell types. The presence of eosinophils was shown to be unnecessary during the sensitization phase of either ovalbumin (OVA) or house dust mite (HDM) acute asthma models. However, eosinophil ablation during airway challenge led to a predominantly neutrophilic phenotype (>15% neutrophils) accompanied by allergen-induced histopathologies and airway hyper-responsiveness in response to methacholine indistinguishable from eosinophilic wild-type mice. Moreover, the iPHIL neutrophilic airway phenotype was shown to be a steroid-resistant allergic respiratory variant that was reversible upon the restoration of peripheral eosinophils. CONCLUSIONS: Eosinophil contributions to allergic immune/inflammatory responses appear to be limited to the airway challenge and not to the sensitization phase of allergen provocation models. The reversible steroid-resistant character of the iPHIL neutrophilic airway variant suggests underappreciated mechanisms by which eosinophils shape the character of allergic respiratory responses.

Myeloblastic cell lines mimic some but not all aspects of human cytomegalovirus experimental latency defined in primary CD34+ cell populations.

Human cytomegalovirus (HCMV) is a significant human pathogen that achieves lifelong persistence by establishing latent infections in undifferentiated cells of the myeloid lineage, such as CD34(+) hematopoietic progenitor cells. When latency is established, viral lytic gene expression is silenced in part by a cellular intrinsic defense consisting of Daxx and histone deacetylases (HDACs) because pp71, the tegument transactivator that travels to the nucleus and inactivates this defense at the start of a lytic infection in differentiated cells, remains in the cytoplasm. Because the current in vitro and ex vivo latency models have physiological and practical limitations, we evaluated two CD34(+) myeloblastic cell lines, KG-1 and Kasumi-3, for their ability to establish, maintain, and reactivate HCMV experimental latent infections. Tegument protein pp71 was cytoplasmic, and immediate-early (IE) genes were silenced as in primary CD34(+) cells. However, in contrast to what occurs in primary CD34(+) cells ex vivo or in NT2 and THP-1 in vitro model systems, viral IE gene expression from the laboratory-adapted AD169 genome was not induced in the presence of HDAC inhibitors in either KG-1 or Kasumi-3 cells. Furthermore, while the clinical strain FIX was able to reactivate from Kasumi-3 cells, AD169 was not, and neither strain reactivated from KG-1 cells. Thus, KG-1 and Kasumi-3 experimental latent infections differ in important parameters from those in primary CD34(+) cell populations. Aspects of latency illuminated through the use of these myeloblastoid cell lines should not be considered independently but integrated with results obtained in primary cell systems when paradigms for HCMV latency are proposed.

Anticancer chemotherapy-induced intratumoral recruitment and differentiation of antigen-presenting cells.

The therapeutic efficacy of anthracyclines relies on antitumor immune responses elicited by dying cancer cells. How chemotherapy-induced cell death leads to efficient antigen presentation to T cells, however, remains a conundrum. We found that intratumoral CD11c(+)CD11b(+)Ly6C(hi) cells, which displayed some characteristics of inflammatory dendritic cells and included granulomonocytic precursors, were crucial for anthracycline-induced anticancer immune responses. ATP released by dying cancer cells recruited myeloid cells into tumors and stimulated the local differentiation of CD11c(+)CD11b(+)Ly6C(hi) cells. Such cells efficiently engulfed tumor antigens in situ and presented them to T lymphocytes, thus vaccinating mice, upon adoptive transfer, against a challenge with cancer cells. Manipulations preventing tumor infiltration by CD11c(+)CD11b(+)Ly6C(hi) cells, such as the local overexpression of ectonucleotidases, the blockade of purinergic receptors, or the neutralization of CD11b, abolished the immune system-dependent antitumor activity of anthracyclines. Our results identify a subset of tumor-infiltrating leukocytes as therapy-relevant antigen-presenting cells.

Increased accumulation of regulatory granulocytic myeloid cells in mannose receptor C type 1-deficient mice correlates with protection in a mouse model of neurocysticercosis.

Neurocysticercosis (NCC) is a central nervous system (CNS) infection caused by the metacestode stage of the parasite Taenia solium. During NCC, the parasites release immunodominant glycan antigens in the CNS environment, invoking immune responses. The majority of the associated pathogenesis is attributed to the immune response against the parasites. Glycans from a number of pathogens, including helminths, act as pathogen-associated molecular pattern molecules (PAMPs), which are recognized by pattern recognition receptors (PRRs) known as C-type lectin receptors (CLRs). Using a mouse model of NCC by infection with the related parasite Mesocestoides corti, we have investigated the role of mannose receptor C type 1 (MRC1), a CLR which recognizes high-mannose-containing glycan antigens. Here we show that MRC1(-/-) mice exhibit increased survival times after infection compared with their wild-type (WT) counterparts. The decreased disease severity correlates with reduced levels of expression of markers implicated in NCC pathology, such as interleukin-1ß (IL-1ß), IL-6, CCL5, and matrix metalloproteinase 9 (MMP9), in addition to induction of an important repair marker, fibroblast growth factor 2 (FGF2). Furthermore, the immune cell subsets that infiltrate the brain of MRC1(-/-) mice are dramatically altered and characterized by reduced numbers of T cells and the accumulation of granulocytic cells with an immune phenotype resembling granulocytic myeloid-dependent suppressor cells (gMDSCs). The results suggest that MRC1 plays a critical role in myeloid plasticity, which in turn affects the adaptive immune response and immunopathogenesis during murine NCC.

Steady-state neutrophil homeostasis is dependent on TLR4/TRIF signaling.

UNLABELLED: Polymorphonuclear neutrophil granulocytes (neutrophils) are tightly controlled by an incompletely understood homeostatic feedback loop adjusting the marrow's supply to peripheral needs. Although it has long been known that marrow cellularity is inversely correlated with G-CSF levels, the mechanism linking peripheral clearance to production remains unknown. Herein, the feedback response to antibody induced neutropenia is characterized to consist of G-CSF­dependent shifts of marrow hematopoietic progenitor populations including expansion of the lin-/Sca-1/c-kit (LSK) and granulocyte macrophage progenitor (GMP) compartments at the expense of thrombopoietic and red cell precursors. Evidence is provided that positive feedback regulation is independent from commensal germs as well as T, B, and NK cells. However, in vivo feedback is impaired in TLR4-/- and TRIF-/-, but not MyD88-/- animals. In conclusion, steady-state neutrophil homeostasis is G-CSF­dependent and regulated through pattern-recognition receptors,thereby directly linking TLR-triggering to granulopoiesis. KEY POINTS: Steady-state and emergency granulopoiesis are both dependent on TLR signaling.