Neutrophils from the synovial fluid of patients with rheumatoid arthritis express the high affinity immunoglobulin G receptor, Fc gamma RI (CD64): role of immune complexes and cytokines in induction of receptor expression

Hyaluronic Acid in Synovial Fluid Prevents Neutrophil Activation in Spondyloarthritis

Spondyloarthritis (SpA) patients suffer from joint inflammation resulting in tissue damage, characterized by the presence of numerous neutrophils in the synovium and synovial fluid (SF). As it is yet unclear to what extent neutrophils contribute to the pathogenesis of SpA, we set out to study SF neutrophils in more detail. We analyzed the functionality of SF neutrophils of 20 SpA patients and 7 disease controls, determining ROS production and degranulation in response to various stimuli. In addition, the effect of SF on neutrophil function was determined. Surprisingly, our data show that SF neutrophils in SpA patients have an inactive phenotype, despite the presence of many neutrophil-activating stimuli such as GM-CSF and TNF in SF. This was not due to exhaustion as SF neutrophils readily responded to stimulation. Therefore, this finding suggests that one or more inhibitors of neutrophil activation may be present in SF. Indeed, when blood neutrophils from healthy donors were activated in the presence of increasing concentrations of SF from SpA patients, degranulation and ROS production were dose-dependently inhibited. This effect was independent of diagnosis, gender, age, and medication in the patients from which the SF was isolated. Treatment of SF with the enzyme hyaluronidase strongly reduced the inhibitory effect of SF on neutrophil activation, indicating that hyaluronic acid that is present in SF may be an important factor in preventing SF neutrophil activation. This finding provides novel insights into the role of soluble factors in SF regulating neutrophil function and may lead to the development of novel therapeutics targeting neutrophil activation via hyaluronic acid or associated pathways.

Ageing and interferon gamma response drive the phenotype of neutrophils in the inflamed joint

OBJECTIVE

Neutrophils are typically the most abundant leucocyte in arthritic synovial fluid. We sought to understand changes that occur in neutrophils as they migrate from blood to joint.

METHODS

We performed RNA sequencing of neutrophils from healthy human blood, arthritic blood and arthritic synovial fluid, comparing transcriptional signatures with those from murine K/BxN serum transfer arthritis. We employed mass cytometry to quantify protein expression and sought to reproduce the synovial fluid phenotype ex vivo in cultured healthy blood neutrophils.

RESULTS

Blood neutrophils from healthy donors and patients with active arthritis showed largely similar transcriptional signatures. By contrast, synovial fluid neutrophils exhibited more than 1600 differentially expressed genes. Gene signatures identified a prominent response to interferon gamma (IFN-γ), as well as to tumour necrosis factor, interleukin-6 and hypoxia, in both humans and mice. Mass cytometry confirmed that healthy and arthritic donor blood neutrophils are largely indistinguishable but revealed a range of neutrophil phenotypes in synovial fluid defined by downregulation of CXCR1 and upregulation of FcγRI, HLA-DR, PD-L1, ICAM-1 and CXCR4. Reproduction of key elements of this signature in cultured blood neutrophils required both IFN-γ and prolonged culture.

CONCLUSIONS

Circulating neutrophils from patients with arthritis resemble those from healthy controls, but joint fluid cells exhibit a network of changes, conserved across species, that implicate IFN-γ response and ageing as complementary drivers of the synovial fluid neutrophil phenotype.

Fc receptors gone wrong: A comprehensive review of their roles in autoimmune and inflammatory diseases

Systemic autoimmune and inflammatory diseases have a complex and only partially known pathophysiology with various abnormalities involving all the components of the immune system. Among these components, antibodies, and especially autoantibodies are key elements contributing to autoimmunity. The interaction of antibody fragment crystallisable (Fc) and several distinct receptors, namely Fc receptors (FcRs), have gained much attention during the recent years, with possible major therapeutic perspectives for the future. The aim of this review is to comprehensively describe the known roles for FcRs (activating and inhibitory FcγRs, neonatal FcR [FcRn], FcαRI, FcεRs, Ro52/tripartite motif containing 21 [Ro52/TRIM21], FcδR, and the novel Fc receptor-like [FcRL] family) in systemic autoimmune and inflammatory disorders, namely rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, systemic sclerosis, idiopathic inflammatory myopathies, mixed connective tissue disease, Crohn's disease, ulcerative colitis, immunoglobulin (Ig) A vasculitis, Behçet's disease, Kawasaki disease, IgG4-related disease, immune thrombocytopenia, autoimmune hemolytic anemia, antiphospholipid syndrome and heparin-induced thrombocytopenia.

Rheumatoid Arthritis Synovial Fluid Neutrophils Drive Inflammation Through Production of Chemokines, Reactive Oxygen Species, and Neutrophil Extracellular Traps

Rheumatoid arthritis (RA) is a chronic inflammatory disorder affecting synovial joints. Neutrophils are believed to play an important role in both the initiation and progression of RA, and large numbers of activated neutrophils are found within both synovial fluid (SF) and synovial tissue from RA joints. In this study we analyzed paired blood and SF neutrophils from patients with severe, active RA (DAS28>5.1, n=3) using RNA-seq. 772 genes were significantly different between blood and SF neutrophils. IPA analysis predicted that SF neutrophils had increased expression of chemokines and ROS production, delayed apoptosis, and activation of signaling cascades regulating the production of NETs. This activated phenotype was confirmed experimentally by incubating healthy control neutrophils in cell-free RA SF, which was able to delay apoptosis and induce ROS production in both unprimed and TNFα primed neutrophils (p<0.05). RA SF significantly increased neutrophil migration through 3μM transwell chambers (p<0.05) and also increased production of NETs by healthy control neutrophils (p<0.001), including exposure of myeloperoxidase (MPO) and citrullinated histone-H3-positive DNA NETs. IPA analysis predicted NET production was mediated by signaling networks including AKT, RAF1, SRC, and NF-κB. Our results expand the understanding of the molecular changes that take place in the neutrophil transcriptome during migration into inflamed joints in RA, and the altered phenotype in RA SF neutrophils. Specifically, RA SF neutrophils lose their migratory properties, residing within the joint to generate signals that promote joint damage, as well as inflammation via recruitment and activation of both innate and adaptive immune cells. We propose that this activated SF neutrophil phenotype contributes to the chronic inflammation and progressive damage to cartilage and bone observed in patients with RA.

Anti-citrullinated protein antibodies are associated with neutrophil extracellular trap formation in rheumatoid arthritis

Objectives

We evaluated the associations of anti‐citrullinated protein antibodies (ACPAs) and serological and cytological levels of neutrophil extracellular trap (NET) formation in rheumatoid arthritis (RA) patients.

Methods

Serum levels of myeloperoxidase‐DNA and elastase‐DNA complexes (NET remnants) were examined in 51 patients with RA and 40 healthy controls using a modified enzyme‐linked immunosorbent assay. Neutrophils were isolated by density gradient centrifugation. IgG antibodies were purified by affinity chromatography. NET formation in RA and control neutrophils was assessed by microscopy in vitro. NETs were purified and co‐incubated with fibroblast‐like synoviocyte (FLS) cells. Interleukin (IL)‐6 and IL‐8 mRNA expression and protein levels in FLS cells were determined by real‐time polymerase chain reaction and enzyme‐linked immunosorbent assay, respectively.

Results

In RA patients, NET remnants in the peripheral circulation were higher in extremely high ACPA titers when compared to in moderate ACPA titers. And IgG antibodies containing ACPA can stimulate neutrophils to form NETs in a concentration‐dependent manner. Furthermore, significantly higher expression of the pro‐inflammatory cytokines IL‐6 and IL‐8 is detected after FLS cells interacted with NETs which derived from neutrophils stimulated with ACPA‐containing IgG antibodies.

Conclusions

Anti‐citrullinated protein antibodies may enhance NET formation and contribute to inflammation development in RA by stimulating NET formation, such as by subsequent activation of FLS cells by NETs.

Type I interferon regulates cytokine-delayed neutrophil apoptosis, reactive oxygen species production and chemokine expression

Interferons (IFNs) are key regulators of a number of inflammatory conditions in which neutrophils play an important role in pathology, such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), where type I IFNs are implicated in disease pathology. However, IFNs are usually generated in vivo together with other cytokines that also have immunoregulatory functions, but such interactions are poorly defined experimentally. We measured the effects of type I (IFN-α) IFN, elevated in both RA and SLE, on the functions of healthy neutrophils incubated in vitro in the absence and presence of proinflammatory cytokines typically elevated in inflammatory diseases [tumour necrosis factor (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF)]. IFN-α alone had no effect on neutrophil apoptosis; however, it abrogated the anti-apoptotic effect of GM-CSF (18 h, P < 0·01). The enhanced stability of the anti-apoptotic protein myeloid cell leukaemia 1 (Mcl-1) and delayed activation of caspase activation normally regulated by GM-CSF were blocked by IFN-α: this effect was mediated, in part, by activation of p38 mitogen-activated protein kinase (MAPK). IFN-α alone also primed reactive oxygen species (ROS) production and maintained the transient priming effect of TNF-α for up to 4 h: it also down-regulated GM-CSF- and TNF-α-activated expression of chemokine (C-X-C motif) ligand (CXCL)1, CXCL2, CXCL3, CXCL8, CCL3 and CCL4 but, in contrast, increased the expression of CXCL10. These novel data identify complex regulatory signalling networks in which type I IFNs profoundly alter the response of neutrophils to inflammatory cytokines. This is likely to have important consequences in vivo and may explain the complexity and heterogeneity of inflammatory diseases such as RA, in which multiple cytokine cascades have been activated.

Anti-Citrullinated Protein Antibodies in Patients with Rheumatoid Arthritis: Biological Effects and Mechanisms of Immunopathogenesis

Individuals with high anti-citrullinated protein antibody (ACPA) titers have an increased risk of developing rheumatoid arthritis (RA). Although our knowledge of the generation and production of ACPAs has continuously advanced during the past decade, our understanding on the pathogenic mechanisms of how ACPAs interact with immune cells to trigger articular inflammation is relatively limited. Citrullination disorders drive the generation and maintenance of ACPAs, with profound clinical significance in patients with RA. The loss of tolerance to citrullinated proteins, however, is essential for ACPAs to exert their pathogenicity. N-linked glycosylation, cross-reactivity and the structural interactions of ACPAs with their citrullinated antigens further direct their biological functions. Although questions remain in the pathogenicity of ACPAs acting as agonists for a receptor-mediated response, immune complex (IC) formation, complement system activation, crystallizable fragment gamma receptor (FcγR) activation, cross-reactivity to joint cartilage and neutrophil extracellular trap (NET)-related mechanisms have all been suggested recently. This paper presents a critical review of the characteristics and possible biological effects and mechanisms of the immunopathogenesis of ACPAs in patients with RA.

Regulation of neutrophil pro-inflammatory functions sheds new light on the pathogenesis of rheumatoid arthritis

For more than two centuries now, rheumatoid arthritis (RA) is under investigation intending to discover successful treatment. Despite decades of scientific advances, RA is still representing a challenge for contemporary medicine. Current drug therapies allow to improve significantly the quality of life of RA patients; however, they are still insufficient to reverse tissue injury and are often generating side-effects. The difficulty arises from the considerable fluctuation of the clinical course of RA among patients, making the predictive prognosis difficult. More and more studies underline the profound influence of the neutrophil multifaceted functions in the pathogenesis of RA. This renewed interest in the complexity of neutrophil functions in RA offers new exciting opportunities for valuable therapeutic targets as well as for safe and well-tolerated RA treatments. In this review, we aim to update the recent findings on the multiple facets of neutrophils in RA, in particular their impact in promoting the RA-based inflammation through the release of the cytokine-like S100A8/A9 protein complex, as well as the importance of NETosis in the disease progression and development. Furthermore, we delve into the complex question of neutrophil heterogeneity and plasticity and discuss the emerging role of miRNAs and epigenetic markers influencing the inflammatory response of neutrophils in RA and how they could constitute the starting point for novel attractive targets in RA therapy.

Recent advances in our understanding of the pathogenesis of juvenile idiopathic arthritis and their potential clinical implications

INTRODUCTION

Juvenile idiopathic arthritis (JIA) comprises systemic and non-systemic forms of chronic childhood arthritis diagnosed prior to age 16. Significant improvement in treatment outcomes has been witnessed since the introduction of biologics. In particular, advances in research in the area of multidimensional interrogation and network analysis have facilitated understanding of the complex cacophony of components orchestrating disease immunopathogenesis. Areas covered: In this review, we will examine the scientific advances that have augmented our understanding of JIA pathogenesis, focusing on the progress made in systemic, poly, and oligo JIA in four major aspects: (a) unraveling the pathogenic mechanisms, (b) disease classification, (c) therapeutic selection, and (d) decision for withdrawal of medications after achieving remission. Expert commentary: Dysregulation of innate immune cell physiology and function in sJIA will be highlighted. MicroRNAs contribute to monocyte/macrophage polarization with resulting consequences on macrophage activation syndrome development. The involvement of neutrophils, a major source of S100A8/9/12, in the active inflammatory phase of sJIA is compelling. In non-sJIA, circulating CD4 subsets in T effector and regulatory compartments possessing a strong synovial T-cell receptor coverage and disease activity correlation, acted as an accessible reservoir of pathogenic cells exploitable for clinical management.

C5a and C5aR are elevated in joints of rheumatoid and psoriatic arthritis patients, and C5aR blockade attenuates leukocyte migration to synovial fluid

Complement activation correlates to rheumatoid arthritis disease activity, and increased amounts of the complement split product C5a is observed in synovial fluids from rheumatoid arthritis patients. Blockade of C5a or its receptor (C5aR) is efficacious in several arthritis models. The aim of this study was to investigate the role of C5a and C5aR in human rheumatoid arthritis and psoriatic arthritis–both with respect to expression and function. Synovial fluid, blood and synovial samples were obtained from rheumatoid arthritis, psoriatic arthritis and osteoarthritis patients as a less inflammatory arthritis type, and blood from healthy subjects. Cells infiltrating synovial tissue were analysed by immunohistochemistry and flow cytometry. SF and blood were analysed for biomarkers by flow cytometry or ELISA. The effect of a blocking anti-human C5aR mAb on leukocyte migration was determined using a Boyden chamber. Appropriate statistical tests were applied for comparisons. C5aR⁺ cells were detected in most rheumatoid arthritis, in all psoriatic arthritis, but not in non-inflammatory control synovia. C5aR⁺ cells were primarily neutrophils and macrophages. C5aR⁺ macrophages were mainly found in lymphoid aggregates in close contact with T cells. C5a levels were increased in both rheumatoid arthritis and psoriatic arthritis synovial fluid compared to osteoarthritis, and in blood from rheumatoid arthritis compared to healthy subjects. Neutrophil and monocyte migration to rheumatoid arthritis synovial fluid was significantly inhibited by anti-C5aR. The data support that the C5a-C5aR axis may be driving the infiltration of inflammatory cells into the synovial fluid and synovium in both rheumatoid and psoriatic arthritis, and suggest that C5a or C5aR may be a promising treatment target in both diseases.

Neutrophils in chronic lymphocytic leukemia are permanently activated and have functional defects

A growing body of studies highlights involvement of neutrophils in cancer development and progression. Our aim was to assess the phenotypic and functional properties of circulating neutrophils from patients with chronic lymphocytic leukemia (CLL). The percentage of CD54+ and CD64+ neutrophils as well as CD54 expression on these cells were higher in CLL patients than in age-matched healthy controls. Neutrophils from CLL produced more reactive oxygen species (ROS) compared to controls in both resting and activated conditions. Lipopolysaccharide-induced production of IL-1β and TNF-a as well as reduced TLR2 expression in neutrophils from CLL than in neutrophils from controls suggesting their tolerant state. Finally, phenotypic alterations of neutrophils, particularly elevation of CD64 and CD54 markers, correlated with disease activity and treatment, and low percentage of neutrophils. Taken together, the alterations in percentage and functional characteristics of neutrophils reflect the clinical course of CLL. Our data provide first evidence that neutrophils in CLL are permanently primed and have functional defects.

PTPN22 Is a Critical Regulator of Fcγ Receptor-Mediated Neutrophil Activation

Neutrophils act as a first line of defense against bacterial and fungal infections, but they are also important effectors of acute and chronic inflammation. Genome-wide association studies have established that the gene encoding the protein tyrosine phosphatase nonreceptor 22 (PTPN22) makes an important contribution to susceptibility to autoimmune disease, notably rheumatoid arthritis. Although PTPN22 is most highly expressed in neutrophils, its function in these cells remains poorly characterized. We show in this article that neutrophil effector functions, including adhesion, production of reactive oxygen species, and degranulation induced by immobilized immune complexes, were reduced in Ptpn22-/- neutrophils. Tyrosine phosphorylation of Lyn and Syk was altered in Ptpn22-/- neutrophils. On stimulation with immobilized immune complexes, Ptpn22-/- neutrophils manifested reduced activation of key signaling intermediates. Ptpn22-/- mice were protected from immune complex-mediated arthritis, induced by the transfer of arthritogenic serum. In contrast, in vivo neutrophil recruitment following thioglycollate-induced peritonitis and in vitro chemotaxis were not affected by lack of PTPN22. Our data suggest an important role for PTPN22-dependent dephosphorylation events, which are required to enable full FcγR-induced activation, pointing to an important role for this molecule in neutrophil function.

Mouse and human FcR effector functions

Mouse and human FcRs have been a major focus of attention not only of the scientific community, through the cloning and characterization of novel receptors, and of the medical community, through the identification of polymorphisms and linkage to disease but also of the pharmaceutical community, through the identification of FcRs as targets for therapy or engineering of Fc domains for the generation of enhanced therapeutic antibodies. The availability of knockout mouse lines for every single mouse FcR, of multiple or cell-specific--'à la carte'--FcR knockouts and the increasing generation of hFcR transgenics enable powerful in vivo approaches for the study of mouse and human FcR biology. This review will present the landscape of the current FcR family, their effector functions and the in vivo models at hand to study them. These in vivo models were recently instrumental in re-defining the properties and effector functions of FcRs that had been overlooked or discarded from previous analyses. A particular focus will be made on the (mis)concepts on the role of high-affinity IgG receptors in vivo and on results from antibody engineering to enhance or abrogate antibody effector functions mediated by FcRs.

Diagnosing sepsis - The role of laboratory medicine

Sepsis is the host response to microbial pathogens resulting in significant morbidity and mortality. An accurate and timely diagnosis of sepsis allows prompt and appropriate treatment. This review discusses laboratory testing for sepsis because differentiating systemic inflammation from infection is challenging. Procalcitonin (PCT) is currently an FDA approved test to aid in the diagnosis of sepsis but with questionable efficacy. However, studies support the use of PCT for antibiotic de-escalation. Serial lactate measurements have been recommended for monitoring treatment efficacy as part of sepsis bundles. The 2016 sepsis consensus definitions include lactate concentrations >2mmol/L (>18mg/dL) as part of the definition of septic shock. Also included in the 2016 definitions are measuring bilirubin and creatinine to determine progression of organ failure indicating worse prognosis. Hematologic parameters, including a simple white blood cell count and differential, are frequently part of the initial sepsis diagnostic protocols. Several new biomarkers have been proposed to diagnose sepsis or to predict mortality, but they currently lack sufficient sensitivity and specificity to be considered as stand-alone testing. If sepsis is suspected, new technologies and microbiologic assays allow rapid and specific identification of pathogens. In 2016 there is no single laboratory test that accurately diagnoses sepsis.

The role of the neutrophil Fcγ receptor I (CD64) index in diagnosing spontaneous bacterial peritonitis in cirrhotic patients

OBJECTIVE

To investigate the role of the neutrophil Fcγ receptor I (CD64) index in the diagnosis of spontaneous bacterial peritonitis (SBP) in cirrhotic patients.

METHODS

A total of 123 cirrhotic patients with ascites who fulfilled the inclusion criteria were enrolled in this study. Ascites and blood samples were collected; the polymorphonuclear neutrophil (PMN) count, bacterial culture, and related laboratory tests were performed. The CD64 index was determined for each sample using flow cytometry.

RESULTS

The neutrophil CD64 index results were significantly higher in cirrhotic patients with SBP than in those without SBP (p<0.001). There was a positive correlation between the neutrophil CD64 index and the PMN count in ascites. In the receiver operating characteristic curve (ROC) analysis, the area under the curve (AUC) was 0.894 (95% confidence interval 0.823-0.964, p<0.001). The optimal cut-off value for the neutrophil CD64 index was 2.02. The sensitivity and specificity of the neutrophil CD64 index for cirrhotic patients with SBP were 80.49% and 93.90%, respectively. The elevated neutrophil CD64 index was down-regulated by antibiotic therapy (p=0.002).

CONCLUSIONS

The neutrophil CD64 index could be used as a sensitive and specific indicator for the diagnosis of SBP in cirrhotic patients with ascites and is also modulated by antibiotic therapy.

Neutrophils and arthritis: Role in disease and pharmacological perspectives

The inflammatory response in the joint can induce an intense accumulation of leukocytes in the tissue that frequently results in severe local damage and loss of function. Neutrophils are essential cells to combat many pathogens, but their arsenal can contribute or aggravate articular inflammation. Here we summarized some aspects of neutrophil biology, their role in inflammation and indicated how the modulation of neutrophil functions could be useful for the treatment of different forms of arthritis.

Antibody induced CD4 down-modulation of T cells is site-specifically mediated by CD64(+) cells

Treatment of PBMC with the CD4-specific mAb BT-061 induces CD4 down-modulation of T cells. Here we report that addition of BT-061 to purified T cells did not confer this effect, whereas incubation of T cells in BT-061 coated wells restored CD4 down-modulation. These results implied that Fcγ receptor mediated cell-cell interactions played a role. In consistence with this hypothesis PBMC depleted of CD64⁺ monocytes did not confer CD4 down-modulation of BT-061 decorated T cells. Strikingly, CD4 down-modulation was observed in BT-061 treated synovial fluid punctuated from patients’ inflamed joints that comprised enhanced numbers of CD64⁺ cells. In contrast, in a circulating whole blood system injection of BT-061 did not induce CD4 down-modulation, due to CD64 saturation by serum IgG. Similarly, tonsil derived mononuclear cells devoid of CD64⁺ cells did not show CD4 down-modulation, whereas addition of blood derived monocytes restored the effect. Thus, the interaction of BT-061 decorated T cells with CD64⁺ cells is needed for CD4 down-modulation, implying that in patients BT-061 would primarily induce CD4 down-modulation at inflammatory sites. These results highlight the need not only to examine the interaction of a given mAb with single FcγR, but also the immunological environment that is appropriate to support such interactions.

Could CD64 expression be used as a predictor of positive culture results in children with febrile neutropenia?

Background

Early recognition of infectious processes in neutropenic patients is hampered by the fact that these processes may have dissimilar and non-specific clinical presentations. CD64 is a neutrophil surface marker that is not expressed in non-sensitized neutrophils. When the neutrophil is exposed to tumor necrosis factor-alpha it is activated and is measured via the CD64 index.

Methods

This paper evaluated the relationship between the index value of CD64 on the first day of febrile neutropenia and a positive blood culture. The correlations with white blood count, C-reactive protein and erythrocyte sedimentation rate were also evaluated. This case–control, prospective, diagnostic study included 64 episodes of neutropenia. Case group (n = 14) comprised positive blood cultures, and the control group (n = 50), negative blood cultures.

Results

The median rates of CD64 were 2.1 (σ ± 3.9) in the case group and 1.76 (σ ± 5.02) in the control group. There was no correlation between the value of the CD64 index and blood cultures. The CD64 index was also not correlated with C-reactive protein positivity. Furthermore, the CD64 index was not able to predict blood culture positivity. The sensitivity was 64.3%, the specificity was 42%, the positive predictive value was 23.7% and the negative predictive value was 80%. For C-reactive protein, the sensitivity, specificity, positive predictive value, and negative predictive value were 71.4%, 32%, 22.7%, and 80%, respectively.

Conclusion

The CD64 index is not suitable for predicting the positivity of blood cultures in this specific population of patients with febrile neutropenia.

Expression of CD11c and EMR2 on neutrophils: potential diagnostic biomarkers for sepsis and systemic inflammation

There is a need for cellular biomarkers to differentiate patients with sepsis from those with the non-infectious systemic inflammatory response syndrome (SIRS). In this double-blind study we determined whether the expression of known (CD11a/b/c, CD62L) and putative adhesion molecules [CD64, CD97 and epidermal growth factor (EGF)-like molecule containing mucin-like hormone receptor (EMR2)] on blood neutrophils could serve as useful biomarkers of infection and of non-infectious SIRS in critically ill patients. We studied 103 patients with SIRS, 83 of whom had sepsis, and 50 healthy normal subjects, using flow cytometry to characterize neutrophils phenotypically in whole blood samples. Patients with SIRS had an increased prevalence of neutrophils expressing CD11c, CD64 and EMR2 in comparison with healthy subjects (P < 0.001), but normal expression of CD11a, CD11b, CD62L and CD97. An increase in the percentage of neutrophils bearing CD11c was associated with sepsis, EMR2 with SIRS and CD64 with sepsis and SIRS. Neutrophils expressing CD11c had the highest sensitivity (81%) and specificity (80%) for the detection of sepsis, and there was an association between the percentage of neutrophils expressing EMR2 and the extent of organ failure (P < 0.05). Contrary to other reports, we did not observe an abnormal expression of CD11b or CD62L on neutrophils from patients with SIRS, and suggest that this discrepancy is due to differences in cell processing protocols. We propose that blood neutrophils expressing CD11c and EMR2 be considered as potential biomarkers for sepsis and SIRS, respectively.

Fcγ and Complement Receptors and Complement Proteins in Neutrophil Activation in Rheumatoid Arthritis: Contribution to Pathogenesis and Progression and Modulation by Natural Products

Rheumatoid arthritis (RA) is a highly disabling disease that affects all structures of the joint and significantly impacts on morbidity and mortality in RA patients. RA is characterized by persistent inflammation of the synovial membrane lining the joint associated with infiltration of immune cells. Eighty to 90% of the leukocytes infiltrating the synovia are neutrophils. The specific role that neutrophils play in the onset of RA is not clear, but recent studies have evidenced that they have an important participation in joint damage and disease progression through the release of proteolytic enzymes, reactive oxygen species (ROS), cytokines, and neutrophil extracellular traps, in particular during frustrated phagocytosis of immune complexes (ICs). In addition, the local and systemic activation of the complement system contributes to the pathogenesis of RA and other IC-mediated diseases. This review discusses (i) the participation of Fcγ and complement receptors in mediating the effector functions of neutrophils in RA; (ii) the contribution of the complement system and ROS-dependent and ROS-independent mechanisms to joint damage in RA; and (iii) the use of plant extracts, dietary compounds, and isolated natural compounds in the treatment of RA, focusing on modulation of the effector functions of neutrophils and the complement system activity and/or activation.

Anti-type II collagen immune complex-induced granulocyte reactivity is associated with joint erosions in RA patients with anti-collagen antibodies

Introduction

Rheumatoid arthritis (RA) patients with autoantibodies against collagen type II (CII) are characterized by acute RA onset with elevated inflammatory measures and early joint erosions as well as increased production of tumor necrosis factor-α (ΤΝF-α) by peripheral blood mononuclear cells (PBMC) stimulated by anti-CII immune complexes (IC) in vitro. Polymorphonuclear granulocytes (PMN) are abundant in RA synovial fluids, where they might interact directly with anti-CII IC in the articular cartilage, but no studies have investigated PMN responses towards anti-CII IC. The aim was to investigate whether PMN react towards anti-CII IC, and to what extent such reactivity might relate to the clinical acute onset RA phenotype associated with elevated levels of anti-CII.

Methods

PMN and PBMC isolated from healthy donors were stimulated with IC made with a set of 72 baseline patient sera (24 anti-CII positive, 48 anti-CII negative) chosen from a clinically well-characterized RA cohort with two-year radiological follow-up with Larsen scoring. PMN expression of cluster of differentiation (CD)11b, CD66b, CD16 and CD32 was measured by flow cytometry, whereas PMN production of myeloperoxidase (MPO) and interleukin (IL)-17, and PBMC production of ΤΝF-α was measured with enzyme linked immunosorbent assay.

Results

PMN expression of CD11b, CD66b and MPO, and PBMC production of ΤΝF-α were upregulated whereas PMN expression of CD16 and CD32 were downregulated by anti-CII IC. CD16, CD66b, and MPO production correlated to serum anti-CII levels (Spearman’s ρ = 0.315, 0.675 and 0.253, respectively). CD16 was associated with early joint erosions (P = 0.024, 0.034, 0.046 at baseline, one and two years) and CD66b was associated with changes in joint erosions (P = 0.017 and 0.016, at one and two years compared to baseline, respectively). CD66b was associated with baseline C-reactive protein and PBMC production of ΤΝF-α was associated with baseline erythrocyte sedimentation rate, in accordance with our earlier findings. No clinical associations were observed for MPO or IL-17.

Conclusion

PMN responses against anti-CII IC are more closely associated with early joint erosions than are PBMC cytokine responses. PMN reactivity against anti-CII IC may contribute to joint destruction in newly diagnosed RA patients with high levels of anti-CII.

Bridging autoantibodies and arthritis: the role of Fc receptors

Autoantibodies represent a hallmark of Rheumatoid arthritis (RA), which is a chronic inflammatory autoimmune disease characterized by inflammation and damage in the joints. Anti-Citrullinated Protein Antibodies (ACPA) are the most prominent autoantibodies present in RA patients. These autoantibodies have been intensively investigated during the last 20 years due to their diagnostic and predictive value. Furthermore, they are believed to be involved in mediating the damage associated with RA. Antibodies of the IgG isotype interact with the immune system via Fcγ receptors expressed on immune cells as well as nonimmune cells. These receptors, therefore, form the bridge between Fcγ receptor-positive cells and antibodies complexed to antigen allowing the modulation and activation of cellular immune responses that are involved in immune defense against invading microorganisms. However, in case triggered by antibodies against self-antigens, they can also play a pivotal role in the induction and perpetuation of autoimmune diseases such as RA. Mouse models have been indispensably important for understanding the role of Fcγ receptors in the development of arthritis. Here we discuss the contribution of autoantibodies to the pathogenesis of arthritis in preclinical animal models, as well as RA, in relation to their interaction with the different (immune inhibitory and activating) Fcγ receptors.

The multifactorial role of neutrophils in rheumatoid arthritis

Of all cells implicated in the pathology of rheumatoid arthritis (RA), neutrophils possess the greatest cytotoxic potential, owing to their ability to release degradative enzymes and reactive oxygen species. Neutrophils also contribute to the cytokine and chemokine cascades that accompany inflammation, and regulate immune responses via cell-cell interactions. Emerging evidence suggests that neutrophils also have a previously unrecognised role in autoimmune diseases: neutrophils can release neutrophil extracellular traps (NETs) containing chromatin associated with granule enzymes, which not only kill extracellular microorganisms but also provide a source of autoantigens. For example, citrullinated proteins that can act as neoepitopes in loss of immune tolerance are generated by peptidylarginine deiminases, which replace arginine with citrulline residues, within neutrophils. Indeed, antibodies to citrullinated proteins can be detected before the onset of symptoms in patients with RA, and are predictive of erosive disease. Neutrophils from patients with RA have an increased tendency to form NETs containing citrullinated proteins, and sera from such patients contain autoantibodies that recognize these proteins. Thus, in addition to their cytotoxic and immunoregulatory role in RA, neutrophils may be a source of the autoantigens that drive the autoimmune processes underlying this disease.

Neutrophils in local and systemic antibody-dependent inflammatory and anaphylactic reactions

Neutrophils are notorious for their efficacy in microbial killing. Various mechanisms, such as phagocytosis, production of ROS, cytokines/chemokines and lipid mediators, degranulation of antimicrobials and enzymes, as well as NETosis contribute to this capacity. However, every incidence of neutrophil activation bears a risk to cause damage to the host. Several distinct steps, i.e., adhesion to endothelial cells, transmigration, chemotaxis, cytokine stimulation, and TLR signaling, are thought to control the extent of neutrophil activation. In the absence of a microbial stimulus, other pathways can induce neutrophil activation, among which FcR-induced activation when neutrophils encounter ICs. In these situations (inflammation, autoimmunity, allergy), neutrophils may act as primary or secondary effectors of immune reactions. In the presence of circulating ICs, neutrophils can indeed get stimulated directly in the bloodstream and trigger an immune response. Upon deposition of antibody complexes inside of tissues, neutrophils are first recruited and primed before being highly activated to amplify the ongoing inflammation. This review focuses on the engagement, activation, and responses of neutrophils to antibody ICs, inside of tissues or in the vasculature.

The high-affinity human IgG receptor FcγRI (CD64) promotes IgG-mediated inflammation, anaphylaxis, and antitumor immunotherapy

Human FcγRI can trigger antibody-induced inflammatory arthritis, thrombocytopenia, airway inflammation, and systemic anaphylaxis. Human FcγRI can trigger antibody-mediated immunotherapy of mouse metastatic melanoma.

Analysis of candidate genes of spontaneous arthritis in mice deficient for interleukin-1 receptor antagonist

Previously, we identified a major quantitative trait locus (QTL) on mouse chromosome 1 that regulates the susceptibility to arthritis in an F2 population generated from arthritis-prone BALB/c and arthritis-resistant DBA/1 mice deficient for interleukin-1 receptor antagonist. To further select candidate genes for the QTL, we analyzed the expression patterns of arthritis in 38 F2 individuals and compared the expression levels of key candidate genes to the parental strains. Two distinct subpopulations of arthritic mice were identified in the 38 F2 mice. One subgroup of diseased mice was characterized by myeloid cell dominant inflammation, whereas the other was mainly associated with increased anti-apoptotic activities of inflammatory cells. Several differentially expressed important candidate genes in parental strains in the QTL region are relevant to myeloid cell, apoptotic activities, or to both. About one-quarter of those genes have been previously linked to arthritis in literature. The present study reveals two distinct subpopulations of arthritic mice with spontaneous arthritis due to deficiency for interleukin-1 receptor antagonist, suggesting that genes with function relevant to myeloid cell and/or apoptotic activities are most likely the key candidate genes for the QTL.

Simultaneous quantitative analysis of the expression of CD64 and CD35 on neutrophils as markers to differentiate between bacterial and viral infections in patients with rheumatoid arthritis

OBJECTIVES

The expression level of CD64 on neutrophils can be used to differentiate between an infection and a disease flare in rheumatoid arthritis (RA) patients. However, the CD64 expression is elevated by both bacteria and viruses, so it cannot be used to distinguish the type of infection. We herein investigated the results of a simultaneous quantitative analysis of the expression of CD64 and CD35 on neutrophils to determine whether these molecules can be used to distinguish between bacterial and viral infections in RA patients.

METHODS

We collected blood from 22 RA patients with pathogen-proven infections (15 bacterial and 7 viral infections). Blood samples were stained with QuantiBRITE CD64PE/CD45PerCP and CD35PE, and the mean fluorescence intensities were assessed by a flow cytometer. The mean numbers of molecules were calculated using QuantiBrite PE beads.

RESULTS

We calculated the ratio of CD64 to the CD35 level (CD35/CD64), and used a cut-off value of 2.8 for the CD35/CD64 ratio. At this value, the sensitivity for diagnosing a bacterial infection was 87%, and the specificity was 86%.

CONCLUSIONS

Simultaneous quantitative analysis of CD64 and CD35 expression on neutrophils might be useful to distinguish between bacterial and viral infections in RA patients.

Diagnostic accuracy of HMGB-1, sTREM-1, and CD64 as markers of sepsis in patients recently admitted to the emergency department

OBJECTIVES

The objectives were to evaluate the diagnostic accuracy for sepsis in an emergency department (ED) population of the cluster of differentiation-64 (CD64) glycoprotein expression on the surface of neutrophils (nCD64), serum levels of soluble triggering receptor expressed on myeloid cells-1 (s-TREM-1), and high-mobility group box-1 protein (HMGB-1).

METHODS

Patients with any of the following as admission diagnosis were enrolled: 1) suspected infection, 2) fever, 3) delirium, or 4) acute hypotension of unexplained origin within 24 hours of ED presentation. Levels of nCD64, HMGB-1, and s-TREM-1 were measured within the first 24 hours of the first ED evaluation. Baseline clinical data, Sepsis-related Organ Failure Assessment (SOFA) score, Acute Physiology and Chronic Health Evaluation (APACHE II) score, daily clinical and microbiologic information, and 28-day mortality rate were collected. Because there is not a definitive criterion standard for sepsis, the authors used expert consensus based on clinical, microbiologic, laboratory, and radiologic data collected for each patient during the first 7 days of hospitalization. This expert consensus defined the primary outcome of sepsis, and the primary data analysis was based in the comparison of sepsis versus nonsepsis patients. The cut points to define sensitivity and specificity values, as well as positive and negative likelihood ratios (LRs) for the markers related to sepsis diagnosis, were determined using receiver operative characteristics (ROC) curves. The patients in this study were a prespecified nested subsample population of a larger study.

RESULTS

Of 631 patients included in the study, 66% (95% confidence interval [CI] = 62% to 67%, n = 416) had sepsis according with the expert consensus diagnosis. Among these sepsis patients, SOFA score defined 67% (95% CI = 62% to 71%, n = 277) in severe sepsis and 1% (95% CI = 0.3% to 3%, n = 6) in septic shock. The sensitivities for sepsis diagnosis were CD64, 65.8% (95% CI = 61.1% to 70.3%); HMGB-1, 57.5% (95% CI = 52.7% to 62.3%); and s-TREM-1, 60% (95% CI = 55.2% to 64.7%). The specificities were CD64, 64.6% (95% CI = 57.8% to 70.8%), HMGB-1, 57.8% (95% CI = 51.1% to 64.3%), and s-TREM-1, 59.2% (95% CI = 52.5% to 65.6%). The positive LR (LR+) for CD64 was 1.85 (95% CI = 1.52 to 2.26) and the negative LR (LR-) was 0.52 (95% CI = 0.44 to 0.62]; for HMGB-1 the LR+ was 1.36 (95% CI = 1.14 to 1.63) and LR- was 0.73 (95% CI = 0.62 to 0.86); and for s-TREM-1 the LR+ was 1.47 (95% CI = 1.22 to 1.76) and the LR- was 0.67 (95% CI = 0.57 to 0.79).

CONCLUSIONS

In this cohort of patients suspected of having any infection in the ED, the accuracy of nCD64, s-TREM-1, and HMGB-1 was not significantly sensitive or specific for diagnosis of sepsis.

The usefulness of neutrophil CD64 expression in the diagnosis of local infection in patients with rheumatoid arthritis in daily practice

BACKGROUND

The diagnosis of local infection in patients with rheumatoid arthritis (RA) is frequently difficult because clinical signs and symptoms and laboratory test results of local infection are also observed in arthritis of active RA. The need for a specific marker of infection is high in RA patients. The usefulness of neutrophil CD64 expression (CD64) to diagnose local musculoskeletal infection (local infection) and discriminate local infection from RA-related inflammation in RA patients was examined.

METHODS

CD64 was measured by a quantitative method using flow cytometry in 61 RA patients in whom local infection was suspected, and the usefulness of CD64 was examined by comparing the findings with clinical results.

RESULTS

There were 25 patients with local infection and 36 patients without infection. The median CD64 value the patients with local infection was 3148 molecules/cell (interquartile range [IQR], 2140-6231) and that of the patients without infection was 1106 molecules/cell (IQR, 804-1464) with a statistically significant difference (P < 0.0001). In contrast, no significant difference between the groups was observed in C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and white blood cell (WBC) count. The area under the curve of CD64 calculated by receiver operating characteristic curve analysis was larger than that of CRP, ESR, or WBC count, suggesting that CD64 has superior ability to discriminate of infection compared to these other markers. When the cutoff value of CD64 was set at 2000 molecules/cell, the sensitivity and specificity of CD64 for the detection of local infection in RA patients were 76.0% and 94.4%, respectively.

CONCLUSIONS

CD64 is a useful marker in RA patients to discriminate local infection from RA-related inflammation.

Neutrophil CD64 expression as a diagnostic marker for local infection and crystal-induced arthritis

The usefulness of neutrophil CD64 expression was examined in diagnosing local infection, including soft tissue, bone, and joint infections. Among 99 patients suspected of local infection, 31 were confirmed and 68 patients were not. The CD64 level of patients with local infection was significantly higher than in those without infection [4,193 ± 1,132 vs. 1,017 ± 59 molecules/cell (mean ± standard deviation); p < 0.001]. The area under the curve of CD64 calculated by receiver operating characteristic curve analysis was larger than that of C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), or white blood cell (WBC) count. In addition, CD64 levels of patients with crystal-induced arthritis remained within cutoff value (2,000 molecules/cell). These data suggest that measuring CD64 expression can be a useful diagnostic marker for local musculoskeletal infection and crystal-induced arthritis.

Neutrophil function in inflammation and inflammatory diseases

In inflammatory conditions such as RA, the neutrophil has tended to be dismissed as a short-lived, terminally differentiated, irrelevant bystander cell. However, this is clearly not the case. A better understanding of the complex heterogeneous pathways and processes that constitute RA, in parallel with a more sophisticated knowledge of neutrophil biology has identified many potential roles for these cells in the persistence of inflammation and progression of joint damage, which should not be underestimated. Not only are neutrophils found in high numbers within the rheumatoid joint, both in synovial tissue and in joint fluid, they have a huge potential to directly inflict damage to tissue, bone and cartilage via the secretion of proteases and toxic oxygen metabolites, as well as driving inflammation through antigen presentation and secretion of cytokines, chemokines, prostaglandins and leucotrienes. Drugs already used to treat RA down-regulate many neutrophil functions, including migration to the joint, degranulation and production of inflammatory mediators, and these cells should be considered as important targets for the development of new therapies in the future.

Simultaneous quantitative analysis of FcgammaRI (CD64) expression on neutrophils and monocytes: a new, improved way to detect infections

We performed simultaneous quantitative flow cytometric analysis of neutrophil and monocyte FcgammaRI (CD64) in 289 hospitalized febrile patients. Microbiological evaluation or clinical diagnosis confirmed bacterial (n=89) or viral (n=46) infection in 135 patients. Patient data were compared with data from 60 healthy controls. The average number of FcgammaRI on the surfaces of both neutrophils and monocytes was significantly increased in patients with febrile viral and bacterial infections, compared to healthy controls. Furthermore, we describe a novel marker of febrile infection, designated 'CD64 score point', which incorporates the quantitative analysis of FcgammaRI expressed on both neutrophils and monocytes, with 94% sensitivity and 98% specificity in distinguishing between febrile infections and healthy controls. By contrast, analysis of FcgammaRI expression on neutrophils and monocytes displayed poor sensitivity (73% and 52%) and specificity (65% and 52%) in distinguishing between bacterial and viral infections, and the levels did not differ significantly between systemic (sepsis), local, and clinically diagnosed bacterial infections. In summary, our results clearly show that the increased number of FcgammaRI on neutrophils and monocytes is a useful marker of febrile infection, but cannot be applied for differential diagnosis between bacterial and viral infections or between systemic and local bacterial infections.

Major histocompatibility complex class II (DR) antigen and costimulatory molecules on in vitro and in vivo activated human polymorphonuclear neutrophils

We have previously shown that normal human peripheral blood polymorphonuclear neutrophils (PMNs) contain cytoplasmic 'stores' of three key molecules normally associated with antigen presentation and T-cell costimulation, i.e. major histocompatibility complex class II (DR) antigen, CD80 (B7-1) and CD86 (B7-2). These cytoplasmic molecules were found to translocate to the cell surface within a few minutes following cross-linking (X-L) of Mac-1: an early neutrophil activation signal. In this study we have compared X-L of Mac -1 in parallel with four other well documented in vitro neutrophil activators: phorbol myristate acetate, N-formyl methionyl leucyl phenylalanine, lipopolysaccharide, and phagocytosis of immunoglobulin G-Latex particles. In addition, we have used paired samples of neutrophils obtained from peripheral blood (as a control) and synovial fluid from patients with rheumatoid arthritis as a source of in vivo activated cells. With the exception of phagocytosis, all activators resulted in the rapid (within 30 min) generation of two populations of activated neutrophils (designated P1 and P2) based on flow-cytometry measurements of size, granularity and phenotype. Significant up-regulation of DR and costimulatory molecules was observed, predominantly on P2 cells, with all activators except phagocytosis. CD80 and CD86 were noted to respond to the various activation signals in a different pattern suggesting that their intracellular granule location may be different. Dual-staining confocal laser microscopy studies showed that CD80 is largely confined to secretory vesicles (SVs) while CD86 appears to have a much wider distribution being found in SVs and within secondary (specific) and primary (azurophilic) granules. Increased surface expression of these antigens was also observed on P2 synovial fluid neutrophils appearing as large heterogeneous clusters on the cell surface when visualized by confocal laser microscopy.

Neutrophil gene expression in rheumatoid arthritis

There is now a growing awareness that infiltrating neutrophils play an important role in the molecular pathology of rheumatoid arthritis. In part, this arises from the fact that neutrophils have potent cytotoxic activity, but additionally from the fact that inflammatory neutrophils can generate a number of cytokines and chemokines that can have a direct influence on the progress of an inflammatory episode. Furthermore, the molecular properties of inflammatory neutrophils are quite different from those normally found in the circulation. For example, inflammatory neutrophils, but not blood neutrophils, can express cell surface receptors (such as MHC Class II molecules and FcgammaRI) that dramatically alter the way in which these cells can interact with ligands to modulate immune function. Cytokine/chemokine expression and surface expression of these novel cell surface receptors is dependent upon the neutrophil responding to local environmental factors to selectively up-regulate the expression of key cellular components via signalling pathways coupled to transcriptional activation. However, major changes in the expression levels of some proteins are also regulated by post-translational modifications that alter rates of proteolysis, and hence changes in the steady-state levels of these molecules.

Improved diagnostic approaches to infection/sepsis detection

Sepsis is a major healthcare problem from the perspective of mortality and economics. Advances in diagnostic detection of infection and sepsis have been slow, but recent advances in both soluble biomarker detection and quantitative cellular measurements promise the availability of improved diagnostic techniques. Though the promise of cytokine measurements reaching clinical practice have not matured, procalcitonin levels are currently available in many countries and appear to offer enhanced diagnostic distinction between bacterial and viral etiologies. Cellular diagnostics is poised to enter clinical laboratory practice in the form of neutrophil CD64 measurements, which offer superior sensitivity and specificity to conventional laboratory assessment of sepsis. Neutrophil CD64 expression is negligible in the healthy state. However, it increases as part of the systemic response to severe infection or sepsis. The combination of cellular proteomics, as in the case of neutrophil CD64 quantification, and selected soluble biomarkers of the inflammatory response, such as procalcitonin or triggering receptor expressed on myeloid cells (TREM)-1, is predicted to remove the current subjectivity and uncertainty in the diagnosis and therapeutic monitoring of infection and sepsis.

Joint inflammation and chondrocyte death become independent of Fcγ receptor type III by local overexpression of interferon-γ during immune complex-mediated arthritis

OBJECTIVE

It has previously been shown that the onset and the degree of joint inflammation during immune complex (IC)-mediated arthritis depend on Fcgamma receptor type III (FcgammaRIII). Local adenoviral overexpression of interferon-gamma (IFNgamma) in the knee joint prior to onset of IC-mediated arthritis aggravated severe cartilage destruction. In FcgammaRI(-/-) mice, however, chondrocyte death was not enhanced by IFNgamma, whereas matrix metalloproteinase (MMP)-mediated aggrecan breakdown was markedly elevated, suggesting a role for the activating FcgammaRIII in the latter process. We undertook this study to determine the role of FcgammaRIII in joint inflammation and severe cartilage destruction in IFNgamma-stimulated IC-mediated arthritis, using FcgammaRIII(-/-) mice.

METHODS

FcgammaRIII(-/-) and wild-type (WT) mice were injected in the knee joint with recombinant adenovirus encoding murine IFNgamma (AdIFNgamma) or with adenovirus encoding enhanced green fluorescent protein 1 day prior to induction of IC-mediated arthritis. Histologic sections were obtained 3 days after arthritis onset to study inflammation and cartilage damage. MMP-mediated expression of the VDIPEN neoepitope was detected by immunolocalization. Chemokine and FcgammaR expression levels were determined in synovial washouts and synovium, respectively.

RESULTS

Injection of AdIFNgamma in naive knee joints markedly increased levels of messenger RNA for FcgammaRI, FcgammaRII, and FcgammaRIII. Upon IFNgamma overexpression prior to induction of IC-mediated arthritis, joint inflammation was similar in FcgammaRIII(-/-) and WT mice. The percentage of macrophages in the knee joint was increased, which correlated with high concentrations of the macrophage attractant macrophage inflammatory protein 1alpha. Furthermore, IFNgamma induced 2-fold and 3-fold increases in chondrocyte death in WT controls and FcgammaRIII(-/-) mice, respectively. Notably, VDIPEN expression also remained high in FcgammaRIII(-/-) mice.

CONCLUSION

IFNgamma bypasses the dependence on FcgammaRIII in the development of IC-mediated arthritis. Furthermore, both FcgammaRI and FcgammaRIII can mediate MMP-dependent cartilage matrix destruction.

Circulating immune complexes as indicators of environmental contamination

The aim of this study was to examine the effect of environmental contamination on the concentration of circulating immune complexes (CIC) in bovine blood. We determined that in a conventionally ecologically clear district, the CIC concentration in healthy bovine blood serum was within the limits of 0.18-0.52 mg/mL, (mean = 0.31 mg/mL, V = 30.14%). In a conventionally ecologically contaminated district, the CIC concentration in healthy bovine blood serum was detected within the limits of 0.48-0.99 mg/mL (mean = 0.65 mg/mL, V = 17.97%; P < 0.05). The CIC concentration in serum of bovine leukemia virus (BLV)-infected bovines from different districts was within the limits of 0.29-1.76 mg/mL (mean = 0.81 mg/mL, V = 36.67%; P < 0.05). According to these preliminary results of the investigation, it may be supposed that the increased concentration of CIC is closely related to the environmental contamination. Therefore, studies of CIC concentration in healthy mammals are of great importance for the monitoring of anthropogenic factors and can be exploited as an indicator of environmental contamination.

Up-regulated expression and activation of the orphan chemokine receptor, CCRL2, in rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a chronic inflammatory condition characterized by a cellular influx and destruction of the joint architecture. Chemokines characteristically regulate leukocyte recruitment and activation. Chemokine (CC motif) receptor-like 2 (CCRL2) is an orphan receptor with homology to other CC chemokine receptors. We undertook this study to examine CCRL2 expression in RA, cytokine regulation of expression, and the source of a putative ligand in an attempt to determine the role of this receptor during inflammation.

METHODS

Expression of CCRL2 on joint-infiltrating leukocytes was examined by immunocytochemistry. In vitro studies evaluated CCRL2 expression in primary neutrophils using Northern and Western blotting and reverse transcriptase-polymerase chain reaction. HEK 293 cells expressing two splice variants of CCRL2 (HEK/CCRL2A or HEK/CCRL2B) were generated with a retroviral expression system, and their migration in response to fractions of synovial fluid (SF) from RA patients was examined using a 48-well chamber.

RESULTS

CCRL2 expression was observed on all infiltrating neutrophils and on some macrophages obtained from the SF of 5 RA patients. In vitro studies of primary neutrophils revealed that CCRL2 messenger RNA (mRNA) was rapidly up-regulated following stimulation with lipopolysaccharide (1 microg/ml) or tumor necrosis factor (5 ng/ml). The mRNA for both CCRL2A and CCRL2B were expressed in cytokine-stimulated neutrophils. Cells expressing either of these splice variants migrated in response to a fraction of RA SF.

CONCLUSION

CCRL2 expression is up-regulated on synovial neutrophils of RA patients. Inflammatory products present in the SF activate this receptor, indicating that CCRL2 is a functional receptor that may be involved in the pathogenesis of RA.

Synovial fluid neutrophils transcribe and express class II major histocompatibility complex molecules in rheumatoid arthritis

OBJECTIVE

To investigate a potential interaction between neutrophils and T cells in rheumatoid arthritis (RA), by defining the optimal conditions for induction of class II major histocompatibility complex (MHC) expression on peripheral blood neutrophils in vitro and investigating the capacity for neutrophils to express class II MHC molecules in RA.

METHODS

Surface expression of class II MHC and costimulatory molecules by peripheral blood and synovial fluid (SF) neutrophils obtained from healthy controls and patients with RA was measured by flow cytometry and fluorescence microscopy. Intracellular class II MHC protein and messenger RNA (mRNA) were detected by Western blotting and Northern blotting, respectively.

RESULTS

Freshly isolated peripheral blood neutrophils from controls did not express surface class II MHC; expression was induced by culture with appropriate cytokines. Freshly isolated peripheral blood neutrophils from patients with RA expressed mRNA, but there was no surface expression of class II MHC. Freshly isolated SF neutrophils from patients with RA contained high levels of class II MHC mRNA, did not express surface class II MHC, but did have large intracellular amounts of this protein as detected by Western blotting. After culture for 20 hours in vitro, SF neutrophils from RA patients expressed large amounts of surface class II MHC but very low levels of costimulatory molecules CD80 and CD86. Fluorescence microscopy localized surface class II MHC to discrete areas on the neutrophil. Class II MHC-expressing neutrophils stimulated T cell proliferation.

CONCLUSION

Peripheral blood neutrophils from patients with RA but not healthy controls express class II MHC mRNA. SF neutrophils in RA synthesize and express large amounts of class II MHC but not costimulatory molecules. This might underlie a novel interaction with T cells that is important in terms of disease pathology.

Selective elimination of synovial inflammatory macrophages in rheumatoid arthritis by an Fcgamma receptor I-directed immunotoxin

OBJECTIVE

To determine whether monocyte/macrophages from rheumatoid arthritis (RA) patients can be selectively eliminated by a toxin-conjugated antibody CD64-ricin A (CD64-RiA) directed toward the high-affinity receptor for IgG (FcgammaRI), exploiting the capacity of FcgammaRI to efficiently endocytose antibody which it has bound.

METHODS

Mononuclear cells from peripheral blood (PB) and synovial fluid (SF) obtained from RA patients were cultured in the presence of CD64-RiA. Cell death of monocyte/macrophages was measured by phenotypic changes (light-scatter patterns and CD14 and FcgammaRI expression) and apoptosis (nuclear DNA fragmentation). We then tested whether CD64-RiA-induced cell death of macrophages affected their capacity to stimulate antigen-induced lymphocyte proliferation and to secrete cytokines. Additionally, the capacity of CD64-RiA to inhibit proinflammatory activity and cartilage degradation by RA synovial tissue explants was evaluated.

RESULTS

Inflammatory macrophages from RA SF expressed elevated levels of FcgammaRI and were selectively eliminated by CD64-RiA via apoptotic cell death. Monocyte/macrophages from RA PB, which had lower levels of FcgammaRI expression, were much less affected. Induction of SF macrophage apoptosis was associated with efficient inhibition of antigen-induced lymphocyte proliferation and a reduction in tumor necrosis factor alpha (TNFalpha) release. Consistent with these effects on SF macrophages, CD64-RiA also inhibited TNFalpha production, interleukin-1beta production, and cartilage-degrading activity of RA synovial tissue explants.

CONCLUSION

Together, these data underscore the crucial role of synovial macrophages in RA joint inflammation and indicate that selective elimination of these cells through FcgammaRI-directed immunotoxins could be a novel approach to the treatment of RA.

Neutrophil CD64 expression: distinguishing acute inflammatory autoimmune disease from systemic infections

BACKGROUND

Common bacterial and opportunistic infections are a major cause of mortality in patients who are immunosuppressed owing to treatment with corticosteroids or cytotoxic drugs. Common laboratory tests for infection lack sensitivity and specificity. One of the new generation of tests to detect early systemic infections measures the up regulation of an Fc receptor (Fcgamma R1, or CD64) on neutrophils. The Fc receptors on white blood cells are very important for effective phagocytosis of bacteria and are up regulated during an infection.

OBJECTIVE

To measure the clinical usefulness of quantitative CD64 measurements to differentiate between systemic infection and active autoimmune inflammation in an ongoing study.

METHODS

Patients with systemic infection (n=27), active autoimmune inflammatory disease (n=44), vasculitis (n=5), and controls (n=20) were studied for neutrophil CD64 expression using monoclonal antibodies and flow cytometry.

RESULTS

The median (interquartile range (IQR)) CD64 expression in patients with active inflammatory disease and systemic infection was 907.5 (586-1550) and 3647 (2380-6642), respectively (p<0.0001). The median (IQR) CD64 expression in control patients (osteoarthritis and fibromyalgia) was 505 (359-599). The sensitivity and specificity of CD64 expression on neutrophils to diagnose systemic infection (using a cut off value of 2000) was 85% and 91%, respectively.

CONCLUSION

These results indicate that quantitative measurement of CD64 can distinguish between systemic infection and the flare of autoimmune diseases.