Inactivation of the F4/80 glycoprotein in the mouse germ line

Tackling Tissue Macrophage Heterogeneity by SplitCre Transgenesis

Macrophages represent a broad spectrum of distinct, but closely related tissue-resident immune cells. This presents a major challenge for the study of functional aspects of these cells using classical Cre recombinase-mediated conditional mutagenesis in mice, since single promoter-driven Cre transgenic models often display limited specificity toward their intended target. The advent of CRISPR/Cas9 technology has now provided a time- and cost-effective method to explore the full potential of binary transgenic, intersectional genetics. Specifically, the use of two promoters driving inactive Cre fragments that, when co-expressed, dimerize and only then gain recombinase activity allows the characterization and manipulation of genetically defined tissue macrophage subpopulations. Here, we will elaborate on the use of this protocol to capitalize on these recent technological advances in mouse genetics and discuss their strengths and pitfalls to improve the study of tissue macrophage subpopulations in physiology and pathophysiology.

Role of Adhesion G Protein-Coupled Receptors in Immune Dysfunction and Disorder

Disorders of the immune system, including immunodeficiency, immuno-malignancy, and (auto)inflammatory, autoimmune, and allergic diseases, have a great impact on a host’s health. Cellular communication mediated through cell surface receptors, among different cell types and between cell and microenvironment, plays a critical role in immune responses. Selective members of the adhesion G protein-coupled receptor (aGPCR) family are expressed differentially in diverse immune cell types and have been implicated recently in unique immune dysfunctions and disorders in part due to their dual cell adhesion and signaling roles. Here, we discuss the molecular and functional characteristics of distinctive immune aGPCRs and their physiopathological roles in the immune system.

A Human CD68 Promoter-Driven Inducible Cre-Recombinase Mouse Line Allows Specific Targeting of Tissue Resident Macrophages

Current genetic tools designed to target macrophages in vivo often target cells from all myeloid lineages. Therefore, we sought to generate a novel transgenic mouse which has a tamoxifen inducible Cre-recombinase under the control of the human CD68 promoter (hCD68-CreERT2). To test the efficiency and specificity of the of Cre-recombinase activity we crossed the hCD68-CreERT2 mice with a loxP-flanked STOP cassette red fluorescent protein variant (tdTomato) mouse. We established that orally dosing mice with 2 mg of tamoxifen for 5 consecutive days followed by a 5-day induction period resulted in robust expression of tdTomato in CD11b+ F4/80+ tissue resident macrophages. Using this induction protocol, we demonstrated tdTomato expression within peritoneal, liver and spleen macrophages and blood Ly6Clow monocytes. Importantly there was limited or no inducible tdTomato expression within other myeloid cells (neutrophils, monocytes, dendritic cells and eosinophils), T cells (CD4+ and CD8+) and B cells (CD19+). We also demonstrated that the level of tdTomato expression can be used as a marker to identify different populations of peritoneal and liver macrophages. We next assessed the longevity of tdTomato expression in peritoneal macrophages, liver and splenic macrophages and demonstrated high levels of tdTomato expression as long as 6 weeks after the last tamoxifen dose. Importantly, hCD68-CreERT2 expression is more restricted than that of LysM-Cre which has significant expression in major myeloid cell types (monocytes and neutrophils). To demonstrate the utility of this novel macrophage-specific Cre driver line we demonstrated tdTomato expression in recruited CD11b+CD64+F4/80+ monocyte-derived macrophages within the atherosclerotic lesions of AAV8-mPCSK9 treated mice, with limited expression in recruited neutrophils. In developing this new hCD68-CreERT2 mouse we have a tool that allows us to target tissue resident macrophages, with the advantage of not targeting other myeloid cells namely neutrophils and inflammatory monocytes.

Transcriptional Control of Gene Expression and the Heterogeneous Cellular Identity of Erythroblastic Island Macrophages

During definitive erythropoiesis, maturation of erythroid progenitors into enucleated reticulocytes requires the erythroblastic island (EBI) niche comprising a central macrophage attached to differentiating erythroid progenitors. Normally, the macrophage provides a nurturing environment for maturation of erythroid cells. Its critical physiologic importance entails aiding in recovery from anemic insults, such as systemic stress or acquired disease. Considerable interest in characterizing the central macrophage of the island niche led to the identification of putative cell surface markers enriched in island macrophages, enabling isolation and characterization. Recent studies focus on bulk and single cell transcriptomics of the island macrophage during adult steady-state erythropoiesis and embryonic erythropoiesis. They reveal that the island macrophage is a distinct cell type but with widespread cellular heterogeneity, likely suggesting distinct developmental origins and biological function. These studies have also uncovered transcriptional programs that drive gene expression in the island macrophage. Strikingly, the master erythroid regulator EKLF/Klf1 seems to also play a major role in specifying gene expression in island macrophages, including a putative EKLF/Klf1-dependent transcription circuit. Our present review and analysis of mouse single cell genetic patterns suggest novel expression characteristics that will enable a clear enrichment of EBI subtypes and resolution of island macrophage heterogeneity. Specifically, the discovery of markers such as Epor, and specific features for EKLF/Klf1-expressing island macrophages such as Sptb and Add2, or for SpiC-expressing island macrophage such as Timd4, or for Maf/Nr1h3-expressing island macrophage such as Vcam1, opens exciting possibilities for further characterization of these unique macrophage cell types in the context of their critical developmental function.

Ginsenoside Rk3 Suppresses Hepatocellular Carcinoma Development through Targeting the Gut-Liver Axis

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide. Our previous reports showed that ginsenoside Rk3 provided excellent efficacy in alleviating the intestinal inflammatory response and protecting the liver, but its mechanism for HCC prevention remains to be explored. Here, the results suggested that Rk3 displayed potent antitumor effects against a dimethyl nitrosamine- and CCl₄-induced HCC mouse model. Results revealed that Rk3 application inhibited liver injury, fibrosis, and cirrhosis. In parallel, Rk3 lowered the inflammatory response by decreasing the expression of inflammatory cytokines, inducing apoptosis, and blocking the cell cycle. Meanwhile, Rk3 effectively ameliorated the gut microbiota dysbiosis. Furthermore, correlation analysis revealed that the LPS-TLR4 signaling pathway, which was inhibited by Rk3, plays a key role in preventing HCC. To conclude, our research provides valuable insights into how Rk3 application targets the gut-liver axis and suppresses HCC development, suggesting that Rk3 might be a promising candidate for clinical treatment of HCC.

Controlling the Biological Fate of Micellar Nanoparticles: Balancing Stealth and Targeting

Integrating nanomaterials with biological entities has led to the development of diagnostic tools and biotechnology-derived therapeutic products. However, to optimize the design of these hybrid bionanomaterials, it is essential to understand how controlling the biological interactions will influence desired outcomes. Ultimately, this knowledge will allow more rapid translation from the bench to the clinic. In this paper, we developed a micellar system that was assembled using modular antibody-polymer amphiphilic materials. The amphiphilic nature was established using either poly(ethylene glycol) (PEG) or a single-chain variable fragment (scFv) from an antibody as the hydrophile and a thermoresponsive polymer (poly(oligoethylene glycol) methyl ether methacrylate) as the hydrophobe. By varying the ratios of these components, a series of nanoparticles with different antibody content was self-assembled, where the surface presentation of targeting ligand was carefully controlled. In vitro and in vivo analysis of these systems identified a mismatch between the optimal targeting ligand density to achieve maximum cell association in vitro compared to tumor accumulation in vivo. For this system, we determined an optimum antibody density for both longer circulation and enhanced targeting to tumors that balanced stealthiness of the particle (to evade immune recognition as determined in both mouse models and in whole human blood) with enhanced accumulation achieved through receptor binding on tumor cells in solid tumors. This approach provides fundamental insights into how different antibody densities affect the interaction of designed nanoparticles with both target cells and immune cells, thereby offering a method to probe the intricate interplay between increased targeting efficiency and the subsequent immune response to nanoparticles.

Fetal exposure to oncoantigen elicited antigen-specific adaptive immunity against tumorigenesis

BACKGROUND

Envisioned as a similar process to tumorigenesis in terms of biological behaviors and molecular basis, embryogenesis necessitates an immune surveillance system to eliminate erratically transformed cells. Our previous study demonstrated that fetal macrophage-like phagocytes triggered Th2-skewed immunity following endocytosing prenatally administered ovalbumin to facilitate postnatal allergic airway responses, highlighting the critical role fetal phagocytes played in dealing with antigens present in developing fetuses and shaping subsequent immune responses. It prompted us to examine whether fetuses could mount Th1 tumoricidal immunity against tumorigenesis following in utero exposure to tumor antigens.

METHODS

Gestational day 14 murine fetuses underwent in utero injection of Th1-promoting human papilloma virus (HPV) E7 peptides. Postnatally, recipients were examined for immunological consequences and the resistance to TC-1 tumorigenesis.

RESULTS

Fetal exposure to HPV E7 did not cause tolerance but rather immunization in the recipients, characterized by proinflammatory Th1 polarization of their lymphocytes. Fetal macrophage-like phagocytes were responsible for taking up HPV E7 and triggering HPV E7-specific T-cell cytotoxicity and humoral immunity that rendered recipients resistant to TC-1 tumorigenesis in postnatal life. Adoptive transfer of HPV E7-loaded fetal phagocytes also elicited Th1 immunity with rapid expansion of HPV E7-specific cytotoxic CD8+ T-cell clones in response to TC-1 cell challenge so as to protect the recipients from TC-1 tumorigenesis, but failed to completely eliminate pre-existing TC-1 cells despite perceptible attenuation of local TC-1 tumor growth.

CONCLUSIONS

Our study revealed that Th2-biasing fetus was not immune-privileged to foreign peptides, but competent to mount Th1 cytotoxic immunity and generate immunoglobulins against tumorigenesis following in utero exposure to Th1-promoting oncoantigen. It shed light on the role of fetal macrophage-like phagocytes in bridging toward tumor antigen-specific cellular and humoral immunity potentially as an immune surveillance system to eliminate transformed cells that might be egressing during embryogenesis and leftover until postnatal life.

Enhanced expression of the sphingosine-1-phosphate-receptor-3 causes acute myelogenous leukemia in mice

Acute myeloid leukemia (AML) carries a 10-100 fold lower mutational burden than other neoplastic entities. Mechanistic explanations for why a low number of mutations suffice to induce leukemogenesis are therefore required. Here we demonstrate that transgenic overexpression of the wild type sphingosine-1-phosphate receptor 3 (S1P₃) in murine hematopoietic stem cells is sufficient to induce a transplantable myeloid leukemia. In contrast, S1P₃ expression in more mature compartments does not cause malignant transformation. Treatment with the sphingosine phosphate receptor modulator Fingolimod, which prevents receptor signaling, normalized peripheral blood cell counts and reduced spleen sizes in S1P₃ expressing mice. Gene expression analyses in AML patients revealed elevated S1P₃ expression specifically in two molecular subclasses. Our data suggest a previously unrecognized contribution of wild type S1P₃ signaling to leukemogenesis that warrants the exploration of S1P₃ antagonists in preclinical AML models.

Delineating the origins, developmental programs and homeostatic functions of tissue-resident macrophages

A literature covering 150 years of research indicates that macrophages are a diverse family of professional phagocytes that continuously explore their environment, recognize and scavenge pathogens, unfit cells, cell debris as well as metabolites, and produce a large range of bioactive molecules and growth factors. A new paradigm suggests that most tissue-resident macrophages originate from fetal precursors that colonize developing organs and self-maintain independently of bone marrow-derived cells throughout life. The differentiation of these precursors is driven by a core macrophage transcriptional program and immediately followed by their specification through expression of tissue-specific transcriptional regulators early during embryogenesis. Despite our increasing understanding of ontogeny and genetic programs that shape differentiation processes and functions of macrophages, the precise developmental trajectories of tissue-resident macrophages remain undefined. Here, I review current models of fetal hematopoietic waves, possible routes of macrophage development and their roles during homeostasis. Further, transgenic mouse models are discussed providing a toolset to study the developmentally and functionally distinct arms of the phagocyte system in vivo.

Fetal origin confers radioresistance on liver macrophages via p21cip1/WAF1

BACKGROUND & AIMS

Cells of hematopoietic origin, including macrophages, are generally radiation sensitive, but a subset of Kupffer cells (KCs) is relatively radioresistant. Here, we focused on the identity of the radioresistant KCs in unmanipulated mice and the mechanism of radioresistance.

METHODS

We employed Emr1- and inducible CX3Cr1-based fate-mapping strategies combined with the RiboTag reporter to identify the total KCs and the embryo-derived KCs, respectively. The KC compartment was reconstituted with adult bone-marrow-derived KCs (bm-KCs) using clodronate depletion. Mice were lethally irradiated and transplanted with donor bone marrow, and the radioresistance of bone-marrow- or embryo-derived KCs was studied. Gene expression was analyzed using in situ mRNA isolation via RiboTag reporter mice, and the translatomes were compared among subsets.

RESULTS

Here, we identified the radioresistant KCs as the long-lived subset that is derived from CX3CR1-expressing progenitor cells in fetal life, while adult bm-KCs do not resist irradiation. While both subsets upregulated the Cdkn1a gene, encoding p21-^cip1/WAF1 protein, radioresistant embryo-derived KCs showed a greater increase in response to irradiation. In the absence of this molecule, the radioresistance of KCs was compromised. Replacement KCs, derived from adult hematopoietic stem cells, differed from radioresistant KCs in their expression of genes related to immunity and phagocytosis.

CONCLUSIONS

Here, we show that, in the murine liver, a subset of KCs of embryonic origin resists lethal irradiation through Cdkn1a upregulation and is maintained for a long period, while bm-KCs do not survive lethal irradiation.

LAY SUMMARY

Kupffer cells (KCs) are the tissue-resident macrophages of the liver. KCs can be originated from fetal precursors and from monocytes during the fetal stage and post-birth, respectively. Most immune cells in mice are sensitive to lethal-irradiation-induced death, while a subset of KCs resists radiation-induced death. These radioresistant KCs continue to live in the irradiated mice. We discovered that this relatively radioresistant KC subset are the fetal-derived KCs, and they achieve this through cell-cycle arrest. Understanding the radiobiology of KCs will provide valuable insights into the mechanisms that elicit radiation-induced liver disease.

PTPN2 Regulates Inflammasome Activation and Controls Onset of Intestinal Inflammation and Colon Cancer

Variants in the gene locus encoding protein tyrosine phosphatase non-receptor type 2 (PTPN2) are associated with inflammatory disorders, including inflammatory bowel diseases, rheumatoid arthritis, and type 1 diabetes. The anti-inflammatory role of PTPN2 is highlighted by the fact that PTPN2-deficient mice die a few weeks after birth because of systemic inflammation and severe colitis. However, the tissues, cells, and molecular mechanisms that contribute to this phenotype remain unclear. Here, we demonstrate that myeloid cell-specific deletion of PTPN2 in mice (PTPN2-LysMCre) promotes intestinal inflammation but protects from colitis-associated tumor formation in an IL-1β-dependent manner. Elevated levels of mature IL-1β production in PTPN2-LysMCre mice are a consequence of increased inflammasome assembly due to elevated phosphorylation of the inflammasome adaptor molecule ASC. Thus, we have identified a dual role for myeloid PTPN2 in directly regulating inflammasome activation and IL-1β production to suppress pro-inflammatory responses during colitis but promote intestinal tumor development.

Astrocytes and microglia: Models and tools

An amazing array of tools both old and new are available to investigate the function of astrocytes and microglia. Guttenplan and Liddelow discuss tools available to study the physiology and pathophysiology of these cells both in vivo and in culture systems.

Glial cells serve as fundamental regulators of the central nervous system in development, homeostasis, and disease. Discoveries into the function of these cells have fueled excitement in glial research, with enthusiastic researchers addressing fundamental questions about glial biology and producing new scientific tools for the community. Here, we outline the pros and cons of in vivo and in vitro techniques to study astrocytes and microglia with the goal of helping researchers quickly identify the best approach for a given research question in the context of glial biology. It is truly a great time to be a glial biologist.

Cre Driver Mice Targeting Macrophages

The Cre/loxP system is a widely applied technology for site-specific genetic manipulation in mice. This system allows for deletion of the genes of interest in specific cells, tissues, and whole organism to generate a diversity of conditional knockout mouse strains. Additionally, the Cre/loxP system is useful for development of cell- and tissue-specific reporter mice for lineage tracing, and cell-specific conditional depletion models in mice. Recently, the Cre/loxP technique was extensively adopted to characterize the monocyte/macrophage biology in mouse models. Compared to other relatively homogenous immune cell types such as neutrophils, mast cells, and basophils, monocytes/macrophages represent a highly heterogeneous population which lack specific markers or transcriptional factors. Though great efforts have been made toward establishing macrophage-specific Cre driver mice in the past decade, all of the current available strains are not perfect with regard to their depletion efficiency and targeting specificity for endogenous macrophages. Here we overview the commonly used Cre driver mouse strains targeting macrophages and discuss their major applications and limitations.

F4/80 inhibits osteoclast differentiation via downregulation of nuclear factor of activated T cells, cytoplasmic 1

Osteoclastogenesis is an essential process in bone metabolism, which can be induced by RANKL stimulation. The F4/80 glycoprotein is a member of the EGF-transmembrane 7 (TM7) family and has been established as a specific cell-surface marker for murine macrophages. This study aimed to identify the role of F4/80 in osteoclastogenesis. Using mouse bone marrow-derived macrophages (BMMs), we observed that the mRNA level of F4/80 was dramatically reduced as these cells differentiated into osteoclasts. Furthermore, osteoclastogenesis was decreased in F4/80^high BMMs compared to F4/80^-/low BMMs. The inhibitory effect of F4/80 was associated with decreased expression of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1). Ectopic overexpression of a constitutively active form of NFATc1 rescued the anti-osteoclastogenic effect of F4/80 completely, suggesting that the anti-osteoclastogenic effect of F4/80 was mainly due to reduction in NFATc1 expression. As an underlying mechanism, we demonstrated that the presence of F4/80 abrogated the effect of RANKL on the phosphorylation of CREB and activated the expression of IFN-β, which are restored by cyclic AMP. Collectively, our results demonstrate that the presence of F4/80 suppresses RANKL-induced osteoclastogenesis by impairing the expression of NFATc1 via CREB and IFN-β. Therefore, F4/80 may hold therapeutic potential for bone destructive diseases.

F4/80 as a Major Macrophage Marker: The Case of the Peritoneum and Spleen

Tissue macrophages are a heterogeneous cell population residing in all body tissues that contribute to the maintenance of homeostasis and trigger immune activation in response to injurious stimuli. This heterogeneity may be associated with tissue-specific functions; however, the presence of distinct macrophage populations within the same microenvironment indicates that macrophage heterogeneity may also be influenced outside of tissue specialization. The F4/80 molecule was established as a unique marker of murine macrophages when a monoclonal antibody was found to recognize an antigen exclusively expressed by these cells. However, recent research has shown that F4/80 is expressed by other immune cells and is not equivalently expressed across tissue-specific macrophage lineages, including those residing in the same microenvironment, such as the peritoneum and spleen. In this context, two murine macrophage subtypes with distinct F4/80 expression patterns were recently found to coexist in the peritoneum, termed large peritoneal macrophages (LPMs) and small peritoneal macrophages (SPMs). However, the presence of phenotypic and functional heterogeneous macrophage subpopulations in the spleen was already known. Thus, although F4/80 surface expression continues to be the best method to identify tissue macrophages, additional molecules must also be examined to distinguish these cells from other immune cells.

Depletion of Gut Microbiota Protects against Renal Ischemia-Reperfusion Injury

An accumulating body of evidence shows that gut microbiota fulfill an important role in health and disease by modulating local and systemic immunity. The importance of the microbiome in the development of kidney disease, however, is largely unknown. To study this concept, we depleted gut microbiota with broad-spectrum antibiotics and performed renal ischemia-reperfusion (I/R) injury in mice. Depletion of the microbiota significantly attenuated renal damage, dysfunction, and remote organ injury and maintained tubular integrity after renal I/R injury. Gut flora-depleted mice expressed lower levels of F4/80 and chemokine receptors CX3CR1 and CCR2 in the F4/80⁺ renal resident macrophage population and bone marrow (BM) monocytes than did control mice. Additionally, compared with control BM monocytes, BM monocytes from gut flora-depleted mice had decreased migratory capacity toward CX3CL1 and CCL2 ligands. To study whether these effects were driven by depletion of the microbiota, we performed fecal transplants in antibiotic-treated mice and found that transplant of fecal material from an untreated mouse abolished the protective effect of microbiota depletion upon renal I/R injury. In conclusion, we show that depletion of gut microbiota profoundly protects against renal I/R injury by reducing maturation status of F4/80⁺ renal resident macrophages and BM monocytes. Therefore, dampening the inflammatory response by targeting microbiota-derived mediators might be a promising therapy against I/R injury.

Mafb lineage tracing to distinguish macrophages from other immune lineages reveals dual identity of Langerhans cells

Current systems for conditional gene deletion within mouse macrophage lineages are limited by ectopic activity or low efficiency. In this study, we generated a Mafb-driven Cre strain to determine whether any dendritic cells (DCs) identified by Zbtb46-GFP expression originate from a Mafb-expressing population. Lineage tracing distinguished macrophages from classical DCs, neutrophils, and B cells in all organs examined. At steady state, Langerhans cells (LCs) were lineage traced but also expressed Zbtb46-GFP, a phenotype not observed in any other population. After exposure to house dust mite antigen, Zbtb46-negative CD64⁺ inflammatory cells infiltrating the lung were substantially lineage traced, but Zbtb46-positive CD64^- cells were not. These results provide new evidence for the unique identity of LCs and challenge the notion that some inflammatory cells are a population of monocyte-derived DCs.

Developmental origin of lung macrophage diversity

Macrophages are specialized phagocytic cells, present in all tissues, which engulf and digest pathogens, infected and dying cells, and debris, and can recruit and regulate other immune cells and the inflammatory response and aid in tissue repair. Macrophage subpopulations play distinct roles in these processes and in disease, and are typically recognized by differences in marker expression, immune function, or tissue of residency. Although macrophage subpopulations in the brain have been found to have distinct developmental origins, the extent to which development contributes to macrophage diversity between tissues and within tissues is not well understood. Here, we investigate the development and maintenance of mouse lung macrophages by marker expression patterns, genetic lineage tracing and parabiosis. We show that macrophages populate the lung in three developmental waves, each giving rise to a distinct lineage. These lineages express different markers, reside in different locations, renew in different ways, and show little or no interconversion. Thus, development contributes significantly to lung macrophage diversity and targets each lineage to a different anatomical domain.

The Relevance of Genomic Signatures at Adhesion GPCR Loci in Humans

Adhesion G protein-coupled receptors (aGPCRs) have a long evolutionary history dating back to very basal unicellular eukaryotes. Almost every vertebrate is equipped with a set of different aGPCRs. Genomic sequence data of several hundred extinct and extant species allows for reconstruction of aGPCR phylogeny in vertebrates and non-vertebrates in general but also provides a detailed view into the recent evolutionary history of human aGPCRs. Mining these sequence sources with bioinformatic tools can unveil many facets of formerly unappreciated aGPCR functions. In this review, we extracted such information from the literature and open public sources and provide insights into the history of aGPCR in humans. This includes comprehensive analyses of signatures of selection, variability of human aGPCR genes, and quantitative traits at human aGPCR loci. As indicated by a large number of genome-wide genotype-phenotype association studies, variations in aGPCR contribute to specific human phenotypes. Our survey demonstrates that aGPCRs are significantly involved in adaptation processes, phenotype variations, and diseases in humans.

Adhesion GPCRs as Modulators of Immune Cell Function

Immune cells express several adhesion G protein-coupled receptors (aGPCRs), including the ADGRE subfamily members EMR1 (F4/80, ADGRE1), EMR2 (ADGRE2), EMR3 (ADGRE3), EMR4 (FIRE, ADGRE4), and CD97 (ADGRE5), the ADGRB subfamily member BAI1 (ADGRB1), and the ADGRG subfamily members GPR56 (ADGRG1), GPR97 (Pb99, ADGRG3), and GPR114 (ADGRG5). Expression of these molecules in hematopoietic stem and progenitor cells, monocytes/macrophages (Mφs), dendritic cells, granulocytes, and lymphocytes depends on lineage diversification and maturation, making them suitable markers for individual leukocyte subsets (e.g., F4/80 on mouse Mφs). Recent studies revealed intriguing activities of aGPCRs in tolerance induction (EMR1), granulopoiesis (CD97), engulfment of apoptotic cells and bacteria (BAI1), hematopoietic stem cell formation (GPR56), and control of cytotoxicity (GPR56). Here, we review these findings and discuss their biological and translational implications.

Subpopulations of M-MDSCs from mice infected by an immunodeficiency-causing retrovirus and their differential suppression of T- vs B-cell responses

Monocytic (CD11b(+)Ly6G(±/Lo)Ly6C(+)) myeloid derived suppressor cells (M-MDSCs) expand following murine retroviral LP-BM5 infection and suppress ex vivo polyclonal T-cell and B-cell responses. M-MDSCs 3 weeks post LP-BM5 infection have decreased suppression of T-cell, but not B-cell, responses and alterations in the degree of iNOS/NO dependence of suppression. M-MDSCs from LP-BM5 infected mice were sorted into four quadrant populations (Ly6C/CD11b density): all quadrants suppressed B-cell responses, but only M-MDSCs expressing the highest levels of Ly6C and CD11b (Q2) significantly suppressed T-cell responses. Further subdivision of this Q2 population revealed the Ly6C(+/Hi) M-MDSC subpopulation as the most suppressive, inhibiting T- and B-cell responses in a full, or partially, iNOS/NO-dependent manner, respectively. In contrast, the lower/moderate levels of suppression by the Ly6C(+/Lo) and Ly6C(+/Mid) M-MDSC Q2 subpopulations, whether versus T- and/or B-cells, displayed little/no iNOS dependency for suppression. These results highlight differential phenotypic and functional immunosuppressive M-MDSC subsets in a retroviral immunodeficiency model.

The PPARβ/δ agonist GW501516 attenuates peritonitis in peritoneal fibrosis via inhibition of TAK1-NFκB pathway in rats

Peritoneal fibrosis is a common consequence of long-term peritoneal dialysis (PD), and peritonitis is a factor in its onset. Agonist-bound peroxisome proliferator-activated receptors (PPARs) function as key regulators of energy metabolism and inflammation. Here, we examined the effects of PPARβ/δ agonist GW501516 on peritonitis in a rat peritoneal fibrosis model. Peritoneal fibrosis secondary to inflammation was induced into uremic rats by daily injection of Dianeal 4.25% PD solutions along with six doses of lipopolysaccharide before commencement of GW501516 treatment. Normal non-uremic rats served as control, and all rats were fed with a control diet or a GW501516-containing diet. Compared to control group, exposure to PD fluids caused peritoneal fibrosis that was accompanied by increased mRNA levels of monocyte chemoattractant protein-1, tumor necrotic factor-α, and interleukin-6 in the uremic rats, and these effects were prevented by GW501516 treatment. Moreover, GW501516 was found to attenuate glucose-stimulated inflammation in cultured rat peritoneal mesothelial cells via inhibition of transforming growth factor-β-activated kinase 1 (TAK1), and nuclear factor kappa B (NFκB) signaling pathway (TAK1-NFκB pathway), a main inflammation regulatory pathway. In conclusion, inhibition of TAK1-NFκB pathway with GW501516 may represent a novel therapeutic approach to ameliorate peritonitis-induced peritoneal fibrosis for patients on PD.

Estrogen contributes to regulating iron metabolism through governing ferroportin signaling via an estrogen response element

Ferroportin (FPN) is the only known iron exporter in mammalian cells, and is universally expressed in most types of cells. FPN signaling plays a crucial role in maintaining iron homeostasis through governing the level of intracellular iron. Serum iron storage is conversely related with the estrogen level in the female bodies, and women in post-menopause are possibly subjected to iron retention. However, the potential effects of estrogen on iron metabolism are not clearly understood. Here, FPN mRNA transcription in all selected estrogen receptor positive (ER+) cells was significantly reduced upon 17β-estradiol (E2) treatment; and this inhibitory effect could be attenuated by ER antagonist tamoxifen. Likewise, in murine bone marrow-derived macrophages (BMDMs), FPN reduction with elevated intracellular iron (reflected by increased ferritin) was observed in response to E2; however, ferritin level barely responded to E2 in FPN-null BMDMs. The observation of inhibition of FPN mRNA expression was not replicated in ER(-) cells upon E2. A functional estrogen response element (ERE) was identified within the promoter of FPN, and this ERE was responsible for the suppressive effect of E2 on FPN expression. Moreover, ovariectomized (OVX) and sham-operated (SHAM) mice were used to further confirm the in vitro finding. The expression of hepatic FPN was induced in OVX mice, compared to that in the SHAM mice. Taken together, our results demonstrated that estrogen is involved in regulating FPN expression through a functional ERE on its promoter, providing additional insights into a vital role of estrogen in iron metabolism.

Genetic targeting of microglia

Genetic targeting of microglia and other myeloid cells in the central nervous system (CNS) is highly desirable as they are critical effectors and regulators of changes in CNS homeostasis during development as well as in health and disease. Therefore, genetic reprogramming of microglia could constitute a central approach for potentially reducing disease burden. Previous attempts to target only microglia in vivo failed because of the similarities to their hematopoietic relatives in the circulation. However, this concept has been challenged by recent results of developmental and gene expression profiling studies which used novel molecular biological tools to unravel the origin of microglia and to define their role as specialized tissue macrophages clearly distinct from monocytes or monocyte-derived macrophages. The aim of this review is to recapitulate the history of microglia targeting approaches and finally highlight recent achievements in the field. We will discuss the pros and cons of the newly available genetic tools, their potential for future microglia research and genetic strategies.

Comparative analysis of the efficiency and specificity of myeloid-Cre deleting strains using ROSA-EYFP reporter mice

Since the first example of conditional gene targeting in mice in 1994, the use of Cre recombinase and loxP flanked sequences has become an invaluable technique to generate tissue and temporal specific gene knockouts. The number of mouse strains expressing floxed-gene sequences, and tissue-specific or temporal-specific Cre-recombinase that have been reported in the literature has grown exponentially. However, increased use of this technology has highlighted several problems that can impact the interpretation of any phenotype observed in these mouse models. In particular, accurate knowledge of the specificity of Cre expression in each strain is critical in order to make conclusions about the role of specific cell types in the phenotypes observed. Cre-mediated deletion specificity and efficiency have been described in many different ways in the literature, making direct comparisons between these Cre strains impossible. Here we report crossing thirteen different myeloid-Cre mouse strains to ROSA-EYFP reporter mice and assaying YFP expression in a variety of naïve unstimulated hematopoietic cells, in parallel. By focusing on myeloid subsets, we directly compare the relative efficiency and specificity of myeloid deletion in these strains under steady-state conditions.

The eosinophil surface receptor epidermal growth factor-like module containing mucin-like hormone receptor 1 (EMR1): a novel therapeutic target for eosinophilic disorders

BACKGROUND

Although several novel agents are currently in clinical trials for eosinophilic disorders, none has demonstrated efficacy in reducing blood and tissue eosinophilia in all subjects. Additional approaches are clearly needed.

OBJECTIVE

We sought to explore the potential of the human eosinophil surface receptor epidermal growth factor-like module containing mucin-like hormone receptor 1 (EMR1) as a therapeutic target for eosinophilic disorders.

METHODS

EMR1 expression was assessed in blood and bone marrow specimens from eosinophilic and healthy subjects, cell lines, CD34(+) cells differentiated in vitro, and tissue biopsy specimens by using flow cytometry, quantitative PCR, and immunostaining. Eosinophil targeting by a novel, humanized, afucosylated anti-EMR1 IgG1 was evaluated in vitro by using a natural killer cell-mediated killing assay and in vivo in cynomolgus monkeys.

RESULTS

Analysis of blood and bone marrow cells from healthy and eosinophilic donors and in vitro-differentiated CD34(+) cells confirmed restriction of human EMR1 surface and mRNA expression to mature eosinophils. Tissue eosinophils also expressed EMR1. Although EMR1 was highly expressed on eosinophils from all subjects, surface expression was negatively correlated with absolute eosinophil counts (r = -0.46, P < .001), and soluble plasma levels correlated positively with absolute eosinophil counts (r = 0.69, P < .001), suggesting modulation of EMR1 in vivo. Nevertheless, afucosylated anti-EMR1 mAb dramatically enhanced natural killer cell-mediated killing of eosinophils from healthy and eosinophilic donors and induced a rapid and sustained depletion of eosinophils in monkeys.

CONCLUSION

EMR1 expression is restricted to mature blood and tissue eosinophils. Targeting of eosinophils with afucosylated anti-EMR1 antibody shows promise as a treatment for eosinophilic disorders.

Experimental liver fibrosis research: update on animal models, legal issues and translational aspects

Liver fibrosis is defined as excessive extracellular matrix deposition and is based on complex interactions between matrix-producing hepatic stellate cells and an abundance of liver-resident and infiltrating cells. Investigation of these processes requires in vitro and in vivo experimental work in animals. However, the use of animals in translational research will be increasingly challenged, at least in countries of the European Union, because of the adoption of new animal welfare rules in 2013. These rules will create an urgent need for optimized standard operating procedures regarding animal experimentation and improved international communication in the liver fibrosis community. This review gives an update on current animal models, techniques and underlying pathomechanisms with the aim of fostering a critical discussion of the limitations and potential of up-to-date animal experimentation. We discuss potential complications in experimental liver fibrosis and provide examples of how the findings of studies in which these models are used can be translated to human disease and therapy. In this review, we want to motivate the international community to design more standardized animal models which might help to address the legally requested replacement, refinement and reduction of animals in fibrosis research.

Emulsified phosphatidylserine, simple and effective peptide carrier for induction of potent epitope-specific T cell responses

Background

To induce potent epitope-specific T cell immunity by a peptide-based vaccine, epitope peptides must be delivered efficiently to antigen-presenting cells (APCs) in vivo. Therefore, selecting an appropriate peptide carrier is crucial for the development of an effective peptide vaccine. In this study, we explored new peptide carriers which show enhancement in cytotoxic T lymphocyte (CTL) induction capability.

Methodology/Principal Findings

Data from an epitope-specific in vivo CTL assay revealed that phosphatidylserine (PS) has a potent adjuvant effect among candidate materials tested. Further analyses showed that PS-conjugated antigens were preferentially and efficiently captured by professional APCs, in particular, by CD11c⁺CD11b⁺MHCII⁺ conventional dendritic cells (cDCs) compared to multilamellar liposome-conjugates or unconjugated antigens. In addition, PS demonstrated the stimulatory capacity of peptide-specific helper T cells in vivo.

Conclusions/Significance

This work indicates that PS is the easily preparable efficient carrier with a simple structure that delivers antigen to professional APCs effectively and induce both helper and cytotoxic T cell responses in vivo. Therefore, PS is a promising novel adjuvant for T cell-inducing peptide vaccines.

Systemic and local infection routes govern different cellular dissemination pathways during gammaherpesvirus infection in vivo

Human gammaherpesviruses cause morbidity and mortality associated with infection and transformation of lymphoid and endothelial cells. Knowledge of cell types involved in virus dissemination from primary virus entry to virus latency is fundamental for the understanding of gammaherpesvirus pathogenesis. However, the inability to directly trace cell types with respect to virus dissemination pathways has prevented definitive conclusions regarding the relative contribution of individual cell types. Here, we describe that the route of infection affects gammaherpesvirus dissemination pathways. We constructed a recombinant murine gammaherpesvirus 68 (MHV-68) variant harboring a cassette which switches fluorescent markers in a Cre-dependent manner. Since the recombinant virus which was constructed on the wild-type background was attenuated, in this study we used an M1-deleted version, which infected mice with normal kinetics. Infection of Cre-transgenic mice with this convertible virus was used to estimate the quantitative contribution of defined cell types to virus productivity and dissemination during the acute phase of MHV-68 infection. In systemic infection, we found splenic vascular endothelial cells (EC) among the first and main cells to produce virus. After local infection, the contribution of EC to splenic virus production did not represent such early kinetics. However, at later time points, B cell-derived viruses dominated splenic productivity independently of systemic or local infection. Systemic versus local infection also governed the cell types involved in loading peritoneal exudate cells, leading to latency in F4/80- and CD11b-positive target cells. Systemic infection supported EC-driven dissemination, whereas local infection supported B cell-driven dissemination.

Losartan Enhances the Success of Myoblast Transplantation

Duchenne muscular dystrophy is a recessive X-linked genetic disease caused by dystrophin gene mutations. Cell therapy can be a potential approach aiming to introduce a functional dystrophin in the dystrophic patient myofibers. However, this strategy produced so far limited results. Transforming growth factor-β (TGF-β) is a negative regulator of skeletal muscle development and is responsible for limiting myogenic regeneration. The combination of TGF-β signaling inhibition with myoblast transplantation can be an effective therapeutic approach in dystrophin-deficient patients. Our aim was to verify whether the success of human myoblast transplantation in immunodeficient dystrophic mice is enhanced with losartan, a molecule that downregulates TGF-β expression. In vitro, blocking TGF-β activity with losartan increased proliferation and fusion and decreased apoptosis in human myoblasts. In vivo, human myoblasts were transplanted in mice treated with oral losartan. Immunodetection of human dystrophin in tibialis anterior cross sections 1 month posttransplantation revealed more human dystrophin-positive myofibers in these mice than in nontreated dystrophic mice. Thus, blocking the TGF-β signal with losartan treatment improved the success of myoblast transplantation probably by increasing myoblast proliferation and fusion, decreasing macrophage activation, and changing the expression of myogenic regulator factors.

A novel Ly6C/Ly6G-based strategy to analyze the mouse splenic myeloid compartment

Currently, there is no standardized panel for immunophenotyping myeloid cells in mouse spleen using flow cytometry. Markers such as CD11b, CD11c, F4/80, Gr-1, Ly6C, and Ly6G have long been used to identify various splenic cell myeloid populations. Flow cytometry and fluorescence-activated cell sorting (FACS) analysis demonstrated that Ly6G/Ly6C markers are superior to Gr-1 for identifying splenic neutrophils, eosinophils, and subsets of monocytes/macrophages. Moreover, these experiments showed that F4/80 is not required for identifying these myeloid subsets and that many of the commercially available preparations of anti-F4/80 antibodies stain poorly for this antigen in spleen. Taken together, we have now developed an informative flow cytometry panel that can be combined with other cell markers to further delineate subpopulations of mouse splenic myeloid cells. This panel will be highly useful to investigators in the flow cytometry field, as there is a critical need to standardize the analysis of myeloid cell subsets.

Genetic approaches to study glial cells in the rodent brain

The development, function, and pathology of the brain depend on interactions of neurons and different types of glial cells, namely astrocytes, oligodendrocytes, microglia, and ependymal cells. Understanding neuron-glia interactions in vivo requires dedicated experimental approaches to manipulate each cell type independently. In this review, we first summarize techniques that allow for cell-specific gene modification including targeted mutagenesis and viral transduction. In the second part, we describe the genetic models that allow to target the main glial cell types in the central nervous system. The existing arsenal of approaches to study glial cells in vivo and its expansion in the future are key to understand neuron-glia interactions under normal and pathologic conditions.

F4/80 and the related adhesion-GPCRs

The F4/80 monoclonal antibody was first reported in this journal 30 years ago (Eur. J. Immunol. 1981. 11: 805-815). F4/80 has become a widely used marker for monocytes and many, but not all, tissue macrophages in the mouse. F4/80 is a member of the EGF-TM7 family of leukocyte plasma membrane heptahelical molecules, which includes CD97 and EMR2. This Viewpoint summarises current knowledge of the expression, structure and functions of the EGF-TM7 family, as part of a larger family of tissue adhesion-GPCRs.

The structure of the Klf4 DNA-binding domain links to self-renewal and macrophage differentiation

Krueppel-like factor 4 (Klf4) belongs to the Sp/Klf family of zinc-finger transcription factors and is indispensable for terminal maturation of epithelial tissues. Furthermore, it is part of a small set of proteins that are used to generate pluripotent embryonic stem cells from differentiated tissues. Herein, we describe that a Klf4 zinc-finger domain mutant induces self-renewal and block of maturation, while wild-type Klf4 induces terminal macrophage differentiation. Moreover, we present the crystal structure of the zinc-finger domain of Klf4 bound to its target DNA, revealing that primarily the two C-terminal zinc-finger motifs are required for site specificity. Lack of those two zinc fingers leads to deficiency of Klf4 to induce macrophage differentiation. The first zinc finger, on the other hand, inhibits the otherwise cryptic self-renewal and block of differentiation activity of Klf4. Our data show that impairing the DNA binding could potentially contribute to a monocytic leukemia.

Comparison of immune response generated against Japanese encephalitis virus envelope protein expressed by DNA vaccines under macrophage associated versus ubiquitous expression promoters

Background

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis, with ~50,000 cases reported annually worldwide. Vaccination is the only measure for prevention. Recombinant vaccines are an efficient and safe alternative for formalin inactivated or live attenuated vaccines. Nowadays, incorporation of molecular adjuvants has been the main strategy for melioration of vaccines. Our attempt of immunomodulation is based on targeting antigen presenting cells (APC) "majorly macrophages" by using macrosialin promoter. We have compared the immune response of the constructed plasmids expressing JEV envelope (E) protein under the control of aforesaid promoter and cytomegalovirus (CMV) immediate early promoter in mouse model. Protection of immunized mice from lethal challenge with JEV was also studied.

Results

The E protein was successfully expressed in the macrophage cell line and was detected using immunofluorescence assay (IFA) and Western blotting. APC expressing promoter showed comparable expression to CMV promoter. Immunization of mice with either of the plasmids exhibited induction of variable JEV neutralizing antibody titres and provided protection from challenge with a lethal dose of JEV. Immune splenocytes showed proliferative response after stimulation with the JEV antigen (Ag), however, it was higher for CMV promoter. The magnitude of immunity provided by APC dominant promoter was non-significantly lower in comparison to CMV promoter. More importantly, immune response directed by APC promoter was skewed towards Th1 type in comparison to CMV promoter, this was evaluated by cytokine secretion profile of immune splenocytes stimulated with JEV Ag.

Conclusions

Thus, our APC-expressing DNA vaccination approach induces comparable immunity in comparison to ubiquitous promoter construct. The predominant Th1 type immune responses provide opportunities to further test its potency suitable for response in antiviral or anticancer vaccines.

F4/80: the macrophage-specific adhesion-GPCR and its role in immunoregulation

As a macrophage-restricted reagent, the generation and application of the F4/80 mAb has greatly benefited the phenotypic characterization of mouse tissue macrophages for three decades. Following the molecular identification of the F4/80 antigen as an EGF-TM7 member of the adhesion-GPCR family, great interest was ignited to understand its cell type-specific expression pattern as well as its functional role in macrophage biology. Recent studies have shown that the F4/80 gene is regulated by a novel set of transcription factors that recognized a unique promoter sequence. Gene targeting experiments have produced two F4/80 knock out animal models and showed that F4/80 is not required for normal macrophage development. Nevertheless, the F4/80 receptor was found to be necessary for the induction of efferent CD8+ regulatory T cells responsible for peripheral immune tolerance. The identification of cellular ligands for F4/80 and delineation of its signaling pathway remain elusive but are critical to understand the in vivo role of this macrophage-specific adhesion-GPCR.

Ferroportin1 deficiency in mouse macrophages impairs iron homeostasis and inflammatory responses

Systemic iron requirements are met predominantly through the recycling of iron from senescent erythrocytes by macrophages, a process in which the iron exporter ferroportin (Fpn1) is considered to be essential. Yet the role of Fpn1 in macrophage iron recycling and whether it influences innate immune responses are poorly understood in vivo. We inactivated Fpn1 in macrophages by crossing Fpn1-floxed animals with macrophage-targeted LysM-Cre or F4/80-Cre transgenic mice. Macrophage Fpn1 deletion mice were overtly normal; however, they displayed a mild anemia and iron accumulation in splenic, hepatic, and bone marrow macrophages when fed a standard diet. Iron loading was exacerbated after the administration of iron dextran or phenylhydrazine. When Fpn1(LysM/LysM) mice were challenged with an iron-deficient diet, they developed a more severe anemia and strikingly higher splenic iron levels than control mice, indicating significantly impaired iron mobilization from macrophages. Because immune responses can be altered by modulating iron status, we also examined the expression of proinflammatory cytokines. We found that expression levels of TNF-α and IL-6 were significantly enhanced in Fpn1(LysM/LysM) macrophages lacking Fpn1. These studies demonstrate that Fpn1 plays important roles in macrophage iron release in vivo and in modulating innate immune responses.

Myeloid cells migrate in response to IL-24

IL-24 (melanoma differentiation associated gene 7 product) is a member of the IL-10 cytokine family that has been reported to possess anti-tumor activity. IL-24 is produced by immune tissues and its expression can be induced in human peripheral blood mononuclear cells by pathogen-associated molecules. While immune cells are known to produce IL-24, the response of immune cells to IL-24 is unclear. Using recombinant human IL-24, we demonstrated that IL-24 induces human monocyte and neutrophil migration, in vitro. An in vivo chemotaxis model showed that IL-24 attracted CD11b positive myeloid cells. To further characterize the chemotactic IL-24 response and type(s) of receptor(s) utilized by IL-24, we treated monocytes with signaling pathway inhibitors. IL-24-induced migration was reduced by pertussis toxin treatment, thus implicating G-protein coupled receptors in this process. Additionally, MEK and JAK inhibitors markedly decreased monocyte migration toward IL-24. These results suggest that IL-24 activates several signaling cascades in immune cells eliciting migration of myeloid cells, which may contribute to the known anti-cancer effects of IL-24.

Comparative analysis of macrophage associated vectors for use in genetic vaccine

Background

Antigen presentation by non professional antigen presenting cells (APC) can lead to anergy. In genetic vaccines, targeting the macrophages and APC for efficient antigen presentation might lead to balanced immune response. One such approach is to incorporate APC specific promoter in the vector to be used.

Methods

Three promoters known to be active in macrophage were selected and cloned in mammalian expressing vector (pAcGFP1-N1) to reconstruct (pAcGFP-MS), (pAcGFP-EMR) and (pAcGFP-B5I) with macrosialin, EmrI and Beta-5 Integrin promoters respectively. As a positive control (pAcGFP-CMV) was used with CMV promoter and promoterless vector (pAcGFP-NIX) which served as a negative control. GFP gene was used as readout under the control of each of the promoter. The expression of GFP was analyzed on macrophage and non-macrophage cell lines using Flow cytometry and qRT-PCR with TaqMan probe chemistries.

Results

All the promoters in question were dominant to macrophage lineage cell lines as observed by fluorescence, Western blot and quantitative RT-PCR. The activity of macrosialin was significantly higher than other macrophage promoters. CMV promoter showed 1.83 times higher activity in macrophage cell lines. The expression of GFP driven by macrosialin promoter after 24 hours was 4.40 times higher in macrophage derived cell lines in comparison with non macrophage cell lines.

Conclusions

Based on this study, macrosialin promoter can be utilized for targeting macrophage dominant expression. In vivo study needs to be carried out for its utility as a vaccine candidate.

c-Maf plays a crucial role for the definitive erythropoiesis that accompanies erythroblastic island formation in the fetal liver

c-Maf is one of the large Maf (musculoaponeurotic fibrosarcoma) transcription factors that belong to the activated protein-1 super family of basic leucine zipper proteins. Despite its overexpression in hematologic malignancies, the physiologic roles c-Maf plays in normal hematopoiesis have been largely unexplored. On a C57BL/6J background, c-Maf(-/-) embryos succumbed from severe erythropenia between embryonic day (E) 15 and E18. Flow cytometric analysis of fetal liver cells showed that the mature erythroid compartments were significantly reduced in c-Maf(-/-) embryos compared with c-Maf(+/+) littermates. Interestingly, the CFU assay indicated there was no significant difference between c-Maf(+/+) and c-Maf(-/-) fetal liver cells in erythroid colony counts. This result indicated that impaired definitive erythropoiesis in c-Maf(-/-) embryos is because of a non-cell-autonomous effect, suggesting a defective erythropoietic microenvironment in the fetal liver. As expected, the number of erythroblasts surrounding the macrophages in erythroblastic islands was significantly reduced in c-Maf(-/-) embryos. Moreover, decreased expression of VCAM-1 was observed in c-Maf(-/-) fetal liver macrophages. In conclusion, these results strongly suggest that c-Maf is crucial for definitive erythropoiesis in fetal liver, playing an important role in macrophages that constitute erythroblastic islands.

Hemophagocytosis causes a consumptive anemia of inflammation

Cytopenias of uncertain etiology are commonly observed in patients during severe inflammation. Hemophagocytosis, the histological appearance of blood-eating macrophages, is seen in the disorder hemophagocytic lymphohistiocytosis and other inflammatory contexts. Although it is hypothesized that these phenomena are linked, the mechanisms facilitating acute inflammation-associated cytopenias are unknown. We report that interferon γ (IFN-γ) is a critical driver of the acute anemia observed during diverse microbial infections in mice. Furthermore, systemic exposure to physiologically relevant levels of IFN-γ is sufficient to cause acute cytopenias and hemophagocytosis. Demonstrating the significance of hemophagocytosis, we found that IFN-γ acts directly on macrophages in vivo to alter endocytosis and provoke blood cell uptake, leading to severe anemia. These findings define a unique pathological process of broad clinical and immunological significance, which we term the consumptive anemia of inflammation.

Control of intestinal Nod2-mediated peptidoglycan recognition by epithelium-associated lymphocytes

Innate immune recognition of the bacterial cell wall constituent peptidoglycan by the cytosolic nucleotide-binding oligomerization domain 2 (Nod2) receptor has a pivotal role in the maintenance of intestinal mucosal homeostasis. Whereas peptidoglycan cleavage by gut-derived lysozyme preserves the recognition motif, the N-acetylmuramoyl-L-alanine amidase activity of the peptidoglycan recognition protein 2 (PGLYRP-2) destroys the Nod2-detected muramyl dipeptide structure. PGLYRP-2 green fluorescent protein (GFP) reporter and wild-type mice were studied by flow cytometry and quantitative RT-PCR to identify Pglyrp-2 expression in cells of the intestinal mucosa and reveal a potential regulatory function on epithelial peptidoglycan recognition. CD3(+)/CD11c(+) T lymphocytes revealed significant Pglyrp-2 expression, whereas epithelial cells and intestinal myeloid cells were negative. The mucosal Pglyrp-2-expressing lymphocyte population demonstrated a mixed T-cell receptor (TCR) αβ or γδ phenotype with predominant CD8α and less so CD8β expression, as well as significant staining for the activation markers B220 and CD69, presenting a typical intraepithelial lymphocyte phenotype. Importantly, exposure of peptidoglycan to PGLYRP-2 significantly reduced Nod2/Rip2-mediated epithelial activation. Also, moderate but significant alterations of the intestinal microbiota composition were noted in Pglyrp-2-deficient animals. PGLYRP-2 might thus have a significant role in regulation of the enteric host-microbe homeostasis.

The histopathologic and molecular basis for the diagnosis of histiocytic sarcoma and histiocyte-associated lymphoma of mice

Histiocytic sarcoma (HS) and histiocyte-associated lymphoma (HAL) of mice are difficult to distinguish histologically. Studies of multiple cases initially diagnosed as HS or HAL allowed us to define HS as round, fusiform, or mixed cell types that were F4/80+, Mac-2+, and PAX5-; that lacked markers for other sarcomas; and that had immune receptor genes in germline configuration. Two other subsets had clonal populations of lymphocytes. The first, HAL, featured malignant lymphocytes admixed with large populations of normal-appearing histiocytes. The second appeared to be composites of lymphoma and HS. Several cases suggestive of B myeloid-lineage plasticity were also observed.

Partial redundancy of the pattern recognition receptors, scavenger receptors, and C-type lectins for the long-term control of Mycobacterium tuberculosis infection

Mycobacterium tuberculosis is recognized by multiple pattern recognition receptors involved in innate immune defense, but their direct role in tuberculosis pathogenesis remains unknown. Beyond TLRs, scavenger receptors (SRs) and C-type lectins may play a crucial role in the sensing and signaling of pathogen motifs, as well as contribute to M. tuberculosis immune evasion. In this study, we addressed the relative role and potential redundancy of these receptors in the host response and resistance to M. tuberculosis infection using mice deficient for representative SR, C-type lectin receptor, or seven transmembrane receptor families. We show that a single deficiency in the class A SR, macrophage receptor with collagenous structure, CD36, mannose receptor, specific ICAM-3 grabbing nonintegrin-related, or F4/80 did not impair the host resistance to acute or chronic M. tuberculosis infection in terms of survival, control of bacterial clearance, lung inflammation, granuloma formation, and cytokine and chemokine expression. Double deficiency for the SRs class A SR types I and II plus CD36 or for the C-type lectins mannose receptor plus specific ICAM-3 grabbing nonintegrin-related had a limited effect on macrophage uptake of mycobacteria and TNF response and on the long-term control of M. tuberculosis infection. By contrast, mice deficient in the TNF, IL-1, or IFN-gamma pathway were unable to control acute M. tuberculosis infection. In conclusion, we document a functional redundancy in the pattern recognition receptors, which might cooperate in a coordinated response to sustain the full immune control of M. tuberculosis infection, in sharp contrast with the nonredundant, essential role of the TNF, IL-1, or IFN-gamma pathway for host resistance to M. tuberculosis.