CD16. Developmentally regulated IgG Fc receptors on cultured human monocytes

Signaling-biophysical modeling unravels mechanistic control of red blood cell phagocytosis by macrophages in sickle cell disease

Red blood cell (RBC) aging manifests through progressive changes in cell morphology, rigidity, and expression of membrane proteins. To maintain the quality of circulating blood, splenic macrophages detect the biochemical signals and biophysical changes of RBCs and selectively clear them through erythrophagocytosis. In sickle cell disease (SCD), RBCs display alterations affecting their interaction with macrophages, leading to aberrant phagocytosis that may cause life-threatening spleen sequestration crises. To illuminate the mechanistic control of RBC engulfment by macrophages in SCD, we integrate a system biology model of RBC-macrophage signaling interactions with a biophysical model of macrophage engulfment, as well as in vitro phagocytosis experiments using the spleen-on-a-chip technology. Our modeling framework accurately predicts the phagocytosis dynamics of RBCs under different disease conditions, reveals patterns distinguishing normal and sickle RBCs, and identifies molecular targets including Src homology 2 domain-containing protein tyrosine phosphatase-1 (SHP1) and cluster of differentiation 47 (CD47)/signal regulatory protein α (SIRPα) as therapeutic targets to facilitate the controlled clearance of sickle RBCs in the spleen.

Antimyeloperoxidase antibodies modulate inflammatory responses and activate profibrotic pathways in human monocytes

Antimyeloperoxidase (anti-MPO) and antiproteinase 3 (anti-PR3) antibodies are found in anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV). We investigated the effect of both anti-MPO and anti-PR3 IgG on human monocytes. Peripheral blood monocytes were cultured under a range of conditions that included TLR agonists, anti-MPO IgG and anti-PR3 IgG with appropriate controls. Experiments included whole transcriptome profiling and an assessment of the role of Fc receptors. When monocytes were stimulated with LPS or R848, anti-MPO but not anti-PR3 IgG, caused a reduction in IL-10 secretion and had a profound effect on cell-surface marker expression. Anti-MPO but not anti-PR3 IgG enhanced monocyte survival in the absence of TLR stimulation. These effects depended on the Fc receptor CD32a. With TLR stimulation, the effect of anti-MPO but not anti-PR3 IgG on the transcriptional response at 6 h was variable, but we identified a core set of transcripts likely to be important. Without TLR stimulation, there was a robust effect of anti-MPO but not anti-PR3 IgG on the transcriptional response at 24 h, and there was a highly significant enrichment of genes encoding extracellular matrix and extracellular matrix-associated proteins. Analysis with nCounter confirmed many of the differentially expressed transcripts and supported a role for CD32a. These data show that anti-MPO, but not anti-PR3 IgG, from patients with AAV has wide-ranging effects on monocytes which depend on CD32a. The activation of a profibrotic transcriptional response by anti-MPO but not anti-PR3 IgG may give insights into the differences in disease phenotype.

The Innate Immune System and Cardiovascular Disease in ESKD: Monocytes and Natural Killer Cells

Adverse innate immune responses have been implicated in several disease processes, including cardiovascular disease (CVD) and chronic kidney disease (CKD). The monocyte subsets natural killer (NK) cells and natural killer T (NKT) cells are involved in innate immunity. Monocytes subsets are key in atherogenesis and the inflammatory cascade occurring in heart failure. Upregulated activity and counts of proinflammatory CD16+ monocyte subsets are associated with clinical indices of atherosclerosis, heart failure syndromes and CKD. Advanced CKD is a complex state of persistent systemic inflammation characterized by elevated expression of proinflammatory and pro-atherogenic CD14++CD16+ monocytes, which are associated with cardiovascular events and death both in the general population and among patients with CKD. Diminished NK cells and NKT cells counts and aberrant activity are observed in both coronary artery disease and end-stage kidney disease. However, evidence of the roles of NK cells and NKT cells in atherogenesis in advanced CKD is circumstantial and remains to be clarified. This review describes the available evidence regarding the roles of specific immune cell subsets in the pathogenesis of CVD in patients with CKD. Future research is expected to further uncover the links between CKD associated innate immune system dysregulation and accelerated CVD and will ideally be translated into therapeutic targets.

N-Glycosylation of IgG and IgG-Like Recombinant Therapeutic Proteins: Why Is It Important and How Can We Control It?

Regulatory bodies worldwide consider N-glycosylation to be a critical quality attribute for immunoglobulin G (IgG) and IgG-like therapeutics. This consideration is due to the importance of posttranslational modifications in determining the efficacy, safety, and pharmacokinetic properties of biologics. Given its critical role in protein therapeutic production, we review N-glycosylation beginning with an overview of the myriad interactions of N-glycans with other biological factors. We examine the mechanism and drivers for N-glycosylation during biotherapeutic production and the several competing factors that impact glycan formation, including the abundance of precursor nucleotide sugars, transporters, glycosidases, glycosyltransferases, and process conditions. We explore the role of these factors with a focus on the analytical approaches used to characterize glycosylation and associated processes, followed by the current state of advanced glycosylation modeling techniques. This combination of disciplines allows for a deeper understanding of N-glycosylation and will lead to more rational glycan control.

Inflammation in Hypertension

For more than 50 years, evidence has accumulated that inflammation contributes to the pathogenesis of hypertension. Immune cells have been observed in vessels and kidneys of hypertensive humans. Biomarkers of inflammation, including high sensitivity C-reactive protein, various cytokines, and products of the complement pathway are elevated in humans with hypertension. Emerging evidence suggests that hypertension is accompanied and indeed initiated by activation of complement, the inflammasome, and by a change in the phenotype of circulating immune cells, particularly myeloid cells. High-dimensional transcriptomic analyses are providing insight into new subclasses of immune cells that are likely injurious in hypertension. These inflammatory events are interdependent and there is ultimately engagement of the adaptive immune system through mechanisms involving oxidative stress, modification of endogenous proteins, and alterations in antigen processing and presentation. These observations suggest new therapeutic opportunities to reduce end organ damage in hypertension might be used and guided by levels of inflammatory biomarkers.

Multiple Variables at the Leukocyte Cell Surface Impact Fc γ Receptor-Dependent Mechanisms

Fc γ receptors (FcγR) expressed on the surface of human leukocytes bind clusters of immunoglobulin G (IgG) to induce a variety of responses. Many therapeutic antibodies and vaccine-elicited antibodies prevent or treat infectious diseases, cancers and autoimmune disorders by binding FcγRs, thus there is a need to fully define the variables that impact antibody-induced mechanisms to properly evaluate candidate therapies and design new intervention strategies. A multitude of factors influence the IgG-FcγR interaction; one well-described factor is the differential affinity of the six distinct FcγRs for the four human IgG subclasses. However, there are several other recently described factors that may prove more relevant for disease treatment. This review covers recent reports of several aspects found at the leukocyte membrane or outside the cell that contribute to the cell-based response to antibody-coated targets. One major focus is recent reports covering post-translational modification of the FcγRs, including asparagine-linked glycosylation. This review also covers the organization of FcγRs at the cell surface, and properties of the immune complex. Recent technical advances provide high-resolution measurements of these often-overlooked variables in leukocyte function and immune system activation.

A single amino acid distorts the Fc γ receptor IIIb/CD16b structure upon binding immunoglobulin G1 and reduces affinity relative to CD16a

Therapeutic mAbs engage Fc γ receptor III (CD16) to elicit a protective cell-mediated response and destroy the target tissue. Newer drugs designed to bind CD16a with increased affinity surprisingly also elicit protective CD16b-mediated responses. However, it is unclear why IgG binds CD16a with more than 10-fold higher affinity than CD16b even though these receptors share more than 97% identity. Here we identified one residue, Gly-129, that contributes to the greater IgG binding affinity of CD16a. The CD16b variant D129G bound IgG1 Fc with 2-fold higher affinity than CD16a and with 90-fold higher affinity than the WT. Conversely, the binding affinity of CD16a-G129D was decreased 128-fold relative to WT CD16a and comparably to that of WT CD16b. The interaction of IgG1 Fc with CD16a, but not with CD16b, is known to be sensitive to the composition of the asparagine-linked carbohydrates (N-glycans) attached to the receptor. CD16a and CD16b-D129G displaying minimally processed oligomannose N-glycans bound to IgG1 Fc with about 5.2-fold increased affinity compared with variants with highly processed complex-type N-glycans. CD16b and the CD16a-G129D variant exhibited a smaller 1.9-fold affinity increase with oligomannose N-glycans. A model of glycosylated CD16b bound to IgG1 Fc determined to 2.2 Å resolution combined with a 250-ns all-atom molecular dynamics simulation showed that the larger Asp-129 residue deformed the Fc-binding surface. These results reveal how Asp-129 in CD16b affects its binding affinity for IgG1 Fc and suggest that antibodies engineered to engage CD16b with high affinity must accommodate the Asp-129 side chain.

miR-505-3p controls chemokine receptor up-regulation in macrophages: role in familial hypercholesterolemia

Familial hypercholesterolemia (FH) conveys a high risk of premature atherosclerosis as a result of lifelong exposure to high LDL cholesterol levels that are not fully reduced by standard-of-care lipid-lowering treatment. Inflammatory mediators have played a role in the progression of atherosclerotic lesions. Here, we investigated whether innate immunity cells in patients with FH have a specific proinflammatory phenotype that is distinct from that of cells in normal participants. To this end, miR-505-3p-a microRNA related to chronic inflammation-and its target genes were investigated in monocyte-derived macrophages (MACs) of patients with FH (FH-MACs) and non-FH controls (co-MACs). On the basis of the profiler PCR array analysis of agomiR-505-3p-transfected MACs, we identified the chemokine receptors, CCR3, CCR4, and CXCR1, as genes that are regulated by miR-505-3p via the transcription factor, RUNX1. miR-505-3p was significantly down-regulated, whereas CCR3, CCR4, CXCR, and RUNX1 were increased in FH-MAC compared with co-MAC, with the increase being more evident in the proinflammatory M1-like FH-MAC. Chemokine receptor levels were unrelated to LDL plasma levels at entry, but correlated with age in patients with FH, not in controls. In summary, we demonstrate for first time to our knowledge that MACs from FH-MACs have an inflammatory phenotype that is characterized by the up-regulation of CCR3, CCR4, and CXCR1 under the control of miR-505-3p. These results suggest a chronic inflammatory condition in FH innate immunity cells that is not reverted by standard lipid-lowering treatment.-Escate, R., Mata, P., Cepeda, J. M., Padró, T., Badimon, L. miR-505-3p controls chemokine receptor up-regulation in macrophages: role in familial hypercholesterolemia.

Hypertension and increased endothelial mechanical stretch promote monocyte differentiation and activation: roles of STAT3, interleukin 6 and hydrogen peroxide

Aims

Monocytes play an important role in hypertension. Circulating monocytes in humans exist as classical, intermediate, and non-classical forms. Monocyte differentiation can be influenced by the endothelium, which in turn is activated in hypertension by mechanical stretch. We sought to examine the role of increased endothelial stretch and hypertension on monocyte phenotype and function.

Methods and results

Human monocytes were cultured with confluent human aortic endothelial cells undergoing either 5% or 10% cyclical stretch. We also characterized circulating monocytes in normotensive and hypertensive humans. In addition, we quantified accumulation of activated monocytes and monocyte-derived cells in aortas and kidneys of mice with Angiotensin II-induced hypertension. Increased endothelial stretch enhanced monocyte conversion to CD14++CD16+ intermediate monocytes and monocytes bearing the CD209 marker and markedly stimulated monocyte mRNA expression of interleukin (IL)-6, IL-1β, IL-23, chemokine (C-C motif) ligand 4, and tumour necrosis factor α. STAT3 in monocytes was activated by increased endothelial stretch. Inhibition of STAT3, neutralization of IL-6 and scavenging of hydrogen peroxide prevented formation of intermediate monocytes in response to increased endothelial stretch. We also found evidence that nitric oxide (NO) inhibits formation of intermediate monocytes and STAT3 activation. In vivo studies demonstrated that humans with hypertension have increased intermediate and non-classical monocytes and that intermediate monocytes demonstrate evidence of STAT3 activation. Mice with experimental hypertension exhibit increased aortic and renal infiltration of monocytes, dendritic cells, and macrophages with activated STAT3.

Conclusions

These findings provide insight into how monocytes are activated by the vascular endothelium during hypertension. This is likely in part due to a loss of NO signalling and increased release of IL-6 and hydrogen peroxide by the dysfunctional endothelium and a parallel increase in STAT activation in adjacent monocytes. Interventions to enhance bioavailable NO, reduce IL-6 or hydrogen peroxide production or to inhibit STAT3 may have anti-inflammatory roles in hypertension and related conditions.

Methylglyoxal-bis-guanylhydrazone inhibits osteopontin expression and differentiation in cultured human monocytes

Monocyte activation and polarization play essential roles in many chronic inflammatory diseases. An imbalance of M1 and M2 macrophage activation (pro-inflammatory and alternatively activated, respectively) is believed to be a key aspect in the etiology of these diseases, thus a therapeutic approach that regulates macrophage activation could be of broad clinical relevance. Methylglyoxal-bis-guanylhydrazone (MGBG), a regulator of polyamine metabolism, has recently been shown to be concentrated in monocytes and macrophages, and interfere with HIV integration into the DNA of these cells in vitro. RNA expression analysis of monocytes from HIV+ and control donors with or without MGBG treatment revealed the only gene to be consistently down regulated by MGBG to be osteopontin (OPN). The elevated expression of this pro-inflammatory cytokine and monocyte chemoattractant is associated with various chronic inflammatory diseases. We demonstrate that MGBG is a potent inhibitor of secreted OPN (sOPN) in cultured monocytes with 50% inhibition achieved at 0.1 μM of the drug. Furthermore, inhibition of OPN RNA transcription in monocyte cultures occurs at similar concentrations of the drug. During differentiation of monocytes into macrophages in vitro, monocytes express cell surface CD16 and the cells undergo limited DNA synthesis as measured by uptake of BrdU. MGBG inhibited both activities at similar doses to those regulating OPN expression. In addition, monocyte treatment with MGBG inhibited differentiation into both M1 and M2 classes of macrophages at non-toxic doses. The inhibition of differentiation and anti-OPN effects of MGBG were specific for monocytes in that differentiated macrophages were nearly resistant to MGBG activities. Thus MGBG may have potential therapeutic utility in reducing or normalizing OPN levels and regulating monocyte activation in diseases that involve chronic inflammation.

miR-505-3p controls chemokine receptor up-regulation in macrophages: role in familial hypercholesterolemia

Familial hypercholesterolemia (FH) conveys a high risk of premature atherosclerosis as a result of lifelong exposure to high LDL cholesterol levels that are not fully reduced by standard-of-care lipid-lowering treatment. Inflammatory mediators have played a role in the progression of atherosclerotic lesions. Here, we investigated whether innate immunity cells in patients with FH have a specific proinflammatory phenotype that is distinct from that of cells in normal participants. To this end, miR-505-3p-a microRNA related to chronic inflammation-and its target genes were investigated in monocyte-derived macrophages (MACs) of patients with FH (FH-MACs) and non-FH controls (co-MACs). On the basis of the profiler PCR array analysis of agomiR-505-3p-transfected MACs, we identified the chemokine receptors, CCR3, CCR4, and CXCR1, as genes that are regulated by miR-505-3p via the transcription factor, RUNX1. miR-505-3p was significantly down-regulated, whereas CCR3, CCR4, CXCR, and RUNX1 were increased in FH-MAC compared with co-MAC, with the increase being more evident in the proinflammatory M1-like FH-MAC. Chemokine receptor levels were unrelated to LDL plasma levels at entry, but correlated with age in patients with FH, not in controls. In summary, we demonstrate for first time to our knowledge that MACs from FH-MACs have an inflammatory phenotype that is characterized by the up-regulation of CCR3, CCR4, and CXCR1 under the control of miR-505-3p. These results suggest a chronic inflammatory condition in FH innate immunity cells that is not reverted by standard lipid-lowering treatment.-Escate, R., Mata, P., Cepeda, J.M., Padró, T., Badimon, L. miR-505-3p controls chemokine receptor up-regulation in macrophages: role in familial hypercholesterolemia. FASEB J. 32, 601-612 (2018). www.fasebj.org.

Leukocyte filtration of the cardiotomy suction. Does it affect systemic leukocyte activation or pulmonary function?

Background:

Cardiopulmonary bypass is thought to propagate a global systemic response through contact with the non-physiological surfaces of the extracorporeal circuit, leading to the stimulation of leukocytes, their adherence to endothelial cells and the release of cytotoxic molecules. This, in turn, has been shown to accelerate pulmonary injury. This study tested a new leukocyte-filtration system (RemoweLL) against a conventional system with no leukocyte-depleting capacity to determine the efficacy of the filtration system and its effects on pulmonary function.

Methods:

Thirty patients underwent coronary artery bypass graft surgery using either the RemoweLL filtration system (15 patients) or a conventional cardiopulmonary bypass circuit (15 patients). Data were collected on the total number of leukocytes, their differentiation and activation, using the leukocyte adhesion integrin CD11b as a surrogate marker. Pulmonary function was assessed using the Alveolar-arterial Oxygenation Index (AaOI) and patients were categorized using the Berlin definition of acute respiratory distress syndrome (ARDS).

Results:

Both groups showed significant increases in leukocyte numbers during CPB (p<0.001), with no differences noted between the groups. CD11b showed a significant increase in both groups, with peak activation occurring at the end of CPB, but no difference between the groups (p=0.8). There was a trend towards lower AaOI increases in the filtration group, but this did not reach significance (p=0.075) and there was no difference in ARDS definitions (p=0.33).

Conclusions:

Leukocyte filtration of cardiotomy suction did not influence total leukocyte counts or activation as measured by CD11b upregulation. Furthermore, no evidence could be found to suggest improved pulmonary function.

Monocyte Activation in Immunopathology: Cellular Test for Development of Diagnostics and Therapy

Several highly prevalent human diseases are associated with immunopathology. Alterations in the immune system are found in such life-threatening disorders as cancer and atherosclerosis. Monocyte activation followed by macrophage polarization is an important step in normal immune response to pathogens and other relevant stimuli. Depending on the nature of the activation signal, macrophages can acquire pro- or anti-inflammatory phenotypes that are characterized by the expression of distinct patterns of secreted cytokines and surface antigens. This process is disturbed in immunopathologies resulting in abnormal monocyte activation and/or bias of macrophage polarization towards one or the other phenotype. Such alterations could be used as important diagnostic markers and also as possible targets for the development of immunomodulating therapy. Recently developed cellular tests are designed to analyze the phenotype and activity of living cells circulating in patient's bloodstream. Monocyte/macrophage activation test is a successful example of cellular test relevant for atherosclerosis and oncopathology. This test demonstrated changes in macrophage activation in subclinical atherosclerosis and breast cancer and could also be used for screening a panel of natural agents with immunomodulatory activity. Further development of cellular tests will allow broadening the scope of their clinical implication. Such tests may become useful tools for drug research and therapy optimization.

Clinical significance of monocyte heterogeneity

Monocytes are primitive hematopoietic cells that primarily arise from the bone marrow, circulate in the peripheral blood and give rise to differentiated macrophages. Over the past two decades, considerable attention to monocyte diversity and macrophage polarization has provided contextual clues into the role of myelomonocytic derivatives in human disease. Until recently, human monocytes were subdivided based on expression of the surface marker CD16. "Classical" monocytes express surface markers denoted as CD14(++)CD16(-) and account for greater than 70% of total monocyte count, while "non-classical" monocytes express the CD16 antigen with low CD14 expression (CD14(+)CD16(++)). However, recognition of an intermediate population identified as CD14(++)CD16(+) supports the new paradigm that monocytes are a true heterogeneous population and careful identification of specific subpopulations is necessary for understanding monocyte function in human disease. Comparative studies of monocytes in mice have yielded more dichotomous results based on expression of the Ly6C antigen. In this review, we will discuss the use of monocyte subpopulations as biomarkers of human disease and summarize correlative studies in mice that may yield significant insight into the contribution of each subset to disease pathogenesis.

Induced expression of FcγRIIIa (CD16a) on CD4+ T cells triggers generation of IFN-γhigh subset

Whether or not CD4(+) T-cells express low affinity receptor FcγRIIIa (CD16a) in disease pathology has not been examined in great detail. In this study, we show that a subset of activated CD4(+) T-cells in humans express FcγRIIIa. The ligation of FcγRIIIa by immune complexes (ICs) in human CD4(+) T-cells produced co-stimulatory signal like CD28 that triggered IFN-γ production. The induced expression of FcγRIIIa on CD4(+) helper T-cells is an important finding since these receptors via ITAM contribute to intracellular signaling. The induced expression of FcγRIIIa on CD4(+) T helper cells and their ability to co-stimulate T-cell activation are important and novel findings that may reveal new pathways to regulate adaptive immune responses during inflammation and in autoimmunity.

Macrophages in immunopathology of atherosclerosis: a target for diagnostics and therapy

Immunopathology plays important roles in the development of different life-threatening diseases, such as atherosclerosis and its consequences (acute myocardial infarction and stroke), cancer, chronic inflammatory diseases. Effective modulation of the immune system may significantly increase the efficacy of prevention and therapy efforts. Currently there are no marketed drugs capable of normalizing immune system function in an intrinsic and comprehensive way. Here, we describe a test system designed for complex analysis of monocyte activity in individuals to diagnose immunopathology and monitor treatment efficacy. This cell-based test system may also be useful for screening compounds with an immune-correcting effects. Both diagnostic and screening systems are based on primary culture of human monocytes and/or monocyte-derived macrophages. This is the first step in creating a method for assessment of macrophage activity, which is required for further development of immune-correcting drugs. The existing preliminary data provide the basis for realization of this idea.

CD16 expression on monocytes in healthy individuals but not schistosome-infected patients is positively associated with levels of parasite-specific IgG and IgG1

Human IgG1 antibody responses are associated with protection against Schistosoma haematobium infection and are now a target for schistosome vaccine development. This study aimed to investigate the relationship between total IgG and the IgG subclasses and the monocyte IgG receptor, known as FcγRIIIa or CD16, in schistosome exposed people. Systemic levels of schistosome-specific anti-adult worm total IgG and IgG subclass titres were measured by ELISA in 100 individuals from an S. haematobium endemic area in Zimbabwe and, using parametric statistical methods and regression analysis, related to the levels of CD16 expression on individuals' circulating monocytes, determined via flow cytometry. Monocyte CD16 expression rose with parasite-specific total IgG and IgG1 in healthy participants, but not in schistosome infected patients. Similar to parasite-specific IgG and IgG1, CD16 expression in healthy individuals is associated with protection against schistosome infection. This relationship indicates a mechanistic link between the innate and adaptive immune responses to helminth infection in protection against infection. Further understanding the elements of a protective immune response in schistosomiasis may aid in efforts to develop a protective vaccine against this disease.

Schistosomiasis is a parasitic disease caused by the parasite Schistosoma spp. Over 240 million people are infected worldwide, mainly in Sub-Saharan Africa, but an efficacious, protective vaccine has yet to be found. Protection against schistosome infection in individuals living in endemic areas is mediated by antibodies. In particular, IgG1 antibody has been shown to be protective against infection in individuals living in endemic areas, and eliciting IgG1 production has become a cornerstone of vaccine development efforts. However, little is known about the mechanisms by which IgG1 induces protection. The cell surface molecule CD16 is an IgG antibody receptor expressed on monocytes and binds preferentially to IgG antibody subclasses. The work presented here thus investigates the relationship between IgG levels and the monocyte CD16 receptor in a population endemically exposed to infection with schistosomes. We present results linking CD16 expression with IgG1 levels, whereby uninfected individuals have a positive relationship between IgG1 and CD16 expression levels, while schistosome infected individuals did not show any statistically significant relationship between the two. Thus we provide evidence to suggest a mechanistic link between the innate and adaptive immune response in parasitic infection, associating monocyte CD16 expression with a protective immune response.

Monocyte and macrophage differentiation: circulation inflammatory monocyte as biomarker for inflammatory diseases

Monocytes express various receptors, which monitor and sense environmental changes. Monocytes are highly plastic and heterogeneous, and change their functional phenotype in response to environmental stimulation. Evidence from murine and human studies has suggested that monocytosis can be an indicator of various inflammatory diseases. Monocytes can differentiate into inflammatory or anti-inflammatory subsets. Upon tissue damage or infection, monocytes are rapidly recruited to the tissue, where they can differentiate into tissue macrophages or dendritic cells. Given the rapid progress in monocyte research from broad spectrum of inflammatory diseases, there is a need to summarize our knowledge in monocyte heterogeneity and its impact in human disease. In this review, we describe the current understanding of heterogeneity of human and murine monocytes, the function of distinct subsets of monocytes, and a potential mechanism for monocyte differentiation. We emphasize that inflammatory monocyte subsets are valuable biomarkers for inflammatory diseases, including cardiovascular diseases.

Mechanisms of HIV entry into the CNS: increased sensitivity of HIV infected CD14+CD16+ monocytes to CCL2 and key roles of CCR2, JAM-A, and ALCAM in diapedesis

As HIV infected individuals live longer, the prevalence of HIV associated neurocognitive disorders is increasing, despite successful antiretroviral therapy. CD14(+)CD16(+) monocytes are critical to the neuropathogenesis of HIV as they promote viral seeding of the brain and establish neuroinflammation. The mechanisms by which HIV infected and uninfected monocytes cross the blood brain barrier and enter the central nervous system are not fully understood. We determined that HIV infection of CD14(+)CD16(+) monocytes resulted in their highly increased transmigration across the blood brain barrier in response to CCL2 as compared to uninfected cells, which did not occur in the absence of the chemokine. This exuberant transmigration of HIV infected monocytes was due, at least in part, to increased CCR2 and significantly heightened sensitivity to CCL2. The entry of HIV infected and uninfected CD14(+)CD16(+) monocytes into the brain was facilitated by significantly increased surface JAM-A, ALCAM, CD99, and PECAM-1, as compared to CD14(+) cells that are CD16 negative. Upon HIV infection, there was an additional increase in surface JAM-A and ALCAM on CD14(+)CD16(+) monocytes isolated from some individuals. Antibodies to ALCAM and JAM-A inhibited the transmigration of both HIV infected and uninfected CD14(+)CD16(+) monocytes across the BBB, demonstrating their importance in facilitating monocyte transmigration and entry into the brain parenchyma. Targeting CCR2, JAM-A, and ALCAM present on CD14(+)CD16(+) monocytes that preferentially infiltrate the CNS represents a therapeutic strategy to reduce viral seeding of the brain as well as the ongoing neuroinflammation that occurs during HIV pathogenesis.

Ex vivo generated natural killer cells acquire typical natural killer receptors and display a cytotoxic gene expression profile similar to peripheral blood natural killer cells

Ex vivo differentiation systems of natural killer (NK) cells from CD34+ hematopoietic stem cells are of potential importance for adjuvant immunotherapy of cancer. Here, we analyzed ex vivo differentiation of NK cells from cord blood-derived CD34+ stem cells by gene expression profiling, real-time RT-PCR, flow cytometry, and functional analysis. Additionally, we compared the identified characteristics to peripheral blood (PB) CD56(bright) and CD56(dim) NK cells. The data show sequential expression of CD56 and the CD94 and NKG2 receptor chains during ex vivo NK cell development, resulting finally in the expression of a range of genes with partial characteristics of CD56(bright) and CD56(dim) NK cells from PB. Expression of characteristic NK cell receptors and cytotoxic genes was mainly found within the predominant ex vivo generated population of NKG2A+ NK cells, indicating the importance of NKG2A expression during NK cell differentiation and maturation. Furthermore, despite distinct phenotypic characteristics, the detailed analysis of cytolytic genes expressed within the ex vivo differentiated NK cells revealed a pattern close to CD56(dim) NK cells. In line with this finding, ex vivo generated NK cells displayed potent cytotoxicity. This supports that the ex vivo differentiation system faithfully reproduces major steps of the differentiation of NK cells from their progenitors, constitutes an excellent model to study NK cell differentiation, and is valuable to generate large-scale NK cells appropriate for immunotherapy.

Intermediate monocytes but not TIE2-expressing monocytes are a sensitive diagnostic indicator for colorectal cancer

We have conducted the first study to determine the diagnostic potential of the CD14++CD16+ intermediate monocytes as compared to the pro-angiogenic subset of CD14++CD16+TIE2+ TIE2-expressing monocytes (TEMs) in cancer. These monocyte populations were investigated by flow cytometry in healthy volunteers (N = 32) and in colorectal carcinoma patients with localized (N = 24) or metastatic (N = 37) disease. We further determined blood levels of cytokines associated with monocyte regulation. The results revealed the intermediate monocyte subset to be significantly elevated in colorectal cancer patients and to show the highest frequencies in localized disease. Multivariate regression analysis identified intermediate monocytes as a significant independent variable in cancer prediction. With a cut-off value at 0.37% (intermediate monocytes of total leukocytes) the diagnostic sensitivity and specificity ranged at 69% and 81%, respectively. In contrast, TEM levels were elevated in localized cancer but did not differ significantly between groups and none of the cytokines correlated with monocyte subpopulations. Of interest, in vitro analyses supported the observation that intermediate monocytes were more potently induced by primary as opposed to metastatic cancer cells which may relate to the immunosuppressive milieu established in the advanced stage of metastatic disease. In conclusion, intermediate monocytes as compared to TIE2-expressing monocytes are a more sensitive diagnostic indicator of colorectal cancer.

A nonfucosylated variant of the anti-HIV-1 monoclonal antibody b12 has enhanced FcγRIIIa-mediated antiviral activity in vitro but does not improve protection against mucosal SHIV challenge in macaques

Eliciting neutralizing antibodies is thought to be a key activity of a vaccine against human immunodeficiency virus (HIV). However, a number of studies have suggested that in addition to neutralization, interaction of IgG with Fc gamma receptors (FcγR) may play an important role in antibody-mediated protection. We have previously obtained evidence that the protective activity of the broadly neutralizing human IgG1 anti-HIV monoclonal antibody (MAb) b12 in macaques is diminished in the absence of FcγR binding capacity. To investigate antibody-dependent cellular cytotoxicity (ADCC) as a contributor to FcγR-associated protection, we developed a nonfucosylated variant of b12 (NFb12). We showed that, compared to fully fucosylated (referred to as wild-type in the text) b12, NFb12 had higher affinity for human and rhesus macaque FcγRIIIa and was more efficient in inhibiting viral replication and more effective in killing HIV-infected cells in an ADCC assay. Despite these more potent in vitro antiviral activities, NFb12 did not enhance protection in vivo against repeated low-dose vaginal challenge in the simian-human immunodeficiency virus (SHIV)/macaque model compared to wild-type b12. No difference in protection, viral load, or infection susceptibility was observed between animals given NFb12 and those given fully fucosylated b12, indicating that FcγR-mediated activities distinct from FcγRIIIa-mediated ADCC may be important in the observed protection against SHIV challenge.

Monocytes as a diagnostic marker of cardiovascular diseases

Inflammation is an important pathogenic factor of cardiovascular diseases. Inflammatory processes induce the organism systemic changes that are sensed by the cells of innate immune system. These systemic changes include increased concentrations of soluble factors capable of activating monocytes in the blood circulation therefore monocytes represent highly attractive cell population for diagnostic use. To date various parameters of circulating monocytes were associated with cardiovascular diseases. These comprise monocyte count, increased adhesive properties, alteration of lipid metabolism, phagocytosis and endocytosis of LDL. Search for markers, better suitable for clinical use led to identification of monocyte population heterogeneity. One of the best studied markers for identification of monocyte subpopulation is CD16. Although there is no consensus regarding the origin and composition of various monocyte subpopulations, association of increased size of CD16+ monocyte population with atherosclerosis is well established. Further surface markers of monocytes found to be associated with cardiovascular diseases are CD18, CD11b, CXCR1, CD36 and STAB1. Functional studies performed on primary human monocytes support the importance of these molecules for the pathogenesis of cardiovascular diseases. Continuous research on monocyte biology leads to identification of perspective markers that show significant potential of clinical use. These include analysis of monocyte response to a challenge and level of mitochondrial DNA heteroplasmy. Further research involving genomic, proteomic and cell biology techniques supplemented with systems biology approaches for data analysis and computer simulations are required for defining molecular and functional parameters of monocytes to be used as a diagnostic tool or therapeutic target.

Monocyte maturation, HIV susceptibility, and transmigration across the blood brain barrier are critical in HIV neuropathogenesis

HIV continues to be a global health crisis with more than 34 million people infected worldwide (UNAIDS: Report on the Global AIDS Epidemic 2010, Geneva, World Health Organization). HIV enters the CNS within 2 weeks of infection and establishes a spectrum of HAND in a large percentage of infected individuals. These neurologic deficits greatly impact the quality of life of those infected with HIV. The establishment of HAND is largely attributed to monocyte transmigration, particularly that of a mature CD14(+)CD16(+) monocyte population, which is more susceptible to HIV infection, across the BBB into the CNS parenchyma in response to chemotactic signals. To enter the CNS, junctional proteins on the monocytes must participate in homo- and heterotypic interactions with those present on BMVECs of the BBB as they transmigrate across the barrier. This transmigration is responsible for bringing virus into the brain and establishing chronic neuroinflammation. While there is baseline trafficking of monocytes into the CNS, the increased chemotactic signals present during HIV infection of the brain promote exuberant monocyte transmigration into the CNS. This review will discuss the mechanisms of monocyte differentiation/maturation, HIV infectivity, and transmigration into the CNS parenchyma that contribute to the establishment of cognitive impairment in HIV-infected individuals. It will focus on markers of monocyte subpopulations, how differentiation/maturation alters HIV infectivity, and the mechanisms that promote their increased transmigration across the BBB into the CNS.

The role of calcium signaling in phagocytosis

Immune cells kill microbes by engulfing them in a membrane-enclosed compartment, the phagosome. Phagocytosis is initiated when foreign particles bind to receptors on the membrane of phagocytes. The best-studied phagocytic receptors, those for Igs (FcgammaR) and for complement proteins (CR), activate PLC and PLD, resulting in the intracellular production of the Ca(2+)-mobilizing second messengers InsP3 and S1P, respectively. The ensuing release of Ca(2+) from the ER activates SOCE channels in the plasma and/or phagosomal membrane, leading to sustained or oscillatory elevations in cytosolic Ca(2+) concentration. Cytosolic Ca(2+) elevations are required for efficient ingestion of foreign particles by some, but not all, phagocytic receptors and stringently control the subsequent steps involved in the maturation of phagosomes. Ca(2+) is required for the solubilization of the actin meshwork that surrounds nascent phagosomes, for the fusion of phagosomes with granules containing lytic enzymes, and for the assembly and activation of the superoxide-generating NADPH oxidase complex. Furthermore, Ca(2+) entry only occurs at physiological voltages and therefore, requires the activity of proton channels that counteract the depolarizing action of the phagocytic oxidase. The molecules that mediate Ca(2+) ion flux across the phagosomal membrane are still unknown but likely include the ubiquitous SOCE channels and possibly other types of Ca(2+) channels such as LGCC and VGCC. Understanding the molecular basis of the Ca(2+) signals that control phagocytosis might provide new, therapeutic tools against pathogens that subvert phagocytic killing.

The levels of CD16/Fc gamma receptor IIIA on CD14+ CD16+ monocytes are higher in children with severe Plasmodium falciparum anemia than in children with cerebral or uncomplicated malaria

Fc gamma receptor IIIA (CD16/Fc gamma RIIIA) on monocytes/macrophages may play an important role in the pathogenesis of severe malarial anemia (SMA) by promoting phagocytosis of IgG-coated uninfected red cells and by allowing the production of tumor necrosis factor alpha (TNF-alpha) upon cross-linking by immune complexes (ICs). However, not much is known about the differential expression of this receptor on monocytes of children with severe malaria and uncomplicated malaria. Therefore, we investigated the expression of CD16/Fc gamma RIIIA on monocytes of children with SMA, cerebral malaria (CM), and their age-matched uncomplicated malaria controls by flow cytometry. Since CD14 low (CD14(+)) monocytes are considered more mature and macrophage-like than CD14 high (CD14(++)) monocytes, we also compared the level of expression of CD16/Fc gamma RIIIA according to the CD14 level and studied the relationship between CD16/Fc gamma RIIIA expression and intracellular TNF-alpha production upon stimulation by ICs. CD16/Fc gamma RIIIA expression was the highest overall on CD14(+) CD16(+) monocytes of children with SMA at enrollment. At convalescence, SMA children were the only ones to show a significant decline in the same parameter. In contrast, there were no significant differences among groups in the expression of CD16/Fc gamma RIIIA on CD14(++) CD16(+) monocytes. A greater percentage of CD14(+) CD16(+) monocytes produced TNF-alpha upon stimulation than any other monocyte subset, and the amount of intracellular TNF-alpha correlated positively with CD16/Fc gamma RIIIA expression. Furthermore, there was an inverse correlation between hemoglobin levels and CD16/Fc gamma RIIIA expression in children with SMA and their controls. These data suggest that monocytes of children with SMA respond differently to Plasmodium falciparum infection by overexpressing CD16/Fc gamma RIIIA as they mature, which could enhance erythrophagocytosis and TNF-alpha production.

CD19 targeting of chronic lymphocytic leukemia with a novel Fc-domain-engineered monoclonal antibody

CD19 is a B cell-specific antigen expressed on chronic lymphocytic leukemia (CLL) cells but to date has not been effectively targeted with therapeutic monoclonal antibodies. XmAb5574 is a novel engineered anti-CD19 monoclonal antibody with a modified constant fragment (Fc)-domain designed to enhance binding of FcgammaRIIIa. Herein, we demonstrate that XmAb5574 mediates potent antibody-dependent cellular cytotoxicity (ADCC), modest direct cytotoxicity, and antibody-dependent cellular phagocytosis but not complement-mediated cytotoxicity against CLL cells. Interestingly, XmAb5574 mediates significantly higher ADCC compared with both the humanized anti-CD19 nonengineered antibody it is derived from and also rituximab, a therapeutic antibody widely used in the treatment of CLL. The XmAb5574-dependent ADCC is mediated by natural killer (NK) cells through a granzyme B-dependent mechanism. The NK cell-mediated cytolytic and secretory function with XmAb5574 compared with the nonengineered antibody is associated with enhanced NK-cell activation, interferon production, extracellular signal-regulated kinase phosphorylation downstream of Fcgamma receptor, and no increased NK-cell apoptosis. Notably, enhanced NK cell-mediated ADCC with XmAb5574 was enhanced further by lenalidomide. These findings provide strong support for further clinical development of XmAb5574 as both a monotherapy and in combination with lenalidomide for the therapy of CLL and related CD19(+) B-cell malignancies.

The CD14+ CD16+ blood monocytes: their role in infection and inflammation

Blood monocyte subpopulations have been defined in man initially, and the two major types of monocytes are the CD14++ CD16- and the CD14+ CD16+ monocytes. These cells have been shown to exhibit distinct phenotype and function, and the CD14+ CD16+ were labeled proinflammatory based on higher expression of proinflammatory cytokines and higher potency in antigen presentation. The current review describes these properties, including the relationship to dendritic cells, and summarizes the host of publications about CD14+ CD16+ monocytes in inflammation and infectious disease in man, all of which suggest a crucial role of these cells in the disease processes. The review also covers the more recent description of homologues of these cells in other model species, which is expected to better define the role of monocyte subsets in disease.

Defective Antitumor Function of Monocyte-Derived Macrophages from Epithelial Ovarian Cancer Patients

PURPOSE

Monocytes/macrophages (MO/MA) are an important but heterogeneous population of immune inflammatory cells that have diverse effector functions. We examined and compared these differences in peripheral blood and ascites of epithelial ovarian cancer patients with peripheral blood of normal donors.

EXPERIMENTAL DESIGN

Comparisons were made of cell surface subsets, cytokine production, and FcR-dependent cytotoxicity of CD14+ MO/MA and the CD14brightCD16-HLA-DR+ MO/MA subset in normal donor peripheral blood and peripheral blood and ascites from epithelial ovarian cancer patients. Studies were done on monocyte-derived macrophages cultured with macrophage colony-stimulating factor and activated with lipopolysaccharide or a combination of lipopolysaccharide plus recombinant IFN-gamma.

RESULTS

We determined that MO/MA or its subset from epithelial ovarian cancer patients had altered morphology and significantly less antibody-dependent cell-mediated cytotoxicity and phagocytic activity than did MO/MA from normal donors. Our findings also showed that monocyte-derived macrophages from both epithelial ovarian cancer patients and normal donors produce macrophage colony-stimulating factor-stimulated cytokines, including interleukin-8, tumor necrosis factor-alpha, and interleukin-6.

CONCLUSIONS

These findings highlight for the first time the defective antibody-dependent cell-mediated cytotoxicity and phagocyte functions of epithelial ovarian cancer-associated MO/MA, which could have implications for immunobiotherapeutic strategies.

Down-regulation of activating Fcgamma receptors on monocytes of patients with rheumatoid arthritis upon methotrexate treatment

OBJECTIVE

To determine the effect of methotrexate (MTX) on expression levels of activating receptors for IgG (FcgammaRs) on monocytes of rheumatoid arthritis (RA) patients in relation to changes in disease activity.

METHODS

The effect of MTX on FcgammaRs on monocytes of RA patients was evaluated ex vivo as well as in vitro. Recently diagnosed, disease-modifying antirheumatic drug (DMARD)-naive RA patients were treated with low-dose MTX. At baseline and 16 weeks after the start of MTX treatment, changes in FcgammaR expression levels on peripheral blood monocytes were evaluated by fluorescence-activated cell sorting analysis and were correlated to changes in disease parameters. To study the direct effects of MTX on monocytes, these cells were isolated from peripheral blood monocytes of healthy controls and cultured with MTX. Other monocyte surface molecules (CD40, CD80, CD86, MHC class II) were also determined to test the specificity of the effect on FcgammaR expression levels.

RESULTS

Eleven out of 15 patients improved clinically (mean disease activity score before 6.2 +/- 0.8 vs 4.3 +/- 1.7 after). Sixteen weeks after the start of MTX therapy, the expression levels of FcgammaRI and IIa on monocytes were significantly decreased, whereas the decreases in FcgammaRIIIa expression levels on monocytes were less marked. The percentage decrease in FcgammaRI expression correlated with the percentage decrease in CRP and well-being. In vitro MTX selectively decreased FcgammaRI and FcgammaRIIa expression levels of isolated monocytes, in contrast to other surface molecules.

CONCLUSION

The disease-modifying effect of MTX in the treatment of RA is accompanied by down-regulation of activating FcgammaRI and IIa on monocytes, which could be a direct effect of MTX on monocytes. This down-regulation represents a new mode of action of MTX which should be considered in RA patients, especially during conditions that could give rise to monocyte activation by IgG-containing immune complexes, e.g. during antibody-based therapy of RA.

Human immunodeficiency virus 1 favors the persistence of infection by activating macrophages through TNF

Macrophages play a major role in HIV-1 persistence. In the present paper, we demonstrate that the absence of apoptosis in HIV-1-infected primary human monocyte-differentiated macrophages (MDM) correlates with an increase in anti-apoptotic (Bcl-2 and Bcl-x(L)) and a decrease in pro-apoptotic (Bax and Bad) proteins. This is associated with macrophage activation as shown by tumor necrosis factor (TNF) production and NF-kappaB activation upon infection. TNF production was shown to be involved in the upregulation of Bcl-2 and Bcl-x(L) because this increase was abolished by an anti-TNF anti-serum or an inhibitor of TNF synthesis. In parallel, inhibition of TNF production induced an increase in the number of apoptotic cells. Furthermore, using an inhibitor of NF-kappaB activation, we demonstrated that TNF-induced upregulation of Bcl-x(L) and Bcl-2 occurs, respectively, through a NF-kappaB-dependent and an NF-kappaB-independent pathway.

Monocytes with altered phenotypes in posttrauma patients

CONTEXT

Posttrauma patients show impaired immune responsiveness and increased susceptibility to infections. Although monocytes in these patients have been known to express decreased HLA-DR, induction of HLA-DR using interferon gamma failed to reduce susceptibility to infection, suggesting additional factors also may be involved in the impaired immune responsiveness. CD4 plays an integral role in most of the functions of HLA-DR. In newborn infants, who have impaired immune responsiveness, we found a concomitant reduction of CD4 on monocytes with decreased HLA-DR expression.

OBJECTIVE

Because monocytes in posttrauma patients have not been previously studied for morphology, coexpression of CD4 and HLA-DR, and activity of alpha-naphthyl butyrate esterase, the purpose of this study was to analyze these factors in this population.

DESIGN

Monocyte morphology; expression of CD4, CD11b, CD13, CD16, and HLA-DR by 3-color flow cytometry; and analysis of alpha-naphthyl butyrate esterase activity by cytochemical staining were studied in 27 posttrauma patients and 20 control subjects.

RESULTS

Monocytes in posttrauma patients showed significant differences in the following characteristics compared with controls: (1) increase of subsets displaying the phenotypes CD4-/CD14+/HLA-DR- and CD4-/CD14+/CD16-, (2) decrease in mean fluorescence intensity of CD4 and HLA-DR expression in monocytes that were positive for these markers, (3) decrease in alpha-naphthyl butyrate esterase activity, and (4) decreased amount of cytoplasm and cytoplasmic vacuoles.Conclusion.-Our study suggests that in posttrauma patients, as in newborns, there is a marked increase of monocytes with decreased expression of CD4 and HLA-DR, as well as decreased alpha-naphthyl butyrate esterase activity. Concomitant reduction in CD4 and HLA-DR expression on monocytes may contribute to impaired immune responsiveness in these patients.

FcgammaRIII expression on cultured human keratinocytes and upregulation by interferon-gamma

Keratinocytes of human epidermis are actively involved in inflammatory and autoimmune reactions of the skin and interact with resident or infiltrating immunocompetent cells via cytokines, chemokines, and intercellular adhesion mechanisms. Most immunocompetent cells have been reported to express Fcgamma receptors (FcgammaR), which are important for immunoregulatory functions. In this study we investigate FcgammaRIII expression on cultured human keratinocytes and upregulation by interferon-gamma. By real-time polymerase chain reaction, we show basal mRNA expression of both subclasses FcgammaRIIIA and FcgammaRIIIB, but after interferon-gamma treatment mRNA of FcgammaRIIIA and FcgammaRIIIB is increased 4.4 and 6.5 times, respectively. FcgammaRIII protein expression and its increase after interferon-gamma treatment were shown on cultured human keratinocytes by indirect immunofluorescence. In immunoblotting experiments, a bonified anti-CD16 antibody revealed reactivity to a polypeptide of 50-65 kDa on lysates of treated and untreated keratinocytes. In summary, we demonstrate expression of mRNA specific for the FcgammaRIIIA and FcgammaRIIIB subclasses and their upregulation by interferon-gamma on human keratinocytes in vitro, and confirm FcgammaRIII protein expression by indirect immunofluorescence and by immunoblotting experiments.

CD14+,CD16+ blood monocytes and joint inflammation in rheumatoid arthritis

OBJECTIVE

CD14+,CD16+ monocytes, identified as a minor population of monocytes in human peripheral blood (PB), have been implicated in several inflammatory diseases. We undertook this study to investigate the relevance of this phenotype to joint inflammation in rheumatoid arthritis (RA).

METHODS

The expression of CD14, CD16, CC chemokine receptor 1 (CCR1), CCR5, and intercellular adhesion molecule 1 (ICAM-1) on monocytes was measured by flow cytometric analysis. Concentrations of the cytokines known to induce CD16 (including transforming growth factor beta1 [TGFbeta1], macrophage colony-stimulating factor [M-CSF], and interleukin-10 [IL-10]) and concentrations of the soluble form of CD14 (sCD14) in plasma and synovial fluid (SF) samples were measured by enzyme-linked immunosorbent assay. The induction of CD16 on RA blood monocytes cultured for 18 hours with 1 or with all 3 cytokines was determined.

RESULTS

The mean +/- SD frequency of CD14+,CD16+ blood monocytes was significantly increased in RA patients (11.7 +/- 5.6%; n = 105) compared with healthy controls (9.5 +/- 2.2%; n = 15) (P < 0.01), and the patient group with an increased frequency of CD16+ monocytes (> or =13.9%) had active disease, as defined by increased counts of tender and swollen joints, levels of acute-phase reactants, and titers of rheumatoid factor. The response to drug therapy correlated with changes in the frequency of this phenotype. The expression of CD16 on SF monocytes from RA patients was markedly elevated compared with the expression on PB monocytes. CD16 expression on RA blood monocytes was augmented in vitro by IL-10, M-CSF, and TGFbeta1. Plasma concentrations of these cytokines and of sCD14 were significantly higher in RA patients with high CD16+ monocyte frequencies than in those with low CD16+ monocyte frequencies or in healthy controls. CD14+,CD16+ monocytes expressed higher levels of CCR1, CCR5, and ICAM-1 than did regular CD14++,CD16- monocytes, particularly in active RA.

CONCLUSION

These results indicate that the maturation of blood monocytes into tissue-infiltrative CD16+ cells before entry into the joint, induced by cytokine spillover from the inflamed joint, may contribute to the persistent joint inflammation of RA.

The CD16(+) (FcgammaRIII(+)) subset of human monocytes preferentially becomes migratory dendritic cells in a model tissue setting

Much remains to be learned about the physiologic events that promote monocytes to become lymph-homing dendritic cells (DCs). In a model of transendothelial trafficking, some monocytes become DCs in response to endogenous signals. These DCs migrate across endothelium in the ablumenal-to-lumenal direction (reverse transmigration), reminiscent of the migration into lymphatic vessels. Here we show that the subpopulation of monocytes that expresses CD16 (Fcgamma receptor III) is predisposed to become migratory DCs. The vast majority of cells derived from CD16(+) monocytes reverse transmigrated, and their presence was associated with migratory cells expressing high levels of CD86 and human histocompatibility leukocyte antigen (HLA)-DR, and robust capacity to induce allogeneic T cell proliferation. A minority of CD16(-) monocytes reverse transmigrated, and these cells stimulated T cell proliferation less efficiently. CD16 was not functionally required for reverse transmigration, but promoted cell survival when yeast particles (zymosan) were present as a maturation stimulus in the subendothelial matrix. The cell surface phenotype and migratory characteristics of CD16(+) monocytes were inducible in CD16(-) monocytes by preincubation with TGFbeta1. We propose that CD16(+) monocytes may contribute significantly to precursors for DCs that transiently survey tissues and migrate to lymph nodes via afferent lymphatic vessels.

Enhancement of antigen driven lymphocyte proliferation secondary to GP41-induced B7 expression on adherent monocytes

HIV-1 viral proteins are known to have immune regulatory effects. The interplay between these molecules and the host immune cells is complex. In this study the immune regulatory effects of gp41 on lymphocyte proliferation were evaluated as a function of the state of the monocyte. It is shown that monocyte adherence to tissue culture plates prevents suppression of lymphocyte proliferation to recall antigen in the presence of gp41. In addition, gp41 can enhance proliferation to low concentrations of Casta antigen when PBL are permitted time to adhere. It is shown that these effects are in part mediated through enhanced expression of the costimulatory molecules B7 and CD40. Cyclosporin A was not able to fully abrogate gp41-enhanced proliferation, indicating participation of a calcium-independent pathway. In addition, concentrations of anti-IL2 receptor antibody sufficient to inhibit maximal proliferation to antigen did not fully inhibit PBL proliferation to antigen that is augmented with gp41. Taken together these results suggest that modification of the monocyte state of activation or differentiation could mediate a response to gp41 that is immune enhancing.

Expression of membrane C1q in human monocyte-derived macrophages is developmentally regulated and enhanced by interferon-gamma

The present study investigated when during "in vitro" maturation macrophages (MPhi) express membrane C1q (mC1q), and whether cell activation affects expression and function of mC1q. Although C1q mRNA was repeatedly detected in freshly isolated monocytes using reverse transcriptase-polymerase chain reaction, C1q protein was observed only in developing MPhi from day 1 to 4 on using immunodetection and flow cytometry. However, the quantity of mC1q and other MPhi membrane proteins differed strikingly in cells from different donors. We report here for the first time that CD14(+) and CD14(-) mC1q-bearing MPhi can develop, and that interferon-gamma increases mC1q display at the cell surface, and mC1q-mediated phagocytosis.

Expression of Fc(gamma)r1 (CD64) on polymorphonuclear leucocytes during progression to acquired immunodeficiency syndrome in perinatally human immunodeficiency virus-infected children

CD64, the high-affinity receptor in the family of FCgamma receptors, is not expressed constitutively in polymorphonuclear leucocytes (PMN). CD64 is expressed by PMNs in the late stages of human immunodeficiency virus (HIV) infection in adults. We followed the expression of CD64 on PMNs in perinatally HIV-infected children during disease progression. Peripheral blood leucocytes (PBL) from 45 perinatally HIV-infected paediatric patients and 13 healthy age-matched controls were analysed using cytofluorimetry after reaction with a fluorophore-labelled monoclonal antibody (MoAb) to CD64. In parallel, we examined the expression of CD32, CD16, CD11b and the human neutrophil-specific BH2-Ag using fluorophore-labelled MoAbs. We found that up to 79.5% of the PMNs in children in class C3 express CD64. Most importantly, we observed a continuous and significant increase in the appearance of CD64+ PMNs as a function of CDC classification (P < 0.001) but no changes in the expression of CD32, CD16, CD11b and BH2-Ag. This suggests that following the expression of CD64 on PMNs can be useful in evaluating the progression of HIV infection in perinatally HIV-infected children.

Phenotypic and functional characteristics of circulating monocytes of elderly persons

Aging is associated with impairment of immune functions. Age-dependent alterations in T-cells are well known. Although the pivotal role of monocytes in immune regulation by their production of proinflammatory and inhibitory cytokines is acknowledged, limited information is available on monocyte changes in aging. The present study focused on phenotypic changes in circulating monocytes in elderly subjects and in the level of cytokines they produce. The results demonstrated a significant expansion of CD14dim/CD16bright circulating monocytes in elderly. In contrast, the majority of circulating monocytes of healthy young individuals were CD14bright/CD16dim. The CD14dim/CD16bright monocytes are considered to have phenotypic evidence for activation. Furthermore, significant increases of constitutive production of monocytic cytokines including interleukin (IL)-1beta. IL-1 receptor antagonist, and IL-6 by nonstimulated monocytes from elderly was also indicative of activation. This was also observed when monocytes from elderly were cultured with autologous lymphocytes. However, after stimulation, significantly lowered IL-1beta production was observed and IL-6 and IL-10 tended to be higher in the elderly. Collectively, these results indicate that monocytes of aged individuals, in contrast to a younger population exhibit in vivo activation as well as imbalanced production of cytokines. Such age-related alterations in monocytes may contribute to impaired immune competence of aging.

Detection of urinary macrophages expressing the CD16 (Fc gamma RIII) molecule: a novel marker of acute inflammatory glomerular injury

BACKGROUND

The CD16 antigen is the Fc gamma receptor III. CD14+CD16+ cells are proinflammatory monocytes/macrophages (Mo/M phi) that constitute a minor population in the peripheral blood of healthy individuals. Little is known about the expression of CD16 antigen on Mo/M phi in glomerulonephritis.

METHODS

Flow cytometric analyses were performed on urine and blood samples obtained from 209 patients with various renal diseases. Patients variously suffered from rapidly progressive crescentic glomerulonephritis (RPGN), membranoproliferative glomerulonephritis (MPGN), postinfectious acute glomerulonephritis (AGN), Henoch-Schönlein purpura nephritis (HSPN), IgA nephropathy (IgAN), membranous nephropathy (MN), minimal change nephrotic syndrome (MCNS), lupus nephritis (LN), acute interstitial nephritis, hereditary nephropathy, idiopathic renal hematuria (IRH), and renal stone.

RESULTS

The CD16+ M phi population of cells was present in the urine of hematuria-positive patients with proliferative glomerulonephritis, including AGN, IgAN, RPGN, MPGN, and LN with acute inflammatory lesions, such as endocapillary proliferation, tuft necrosis, and cellular crescents. In contrast, the urinary CD16+ M phi population was negligible in hematuria-positive patients with nonproliferative renal disease, including hereditary nephropathy, IRH, and renal stone and also in patients with proliferative glomerulonephritis lacking acute inflammatory lesions. Total urinary M phi of these patients were much less than those of patients having proliferative glomerulonephritis with acute inflammatory lesions. Transient expansion of the CD16+ M phi population in urine was observed during the acute exacerbation of urinary abnormalities, whereas the disappearance of CD16+ M phi closely preceded the amelioration of urinary abnormalities in patients with proliferative glomerulonephritis. In 38 of the 98 patients positive for CD16+ M phi population in urine, the CD16+ Mo population was negligible in peripheral blood. Immunohistochemically, CD16+ M phi were present in the glomeruli of active proliferative glomerulonephritis, whereas such cells were absent in inactive proliferative glomerulonephritis or nonproliferative glomerular diseases.

CONCLUSION

CD16+ M phi may be effector cells involved in the acute inflammation common to all types of proliferative glomerulonephritis. Furthermore, the detection of CD16+ M phi in urine, as well as urinary M phi counts, may serve as a useful indicator of the active stage of proliferative glomerulonephritis.

Soluble CD16 in plasma cell dyscrasias

Soluble forms of Fc gammaR type III (sFc gammaRIII or sCD16) are present in many biological fluids. Their main ligand is IgG in the form of complexes. In plasma, sCD16 essentially derive from cleavage of membrane CD16 (or Fc gammaRIII) present on neutrophils and, to a lesser extent, on NK cells. Determination of sCD16 serum level during monoclonal gammopathies has demonstrated markedly reduced levels in multiple myeloma and in monoclonal gammopathy of undetermined significance (MGUS) rapidly evolving to multiple myeloma, compared to stable MGUS or controls, indicating a prognostic value for this biological parameter. The biology and functions of sCD16 are described, together with the biological significance of modifications of the sCD16 serum level in monoclonal gammopathies.

Development of phagocytic function of cultured human monocytes is regulated by cell surface IL-10

Monocytes differentiating in vitro into macrophages increase their capacity to ingest particles via FcgammaR and CR3. Because human recombinant IL-10 is a potent up-regulator of phagocytosis in human monocytes, we investigated whether spontaneously produced IL-10 could be a signal for the modulation of phagocytosis by cultured monocytes. We show here that culture of monocytes in the presence of anti-IL-10 mAb completely abolished up-regulation of phagocytosis of both EIgG and EIgMC3bi, suggesting a role for spontaneously produced IL-10 in the modulation of phagocytosis by cultured human monocytes. The inhibition exerted by anti-IL-10 mAb on the development of FcgammaR-mediated ingestion was dependent on the concomitant inhibition of FcgammaRIII induction in cultured cells. On the other hand, a similar down-regulation of CR3 expression was not involved in the inhibitory effect exerted by anti-IL-10 mAb on the development of CR3-mediated ingestion. Monocytes secreted detectable levels of IL-10 when cultured in medium but the concentrations of IL-10 in the supernatants decreased with length of time in culture, the decrease being completely reversed by anti-IL-10 mAb. In addition, we showed that monocytes expressed immunoreactive IL-10 on their surface and this expression increased during differentiation into macrophages. Whether this IL-10 was bound to specific membrane receptors or it was an integral membrane protein remains to be determined; however, this latter possibility is consistent with our observations that IL-10 did not elute with acid treatment and exogenous IL-10 did not increase surface staining of monocytes. Our data indicate that human mononuclear phagocytes express IL-10 on their membrane and suggest that this cytokine may represent an autocrine signal for the increased phagocytic function observed during differentiation of monocytes into macrophages.

Effect of granulocyte-macrophage colony-stimulating factor treatment on phenotype, cytokine release and cytotoxicity of circulating blood monocytes and monocyte-derived macrophages

We studied phenotype, function and differentiation of mononuclear phagocytes in 11 cancer patients treated subcutaneously with 10O microg/kg recombinant human (rhu) GM-CSF for 7 d. The rhuGM-CSF treatment induced (1) a 5.9-fold increase in the number of blood monocytes (MO), (2) a decrease of CD14bright/CD16bright cells with a diminution of the mean fluorescence intensity (MFI) of CD14, and (3) a decrease of MO cellular cytotoxicity. In patients' sera, tumour necrosis factor (TNF)-alpha, interleukin (IL)-10, IL-12, neopterin, macrophage-colony-stimulating factor (M-CSF), and IL-1 receptor antagonist (IL-1RA) increased, whereas GM-CSF and granulocyte-colony-stimulating factor (G-CSF) decreased after an initial peak. In whole blood samples the lipopolysaccharide (LPS)-stimulated release of TNF-alpha, IL-6 and IL-1RA increased initially, whereas IL-1beta, IL-10 and IL-12 decreased. During differentiation from MO to macrophages (MAC), interferon (IFN)-gamma-stimulated tumour cytotoxicity increased, but both MO and MAC were less cytotoxic upon rhuGM-CSF treatment. The differentiation-associated increase of LPS-induced TNF-alpha, IL-1RA and IL-10 secretion was reduced by the rhuGM-CSF treatment, and the expression of CD14 on MAC as well as the proportion of CD14+/CD16+, CD14+/MAX.1+ and CD14+/CD71+ cells in 7-d cultured MAC declined. We interpret these findings as (1) an increase of immature MO upon rhuGM-CSF therapy, (2) a priming effect on the LPS-induced proinflammatory cytokine repertoire of MO, and (3) an impact of rhuGM-CSF on the capacity of MO to differentiate to MAC in vitro.

IgG binding sites on human Fc gamma receptors

The structure for the three human Fc gamma receptors classes Fc gamma RI (CD64), Fc gamma RII (CD32) and Fc gamma RIII (CD16) has been well characterized. Here the IgG binding sites on Fc gamma RII and Fc gamma RII with their responsive FG, BC and C'/E loops on the membrane proximal domains are described in detail. For Fc gamma RI the second extracellular domain is suggested as a key structure of IgG binding. The lower hinge regions of human and murine IgG binding to these Fc receptors and their structural relationship in Fc gamma R-IgG interactions are discussed. The potential of inhibiting the pathophysiological effects of Fc gamma receptors by blocking studies are considered for future therapeutic modalities.

Retinoic Acid Inhibits Monocyte to Macrophage Survival and Differentiation

Vitamin A metabolites are potent differentiation-inducing agents for myelomonocytic cell lines in vitro and are successfully used for the treatment of patients with acute promyelocytic leukemia. However, little is known about the effects of vitamin A on normal hematopoietic cells. Therefore, we investigated the effect of vitamin A on differentiation and activation of human blood monocytes (MO). Culturing MO for up to 4 days with 9-cis retinoic acid (RA) and all-trans RA but not retinol reduced MO survival, with the remaining cells being morphologically comparable to control cells. Because macrophage colony-stimulating factor (M-CSF) is a well-known survival factor for MO, we measured the M-CSF content of MO culture supernatants using enzyme-linked immunosorbent assay and found that RA suppressed the constitutive secretion of M-CSF. Northern analysis showed that the M-CSF mRNA expression was only slightly reduced by RA treatment, suggesting regulation on the posttranscriptional level. In contrast to MO, M-CSF secretion by MO-derived macrophages (MAC) was not altered by RA, suggesting a differentiation-dependent switch in the responsiveness of MO/MAC to RA. Because M-CSF is not only a survival-promoting but also a differentiation-promoting factor for myeloid cells, we analyzed the effect of RA on MO to MAC maturation. RA suppressed the expression of the maturation-associated antigen carboxypeptidase M (CPM)/MAX.1 at both the protein and mRNA levels and modulated the lipopolysaccharide-stimulated cytokine secretion of MO/MAC. The addition of exogenous M-CSF to RA-containing MO cultures fails to overcome the RA-induced inhibition of MO differentiation. However, the survival rate was improved by exogenous M-CSF. We conclude that RA acts via two different mechanisms on monocyte survival and differentiation: posttranscriptionally by controlling M-CSF secretion, which decreases MO survival, and transcriptionally regulating the expression of differentiation-associated genes. The regulation of M-CSF production may contribute to the antileukemic effect of RA in vivo by reducing autocrine M-CSF production by leukemic cells.

Retinoic Acid Inhibits Monocyte to Macrophage Survival and Differentiation

Vitamin A metabolites are potent differentiation-inducing agents for myelomonocytic cell lines in vitro and are successfully used for the treatment of patients with acute promyelocytic leukemia. However, little is known about the effects of vitamin A on normal hematopoietic cells. Therefore, we investigated the effect of vitamin A on differentiation and activation of human blood monocytes (MO). Culturing MO for up to 4 days with 9-cis retinoic acid (RA) and all-trans RA but not retinol reduced MO survival, with the remaining cells being morphologically comparable to control cells. Because macrophage colony-stimulating factor (M-CSF) is a well-known survival factor for MO, we measured the M-CSF content of MO culture supernatants using enzyme-linked immunosorbent assay and found that RA suppressed the constitutive secretion of M-CSF. Northern analysis showed that the M-CSF mRNA expression was only slightly reduced by RA treatment, suggesting regulation on the posttranscriptional level. In contrast to MO, M-CSF secretion by MO-derived macrophages (MAC) was not altered by RA, suggesting a differentiation-dependent switch in the responsiveness of MO/MAC to RA. Because M-CSF is not only a survival-promoting but also a differentiation-promoting factor for myeloid cells, we analyzed the effect of RA on MO to MAC maturation. RA suppressed the expression of the maturation-associated antigen carboxypeptidase M (CPM)/MAX.1 at both the protein and mRNA levels and modulated the lipopolysaccharide-stimulated cytokine secretion of MO/MAC. The addition of exogenous M-CSF to RA-containing MO cultures fails to overcome the RA-induced inhibition of MO differentiation. However, the survival rate was improved by exogenous M-CSF. We conclude that RA acts via two different mechanisms on monocyte survival and differentiation: posttranscriptionally by controlling M-CSF secretion, which decreases MO survival, and transcriptionally regulating the expression of differentiation-associated genes. The regulation of M-CSF production may contribute to the antileukemic effect of RA in vivo by reducing autocrine M-CSF production by leukemic cells.

Expanded CD14+ CD16+ monocyte subpopulation in patients with acute and chronic infections undergoing hemodialysis

Infections are frequent complications in end-stage renal failure patients undergoing hemodialysis (HD), and peripheral blood monocytes are important cells in host defense against infections. The majority of circulating monocytes express high levels of lipopolysaccharide receptor antigen CD14 and are negative for the immunoglobulin Fcgamma receptor type III (CD16). We studied the occurrence of a minor subpopulation coexpressing low levels of CD14 together with CD16 in HD patients. In healthy controls CD14+ CD16+ monocytes account for 8% +/- 4% of CD14+ monocytes, with an absolute number of 29 +/- 14 cells/microl. In stable HD patients the CD14+ CD16+ subpopulation was significantly elevated (14% +/- 3%, or 66 +/- 28 cells/microl), while the number of CD14(++) monocytes (monocytes strongly positive for CD14) remained constant. In HD patients suffering from chronic infections a further rise in CD14+ CD16+ monocytes was observed (128 +/- 71 cells/microl; P < 0.01) such that this subpopulation constituted 24% of all blood monocytes. In contrast, numbers of CD14++ cells did not change compared to those for stable HD patients, indicating that the CD14+ CD16+ monocyte subpopulation was selectively expanded. During acute infections the CD14+ CD16+ cell subpopulation always expanded. A whole-blood assay revealed that CD14+ CD16+ monocytes exhibited a higher phagocytosis rate for Escherichia coli bacteria than CD14++ monocytes, underlining their role during host defense. In addition, CD14+ CD16+ monocytes expressed higher levels of major histocompatibility complex (MHC) class II antigens (HLA-DR, -DP, and -DQ) and equal amounts of MHC class I antigens (HLA-ABC). Thus, CD14+ CD16+ cells constitute a potent phagocytosing and antigen-presenting monocyte subpopulation, which is expanded during acute and chronic infections commonly observed in chronic HD patients.

Reduced CD4 and HLA-DR expression in neonatal monocytes

Three-color flow cytometry was used to assess the immunophenotypic characteristics of normal cord blood monocytes after labeling with a variety of antibodies against myeloid/monocyte-specific markers. Monocytes both in cord blood and in peripheral blood from normal adults were defined in a backgating procedure as cells with the light-scattering characteristics of monocytes that also expressed CD14. The percentage of monocytes, defined in this fashion, that also displayed CD4 receptors was significantly lower in cord blood (mean +/- SD = 29.3 +/- 13.9%) than in peripheral blood from normal adult controls (mean +/- SD = 68.9 +/- 13%) (P < 0.005). Similarly, HLA-DR expression was found on only 86 +/- 6.6% of monocytes in cord blood but on 99 +/- 1% of monocytes in adults (P < 0.005). The percentage of monocytes displaying CD16 receptors in cord blood did not show any significant difference in comparison with adult monocytes. When coexpression of CD14, CD16, and CD4 was assessed, cord blood showed a predominant population of monocytes bearing the phenotype CD14+/CD16-/CD4-. Similarly, approximately 10% of CD14+ monocytes in cord blood expressed neither CD4 nor HLA-DR. Cytochemically, monocytes from cord blood revealed intense granular staining for PAS and marginal or absent staining for nonspecific esterase (NSE). These results raise the possibility that reduced expression of CD4 and HLA-DR receptors on cord blood monocytes may contribute to their impaired immune response. Additionally, the high percentage of CD14+/CD16-/CD4- cells in cord blood suggests that these cells may represent a phenotypically immature population of monocytes. Likewise, the unusual cytochemical staining patterns suggest that these cells are biochemically immature as well.