Shedding of CD163, a novel regulatory mechanism for a member of the scavenger receptor cysteine-rich family

The glucocorticoid-inducible transmembrane protein CD163 is a member of the scavenger receptor cysteine-rich (SRCR) family which is expressed exclusively on human monocytes and macrophages. The expression of the protein is significantly downregulated in response to phorbol 12-myristate 13-acetate (PMA) by a yet unknown mechanism. We now demonstrate that PMA induces shedding of a soluble form of CD163 rather than internalization, revealing a novel regulatory mechanism for a member of the SRCR family. Bisindolylmaleimide I was shown to inhibit phorbol ester-induced shedding, thus implying an involvement of protein kinase C (PKC). Furthermore, cleavage could be prevented by protease inhibitors. Therefore, we suggest that PMA-induced activation of PKC leads to protease-mediated shedding of CD163. These results indicate a specific release mechanism of soluble CD163 by human monocytes which could play an important role in modulating inflammatory processes.     

Oxidative stress and 8-iso-prostaglandin F(2alpha) induce ectodomain shedding of CD163 and release of tumor necrosis factor-alpha from human monocytes

CD163 is a membrane glycoprotein of the cysteine-rich scavenger receptor superfamily. Upon an inflammatory stimulus CD163 undergoes ectodomain shedding and the soluble protein has been shown to play a role in downregulation of inflammation. The purpose of the present study was to identify a physiological activator of CD163 shedding that is consistently present under inflammatory conditions. Therefore, we elucidated whether oxidative stress or 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) is involved in shedding of CD163. Oxidative stress induced by H(2)O(2) or a NO donor as well as 8-iso-PGF(2alpha) induced significant shedding of CD163. In contrast, release of CD163 was not stimulated by PGF(2alpha). We identified both calcium and reactive oxygen species as common cellular mediators of CD163 release. Since shedding of both CD163 and tumor necrosis factor-alpha (TNFalpha) is known to be mediated by a TIMP-3-sensitive metalloproteinase we examined whether release of TNFalpha was induced by the same mediators that trigger shedding of CD163. Only oxidative stress generated by H(2)O(2) as well as 8-iso-PGF(2alpha) and PGF(2alpha) enhanced TNFalpha secretion. Thus, we identified novel common and divergent activators of shedding of CD163 and TNFalpha. These inducers of shedding are present in inflammation and might play an important role in membrane protein cleavage.     

Interaction of soluble CD163 with activated T lymphocytes involves its association with non-muscle myosin heavy chain type A

CD163 is a monocyte/macrophage-specific scavenger receptor that undergoes ectodomain shedding upon an inflammatory stimulus. Soluble CD163 (sCD163) actively inhibits lymphocyte proliferation, but to date exactly how it interacts with these cells has remained elusive. We screened T lymphocytes and endothelial cells for proteins binding to sCD163. In both cell types a high affinity binding protein was detected. Partial sequencing of the protein revealed sequence identity to a non-muscle myosin heavy chain type A. Employing labelled sCD163 we found little specific binding of sCD163 to the extracellular domains of T lymphocytes and human umbilical vein endothelial cells (HUVEC). In activated T lymphocytes we demonstrated specific binding of sCD163 to intracellular structures as well as the presence of the native protein within the cell after co-incubation with purified sCD163. Furthermore, we developed a novel ELISA for highly specific detection of sCD163-myosin complexes. These complexes were present in activated T lymphocytes after incubation with shed sCD163. Co-localization of sCD163 and cellular myosin in T lymphocytes was further confirmed by fluorescence microscopy. Our results suggest that sCD163 associates with cellular myosin, thereby possibly modulating the cells' response to an inflammatory stimulus.     

Haemoglobin scavenger receptor: function in relation to disease

Highly efficient systems remove the toxic and proinflammatory haemoglobin from the circulation and local sites of tissue damage. Macrophages are major haemoglobin-clearing cells; CD163 was recently recognized as the specific haemoglobin scavenger receptor (HbSR). It is tightly involved in both physiological as well as pathophysiological processes, such as cytoprotection and inflammation. Haemoglobin functions as a double-edged sword. In moderate quantities and bound to haptoglobin, it forms a ligand for haemoglobin scavenger receptor CD163/HbSR, but when unleashed in large amounts, it can become toxic by mediating oxidative stress and inflammation. CD163/HbSR plays a crucial role in the control of inflammatory processes, probably in part through its effects on both ferritin induction and subsequent induction of antiinflammatory pathways through interleukin-10 and haem oxygenase. Besides the observation that the haemoglobin scavenger receptor provides a promising target for new treatment possibilities, it offers a novel view on the aetiology of diverse physiological as well as pathophysiological processes. In addition, monocyte CD163/HbSR and soluble CD163/HbSR are potential diagnostic tools in a variety of disease states, such as inflammation, atherosclerosis, transplant rejection, and carcinoma.     

CD163 Binding to Haptoglobin-Hemoglobin Complexes Involves a Dual-point Electrostatic Receptor-Ligand Pairing

Formation of the haptoglobin (Hp)-hemoglobin (Hb) complex in human plasma leads to a high affinity recognition by the endocytic macrophage receptor CD163. A fast segregation of Hp-Hb from CD163 occurs at endosomal conditions (pH <6.5). The ligand binding site of CD163 has previously been shown to involve the scavenger receptor cysteine-rich (SRCR) domain 3. This domain and the adjacent SRCR domain 2 of CD163 contain a consensus motif for a calcium-coordinated acidic amino acid triad cluster as originally identified in the SRCR domain of the scavenger receptor MARCO. Here we show that site-directed mutagenesis in each of these acidic triads of SRCR domains 2 and 3 abrogates the high affinity binding of recombinant CD163 to Hp-Hb. In the ligand, Hp Arg-252 and Lys-262, both present in a previously identified CD163 binding loop of Hp, were revealed as essential residues for the high affinity receptor binding. These findings are in accordance with pairing of the calcium-coordinated acidic clusters in SRCR domains 2 and 3 with the two basic Arg/Lys residues in the Hp loop. Such a two-point electrostatic pairing is mechanistically similar to the pH-sensitive pairings disclosed in crystal structures of ligands in complex with tandem LDL receptor repeats or tandem CUB domains in other endocytic receptors.     

A previously unrecognized protein-protein interaction between TWEAK and CD163: potential biological implications

TWEAK (TNF-like weak inducer of apoptosis) is a TNF superfamily member implicated in several mechanisms. Although fibroblast growth factor inducible 14 (Fn14)/TweakR has been reported as its receptor, an as yet unrecognized surface molecule(s) might modulate TWEAK function(s). Thus, we set out to identify TWEAK-binding proteins by screening a combinatorial peptide library. Cyclic peptides containing a consensus motif (WXDDG) bound to TWEAK specifically. These peptides were similar to CD163, a scavenger receptor cysteine-rich domain family member, restricted to the monocyte/macrophage lineage and responsible for the uptake of circulating haptoglobin-hemoglobin (Hp-Hb) complexes. Sequence profile analysis suggested that TWEAK mimicked the CD163 natural ligand (Hp-Hb). Consistently, we show dose-dependent TWEAK binding to CD163 and blockade by an anti-CD163 Ab. In a competition assay, both soluble CD163 and Fn14/TweakR were able to compete off TWEAK binding to coated Fn14/TweakR or CD163, respectively. Flow-cytometry and immunofluorescence assays showed that human monocytes (Fn14/TweakR negative and CD163 positive) bind TWEAK, thus blocking the recognition of CD163 and reducing the activation mediated by a specific mAb in these cells. We demonstrate that monocytes can sequester TWEAK from supernatants, thus preventing tumor cell apoptosis; this effect was reverted by preincubation with the peptide mimicking CD163 or with a mAb anti-CD163, indicating specificity. Finally, we show that recombinant human TWEAK binding to CD163-transfected Chinese hamster ovary cells is inhibited by the presence of either unlabeled TWEAK or the Hp-Hb complex. Together, these data are consistent with the hypothesis that CD163 either acts as a TWEAK scavenger in pathological conditions or serves as an alternate receptor for TWEAK in cells lacking Fn14/TweakR.     

CD163: a signal receptor scavenging haptoglobin-hemoglobin complexes from plasma

CD163 is a highly expressed macrophage membrane protein belonging to the scavenger receptor cysteine rich (SRCR) domain family. The CD163 expression is induced by interleukin-6, interleukin-10 and glucocorticoids. Its function has remained unknown until recently when CD163 was identified as the endocytic receptor binding hemoglobin (Hb) in complex with the plasma protein haptoglobin (Hp). This specific receptor-ligand interaction leading to removal from plasma of the Hp-Hb complex-but not free Hp or Hb-now explains the depletion of circulating Hp in individuals with increased intravascular hemolysis. Besides having a detoxificating effect by removing Hb from plasma, the CD163-mediated endocytosis of the Hp-Hb complex may represent a major pathway for uptake of iron in the tissue macrophages.The novel functional linkage of CD163 and Hp, which both are induced during inflammation, also reveal some interesting perspectives relating to the suggested anti-inflammatory properties of the receptor and the Hp phenotypes.     

α1-Acid Glycoprotein Up-regulates CD163 via TLR4/CD14 Protein Pathway: POSSIBLE PROTECTION AGAINST HEMOLYSIS-INDUCED OXIDATIVE STRESS

CD163, a scavenger receptor that is expressed at high levels in the monocyte-macrophage system, is a critical factor for the efficient extracellular hemoglobin (Hb) clearance during hemolysis. Because of the enormous detrimental effect of liberated Hb on our body by its ability to induce pro-inflammatory signals and tissue damage, an understanding of the molecular mechanisms associated with CD163 expression during the acute phase response is a central issue. We report here that α(1)-acid glycoprotein (AGP), an acute phase protein, the serum concentration of which is elevated under various inflammatory conditions, including hemolysis, up-regulates CD163 expression in both macrophage-like differentiated THP-1 (dTHP-1) cells and peripheral blood mononuclear cells in a time- and concentration-dependent manner. Moreover, the subsequent induction of Hb uptake was also observed in AGP-treated dTHP-1 cells. Among representative acute phase proteins such as AGP, α(1)-antitrypsin, C-reactive protein, and haptoglobin, only AGP increased CD163 expression, suggesting that AGP plays a specific role in the regulation of CD163. Consistently, the physiological concentrations of AGP induced CD163, and the subsequent induction of Hb uptake as well as the reduction of oxidative stress in plasma were observed in phenylhydrazine-induced hemolytic model mice, confirming the in vivo role of AGP. Finally, AGP signaling through the toll-like receptor-4 (TLR4) and CD14, the common innate immune receptor complex that normally recognizes bacterial components, was identified as a crucial stimulus that induces the autocrine regulatory loops of IL-6 and/or IL-10 via NF-κB, p38, and JNK pathways, which leads to an enhancement in CD163 expression. These findings provide possible insights into how AGP exerts anti-inflammatory properties against hemolysis-induced oxidative stress.     

Lesional Accumulation of CD163-Expressing Cells in the Gut of Patients with Inflammatory Bowel Disease

Monocytes/macrophages displaying different markers of activation/differentiation infiltrate the inflamed gut of patients with inflammatory bowel diseases (IBD), but the role that each monocyte/macrophage subpopulation plays in the pathogenesis of IBD is not fully understood. The hemoglobin scavenger receptor CD163, a specific marker of monocytes/macrophages, has been associated with either anti-inflammatory or inflammatory functions of macrophages in several pathologies. In this study we examined the tissue distribution and function of CD163-expressing monocytes/macrophages in IBD. CD163 RNA and protein expression was more pronounced in IBD in comparison to normal controls, with no significant difference between Crohn''s disease and Ulcerative colitis. In IBD, over-expression of CD163 was restricted to areas with active inflammation and not influenced by current therapy. Immunohistochemical analysis confirmed the accumulation of CD163-expressing cells in IBD, mostly around and inside blood vessels, thus suggesting that these cells are partly recruited from the systemic circulation. Indeed, FACS analysis of circulating mononuclear cells showed that the fractions of CD163-positive monocytes were increased in IBD patients as compared to controls. Functionally, interleukin-6 up-regulated CD163 expression in lamina propria mononuclear cells and mucosal explants of normal subjects. In IBD blood and mucosal cell cultures, cross-linking of CD163 with a specific monoclonal anti-CD163 antibody enhanced tumor necrosis factor-α synthesis. These findings indicate that IBD mucosa is abundantly infiltrated with CD163-positive cells, which could contribute to amplify the inflammatory cytokine response.     

CD163-L1 is an endocytic macrophage protein strongly regulated by mediators in the inflammatory response

CD163-L1 belongs to the group B scavenger receptor cysteine-rich family of proteins, where the CD163-L1 gene arose by duplication of the gene encoding the hemoglobin scavenger receptor CD163 in late evolution. The current data demonstrate that CD163-L1 is highly expressed and colocalizes with CD163 on large subsets of macrophages, but in contrast to CD163 the expression is low or absent in monocytes and in alveolar macrophages, glia, and Kupffer cells. The expression of CD163-L1 increases when cultured monocytes are M-CSF stimulated to macrophages, and the expression is further increased by the acute-phase mediator IL-6 and the anti-inflammatory mediator IL-10 but is suppressed by the proinflammatory mediators IL-4, IL-13, TNF-α, and LPS/IFN-γ. Furthermore, we show that CD163-L1 is an endocytic receptor, which internalizes independently of cross-linking through a clathrin-mediated pathway. Two cytoplasmic splice variants of CD163-L1 are differentially expressed and have different subcellular distribution patterns. Despite its many similarities to CD163, CD163-L1 does not possess measurable affinity for CD163 ligands such as the haptoglobin-hemoglobin complex or various bacteria. In conclusion, CD163-L1 exhibits similarity to CD163 in terms of structure and regulated expression in cultured monocytes but shows clear differences compared with the known CD163 ligand preferences and expression pattern in the pool of tissue macrophages. We postulate that CD163-L1 functions as a scavenger receptor for one or several ligands that might have a role in resolution of inflammation.     

Molecular characterization of the haptoglobin.hemoglobin receptor CD163. Ligand binding properties of the scavenger receptor cysteine-rich domain region

CD163 is the macrophage receptor for endocytosis of haptoglobin.hemoglobin complexes. The extracellular region consisting of nine scavenger receptor cysteine rich (SRCR) domains also circulates in plasma as a soluble protein. By ligand binding analysis of a broad spectrum of soluble CD163 truncation variants, the amino-terminal third of the SRCR region was shown to be crucial for the binding of haptoglobin.hemoglobin complexes. By Western blotting of the CD163 variants, a panel of ten monoclonal antibodies was mapped to SRCR domains 1, 3, 4, 6, 7, and 9, respectively. Only the two antibodies binding to SRCR domain 3 exhibited effective inhibition of ligand binding. Furthermore, analysis of purified native CD163 revealed that proteolytic cleavage in SRCR domain 3 inactivates ligand binding. Calcium protects against cleavage in this domain. Analysis of the calcium sensitivity of ligand binding to CD163 demonstrated that optimal ligand binding requires physiological plasma calcium concentrations, and an immediate ligand release occurs at the low calcium concentrations measured in acidifying endosomes. In conclusion, SRCR domain 3 of CD163 is an exposed domain and a critical determinant for the calcium-sensitive coupling of haptoglobin.hemoglobin complexes.     

Evolution of the CD163 family and its relationship to the bovine gamma delta T cell co-receptor WC1

Background  

The scavenger receptor cysteine rich (SRCR) domain is an ancient and conserved protein domain. CD163 and WC1 molecules are classed together as group B SRCR superfamily members, along with Spα, CD5 and CD6, all of which are expressed by immune system cells. There are three known types of CD163 molecules in mammals, CD163A (M130, coded for by CD163), CD163b (M160, coded for by CD163L1) and CD163c-α (CD163L1 or SCART), while their nearest relative, WC1, is encoded by a multigene family so far identified in the artiodactyl species of cattle, sheep, and pigs.     

Structural Basis for Inflammation-driven Shedding of CD163 Ectodomain and Tumor Necrosis Factor-α in Macrophages

The haptoglobin-hemoglobin receptor CD163 and proTNF-α are transmembrane macrophage proteins subjected to cleavage by the inflammation-responsive protease ADAM17. This leads to release of soluble CD163 (sCD163) and bioactive TNF-α. Sequence comparison of the juxtamembrane region identified similar palindromic sequences in human CD163 (¹⁰⁴⁴Arg-Ser-Ser-Arg) and proTNF-α (⁷⁸Arg-Ser-Ser-Ser-Arg). In proTNF-α the Arg-Ser-Ser-Ser-Arg sequence is situated next to the previously established ADAM17 cleavage site. Site-directed mutagenesis revealed that the sequences harbor essential information for efficient cleavage of the two proteins upon ADAM17 stimulation. This was further evidenced by analysis of mouse CD163 that, like CD163 in other non-primates, does not contain the palindromic CD163 sequence in the juxtamembrane region. Mouse CD163 resisted endotoxin- and phorbol ester-induced shedding, and ex vivo analysis of knock-in of the Arg-Ser-Ser-Arg sequence in mouse CD163 revealed a receptor shedding comparable with that of human CD163. In conclusion, we have identified an essential substrate motif for ADAM17-mediated CD163 and proTNF-α cleavage in macrophages. In addition, the present data indicate that CD163, by incorporation of this motif in late evolution, underwent a modification that allows for an instant down-regulation of surface CD163 expression and inhibition of hemoglobin uptake. This regulatory modality seems to have coincided with the evolution of an enhanced hemoglobin-protecting role of the haptoglobin-CD163 system in primates.     

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

CD163 is a glucocorticoid-inducible member of the scavenger receptor cysteine-rich family of proteins. Previous reports have indicated that CD163 is highly expressed on human macrophages, but found on less than 50% of peripheral blood monocytes. We now show that >99% of all CD14 positive monocytes express CD163 and that monocyte derived dendritic cells express low levels of CD163. We also show that IL-10, like glucocorticoids, induces high CD163 expression on cultured human monocytes. Glucocorticoid induced CD163 expression was not inhibited by anti-IL-10 and was additive with IL-10 treatment, suggesting that glucocorticoids increase CD163 expression by an IL-10 independent mechanism. Other anti-inflammatory cytokines (IL-4 and IL-13) did not increase CD163 expression. In addition, we show that p155 (a previously identified monocyte/macrophage marker of unknown function) shares identity with CD163. Western blots and flow cytometric analysis of HEK 293 cells transfected with the cDNA for CD163 were positive when probed with either mAb RM3/1 (which recognizes CD163) or Mac 2-48 (which defines p155).     

Shedding as a mechanism of down-modulation of CD14 on stimulated human monocytes

CD14, expressed on the surface of monocytes as a phospholipid-linked protein, is a receptor for serum LPS binding protein/LPS complex. It was specifically down-modulated after stimulation of monocytes by physiologic activating/differentiating agents such as bacterial LPS and IFN-gamma, by the pharmacologic agents PMA and calcium ionophore A23187, and by anti-CD14 antibodies. The down-modulation was almost totally blocked at 4 degrees C or at pH 4.5 and markedly inhibited by the protease inhibitors diisopropylfluorophosphate and PMSF. A soluble labeled CD14 was isolated from culture supernatant of surface iodinated monocytes after their activation, indicating that CD14 is shed from the cell surface rather than internalized. The size of the soluble CD14 shed from the monocytes in vitro was smaller than that of either the membrane-bound form or a soluble CD14 cleaved from the cell surface by phosphatidyl inositol-specific phospholipase C, but identical to the size of one of the two major soluble CD14 forms normally found in human serum. These data suggest that CD14 shedding induced by monocyte stimulation may play an important role in the regulation of surface CD14 expression.     

Elevated Soluble CD163 Plasma Levels Are Associated with Disease Severity in Patients with Hemorrhagic Fever with Renal Syndrome

Background

Hantaan virus is a major zoonotic pathogen that causesing hemorrhagic fever with renal syndrome (HFRS). Although HFRS pathogenesis has not been entirely elucidated, the importance of host-related immune responses in HFRS pathogenesis has been widely recognized. CD163, a monocyte and macrophage-specific scavenger receptor that plays a vital function in the hosts can reduce inflammation, is shed during activation as soluble CD163 (sCD163). The aim of this study was to investigate the pathological significance of sCD163 in patients with HFRS.

Methods

Blood samples were collected from 81 hospitalized patients in Tangdu Hospital from October 2011 to January 2014 and from 15 healthy controls. The sCD163 plasma levels were measured using a sandwich ELISA, and the relationship between sCD163 and disease severity was analyzed. Furthermore, CD163 expression in 3 monocytes subset was analyzed by flow cytometry.

Results

The results demonstrated that sCD163 plasma levels during the HFRS acute phase were significantly higher in patients than during the convalescent stage and the levels in the healthy controls (P<0.0001). The sCD163 plasma levels in the severe/critical group were higher than those in the mild/moderate group during the acute (P<0.0001). A Spearman correlation analysis indicated that the sCD163 levels were positively correlated with white blood cell, serum creatine, blood urea nitrogen levels, while they were negatively correlated with blood platelet levels in the HFRS patients. The monocyte subsets were significantly altered during the acute stage. Though the CD163 expression levels within the monocyte subsets were increased during the acute stage, the highest CD163 expression level was observed in the CD14++CD16+ monocytes when compared with the other monocyte subsets.

Conclusion

sCD163 may be correlated with disease severity and the disease progression in HFRS patients; however, the underlying mechanisms should be explored further.     

Activation of protein kinase C by phorbol esters in human macrophages reduces the metabolism of modified LDL by down-regulation of scavenger receptor activity

Atherogenesis and inflammation are dependent on macrophage function. Signalling pathways are involved in the modulation of the classical low density lipopotein (LDL)-receptor and scavenger receptors activities, which are both expressed by macrophages. This study has evaluated the role of activation of the protein kinase A and C pathways in human macrophages on the metabolism of lipid carried by native, acetylated and oxidised LDL. We found that [3H]oleate incorporation into cholesteryl ester and triacylglycerol is increased by an analogue of cAMP, but strongly inhibited by treatment with phorbol ester (PMA) (100 nM, 6 h) in the presence of acLDL and oxLDL and, to a lesser extent, nLDL. The mechanisms underlying the effects of the phorbol ester were investigated further. The protein kinase C inhibitors, calphostin C and herbimycin A, prevented the PMA-mediated inhibition of cholesterol esterification. PMA also reduced [14C]acetate incorporation into newly synthesised lipids especially in the presence of nLDL, and reduced the uptake of cholesterol carried by modified LDL. Furthermore, the effects of PMA were not modified by inhibition of proteases activities, ruling out the hypothesis that CD163, a scavenger receptor which is shed by the cell surface in the presence of phorbol, is involved in the phorbol-induced reduction of cholesterol accumulation in macrophages in response to LDL. We conclude that binding of modified LDL to macrophages induces an appropriate pattern of scavenger receptor phosphorylation which, in turn, determines the optimal receptor internalisation process. PMA activates PKC pathways and prevents the optimal ligand-induced phosphorylation of the receptors, compromising the processes of degradation of modified LDL. The data also suggest that this mechanism may be related to the decreased uptake by activated macrophages of lipid carried by modified lipoproteins during the early phases of inflammation (284).     

Differential expression of CD163 on monocyte subsets in healthy and HIV-1 infected individuals

CD163, a haptoglobin-hemoglobin (Hp-Hb) scavenger receptor, expressed by monocytes and macrophages, is important in resolution of inflammation. Age-related non-AIDS co-morbidities in HIV-infected individuals, particularly dementia and cardiovascular disease, result in part from effects of HIV-1 infection on monocyte and macrophage biology. CD163 co-expression on CD14+CD16++ monocytes has been proposed as a useful biomarker for HIV-1 disease progression and the presence of HIV associated dementia. Here we investigated CD163 expression on monocyte subsets ex vivo, on cultured macrophages, and soluble in plasma, in the setting of HIV-1 infection. Whole blood immunophenotyping revealed CD163 expression on CD14++CD16- monocytes but not on CD14+CD16++ monocytes (P = 0.004), supported by CD163 mRNA levels. Incubation with M-CSF induced CD163 protein expression on CD14+CD16++ monocytes to the same extent as CD14++CD16− monocytes. CD163 expression on CD14++CD16+ monocytes from HIV-infected subjects was significantly higher than from uninfected individuals, with a trend towards increased expression on CD14++CD16− monocytes (P = 0.019 and 0.069 respectively), which is accounted for by HIV-1 therapy including protease inhibitors. Shedding of CD163 was shown to predominantly occur from the CD14++CD16− subset after Ficoll isolation and LPS stimulation. Soluble CD163 concentration in plasma from HIV-1 infected donors was similar to HIV-1 uninfected donors. Monocyte CD163 expression in HIV-1 infected patients showed a complicated relationship with classical measures of disease progression. Our findings clarify technical issues regarding CD163 expression on monocyte subsets and further elucidates its role in HIV-associated inflammation by demonstrating that CD163 is readily lost from CD14++CD16− monocytes and induced in pro-inflammatory CD14+CD16++ monocytes by M-CSF. Our data show that all monocyte subsets are potentially capable of differentiating into CD163-expressing anti-inflammatory macrophages given appropriate stimuli. Levels of CD163 expression on monocytes may be a potential biomarker reflecting efforts by the immune system to resolve immune activation and inflammation in HIV-infected individuals.     

High serum sCD163/sTWEAK ratio is associated with lower risk of digital ulcers but more severe skin disease in patients with systemic sclerosis

Introduction

Systemic sclerosis (SSc) is an autoimmune disease characterized by chronic inflammation, vascular injury and excessive fibrosis. CD163 is a scavenger receptor which affects inflammatory response and may contribute to connective tissue remodelling. It has recently been demonstrated that CD163 can bind and neutralize the TNF-like weak inducer of apoptosis (TWEAK), a multifunctional cytokine which regulates inflammation, angiogenesis and tissue remodelling. We aimed to investigate the relationships between serum levels of soluble CD163 (sCD163) and soluble TWEAK (sTWEAK) in relation to disease manifestations in SSc patients.

Methods

This study included 89 patients with SSc who had not received immunosuppressive drugs or steroids for at least 6 months and 48 age- and sex-matched healthy controls (HC) from four European centres. Serum concentrations of sTWEAK and sCD163 were measured using commercially available ELISA kits.

Results

The mean serum concentrations of sTWEAK were comparable between SSc patients (mean +/- SD: 270 +/- 171 pg/mL) and HC (294 +/- 147pg/mL, P >0.05). Concentration of sCD163 and sCD163/sTWEAK ratio were significantly greater in SSc patients (984 +/- 420 ng/mL and 4837 +/- 3103, respectively) as compared to HC (823 +/- 331 ng/mL and 3115 +/- 1346 respectively, P <0.05 for both). High sCD163 levels and a high sCD163/sTWEAK ratio (defined as > mean +2SD of HC) were both associated with a lower risk of digital ulcers in SSc patients (OR, 95%CI: 0.09; 0.01, 0.71, and 0.17; 0.06, 0.51, respectively). Accordingly, patients without digital ulcers had a significantly higher sCD163 concentration and sCD163/sTWEAK ratio as compared to SSc patients with digital ulcers (P <0.01 for both) and HC (P <0.05 for both). A high sCD163/sTWEAK ratio, but not high sCD163 levels, was associated with greater skin involvement.

Conclusions

The results of our study indicate that CD163-TWEAK interactions might play a role in the pathogenesis of SSc and that CD163 may protect against the development of digital ulcers in SSc. Further studies are required to reveal whether targeting of the CD163-TWEAK pathway might be a potential strategy for treating vascular disease and/or skin fibrosis in SSc.