Human monocytes express CD163, which is upregulated by IL-10 and identical to p155

Characterization of restrictions to human immunodeficiency virus type 1 infection of monocytes

Tissue macrophages are an important cellular reservoir for replication of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus. In vitro, the ability of macrophages to support viral replication is differentiation dependent in that precursor monocytes are refractory to infection. There is, however, no consensus as to the exact point at which infection is restricted in monocytes. We have revisited this issue and have compared the efficiencies of early HIV-1 replication events in monocytes and in differentiated macrophages. Although virus entry in monocytes was comparable to that in differentiated macrophages, synthesis of full-length viral cDNAs was very inefficient. Relative to differentiated macrophages, monocytes contained low levels of dTTP due to low thymidine phosphorylase activity. Exogenous addition of D-thymidine increased dTTP levels to that in differentiated macrophages but did not correct the reverse transcription defect. These results point to a restriction in monocytes that is independent of reverse transcription precursors and suggest that differentiation-dependent cellular cofactors of reverse transcription are rate limiting in monocytes.

TGF-beta regulation of human macrophage scavenger receptor CD163 is Smad3-dependent

Tight regulation of the inflammatory response is essential for the maintenance of physiologic homeostasis. A potentially important mediator of this process is CD163, a macrophage-specific member of the scavenger receptor cysteine-rich family. CD163 surface expression is up-regulated by glucocorticoids and the anti-inflammatory cytokine interleukin-10, and CD163 is shed acutely from the cell surface in response to lipopolysaccharide. We now demonstrate that transforming growth factor-beta (TGF-beta) markedly reduces expression of CD163. Treatment of primary human monocytes with TGF-beta inhibited basal as well as dexamethasone-induced CD163 mRNA and protein expression. De novo protein synthesis was not required for this inhibition, suggesting that TGF-beta regulates CD163 expression transcriptionally. To delineate this transcriptional regulation, a 2.5-kb fragment of the CD163 promoter was isolated. This promoter was inhibited by TGF-beta, and suppression was dependent on Smad3 expression. These results define a novel function for TGF-beta and implicate an important role for CD163 in the host response to inflammation.

Cross-linking of FcγR triggers shedding of the hemoglobin-haptoglobin scavenger receptor CD163

CD163, the hemoglobin (Hb)-haptoglobin scavenger receptor, is a monocyte/macrophage-restricted member of the scavenger receptor, cysteine-rich family of proteins. In addition to being expressed on the cell surface, a soluble form of CD163 has also been reported. Like tumor necrosis factor alpha (TNF-alpha), surface CD163 is proteolytically cleaved from the plasma membrane in response to lipopolysaccharide (LPS) stimulation. As cross-linking of the Fcgamma receptor (FcgammaR) is similarly known to induce TNF-alpha shedding, the effect of FcgammaR stimulation on CD163 shedding was investigated. We found that FcgammaR stimulation resulted in a rapid release of surface CD163 into the supernatant that was blocked by inhibitors of protein kinase C and tyrosine kinases. Although LPS and FcgammaR stimulation in short-term cultures suppressed CD163 mRNA expression, long-term cultures of monocytes treated with LPS-but not with a FcgammaR cross-linking reagent-resulted in an interleukin-10-dependent recovery of surface CD163 expression. These studies suggest that the presence of immune complexes in infection or autoimmunity may radically alter the nature of CD163-dependent monocyte/macrophage processes. This may be particularly important in disease states in which immune complexes and high levels of free Hb are present, such as in autoimmune hemolytic anemia, transfusion reactions, or infections by hemolytic bacteria.

Plasma level of the macrophage-derived soluble CD163 is increased and positively correlates with severity in Gaucher's disease

Recently, soluble CD163 (sCD163) has been identified as a macrophage/monocyte-specific plasma protein and increased concentrations have been measured in patients with infection and myeloid leukaemia. In the present study we investigated the levels of sCD163 in patients with Gaucher's disease, an inherited lysosomal storage disorder characterised by hepato- and splenomegaly due to excessive accumulation of macrophages. The sCD163 plasma levels, median (25-75 percentiles), were far above the levels in normal subjects [7.1 mg/L (4.8-10.3) vs. 1.9 mg/L (1.5-2.4), P < 0.0001]. After initiation of enzyme supplementation therapy, the sCD163 levels were significantly reduced [4.7 mg/L (3.2-6.6), P = 0.0004]. sCD163 correlated with disease severity (rho = 0.43, P < 0.0061) and chitotriosidase activity (rho = 0.71, P > 0.0001). This study further establishes that sCD163 may be a valuable laboratory parameter in monitoring disease with increased macrophage activity.

Mycobacteria and other environmental organisms as immunomodulators for immunoregulatory disorders

In the rich, developed parts of the world there has been a steady and simultaneous increase in at least three groups of disease: (1) allergies, (2) inflammatory bowel diseases (IBD; e.g. Crohn's disease and ulcerative colitis) and (3) autoimmunity (e.g. type 1 diabetes and multiple sclerosis). Because the medical world is so compartmentalised it was some time before the connection between these increases was noticed and understood. There is now evidence that the simultaneous increase in these diseases of immunodysregulation is at least partly attributable to malfunction of regulatory T cells (Treg). This paper provides an overview of relevant work in each of these fields of medicine (though with emphasis on the allergic disorders), and concludes that the increasing failure of Treg is a consequence of diminished exposure to certain micro-organisms that are "old friends", because of their continuous presence throughout mammalian evolution. These organisms, which include saprophytic mycobacteria, helminths and lactobacilli, are recognised by the innate immune system as harmless, and as adjuvants for Treg induction. Polymorphisms of components of the innate immune system such as TLR2 and NOD2 appear to define subsets of the population that will develop immunoregulatory disorders when living in the modern environment. A further role of the "old friends" and of the Treg that they induce might be to maintain the levels of regulatory IL-10 secreting macrophages and antigen-presenting cells, which are depleted in asthma and Crohn's disease. These concepts are leading to novel therapies based on harmless organisms or their components. Phase I/II clinical trials have yielded some statistically significant results, and phase II trials are in progress.

Hemoglobin Scavenger Receptor CD163 Mediates Interleukin-10 Release and Heme Oxygenase-1 Synthesis

The recently described hemoglobin scavenger receptor CD163 mediates the endocytosis of hemoglobin:haptoglobin (Hb:Hp) complexes and thereby counters Hb-induced oxidative tissue damage after hemolysis. Although CD163 has been indirectly associated with antiinflammatory and atheroprotective activity, no ligand-receptor-effector pathway has yet been described for this receptor. To understand the significance of CD163 and more clearly define downstream pathways linked to inflammatory resolution, we studied the expression and function of CD163 in human monocytes/macrophages using both in vitro and in vivo models. Differentiation of human blood monocytes into macrophages either by in vitro culture or in resolving cantharidin-induced skin blisters led to an equivalent increase (>15x) in CD163 expression. Elevated CD163 levels were also noted on circulating monocytes in cardiac surgical patients during the resolution phase of the systemic inflammatory response to cardiopulmonary bypass surgery. In each case, binding of Hb:Hp to CD163-bearing cells elicited potent interleukin-10 secretion, and this was inhibited by the anti-CD163 antibody RM3/1. Release of interleukin-10, in turn, induced heme oxygenase-1 stress protein synthesis via an autocrine mechanism. Such induction of heme oxygenase-1 was observed in vivo 24 to 48 hours after the onset of cardiopulmonary bypass surgery. These results identify novel antiinflammatory and cytoprotective effector pathways in human monocytes/macrophages related to Hb scavenging and metabolism, which may have relevance in atheroprotection, wound healing, and patient recovery postoperatively.

Increase in plasma and surface CD163 levels in patients undergoing coronary artery bypass graft surgery

Although haptoglobin polymorphism has been shown to be a genetic risk factor in coronary artery disease, its mechanisms of action are incompletely defined. Recently, a macrophage scavenger receptor for the uptake of haptoglobin-hemoglobin (Hp-Hb) complexes was cloned and designated CD163. Macrophage expression of CD163 is increased by glucocorticoids, IL-10 and IL-6. To better understand the in vivo response of CD163 to an inflammatory stimulus and glucocorticoid treatment, we studied 18 patients who underwent elective coronary artery bypass graft (CABG) surgery with cardiopulmonary bypass (CPB). We report a rapid increase in plasma levels of soluble CD163 by 1 h post-declamping the aorta during CABG surgery with CPB. Furthermore, we demonstrate significant increases in monocyte CD163 on post-operative day 1; 14-fold for patients pre-treated with methylprednisolone and 3-fold for those who did not receive exogenous glucocorticoids. These findings show CD163 to be rapidly mobilized in response to systemic inflammatory stimuli and to be affected significantly by glucocorticoids in vivo. The proposed role of CD163 as a Hp-Hb scavenger and anti-inflammatory molecule, in conjunction with the results of this study, make CD163 an intriguing target for potential manipulation of the acute response to inflammation.

Glucocorticoid receptor nitration leads to enhanced anti-inflammatory effects of novel steroid ligands

It has recently emerged that posttranslational modification of proteins via nitration of tyrosine residues can alter their function. In this study, we describe that specific nitration of the glucocorticoid receptor (GR) by NCX-1015, a novel NO-donating prednisolone derivative (prednisolone 21-[4'-(nitrooxymethyl)benzoate), results in an enhancement of GR-mediated events. Incubation of PBMC and U937 cells with 1-10 micro M NCX-1015 caused faster activation of GR as assessed by augmented 1) binding to [(3)H]dexamethasone, 2) dissociation from heat shock protein 90, and 3) nuclear translocation. PBMCs treated with NCX-1015 contained GR that had undergone tyrosine nitration. The chemistry facilitating the increase in steroid binding capacity observed with NCX-1015 is specific, because changing the position of the NO-donating group or ubiquitous nitration by addition of an NO donor was unable to mimic this event. In vivo treatment with NCX-1015 provoked GR nitration and faster heat shock protein 90 dissociation as assessed in peritoneal cells. Accordingly, NCX-1015, but not prednisolone or other derivatives, produced a rapid inhibition of the early neutrophil recruitment and mediator generation in a model of peritonitis. In conclusion, we report here for the first time that posttranslational modification of GR by this novel nitrosteroid is associated with its enhanced anti-inflammatory activity.

Elevated levels of soluble CD163 in sera and fluids from rheumatoid arthritis patients and inhibition of the shedding of CD163 by TIMP-3

The aim of the present study was to evaluate levels of soluble CD 163 in sera and fluids from rheumatoid arthritis (RA) patients and elucidate the mechanism that regulates the shedding of CD163. Levels of soluble CD163 in sera and fluids from RA patients were examined by a sandwich enzyme immunoassay and Western blotting. To determine the effects of tissue inhibitors of metalloproteinase (TIMPs) on the shedding of CD163 from monocytes/macrophages, levels of soluble CD163 in cultures of monocytes/macrophages and the expression of CD163 on monocytes/macrophages in the presence or absence of TIMPs were examined by a sandwich enzyme immunoassay and flow cytometry, respectively. The clinical marker that was most associated with serum levels of soluble CD163 was levels of CRP. TIMP-3, but not TIMP-1 or TIMP-2, inhibited the shedding of CD163 from monocytes/macrophages. It was shown that serum levels of soluble CD163 are a sensitive and reliable marker to monitor activated macrophages in synovitis from RA patients and the results imply that the responsible proteinase for the shedding of CD163 is not a member of the matrix metalloproteinases, but is likely to be a member of ADAMs.

Only the soluble form of the scavenger receptor CD163 acts inhibitory on phorbol ester-activated T-lymphocytes, whereas membrane-bound protein has no effect

The extracellular moiety of the hemoglobin/haptoglobin scavenger receptor CD163 (RM3/1 antigen) can be shed from monocytes and is a normal plasma component. We found that in a dose-dependent manner soluble CD163 induces a decrease in CD69 expression, a reduced [(3)H]thymidine uptake and a down-regulated matrix metalloproteinase-9 RNA expression in phorbol myristate acetate-stimulated T-cells. Co-culturing T-cells on transgenic fibroblasts, expressing membrane-bound CD163, yielded no differences compared to culture on non-transfected cells. We conclude that CD163 has at least two distinct functions: the clearance of hemoglobin in its cell-bound form and participation in anti-inflammation as a soluble factor, exhibiting cytokine-like functions.

Macrophages expressing the scavenger receptor CD163: a link between immune alterations of the gut and synovial inflammation in spondyloarthropathy

The objective of this study was to investigate CD163+ macrophages in the synovial membrane of patients with spondyloarthropathy (SpA). Immunohistochemistry was performed on synovium of 17 SpA and 18 rheumatoid arthritis (RA) patients, on colonic biopsies of 16 SpA patients and ten healthy controls, and on paired synovial biopsies of eight SpA patients, before and after anti-TNFalpha therapy. Phenotype and cytokine production were analysed by flow cytometry. CD163+ macrophages were increased in the synovial lining and sublining in SpA versus RA, as well as in colonic lamina propria in SpA versus controls. The number of CD163+ macrophages in the synovial sublining correlated with C-reactive protein levels and erythrocyte sedimentation rate. Paralleling the increase of CD163, HLA-DR was increased in the synovial lining and sublining of SpA. In contrast, the co-stimulatory molecules CD80 and CD86 and the dendritic cell markers CD1a and CD83 were scarce in SpA synovium. Flow cytometry indicated that CD163+ macrophages expressed high levels of HLA-DR and could produce in vitro tumour necrosis factor alpha (TNFalpha) but not interleukin-10 (IL-10). Finally, anti-TNFalpha therapy in vivo induced a decrease of CD163+ macrophages in the synovial lining and sublining. In conclusion, macrophages expressing the scavenger receptor CD163 are increased in synovium and in colonic mucosa in SpA, highlighting the relationship between joint and gut in this disease. The correlation with inflammatory parameters, the expression of HLA-DR, the production of TNFalpha but not IL-10, and the reduction by anti-TNFalpha therapy support a role for CD163+ macrophages in the synovial inflammation in SpA.

Identification of the hemoglobin scavenger receptor/CD163 as a natural soluble protein in plasma

The hemoglobin scavenger receptor (HbSR/CD163) is an interleukin-6- and glucocorticoid-regulated macrophage/monocyte receptor for uptake of haptoglobin-hemoglobin complexes. Moreover, there are strong indications that HbSR serves an anti-inflammatory function. Immunoprecipitation and immunoblotting enabled identification of a soluble plasma form of HbSR (sHbSR) having an electrophoretic mobility equal to that of recombinant HbSR consisting of the extracellular domain (scavenger receptor cysteine-rich 1-9). A sandwich enzyme-linked immunosorbent assay was established and used to measure the sHbSR level in 130 healthy subjects (median, 1.87 mg/L; range, 0.73-4.69 mg/L). To evaluate the sHbSR levels in conditions with increased leukocyte stimulation and proliferation, 140 patients admitted to a hematological department were screened. Several patients, with a broad spectrum of diagnoses, had a level of sHbSR above the range of healthy persons. Patients with myelomonocytic leukemias and pneumonia/sepsis exhibited the highest levels (up to 67.3 mg/L). In conclusion, sHbSR is an abundant plasma protein potentially valuable in monitoring patients with infections and myelomonocytic leukemia.

Immunocytochemical detection of Fcgamma receptors in human atherosclerotic lesions

Much evidence indicates that atherosclerotic lesions are largely of an inflammatory nature. Activated macrophages and macrophage-derived foam cells laden with cholesterol esters are a major constituent of these lesions and can influence lesion formation via several potential mechanisms. One such mechanism is Fcgamma receptor activation and/or Fcgamma receptor-mediated clearance of immune complexes containing cholesterol, such as lipoprotein immune complexes. That this mechanism contributes to lesion formation would be further supported if Fcgamma receptor expression in arterial lesions were demonstrated. We therefore used monoclonal antibodies and immunocytochemical methods to analyze frozen sections of human arterial lesions for expression of each of the three primary classes of mononuclear phagocyte Fcgamma receptors. Approximately 800 sections of aorta, carotid, and coronary arteries obtained from five elderly donors were analyzed. The presence of macrophages was determined by assaying reactivity of a monoclonal antibody specific to CD163, which is expressed only on cells of the human mononuclear phagocyte lineage. Results indicate that highly cellular preatheromatous lesions contained numerous macrophages in the zone of proliferation that expressed each class of Fcgamma receptor (FcgammaRIA, FcgammaRIIA, and FcgammaRIIIA). Fcgamma receptor-positive cells were also present in medial and adventitial areas. Fcgamma receptor staining was both punctate and diffuse, the latter suggesting that soluble receptors were present in the extracellular matrix. These data further support that Fcgamma receptor-mediated clearance of immune complexes can occur in arterial lesions during atherogenesis. Expression of both the high affinity (FcgammaRIA) and lower affinity (FcgammaRIIA/FcgammaRIIIA) receptors indicates that mono- and multivalent IgG-containing immune complexes could engage Fcgamma receptors and influence lesion formation through several different inflammatory mechanisms triggered by receptor activation.

Development of an ELISA to measure soluble CD163 in biological fluids

CD163 is a monocyte/macrophage restricted transmembrane glycoprotein and a member of the scavenger receptor cysteine-rich (SRCR) family of proteins. SRCR proteins are typically associated with the immune system. The regulation of CD163 by cytokines and glucocorticoids suggests that it plays a role in inflammatory processes. While CD163 is expressed as a membrane-bound protein, it has been shown to be actively shed from the surface of monocytes in a protease-dependent fashion when cells are stimulated with a phorbol ester. To better elucidate the function and biological importance of CD163, we have developed a solid-phase sandwich enzyme linked immunosorbant assay (ELISA) for the detection of soluble CD163 in biological fluids. This assay has good repeatability both within and between runs (coefficients of variation (CVs) of 3.2% and 7.1% or better, respectively). While detection of CD163 was inhibited by ethylenediamine tetraacetic acid (EDTA), CD163 immunoreactivity was not altered by the addition of heparin or hemoglobin. This report details the development of this novel assay for soluble CD163 and provides the first evidence of CD163 immunoreactivity in normal plasma and serum samples.