Differential induction of apoptosis by Fas-Fas ligand interactions in human monocytes and macrophages

The Spectrum of CAR Cellular Effectors: Modes of Action in Anti-Tumor Immunity

Chimeric antigen receptor-T cells have spearheaded the field of adoptive cell therapy and have shown remarkable results in treating hematological neoplasia. Because of the different biology of solid tumors compared to hematological tumors, response rates of CAR-T cells could not be transferred to solid entities yet. CAR engineering has added co-stimulatory domains, transgenic cytokines and switch receptors to improve performance and persistence in a hostile tumor microenvironment, but because of the inherent cell type limitations of CAR-T cells, including HLA incompatibility, toxicities (cytokine release syndrome, neurotoxicity) and high costs due to the logistically challenging preparation process for autologous cells, the use of alternative immune cells is gaining traction. NK cells and γδ T cells that do not need HLA compatibility or macrophages and dendritic cells with additional properties such as phagocytosis or antigen presentation are increasingly seen as cellular vehicles with potential for application. As these cells possess distinct properties, clinicians and researchers need a thorough understanding of their peculiarities and commonalities. This review will compare these different cell types and their specific modes of action seen upon CAR activation.

Fas Ligand enhances vessel maturation and inhibits vascular leakage associated with age-related macular degeneration

Neovascular age-related macular degeneration (AMD), results from choroidal neovascularization (CNV), retinal edema and loss of photoreceptors. Previous studies suggested that Fas Ligand (FasL) on retinal pigment epithelial cells inhibited CNV by inducing apoptosis of infiltrating Fas+ vascular endothelial cells. However, induction of apoptosis depends on membrane-bound (mFasL) while the FasL cleavage product (sFasL) is neuroprotective. To better understand how FasL regulates the development of CNV, we used a mouse model of laser CNV to evaluate the development of CNV in mice with a FasL cleavage site mutation (ΔCS) and can only express the membrane-bound form of FasL. There was no significant difference in CNV size and area of vascular leakage in homozygous FasLΔCS/ΔCS mice when compared to wild type mice. Unexpectedly, heterozygous FasLΔCS/WT mice developed significantly less vascular leakage and showed accelerated neovessel maturation. However, CNV was not prevented in heterozygous FasLΔCS/WT mice if the Fas receptor was deleted in myeloid cells (FasLΔCS/+ Fasflox/flox CreLysM). Thus, FasL-mediated CNV inhibition depends on the extent of FasL cleavage, and on FasL engagement of Fas+ myeloid cells. Moreover, accelerated neovessel maturation prevents vascular leakage in AMD.

Enhanced apoptotic index in hepatocytes, Kupffer cells, and inflammatory infiltrate showed positive correlation with hepatic lesion intensity, parasite load, and clinical status in naturally Leishmania-infected dogs

It is unknown if Leishmania amastigote infections affect hepatocytes and Kupffer cell apoptosis, and the role played by apoptosis in liver lesions in leishmaniasis is still unclear. Clinically affected and subclinically infected dogs with leishmaniosis and uninfected controls were assessed. Parasite load, biochemical markers for evaluation of liver damage, morphometry (area, perimeter, number of inflammatory focus, major and minor diameters), apoptosis in hepatic tissue (hepatocytes, Kupffer cells, and inflammatory infiltrates) and cellularity in inflammatory foci were quantified. The parasite load in clinically affected dogs proved to be higher than in the other groups. All morphometric parameters (area, perimeter, number of inflammatory focus, major and minor diameters) from clinically affected were higher than the values found in the subclinically infected and uninfected control dogs. Only clinically affected dogs presented high levels of ALT, FA, GGT and cholesterol in serum. Strong positive correlation was observed between biochemical markers for evaluation of liver damage (ALT, FA, GGT and cholesterol) and hepatic apoptosis (hepatocytes, Kupffer cells, and inflammation). Clinically affected dogs showed a more intense hepatic lesion. Hepatocytes showed a higher rate of apoptosis in Leishmania-infected dogs than in uninfected control dogs. The Kupffer cell apoptotic index and apoptosis within the inflammatory infiltrates were higher in clinically affected dogs. The apoptotic index evaluated in hepatocytes, Kupffer cells, and inflammatory infiltrates showed a positive correlation with the intensity of the hepatic lesion, parasite load, and clinical status. Apoptotic cells also showed positive immunostaining for TUNEL, Bcl2, and Bax. Our data showed that hepatic apoptosis was related to the severity of liver damage, the progression of infection, and the parasite load in leishmaniasis. Apoptotic regulated cell recruitment modulated the inflammatory response and favored the survival and dissemination of parasites, depending on the clinical status of the Leishmania-infected dogs.

Plinabulin, a Distinct Microtubule-Targeting Chemotherapy, Promotes M1-Like Macrophage Polarization and Anti-tumor Immunity

Reprogramming tumor infiltrating myeloid cells to elicit pro-inflammatory responses is an exciting therapeutic maneouver to improve anti-tumor responses. We recently demonstrated that a distinct microtubule-targeting drug, plinabulin—a clinical-stage novel agent—modulates dendritic cell maturation and enhances anti-tumor immunity. Here, we investigated the effects of plinabulin on macrophage polarization in vitro and in vivo. Plinabulin monotherapy induced significant tumor growth inhibition in mice bearing subcutaneous MC38 colon cancer. Importantly, the regressing tumors were characterized by an increase in M1-like/M2-like tumor-associated macrophages (TAM) ratio. The efficacy of plinabulin remained unaltered in T cell-deficient Rag2^−/− mice, suggesting an important role of macrophages in driving the drug's anti-tumor effect. Exposure of murine and healthy human macrophages to plinabulin induced polarization toward the M1 phenotype, including increased expression of co-stimulatory molecules CD80, CD86 and pro-inflammatory cytokines IL-1β, IL-6, and IL-12. M2-associated immunosuppressive cytokines IL-10 and IL-4 were reduced. This pro-inflammatory M1-like skewing of TAMs in response to plinabulin was dependent on the JNK pathway. Functionally, plinabulin-polarized human M1 macrophages directly killed HuT 78 tumor cells in vitro. Importantly, plinabulin induced a functional M1-like polarization of tumor infiltrating macrophages in murine tumors as well as in tumor samples from ovarian cancer patients, by preferentially triggering M1 proliferation. Our study uncovers a novel immunomodulatory effect of plinabulin in directly triggering M1 polarization and proliferation as well as promoting TAM anti-tumoral effector functions.

The FasLane to ocular pathology-metalloproteinase cleavage of membrane-bound FasL determines FasL function

Fas ligand (FasL) is best known for its ability to induce cell death in a wide range of Fas-expressing targets and to limit inflammation in immunoprivileged sites such as the eye. In addition, the ability of FasL to induce a much more extensive list of outcomes is being increasingly explored and accepted. These outcomes include the induction of proinflammatory cytokine production, T cell activation, and cell motility. However, the distinct and opposing functions of membrane-associated FasL (mFasL) and the C-terminal soluble FasL fragment (sFasL) released by metalloproteinase cleavage is less well documented and understood. Both mFasL and sFasL can form trimers that engage the trimeric Fas receptor, but only mFasL can form a multimeric complex in lipid rafts to trigger apoptosis and inflammation. By contrast, a number of reports have now documented the anti-apoptotic and anti-inflammatory activity of sFasL, pointing to a critical regulatory function of the soluble molecule. The immunomodulatory activity of FasL is particularly evident in ocular pathology where elimination of the metalloproteinase cleavage site and the ensuing increased expression of mFasL can severely exacerbate the extent of inflammation and cell death. By contrast, both homeostatic and increased expression of sFasL can limit inflammation and cell death. The mechanism(s) responsible for the protective activity of sFasL are discussed but remain controversial. Nevertheless, it will be important to consider therapeutic applications of sFasL for the treatment of ocular diseases such as glaucoma.

Polymyxin-Induced Cell Death of Human Macrophage-Like THP-1 and Neutrophil-Like HL-60 Cells Associated with the Activation of Apoptotic Pathways

Innate immunity is crucial for the host to defend against infections, and understanding the effect of polymyxins on innate immunity is important for optimizing their clinical use. In this study, we investigated the potential toxicity of polymyxins on human macrophage-like THP-1 and neutrophil-like HL-60 cells. Differentiated THP-1 human macrophages (THP-1-dMs) and HL-60 human neutrophils (HL-60-dNs) were employed. Flow cytometry was used to measure the concentration-dependent effects (100 to 2,500 μM for THP-1-dMs and 5 to 2,500 μM for HL-60-dNs) and time-dependent effects (1,000 μM for THP-1-dMs and 300 μM for HL-60-dNs) of polymyxin B over 24 h. Effects of polymyxin B on mitochondrial activity, activation of caspase-3, caspase-8, and caspase-9, and Fas ligand (FasL) expression in both cell lines were examined using fluorescence imaging, colorimetric, and fluorometric assays. In both cell lines, polymyxin B induced concentration- and time-dependent loss of viability at 24 h with 50% effective concentration (EC₅₀) values of 751.8 μM (95% confidence interval [CI], 692.1 to 816.6 μM; Hill slope, 3.09 to 5.64) for THP-1-dM cells and 175.4 μM (95% CI, 154.8 to 198.7 μM; Hill slope, 1.42 to 2.21) for HL-60-dN cells. A concentration-dependent loss of mitochondrial membrane potential and generation of mitochondrial superoxide was also observed. Polymyxin B-induced apoptosis was associated with concentration-dependent activation of all three tested caspases. The death receptor apoptotic pathway activation was demonstrated by a concentration-dependent increase of FasL expression. For the first time, our results reveal that polymyxin B induced concentration- and time-dependent cell death in human macrophage-like THP-1 and neutrophil-like HL-60 cells associated with mitochondrial and death receptor apoptotic pathways.

The Construction and Analysis of ceRNA Network and Patterns of Immune Infiltration in Colon Adenocarcinoma Metastasis

BACKGROUND

Colon adenocarcinoma (COAD) is a malignant and lethal tumor in digestive system and distance metastasis lead to poor prognosis. The metastasis-specific ceRNAs (competitive endogenous RNAs) and tumor-infiltrating immune cells might associate with tumor prognosis and distance metastasis. Nonetheless, few studies have concentrated on ceRNAs and Immune cells in COAD.

METHODS

The gene expression profile and clinical information of COAD were downloaded from TCGA and divided into two groups: primary tumors with or without distance metastasis. We applied comprehensive bioinformatics methods to analyze differential expression genes (DEGs) related to metastasis and establish the ceRNA networks. The Cox analysis and Lasso regression were utilized to screen the pivotal genes and prevent overfitting. Based on them, the prognosis prediction nomograms were established. The cell type identification by estimating relative subsets of RNA transcripts (CIBERSORT) algorithm was then applied to screen significant tumor immune-infiltrating cells associated with COAD metastasis and established another prognosis prediction model. Ultimately, co-expression analysis was applied to explore the relationship between key genes in ceRNA networks and significant immune cells. Multiple databases and preliminary clinical specimen validation were used to test the expressions of key biomarkers at the cellular and tissue levels.

RESULTS

We explored 1 significantly differentially expressed lncRNA, 1 significantly differentially expressed miRNA, 8 survival-related immune-infiltrating cells, 5 immune cells associated with distance metastasis. Besides, 3 pairs of important biomarkers associated with COAD metastasis were also identified: T cells follicular helper and hsa-miR-125b-5p (R = -0.200, P < 0.001), Macrophages M0 and hsa-miR-125b-5p (R = 0.170, P < 0.001) and Macrophages M0 and FAS (R = -0.370, P < 0.001). Multidimensional validation and preliminary clinical specimen validation also supported the results.

CONCLUSION

In this research, we found some significant ceRNAs (FAS and hsa-miR-125b-5p) and tumor-infiltrating immune cells (T cells follicular helper and Macrophages M0) might related to distance metastasis and prognosis of COAD. The nomograms could assist scientific and medical researchers in clinical management.

TRAIL and FasL Functions in Cancer and Autoimmune Diseases: Towards an Increasing Complexity

Tumor Necrosis Factor-Related Apoptosis Inducing Ligand (TRAIL/TNFSF10) and Fas Ligand (FasL/TNFSF6), two major cytokines of the TNF (Tumor Necrosis Factor) superfamily, exert their main functions from the immune system compartment. Mice model studies revealed that TRAIL and FasL-mediated signalling both control the homeostasis of the immune cells, mainly from the lymphoid lineage, and function on cytotoxic cells as effector proteins to eliminate the compromised cells. The first clues in the physiological functions of TRAIL arose from the analysis of TRAIL deficient mice, which, even though they are viable and fertile, are prone to cancer and autoimmune diseases development, revealing TRAIL as an important safeguard against autoimmunity and cancer. The naturally occurring gld (generalized lymphoproliferative disease) and lpr (lymphoproliferation) mutant mice develop lymphadenopathy and lupus-like autoimmune disease. The discovery that they are mutated in the fasl and the fas receptor gene, respectively, demonstrates the critical role of the FasL/Fas system in lymphocyte homeostasis and autoimmunity. This review summarizes the state of current knowledge regarding the key death and non-death immune functions that TRAIL and FasL play in the initiation and progression of cancer and autoimmune diseases.

Relationship between the Regulation of Caspase-8-Mediated Apoptosis and Radioresistance in Human THP-1-Derived Macrophages

Radiosensitivity varies depending on the cell type; highly differentiated cells typically exhibit greater radioresistance. We recently demonstrated that human macrophages derived from THP-1 monocytic cells, which lack TP53, are highly resistant to radiation-induced apoptosis compared with undifferentiated THP-1 cells. However, the mechanisms by which THP-1 cells acquire radioresistance during differentiation remain unknown. Herein, we investigated the mechanisms by which THP-1-derived macrophages develop p53-independent radioresistance by analyzing DNA damage responses and apoptotic pathways. Analysis of γ-H2AX foci, which indicates the formation of DNA double-strand breaks (DSB), suggested that a capacity to repair DSB of macrophages is comparable to that of radiosensitive THP-1 cells. Furthermore, treatment with inhibitors against DSB repair-related proteins failed to enhance radiation-induced apoptosis in THP-1-derrived macrophages. Analysis of the apoptotic pathways showed that radiosensitive THP-1 cells undergo apoptosis through the caspase-8/caspase-3 cascade after irradiation, whereas this was not observed in the macrophages. Caspase-8 protein expression was lower in macrophages than in THP-1 cells, whereas mRNA expressions were comparable between both cell types. Co-treatment with a proteasome inhibitor and ionizing radiation effectively induced apoptosis in macrophages in a caspase-8-dependent manner. Results suggest that the regulation of caspase-8-mediated apoptosis during differentiation plays a role in the p53-independent radioresistance of THP-1-derived macrophages.

Clearance of Apoptotic Cells by Tissue Epithelia: A Putative Role for Hepatocytes in Liver Efferocytosis

Toxic substances and microbial or food-derived antigens continuously challenge the liver, which is tasked with their safe neutralization. This vital organ is also important for the removal of apoptotic immune cells during inflammation and has been previously described as a “graveyard” for dying lymphocytes. The clearance of apoptotic and necrotic cells is known as efferocytosis and is a critical liver function to maintain tissue homeostasis. Much of the research into this form of immunological control has focused on Kupffer cells, the liver-resident macrophages. However, hepatocytes (and other liver resident cells) are competent efferocytes and comprise 80% of the liver mass. Little is known regarding the mechanisms of apoptotic and necrotic cell capture by epithelia, which lack key receptors that mediate phagocytosis in macrophages. Herein, we discuss recent developments that increased our understanding of efferocytosis in tissues, with a special focus on the liver parenchyma. We discuss the impact of efferocytosis in health and in inflammation, highlighting the role of phagocytic epithelia.

The nonreceptor protein tyrosine kinase Pyk2 promotes the turnover of monocytes at steady state

Monocytes are short-lived myeloid cells that perform functions essential for tissue homeostasis and disease resolution. However, the cellular mechanisms controlling the maintenance and turnover of monocyte populations are largely undefined. Proline-rich tyrosine kinase 2 (Pyk2) is a nonreceptor tyrosine kinase that regulates numerous immune cell functions, but its role in monocytes is currently unknown. In this study, we sought to characterize the expression and function of Pyk2 in lineage-committed monocyte populations. Here, we report that Pyk2 protein expression is increased in the Ly6C^- monocyte population. Using a Pyk2 knockout mouse model (Pyk2^-/-), we show that Pyk2 regulates the relative proportion of monocyte subsets normally represented in the bone marrow (BM) at steady state. In support of this conclusion, a similar phenotype was observed in the peripheral blood and spleen. Data from reciprocal BM chimera experiments indicate that the alterations in monocyte populations exhibited by Pyk2^-/- mice are due to factors intrinsic to the monocytes. Lineage-tracing of monocyte populations suggests that Pyk2 promotes apoptosis in BM monocytes, thereby acting as an important homeostatic regulator of turnover in these short-lived, innate immune cells.

AMP-activated protein kinase α1 promotes atherogenesis by increasing monocyte-to-macrophage differentiation

Monocyte-to-macrophage differentiation, which can be initiated by physiological or atherogenic factors, is a pivotal process in atherogenesis, a disorder in which monocytes adhere to endothelial cells and subsequently migrate into the subendothelial spaces, where they differentiate into macrophages and macrophage-derived foam cells and cause atherosclerotic lesions. However, the monocyte-differentiation signaling pathways that are activated by atherogenic factors are poorly defined. Here we report that the AMP-activated protein kinase α1 (AMPKα1) in monocytes promotes atherosclerosis by increasing monocyte differentiation and survival. Exposure of monocytes to oxidized low-density lipoprotein, 7-ketocholesterol, phorbol 12-myristate 13-acetate, or macrophage colony-stimulated factor (M-CSF) significantly activated AMPK and promoted monocyte-to-macrophage differentiation. M-CSF-activated AMPK is via M-CSF receptor-dependent reactive oxygen species production. Consistently, genetic deletion of AMPKα1 or pharmacological inhibition of AMPK blunted monocyte-to-macrophage differentiation and promoted monocyte/macrophage apoptosis. Compared with apolipoprotein E knock-out (ApoE^-/-) mice, which show impaired clearing of plasma lipoproteins and spontaneously develop atherosclerosis, ApoE^-/-/AMPKα1^-/- mice showed reduced sizes of atherosclerotic lesions and lesser numbers of macrophages in the lesions. Furthermore, aortic lesions were decreased in ApoE^-/- mice transplanted with ApoE^-/-/AMPKα1^-/- bone marrow and in myeloid-specific AMPKα1-deficient ApoE^-/- mice. Finally, rapamycin treatment, which abolished delayed monocyte differentiation in ApoE^-/-/AMPKα1^-/- mice, lost its atherosclerosis-lowering effects in these mice. Mechanistically, we found that AMPKα1 regulates FoxO3-dependent expression of both LC3 and ULK1, which are two important autophagy-related markers. Rapamycin treatment increased FoxO3 activity as well as LC3 and ULK1 expressions in macrophages from AMPKα1^-/- mice. Our results reveal that AMPKα1 deficiency impairs autophagy-mediated monocyte differentiation and decreases monocyte/macrophage survival, which attenuates atherosclerosis in ApoE^-/- mice in vivo.

Non-apoptotic functions of caspases in myeloid cell differentiation

Subtle caspase activation is associated with the differentiation of several myeloid lineages. A tightly orchestrated dance between caspase-3 activation and the chaperone HSP70 that migrates to the nucleus to protect the master regulator GATA-1 from cleavage transiently occurs in basophilic erythroblasts and may prepare nucleus and organelle expel that occurs at the terminal phase of erythroid differentiation. A spatially restricted activation of caspase-3 occurs in maturing megakaryocytes to promote proplatelet maturation and platelet shedding in the bloodstream. In a situation of acute platelet need, caspase-3 could be activated in response to IL-1α and promote megakaryocyte rupture. In peripheral blood monocytes, colony-stimulating factor-1 provokes the formation of a molecular platform in which caspase-8 is activated, which downregulates nuclear factor-kappa B (NF-κB) activity and activates downstream caspases whose target fragments such as those generated by nucleophosmin (NPM1) cleavage contribute to the generation of resting macrophages. Human monocytes secrete mature IL-1β in response to lipopolysaccharide through an alternative inflammasome activation that involves caspase-8, a pathway that does not lead to cell death. Finally, active caspase-3 is part of the proteases contained in secretory granules of mast cells. Many questions remain on how these proteases are activated in myeloid cell lineages, which target proteins are cleaved, whereas other are protected from proteolysis, the precise role of cleaved proteins in cell differentiation and functions, and the link between these non-apoptotic functions of caspases and the death of these diverse cell types. Better understanding of these functions may generate therapeutic strategies to control cytopenias or modulate myeloid cell functions in various pathological situations.

Participation of 3-O-sulfated heparan sulfates in the protection of macrophages by herpes simplex virus-1 glycoprotein D and cyclophilin B against apoptosis

Heparan sulfates (HS) are involved in numerous biological processes, which rely on their ability to interact with a large panel of proteins. Although the reaction of 3‐O‐sulfation can be catalysed by the largest family of HS sulfotransferases, very few mechanisms have been associated with this modification and to date, only glycoprotein D (gD) of herpes simplex virus‐1 (HSV‐1 gD) and cyclophilin B (CyPB) have been well‐described as ligands for 3‐O‐sulfated HS. Here, we hypothesized that both ligands could induce the same responses via a mechanism dependent on 3‐O‐sulfated HS. First, we checked that HSV‐1 gD was as efficient as CyPB to induce the activation of the same signalling events in primary macrophages. We then demonstrated that both ligands efficiently reduced staurosporin‐induced apoptosis and modulated the expression of apoptotic genes. In addition to 3‐O‐sulfated HS, HSV‐1 gD was reported to interact with other receptors, including herpes virus entry mediator (HVEM), nectin‐1 and ‐2. Thus, we decided to identify the contribution of each binding site in the responses triggered by HSV‐1 gD and CyPB. We found that knock‐down of 3‐O‐sulfotransferase 2, which is the main 3‐O‐sulfated HS‐generating enzyme in macrophages, strongly reduced the responses induced by both ligands. Moreover, silencing the expression of HVEM rendered macrophages unresponsive to either HSV‐1 gD and CyPB, thus indicating that both proteins induced the same responses by interacting with a complex formed by 3‐O‐sulfated HS and HVEM. Collectively, our results suggest that HSV‐1 might hijack the binding sites for CyPB in order to protect macrophages against apoptosis for efficient infection.

Soluble Fas/FasL ratio as a marker of vasculopathy in children and adolescents with sickle cell disease

OBJECTIVES

Sickle cell disease (SCD) is characterized by chronic inflammation due to ischemic tissue damage, accentuated during acute complications. Fas and its ligand (FasL) are members of tumor necrosis factor receptor superfamily and a major pathway for induction of apoptosis. Fas/FasL interactions may be related to augmentation of inflammatory response. We assessed the levels of sFas and sFasL in 35 children and adolescents with SCD compared with 35 healthy controls in relation to hemolysis, iron overload, sickle vasculopathy including kidney disease.

METHODS

SCD patients, in steady state and asymptomatic for pulmonary hypertension, were studied stressing on hydroxyurea therapy, serum ferritin, urinary albumin creatinine ratio (UACR), high-sensitivity C-reactive protein (hs-CRP) and sFas/sFasL levels.

RESULTS

sFas/sFasL ratio was significantly higher in patients compared with controls. sFas/sFasL ratio was elevated in patients with pulmonary hypertension, nephropathy and those who had history of frequent sickling crisis or serum ferritin ⩾2500. SCD patients treated with hydroxyurea had lower sFas/sFasL ratio than untreated patients. sFas/sFasL ratio was positively correlated to transfusion index, white blood cells, hs-CRP, serum ferritin and UACR. The cutoff value of sFas/sFasL at 8.75pg/mL could differentiate SCD patients with and without nephropathy while the cutoff value at 22pg/mL could differentiate SCD patients with and without pulmonary hypertension risk with high sensitivity and specificity.

CONCLUSION

sFas/sFasL ratio may be considered as a marker for vascular dysfunction in SCD patients and is related to inflammation, iron overload and albuminuria level. Thus, it may be a reliable method to assess renal impairment in SCD.

Role of hexokinase-1 in the survival of HIV-1-infected macrophages

Viruses have developed various strategies to protect infected cells from apoptosis. HIV-1 infected macrophages are long-lived and considered reservoirs for HIV-1. One significant deciding factor between cell survival and cell death is glucose metabolism. We hypothesized that HIV-1 protects infected macrophages from apoptosis in part by modulating the host glycolytic pathway specifically by regulating hexokinase-1 (HK-1) an enzyme that converts glucose to glucose-6-phosphate. Therefore, we analyzed the regulation of HK-1 in HIV-1 infected PBMCs, and in a chronically HIV-1 infected monocyte-like cell line, U1. Our results demonstrate that HIV-1 induces a robust increase in HK-1 expression. Surprisingly, hexokinase enzymatic activity was significantly inhibited in HIV-1 infected PBMCs and in PMA differentiated U1 cells. Interestingly, we observed increased levels of mitochondria-bound HK-1 in PMA induced U1 cells and in the HIV-1 accessory protein, viral protein R (Vpr) transduced U937 cell derived macrophages. Dissociation of HK-1 from mitochondria in U1 cells using a pharmacological agent, clotrimazole (CTZ) induced mitochondrial membrane depolarization and caspase-3/7 mediated apoptosis. Dissociation of HK-1 from mitochondria in Vpr transduced U937 also activated caspase-3/7 activity. These observations indicate that HK-1 plays a non-metabolic role in HIV-1 infected macrophages by binding to mitochondria thereby maintaining mitochondrial integrity. These results suggest that targeting the interaction of HK-1 with the mitochondria to induce apoptosis in persistently infected macrophages may prove beneficial in purging the macrophage HIV reservoir.

FAS Death Receptor: A Breast Cancer Subtype-Specific Radiation Response Biomarker and Potential Therapeutic Target

Although a standardized approach to radiotherapy has been used to treat breast cancer, regardless of subtype (e.g., luminal, basal), recent clinical data suggest that radiation response may vary significantly among subtypes. We hypothesized that this clinical variability may be due, in part, to differences in cellular radiation response. In this study, we utilized RNA samples for microarray analysis from two sources: 1. Paired pre- and postirradiation breast tumor tissue from 32 early-stage breast cancer patients treated in our unique preoperative radiation Phase I trial; and 2. Sixteen biologically diverse breast tumor cell lines exposed to 0 and 5 Gy irradiation. The transcriptome response to radiation exposure was derived by comparing gene expression in samples before and after irradiation. Genes with the highest coefficient of variation were selected for further evaluation and validated at the RNA and protein level. Gene editing and agonistic antibody treatment were performed to assess the impact of gene modulation on radiation response. Gene expression in our cohort of luminal breast cancer patients was distinctly different before and after irradiation. Further, two distinct patterns of gene expression were observed in our biologically diverse group of breast cancer cell lines pre- versus postirradiation. Cell lines that showed significant change after irradiation were largely luminal subtype, while gene expression in the basal and HER2+ cell lines was minimally impacted. The 100 genes with the most significant response to radiation in patients were identified and analyzed for differential patterns of expression in the radiation-responsive versus nonresponsive cell lines. Fourteen genes were identified as significant, including FAS, a member of the tumor necrosis factor receptor family known to play a critical role in programed cell death. Modulation of FAS in breast cancer cell lines altered radiation response phenotype and enhanced radiation sensitivity in radioresistant basal cell lines. Our findings suggest that cell-type-specific, radiation-induced FAS contributes to subtype-specific breast cancer radiation response and that activation of FAS pathways may be exploited for biologically tailored radiotherapy.

Silver nanoparticles impede phorbol myristate acetate-induced monocyte-macrophage differentiation and autophagy

Monocytes/macrophages are important constituents of the innate immune system. Monocyte-macrophage differentiation is not only crucial for innate immune responses, but is also related to some cardiovascular diseases. Silver nanoparticles (AgNPs) are one of the most widely used nanomaterials because of their broad-spectrum antimicrobial properties. However, the effect of AgNPs on the functions of blood monocytes is scarcely reported. Here, we report the impedance effect of AgNPs on THP-1 monocyte differentiation, and that this effect was mediated by autophagy blockade and lysosomal impairment. Firstly, AgNPs inhibit phorbol 12-myristate 13-acetate (PMA)-induced monocyte differentiation by down-regulating both expression of surface marker CD11b and response to lipopolysaccharide (LPS) stimulation. Secondly, autophagy is activated during PMA-induced THP-1 monocyte differentiation, and the autophagy inhibitor chloroquine (CQ) can inhibit this process. Thirdly, AgNPs block the degradation of the autophagy substrate p62 and induce autophagosome accumulation, which demonstrates the blockade of autophagic flux. Fourthly, lysosomal impairments including alkalization and decrease of lysosomal membrane stability were observed in AgNP-treated THP-1 cells. In conclusion, we demonstrate that the impedance of monocyte-macrophage differentiation by AgNPs is mediated by autophagy blockade and lysosomal dysfunction. Our results suggest that crosstalk exists in different biological effects induced by AgNPs.

Apolipoprotein E promotes subretinal mononuclear phagocyte survival and chronic inflammation in age-related macular degeneration

Physiologically, the retinal pigment epithelium (RPE) expresses immunosuppressive signals such as FAS ligand (FASL), which prevents the accumulation of leukocytes in the subretinal space. Age-related macular degeneration (AMD) is associated with a breakdown of the subretinal immunosuppressive environment and chronic accumulation of mononuclear phagocytes (MPs). We show that subretinal MPs in AMD patients accumulate on the RPE and express high levels of APOE. MPs of Cx3cr1(-/-) mice that develop MP accumulation on the RPE, photoreceptor degeneration, and increased choroidal neovascularization similarly express high levels of APOE. ApoE deletion in Cx3cr1(-/-) mice prevents pathogenic age- and stress-induced subretinal MP accumulation. We demonstrate that increased APOE levels induce IL-6 in MPs via the activation of the TLR2-CD14-dependent innate immunity receptor cluster. IL-6 in turn represses RPE FasL expression and prolongs subretinal MP survival. This mechanism may account, in part, for the MP accumulation observed in Cx3cr1(-/-) mice. Our results underline the inflammatory role of APOE in sterile inflammation in the immunosuppressive subretinal space. They provide rationale for the implication of IL-6 in AMD and open avenues toward therapies inhibiting pathogenic chronic inflammation in late AMD.

Involvement of IL‑10 and granulocyte colony‑stimulating factor in the fate of monocytes controlled by galectin‑1

The process of differentiation from monocytes to dendritic cells is critical in immune modulation. Monocyte apoptosis is a key regulator in balancing the immune response. Galectin‑1 has been reported to induce tolerogenic dendritic cells by the autocrine interleukin (IL)‑10 in monocytes. However, IL‑10 has been found to induce apoptosis in IL‑4/granulocyte macrophage colony‑stimulating factor (CSF) stimulating and non‑stimulating monocytes, whereas galectin‑1 has not. After analyzing the factors secreted by galectin-1-activated CD14 monocytes isolated from the peripheral blood, the present study revealed that galectin‑1 upregulates IL‑10 and granulocyte (G)-CSF expression. Furthermore, G‑CSF inhibited IL‑10‑induced apoptosis, implying that galectin‑1 may enhance the immune‑modulating functions of G‑CSF by inducing tolerogenic dendritic cells and maintaining their survival. Therefore, G‑CSF may be further applied in immune therapy, particularly in the IL‑10‑presenting microenvironment.

Fas ligand-expressing lymphocytes enhance alveolar macrophage apoptosis in the resolution of acute pulmonary inflammation

Apoptosis of alveolar macrophages and their subsequent clearance by neighboring phagocytes are necessary steps in the resolution of acute pulmonary inflammation. We have recently identified that activation of the Fas death receptor on the cell surface of macrophages drives macrophage apoptosis. However, the source of the cognate ligand for Fas (FasL) responsible for induction of alveolar macrophage apoptosis is not defined. Given their known role in the resolution of inflammation and ability to induce macrophage apoptosis ex vivo, we hypothesized that T lymphocytes represented a critical source of FasL. To address this hypothesis, C57BL/6J and lymphocyte-deficient (Rag-1(-/-)) mice were exposed to intratracheal lipopolysaccharide to induce pulmonary inflammation. Furthermore, utilizing mice expressing nonfunctional FasL, we adoptively transferred donor lymphocytes into inflamed lymphocyte-deficient mice to characterize the effect of lymphocyte-derived FasL on alveolar macrophage apoptosis in the resolution of inflammation. Herein, evidence is presented that lymphocytes expressing FasL enhance alveolar macrophage apoptosis during the resolution of LPS-induced inflammation. Moreover, lymphocyte induction of alveolar macrophage apoptosis results in contraction of the alveolar macrophage pool, which occurs in a FasL-dependent manner. Specifically, FasL-expressing CD8(+) T lymphocytes potently induce alveolar macrophage apoptosis and contraction of the alveolar macrophage pool. Together, these studies identify a novel role for CD8(+) T lymphocytes in the resolution of acute pulmonary inflammation.

Role of nanostructured gold surfaces on monocyte activation and Staphylococcus epidermidis biofilm formation

The role of material surface properties in the direct interaction with bacteria and the indirect route via host defense cells is not fully understood. Recently, it was suggested that nanostructured implant surfaces possess antimicrobial properties. In the current study, the adhesion and biofilm formation of Staphylococcus epidermidis and human monocyte adhesion and activation were studied separately and in coculture in different in vitro models using smooth gold and well-defined nanostructured gold surfaces. Two polystyrene surfaces were used as controls in the monocyte experiments. Fluorescent viability staining demonstrated a reduction in the viability of S. epidermidis close to the nanostructured gold surface, whereas the smooth gold correlated with more live biofilm. The results were supported by scanning electron microscopy observations, showing higher biofilm tower formations and more mature biofilms on smooth gold compared with nanostructured gold. Unstimulated monocytes on the different substrates demonstrated low activation, reduced gene expression of pro- and anti-inflammatory cytokines, and low cytokine secretion. In contrast, stimulation with opsonized zymosan or opsonized live S. epidermidis for 1 hour significantly increased the production of reactive oxygen species, the gene expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and IL-10, as well as the secretion of TNF-α, demonstrating the ability of the cells to elicit a response and actively phagocytose prey. In addition, cells cultured on the smooth gold and the nanostructured gold displayed a different adhesion pattern and a more rapid oxidative burst than those cultured on polystyrene upon stimulation. We conclude that S. epidermidis decreased its viability initially when adhering to nanostructured surfaces compared with smooth gold surfaces, especially in the bacterial cell layers closest to the surface. In contrast, material surface properties neither strongly promoted nor attenuated the activity of monocytes when exposed to zymosan particles or S. epidermidis.

In vitro infection of bovine monocytes with Mycoplasma bovis delays apoptosis and suppresses production of gamma interferon and tumor necrosis factor alpha but not interleukin-10

Mycoplasma bovis is one of the major causative pathogens of bovine respiratory complex disease (BRD), which is characterized by enzootic pneumonia, mastitis, pleuritis, and polyarthritis. M. bovis enters and colonizes bovine respiratory epithelial cells through inhalation of aerosol from contaminated air. The nature of the interaction between M. bovis and the bovine innate immune system is not well understood. We hypothesized that M. bovis invades blood monocytes and regulates cellular function to support its persistence and systemic dissemination. We used bovine-specific peptide kinome arrays to identify cellular signaling pathways that could be relevant to M. bovis-monocyte interactions in vitro. We validated these pathways using functional, protein, and gene expression assays. Here, we show that infection of bovine blood monocytes with M. bovis delays spontaneous or tumor necrosis factor alpha (TNF-α)/staurosporine-driven apoptosis, activates the NF-κB p65 subunit, and inhibits caspase-9 activity. We also report that M. bovis-infected bovine monocytes do not produce gamma interferon (IFN-γ) and TNF-α, although the level of production of interleukin-10 (IL-10) is elevated. Our findings suggest that M. bovis takes over the cellular machinery of bovine monocytes to prolong bacterial survival and to possibly facilitate subsequent systemic distribution.

Reduced expressions of Fas and Bcl-2 proteins in CD14+ monocytes and normal CD14 soluble levels in juvenile systemic lupus erythematosus

In order to evaluate Fas and Bcl-2 expressions in CD14+ monocytes, to measure soluble CD14 serum levels and to analyze the relationships with lupus nephritis and disease activity, we enrolled 41 patients with juvenile systemic lupus erythematosus (JSLE) and 27 healthy volunteers. Disease activity was determined by SLEDAI score. Peripheral monocytes were stained for CD14, Fas and Bcl-2 molecules, and cellular expressions were determined by flow cytometry. Soluble CD14 levels were measured by a quantitative ELISA kit. JSLE patients, those with active disease and those with nephritis, presented significantly reduced expressions of Fas and Bcl-2 proteins in CD14+ monocytes compared with healthy controls. Significant inverse correlations between percentages of CD14+Fas+ cells, SLEDAI score and anti-dsDNA antibodies were observed. JSLE patients had soluble CD14 levels similar to controls, although sCD14 levels positively correlated with ESR, but not with SLEDAI score. JSLE patients with nephritis also presented sCD14 levels similar to controls. In conclusion, the reduced expressions of Fas and Bcl-2 proteins in CD14+ monocytes from JSLE patients depict that monocyte apoptotic mechanisms may be important in lupus pathogenesis.

The effect of pre-storage whole-blood leukocyte reduction on cytokines/chemokines levels in autologous CPDA-1 whole blood

BACKGROUND

In this study, we aimed to investigate the effectiveness of pre-storage leukocyte filtration of autologous blood (AB), especially focusing on the cytokines/chemokines accumulation on blood products.

MATERIALS AND METHODS

After approval of the ethics committee of the University of Tokyo, a total of 26 orthopedic patients, who donated AB prior to surgery after informed consent, were enrolled. The effects of filtration on blood cell counts were analyzed, and the accumulation of cytokines and chemokines were measured on pre- and post-leukoreduced (LR) samples, using the Luminex system. The time-dependent changes of the cytokines/chemokines and the effect of the filtration on their concentration were analyzed, and compared with the normal plasma levels reported in the literature.

RESULTS

LR effectively reduced the number of leukocytes and platelets, without affecting that of red cells. The concentration of most of the cytokines/chemokines analyzed, except the EGF, sCD40-L and sFas-L, decreased time-dependently of storage or did not change in pre-LR samples. However, EGF, sCD40L and sFas-L were significantly reduced by LR. Some, such as IL-8 and RANTES, were also importantly decreased by LR, and others, such as IL-1β and TNF-α, were not significantly affected by LR.

CONCLUSIONS

Leukocyte filtration effectively removes platelets and leukocytes from AB, thus preventing the accumulation of cytokines/chemokines. Since adverse effects due to AB transfusion, although rare, are observed, there is need to consider the implementation of pre-storage leukocyte reduction (PSLR) for AB.

Intracellular Signaling Pathways in Rheumatoid Arthritis

Dysfunctional intracellular signaling involving deregulated activation of the Janus Kinase/Signal Transducers and Activators of Transcription (JAK/STAT) and "cross-talk" between JAK/STAT and the stress-activated protein kinase/mitogen-activated protein kinase (SAPK/MAPK) and Phosphatidylinositide-3-Kinase/AKT/mammalian Target of Rapamycin (PI-3K/AKT/mTOR) pathways play a critical role in rheumatoid arthritis. This is exemplified by immune-mediated chronic inflammation, up-regulated matrix metalloproteinase gene expression, induction of articular chondrocyte apoptosis and "apoptosis-resistance" in rheumatoid synovial tissue. An important consideration in the development of novel therapeutics for rheumatoid arthritis will be the extent to which inhibiting these signal transduction pathways will sufficiently suppress immune cell-mediated inflammation to produce a lasting clinical remission and halt the progression of rheumatoid arthritis pathology. In that regard, the majority of the evidence accumulated over the past decade indicated that merely suppressing pro-inflammatory cytokine-mediated JAK/ STAT, SAPK/MAPK or PI-3K/AKT/mTOR activation in RA patients may be necessary but not sufficient to result in clinical improvement. Thus, targeting aberrant enzyme activities of spleen tyrosine kinase, sphingosine kinases-1, -2, transforming growth factor β-activated kinase-1, bone marrow kinase, and nuclear factor-κB-inducing kinase for intervention may also have to be considered.

Monocytes regulate the mechanism of T-cell death by inducing Fas-mediated apoptosis during bacterial infection

Monocytes and T-cells are critical to the host response to acute bacterial infection but monocytes are primarily viewed as amplifying the inflammatory signal. The mechanisms of cell death regulating T-cell numbers at sites of infection are incompletely characterized. T-cell death in cultures of peripheral blood mononuclear cells (PBMC) showed 'classic' features of apoptosis following exposure to pneumococci. Conversely, purified CD3(+) T-cells cultured with pneumococci demonstrated necrosis with membrane permeabilization. The death of purified CD3(+) T-cells was not inhibited by necrostatin, but required the bacterial toxin pneumolysin. Apoptosis of CD3(+) T-cells in PBMC cultures required 'classical' CD14(+) monocytes, which enhanced T-cell activation. CD3(+) T-cell death was enhanced in HIV-seropositive individuals. Monocyte-mediated CD3(+) T-cell apoptotic death was Fas-dependent both in vitro and in vivo. In the early stages of the T-cell dependent host response to pneumococci reduced Fas ligand mediated T-cell apoptosis was associated with decreased bacterial clearance in the lung and increased bacteremia. In summary monocytes converted pathogen-associated necrosis into Fas-dependent apoptosis and regulated levels of activated T-cells at sites of acute bacterial infection. These changes were associated with enhanced bacterial clearance in the lung and reduced levels of invasive pneumococcal disease.

Critical role for antiapoptotic Bcl-xL and Mcl-1 in human macrophage survival and cellular IAP1/2 (cIAP1/2) in resistance to HIV-Vpr-induced apoptosis

Macrophages are resistant to HIV cytopathic effects, which contributes to viral persistence and reservoir formation. HIV viral protein R (Vpr) is a potent apoptosis-inducing agent for primary monocytes. Because the biologically active Vpr is found in serum and cerebrospinal fluid of HIV-infected patients, we investigated the apoptotic effect of Vpr on monocyte-derived macrophages and phorbol 12-myristate 13-acetate-activated THP1 macrophages. Our results show that primary monocytes and THP1 cells develop resistance to Vpr-induced apoptosis following differentiation into macrophages. To determine the effect of Vpr on the expression of antiapoptotic proteins, we show that in contrast to the undifferentiated cells, Vpr did not down-regulate the expression of antiapoptotic inhibitors of apoptosis (IAPs) and Bcl2 family members in macrophages, suggesting their involvement in resistance to Vpr-induced apoptosis. However, knocking down Bcl-xL and Mcl-1 proteins induced spontaneous apoptosis with no impact on susceptibility to Vpr-induced apoptosis. In contrast, down-regulation of cellular IAP1 (cIAP1) and cIAP2 by using siRNAs and SMAC (second mitochondria-derived activator of caspases) mimetic sensitized macrophages to Vpr-induced apoptosis. Overall, our results suggest that resistance to Vpr-induced apoptosis is specifically mediated by cIAP1/2 genes independent of Bcl-xL and Mcl-1, which play a key role in maintaining cell viability. Moreover, IAP modulation may be a potential strategy to eliminate HIV persistence in macrophages.

Induction of autophagy is essential for monocyte-macrophage differentiation

Monocytes are programmed to undergo apoptosis in the absence of stimulation. Stimuli that promote monocyte-macrophage differentiation not only cause cellular changes, but also prevent the default apoptosis of monocytes. In the present study, we demonstrate that autophagy is induced when monocytes are triggered to differentiate and that the induction of autophagy is pivotal for the survival and differentiation of monocytes. We also show that inhibition of autophagy results in apoptosis of cells that are engaged in differentiation. We found that the differentiation signal releases Beclin1 from Bcl-2 by activating JNK and blocks Atg5 cleavage, both of which are critical for the induction of autophagy. Preventing autophagy induction hampers differentiation and cytokine production; therefore, autophagy is an important transition from monocyte apoptosis to differentiation.

FAS/FAS-L dependent killing of activated human monocytes and macrophages by CD4+CD25- responder T cells, but not CD4+CD25+ regulatory T cells

Conclusive resolution of an immune response is critical for the prevention of autoimmunity and chronic inflammation. We report that following co-culture with autologous CD4+CD25- responder T cells, human CD14+ monocytes and monocyte-derived macrophages become activated but also significantly more prone to apoptosis than monocytes/macrophages cultured alone. In contrast, in the presence of CD4+CD25+ regulatory T cells (Tregs), monocytes and macrophages survive whilst adopting an anti-inflammatory phenotype. The induction of monocyte death requires responder T cell activation and cell-contact between responder T cells and monocytes. We demonstrate a critical role for FAS/FAS-L ligation in responder T cell-induced monocyte killing since responder T cells, but not Tregs, upregulate FAS-ligand (FAS-L) mRNA, and induce FAS expression on monocytes. Furthermore, responder T cell-induced monocyte apoptosis is blocked by neutralising FAS/FAS-L interaction, and is not observed when monocytes from an autoimmune lymphoproliferative syndrome (ALPS) patient with complete FAS-deficiency are used as target cells. Finally, we show that responder T cell-induced killing of monocytes is impaired in patients with active rheumatoid arthritis (RA). Our data suggest that resolution of inflammation in the course of a healthy immune response is aided by the unperturbed killing of monocytes with inflammatory potential by responder T cells and the induction of longer-lived, Treg-induced, anti-inflammatory monocytes.

Murine antithymocyte globulin T-cell depletion is mediated predominantly by macrophages, but the Fas/FasL pathway selectively targets regulatory T cells

BACKGROUND

Thymoglobulin is a T-cell-depleting polyclonal rabbit anti-human thymocyte antibody used clinically for immunosuppression in solid organ and hematopoietic stem-cell transplantation. By using a surrogate rabbit anti-mouse thymocyte globulin (mATG), we previously demonstrated that murine regulatory and memory T cells are preferentially spared from mATG depletion in vivo. The current studies were designed to determine whether different effector mechanisms are involved in differential depletion of T-cell subsets by mATG.

METHODS

Complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity (ADCC), and apoptotic mechanisms of depletion by mATG were evaluated in vitro and in vivo.

RESULTS

In vitro, there was evidence of differential susceptibility of T-cell subsets by different effector mechanisms where naïve and CD4 effector memory T cells show reduced susceptibility to apoptosis, whereas regulatory T cells are less susceptible to mATG-mediated complement-dependent cytotoxicity and ADCC. However, mATG treatment of mice depleted of ADCC effector cell types (neutrophils, natural killer cells, or macrophages) or deficient in complement C5 or Fas demonstrated that mATG depletion of all T-cell subsets is mediated primarily by macrophages and that the role of neutrophils, natural killer cells, and complement is minimal in vivo. Interestingly, the Fas/FasL pathway does play a role in regulatory T-cell depletion, which is likely a result of increased basal expression of Fas on these cells.

CONCLUSIONS

These data suggest that macrophages deplete most T cells by mATG in mice, but regulatory T cells are also uniquely susceptible to mATG-mediated Fas-dependent depletion.

Anti-apoptotic genes in the survival of monocytic cells during infection

Macrophages are cells of the immune system that protect organisms against invading pathogens by fulfilling critical roles in innate and adaptive immunity and inflammation. They originate from circulating monocytes and show a high degree of heterogeneity, which reflects the specialization of function given by different anatomical locations. Differentiation of monocytes towards a macrophage phenotype is also accompanied by an increase of resistance against various apoptotic stimuli, a required characteristic that allows macrophages to accomplish their function in a stressful environment.

Apoptosis, a form of programmed cell death, is a tightly regulated process, needed to maintain homeostasis by balancing proliferation with cellular demise. Caspases, a family of cysteine proteases that are highly conserved in multicellular organisms, function as central regulators of apoptosis. FLIP (FLICE-inhibitory protein), anti-apoptotic members of the Bcl2 family and inhibitors of apoptosis (IAP) are the main three groups of anti-apoptotic genes that counteract caspase activation through both the extrinsic and intrinsic apoptotic pathways.

Modulation of the apoptotic machinery during viral and bacterial infections, as well as in various malignancies, is a wellestablished mechanism that promotes the survival of affected cells. The involvement of anti-apoptotic genes in the survival of monocytes/macrophages, either physiological or pathological, will be described in this review. How viral and bacterial infections that target cells of the monocytic lineage affect the expression of anti-apoptotic genes is important in understanding the pathological mechanisms that lead to manifested disease. The latest therapeutic approaches that target anti-apoptotic genes will also be discussed.

HIV/SIV infection primes monocytes and dendritic cells for apoptosis

Subversion or exacerbation of antigen-presenting cells (APC) death modulates host/pathogen equilibrium. We demonstrated during in vitro differentiation of monocyte-derived macrophages and monocyte-derived dendritic cells (DCs) that HIV sensitizes the cells to undergo apoptosis in response to TRAIL and FasL, respectively. In addition, we found that HIV-1 increased the levels of pro-apoptotic Bax and Bak molecules and decreased the levels of anti-apoptotic Mcl-1 and FLIP proteins. To assess the relevance of these observations in the context of an experimental model of HIV infection, we investigated the death of APC during pathogenic SIV-infection in rhesus macaques (RMs). We demonstrated increased apoptosis, during the acute phase, of both peripheral blood DCs and monocytes (CD14⁺) from SIV⁺RMs, associated with a dysregulation in the balance of pro- and anti-apoptotic molecules. Caspase-inhibitor and death receptors antagonists prevented apoptosis of APCs from SIV⁺RMs. Furthermore, increased levels of FasL in the sera of pathogenic SIV⁺RMs were detected, compared to non-pathogenic SIV infection of African green monkey. We suggest that inappropriate apoptosis of antigen-presenting cells may contribute to dysregulation of cellular immunity early in the process of HIV/SIV infection.

Antigen-presenting cells (APCs) are critical for both innate and adaptive immunity. They have a profound impact on the hosts' ability to combat microbes. Dysfunction and premature death by apoptosis of APCs may contribute to an abnormal immune response unable to clear pathogens. Circulating blood monocytes exhibit developmental plasticity, with the capability of differentiating into either macrophages or dendritic cells (DCs), and they represent important cellular targets for HIV-1. We report that HIV infection renders monocytes/macrophages and DCs in vitro more prone to undergo apoptosis and this heightened susceptibility is associated with changes in the expression of anti- and pro-apoptotic molecules. Our results show that during the acute phase of SIV-infection of rhesus macaques, monocytes and DCs are more prone to die by apoptosis. They express lower levels of Mcl-1 and FLIP proteins, two anti-apoptotic molecules, but higher expression of the active form of Bax and Bak, the gatekeepers of the mitochondria, major sensor of the apoptotic machinery. Because the early events are important in the pathogenesis of this disease, early death of APCs should play a major role leading to the defective immune response. Strategies aimed at preventing death of APCs could be beneficial in helping the immune response to fight HIV-1.

Increased cell surface Fas expression is necessary and sufficient to sensitize lung fibroblasts to Fas ligation-induced apoptosis: implications for fibroblast accumulation in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is associated with the accumulation of collagen-secreting fibroblasts and myofibroblasts in the lung parenchyma. Many mechanisms contribute to their accumulation, including resistance to apoptosis. In previous work, we showed that exposure to the proinflammatory cytokines TNF-α and IFN-γ reverses the resistance of lung fibroblasts to apoptosis. In this study, we investigate the underlying mechanisms. Based on an interrogation of the transcriptomes of unstimulated and TNF-α- and IFN-γ-stimulated primary lung fibroblasts and the lung fibroblast cell line MRC5, we show that among Fas-signaling pathway molecules, Fas expression was increased ∼6-fold in an NF-κB- and p38(mapk)-dependent fashion. Prevention of the increase in Fas expression using Fas small interfering RNAs blocked the ability of TNF-α and IFN-γ to sensitize fibroblasts to Fas ligation-induced apoptosis, whereas enforced adenovirus-mediated Fas overexpression was sufficient to overcome basal resistance to Fas-induced apoptosis. Examination of lung tissues from IPF patients revealed low to absent staining of Fas in fibroblastic cells of fibroblast foci. Collectively, these findings suggest that increased expression of Fas is necessary and sufficient to overcome the resistance of lung fibroblasts to Fas-induced apoptosis. Our findings also suggest that approaches aimed at increasing Fas expression by lung fibroblasts and myofibroblasts may be therapeutically relevant in IPF.

The CD14(+/low)CD16(+) monocyte subset is more susceptible to spontaneous and oxidant-induced apoptosis than the CD14(+)CD16(-) subset

Human monocytes can be classified into two subsets with distinctive characteristics. In this study, we report a difference in apoptotic potential between these two subsets with CD14^+/lowCD16⁺ monocytes being more susceptible than CD14⁺CD16⁻ monocytes to undergo spontaneous apoptosis and apoptosis induced by reactive oxygen species (ROS). By global transcriptomic and proteomic approaches, we observed that CD14^+/lowCD16⁺ monocytes expressed higher levels of pro-apoptotic genes and proteins such as TNFα, caspase 3, Bax and cytochrome c and showed more caspases 3 and 7 activities. They also exhibited greater aerobic respiration resulting in a higher production of ROS from the mitochondria. CD14⁺CD16⁻ monocytes, in contrast, showed higher expression of glutathione (GSH)-metabolizing genes such as GSH peroxidase and microsomal GSH S-transferase and were more resistant to oxidative stress than CD14^+/lowCD16⁺ monocytes. The apoptosis of CD14^+/lowCD16⁺ monocytes was ROS dependent as reducing ROS levels significantly reduced cell death. This is the first report of a differential apoptotic propensity of human monocyte subsets, and gaining a better understanding of this process may help to provide a better understanding of the roles of these subsets during homeostasis and under pathological conditions, particularly in situations in which high levels of oxidants are present.

Apoptosis as a mechanism for liver disease progression

Hepatocyte injury is ubiquitous in clinical practice, and the mode of cell death associated with this injury is often apoptosis, especially by death receptors. Information from experimental systems demonstrates that hepatocyte apoptosis is sufficient to cause liver hepatic fibrogenesis. The mechanisms linking hepatocyte apoptosis to hepatic fibrosis remain incompletely understood, but likely relate to engulfment of apoptotic bodies by professional phagocytic cells and stellate cells, and release of mediators by cells undergoing apoptosis. Inhibition of apoptosis with caspase inhibitors has demonstrated beneficial effects in murine models of hepatic fibrosis. Recent studies implicating Toll-like receptor 9 in liver injury and fibrosis are also of particular interest. Engulfment of apoptotic bodies is one mechanism by which the TLR9 ligand (CpG DNA motifs) could be delivered to this intracellular receptor. These concepts suggest therapy focused on interrupting the cellular mechanisms linking apoptosis to fibrosis would be useful in human liver diseases.

Hepatocyte death: a clear and present danger

The hepatocyte is especially vulnerable to injury due to its central role in xenobiotic metabolism including drugs and alcohol, participation in lipid and fatty acid metabolism, its unique role in the enterohepatic circulation of bile acids, the widespread prevalence of hepatotropic viruses, and its existence within a milieu of innate immune responding cells. Apoptosis and necrosis are the most widely recognized forms of hepatocyte cell death. The hepatocyte displays many unique features regarding cell death by apoptosis. It is quite susceptible to death receptor-mediated injury, and its death receptor signaling pathways involve the mitochondrial pathway for efficient cell killing. Also, death receptors can trigger lysosomal disruption in hepatocytes which further promote cell and tissue injury. Interestingly, hepatocytes are protected from cell death by only two anti-apoptotic proteins, Bcl-x(L) and Mcl-1, which have nonredundant functions. Endoplasmic reticulum stress or the unfolded protein response contributes to hepatocyte cell death during alterations of lipid and fatty acid metabolism. Finally, the current information implicating RIP kinases in necrosis provides an approach to more fully address this mode of cell death in hepatocyte injury. All of these processes contributing to hepatocyte injury are discussed in the context of potential therapeutic strategies.

Th-17 cells in the lungs?

Naive CD4 cells are capable of integrating signals from antigen-activated cells of the innate immune system and differentiating into effector CD4 cells, also termed T helper (Th) cells. According to the traditional paradigm explaining adaptive CD4 cell responses, there are two subsets of Th cells: the Th-1 and Th-2 subset. Each of these subsets undergoes a distinct differentiation pathway (a pathway that is characterized by a unique profile of cytokine production and has specific immunoregulatory functions). However, recent studies in mouse models have forwarded evidence of a third subset of Th cells: the Th-17 subset. As indicated predominantly in studies on mice, the Th-17 subset is characterized by an ability to produce the neutrophil-mobilizing cytokine IL-17 in response to stimulation with the cytokine IL-23, an IL-12-related cytokine released from antigen-presenting cells. There is now a growing body of evidence from animal models that the Th-17 subset plays an important role in host defence in the lungs and other organs. Altered IL-17 levels have also been demonstrated in human patients with asthma, exacerbations of cystic fibrosis or following lung transplantation. There is now also evidence that the Th-17 subset is functionally distinct from the Th-2 subset but little is known of the functional inter-relationship between the Th-1 and Th-17 cell subsets; this is particularly true in human lungs. It has been proposed that the Th-17 subset plays a unique role by linking the arms of innate and adaptive immunity. Thus, an improved understanding of the human correlate to the Th-17 subset may reveal new targets for pharmacotherapy against lung disorders that are characterized by aberrant innate responses in host defense.

Monocytes are resistant to apoptosis in systemic juvenile idiopathic arthritis

We investigated whether circulating monocytes from patients with systemic juvenile idiopathic arthritis (SJIA) are resistant to apoptosis and which apoptotic pathway(s) may mediate this resistance. A microarray analysis of peripheral blood mononuclear cells (PBMC) of SJIA samples and RT-PCR analysis of isolated monocytes showed that monocytes from active SJIA patients express transcripts that imply resistance to apoptosis. SJIA monocytes incubated in low serum show reduced annexin binding and diminished FasL up-regulation compared to controls. SJIA monocytes are less susceptible to anti-Fas-induced apoptosis and, upon activation of the mitochondrial pathway with staurosporine, show diminished Bid cleavage and Bcl-w down-regulation compared to controls. Exposure to SJIA plasma reduces responses to apoptotic triggers in normal monocytes. Thus, SJIA monocytes are resistant to apoptosis due to alterations in both the extrinsic and intrinsic apoptosis pathways, and circulating factors associated with active SJIA may confer this phenotype.

Macrophage dysfunction impairs resolution of inflammation in the wounds of diabetic mice

BACKGROUND

Chronic inflammation is a characteristic feature of diabetic cutaneous wounds. We sought to delineate novel mechanisms involved in the impairment of resolution of inflammation in diabetic cutaneous wounds. At the wound-site, efficient dead cell clearance (efferocytosis) is a pre-requisite for the timely resolution of inflammation and successful healing.

METHODOLOGY/PRINCIPAL FINDINGS

Macrophages isolated from wounds of diabetic mice showed significant impairment in efferocytosis. Impaired efferocytosis was associated with significantly higher burden of apoptotic cells in wound tissue as well as higher expression of pro-inflammatory and lower expression of anti-inflammatory cytokines. Observations related to apoptotic cell load at the wound site in mice were validated in the wound tissue of diabetic and non-diabetic patients. Forced Fas ligand driven elevation of apoptotic cell burden at the wound site augmented pro-inflammatory and attenuated anti-inflammatory cytokine response. Furthermore, successful efferocytosis switched wound macrophages from pro-inflammatory to an anti-inflammatory mode.

CONCLUSIONS/SIGNIFICANCE

Taken together, this study presents first evidence demonstrating that diabetic wounds suffer from dysfunctional macrophage efferocytosis resulting in increased apoptotic cell burden at the wound site. This burden, in turn, prolongs the inflammatory phase and complicates wound healing.

Apoptosis of resident and inflammatory macrophages before and during the inflammatory response of the virgin bovine mammary gland

Background

Macrophages may play a prominent role in defense of the bovine mammary gland, and their functionality is necessary for successful eradication of bacterial pathogens. In contrast to necrosis, however, apoptosis has not yet been studied in macrophages from bovine mammary glands. Therefore, the aim of this study was to confirm the occurrence of apoptosis in macrophages from resting heifer mammary glands and during the inflammatory response.

Methods

Inflammatory response was induced by phosphate buffered saline (PBS) and by lipopolysaccharide (LPS). Resident macrophages (_RESMAC) were obtained before and inflammatory macrophages (_INFMAC) 24, 48, 72 and 168 hours after inducing inflammatory response in mammary glands of unbred heifers. Cell samples were analyzed for differential counts, apoptosis and necrosis using flow cytometry.

Results

Populations of _RESMAC and _INFMAC contained monocyte-like cells and vacuolized cells. Apoptosis was detected differentially in both morphologically different types of _RESMAC and _INFMAC and also during initiation and resolution of the inflammatory response. In the _RESMAC population, approximately one-tenth of monocyte-like cells and one-third of vacuolized cells were apoptotic. In the _INFMAC population obtained 24 h after PBS treatment, approximately one-tenth of monocyte-like cells and almost one-quarter of vacuolized cells were apoptotic. At the same time following LPS, however, we observed a significantly lower percentage of apoptotic cells in the population of monocyte-like _INFMAC and vacuolized _INFMAC. Moreover, a higher percentage of apoptotic cells in _INFMAC was detected during all time points after PBS in contrast to LPS. Comparing _RESMAC and _INFMAC, we observed that vacuolized cells from populations of _RESMAC and _INFMAC underwent apoptosis more intensively than did monocyte-like cells.

Conclusions

We conclude that apoptosis of virgin mammary gland macrophages is involved in regulating their lifespan, and it is involved in the resolution process of the inflammatory response.

Paraoxonase 1 interactions with HDL, antioxidants and macrophages regulate atherogenesis - a protective role for HDL phospholipids

Macrophage cholesterol accumulation and foam cell formation is the hallmark of early atherogenesis. In addition to macrophages, at least three more major players regulate atherosclerosis development; paraoxonase 1 (PON1), antioxidants, and HDL. PON1 is an HDL-associated lactonase which posses antioxidant and anti-atherogenic properties. PON1 protects against macrophage-mediated LDL oxidation, and increases HDL binding to macrophages which, in turn, stimulates HDL's ability to promote cholesterol efflux. These two major anti-atherogenic properties of HDL (and of PON1) require, at least in part, macrophage binding sites for HDL-associated PON1. Indeed, PON1, as well as HDL-associated PON1, specifically binds to macrophages, leading to anti-atherogenic effects. Macrophage PON1 binding sites may thus be a target for future cardioprotection therapy. Studying the interactions among PON1, antioxidants, and macrophages can thus assist in achieving appropriate treatment and prevention of atherosclerosis.

CCL2 and interleukin-6 promote survival of human CD11b+ peripheral blood mononuclear cells and induce M2-type macrophage polarization

CCL2 and interleukin (IL)-6 are among the most prevalent cytokines in the tumor microenvironment, with expression generally correlating with tumor progression and metastasis. CCL2 and IL-6 induced expression of each other in CD11b(+) cells isolated from human peripheral blood. It was demonstrated that both cytokines induce up-regulation of the antiapoptotic proteins cFLIP(L) (cellular caspase-8 (FLICE)-like inhibitory protein), Bcl-2, and Bcl-X(L) and inhibit the cleavage of caspase-8 and subsequent activation of the caspase-cascade, thus protecting cells from apoptosis under serum deprivation stress. Furthermore, both cytokines induced hyperactivation of autophagy in these cells. Upon CCL2 or IL-6 stimulation, CD11b(+) cells demonstrated a significant increase in the mannose receptor (CD206) and the CD14(+)/CD206(+) double-positive cells, suggesting a polarization of macrophages toward the CD206(+) M2-type phenotype. Caspase-8 inhibitors mimicked the cytokine-induced up-regulation of autophagy and M2 polarization. Furthermore, E64D and leupeptin, which are able to function as inhibitors of autophagic degradation, reversed the effect of caspase-8 inhibitors in the M2-macrophage polarization, indicating a role of autophagy in this mechanism. Additionally, in patients with advanced castrate-resistant prostate cancer, metastatic lesions exhibited an increased CD14(+)/CD206(+) double-positive cell population compared with normal tissues. Altogether, these findings suggest a role for CCL2 and IL-6 in the survival of myeloid monocytes recruited to the tumor microenvironment and their differentiation toward tumor-promoting M2-type macrophages via inhibition of caspase-8 cleavage and enhanced autophagy.

Induction of copper/zinc-superoxide dismutase by CCL5/CCR5 activation causes tumour necrosis factor-alpha and reactive oxygen species production in macrophages

Using two-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis, we found that copper/zinc superoxide dismutase (Cu/Zn-SOD, SOD-1) was induced in constructed CCR5 stably transfected HEK 293 cells, but not in mock cells, treated with CCL5. CCL5-induced SOD-1 expression was also confirmed in HEK 293-CCR5 cells and CCR5-positive granulocyte-macrophage colony-stimulating factor-induced human macrophages and murine macrophage RAW264.7 cells. CCL5 and CCR5 interaction induced SOD-1 expression mainly via MEK-ERK activation. In addition, we provided evidence that upregulation of SOD-1 by CCL5/CCR5 activation occurred in parallel with the increased release of tumour necrosis factor-alpha and nitric oxide and production of intracellular reactive oxygen species as well as enhanced nuclear factor-kappaB transcriptional activity in CCR5-positive RAW264.7 cells. Conversely, the MEK1/2 inhibitor PD98059 significantly inhibited SOD-1 expression with the decrease of these biological responses. More importantly, inhibition of SOD-1 activity by disulfiram also strongly inhibited the CCL5-induced biological effects. These data suggest that SOD-1 mediates CCR5 activation by CCL5 and that pharmacological modulation of SOD-1 may be beneficial to CCR5-associated diseases.

Radiation-induced apoptosis in peritoneal resident macrophages of C3H mice: Selective involvement of superoxide anion, but not other reactive oxygen species

Remarkably, apoptosis was induced by gamma-ray-irradiation in peritoneal resident macrophages (PRM) of C3H mice, but not other strains of mice. The mechanism of this strain-specific apoptosis induction was studied. Apoptosis in PRM was detected microscopically. Various radical scavengers were examined to identify the critical radicals involved in apoptosis induction. Intracellular peroxide levels were measured with a redox-sensitive dye, 2',7'-dichlorofluorescin diacetate (DCFH). Superoxide dismutase or catalase was introduced into the cells using commercially available Hemagglutinating Virus of Japan (HVJ) envelope vector kit. The enzyme activity of superoxide dismutase was also measured. Radiation-induced apoptosis in C3H mouse PRM was significantly suppressed by treatment with a pharmacological scavenger of superoxide anion, Tiron, but not with other radical scavengers. Intracellular peroxide levels were not elevated by irradiation at doses high enough to induce apoptosis maximally. Radiation-induced apoptosis in C3H mouse PRM was markedly suppressed by superoxide dismutase introduced into the cells using the HVJ envelope vector, but not catalase. The enzyme activity of superoxide dismutase in C3H mouse PRM was comparable with that in B6 mouse PRM. It was concluded that superoxide played the major role in radiation-induced apoptosis in the C3H mouse PRM and that cellular responses downstream or unrelated to superoxide might be responsible for the strain difference in radiation-induced apoptosis of mouse PRM.

The role of T regulatory cells in human sepsis

It is well-known that septic shock undermines immune homeostasis by inducing an initial intense systemic inflammatory response that is rapidly followed by a negative feedback of anti-inflammatory process. This secondary immunoparalysis state is characterized by decreased phagocytic cells, T cells, natural killer cells and B cells function and proinflammatory cytokine release. This persistence of immunoparalysis increased the risk for fatal outcome. In recent studies it was found that following the onset of septic shock, a relative increase in T regulatory cells number and suppressive function appears and makes them an important participant in the inhibition of immune responsiveness during sepsis. Consequently, a question emerging from these findings concerns the degree to which the manipulation of T regulatory cells might improve the outcome of patients with sepsis. Preliminary studies in animal models suggest that more work is needed to understand the conditions under which such a therapy may be effective.

Expression and function of semaphorin 3A and its receptors in human monocyte-derived macrophages

Semaphorins are a large family of secreted and membrane-bound proteins. Recently, several roles of semaphorins in the immune system have emerged. Several semaphorins and their receptors are expressed in a variety of lymphoid and myeloid cells and affect immune cell functions, including cell proliferation, differentiation, chemotaxis, and cytokine production. However, the roles of class 3 semaphorins in human myeloid cells are not well known. Here we examined the regulation of expression of class 3 semaphorins and their receptors by inflammatory stimuli and their function in human macrophages. We show that the expression of Sema3A receptors (neuropilin-1 (NRP-1), NRP-2, plexin A1, plexin A2, and plexin A3) significantly increased during M-CSF-mediated differentiation of monocytes into macrophages under conditions that promote an M2 alternatively activated macrophage phenotype. Consistent with increased NRP-1 expression, cell surface binding of Sema3A increased during M2 differentiation. Interferon (IFN)-gamma and lipopolysaccharide, which promote classical M1 macrophage activation affected expression of NRP-1, NRP-2 and plexin A1. IFN-gamma decreased NRP-1 expression and LPS suppressed NRP-2 and plexin A1 expression. Furthermore we show that Sema3A induced apoptosis in monocyte-derived macrophages and cooperated with anti-Fas CH11 antibody to augment apoptosis. Our results suggest that Sema3A plays a role in induction of apoptosis in monocyte-derived macrophages that are resistant to Fas-induced apoptosis, and that its function can be modulated in inflammatory conditions.