Gating the Radical Hemoglobin to Macrophages: The Anti-Inflammatory Role of CD163, a Scavenger Receptor

Medical Clinic B Research Unit, University of Zurich, Switzerland.
Antioxidants and Redox Signaling (Impact Factor: 7.41). 08/2007; 9(7):991-9. DOI: 10.1089/ars.2007.1576
Source: PubMed


Efficient extracellular hemoglobin (Hb) clearance is essential to prevent oxidative- and nitrosative-mediated toxicity. CD163 belongs to group B of the scavenger receptor cysteine-rich (SRCR) protein family found on the surface of monocytes and macrophages and is responsible for Hb-haptoglobin (Hp) complex uptake. Hb uptake by CD163 was thought to proceed exclusively through an Hp-dependent pathway. However, Hb can interact directly with CD163 via a low affinity binding when Hp is absent. As a result, a two-phase hypothesis of Hb clearance by monocytes/macrophages suggests that Hp-Hb binding to CD163 is the primary mechanism of plasma Hb clearance, while clearance of Hb by direct binding to CD163 is secondary to Hp depletion. The authors have considered the ligand specificity of CD163 in human macrophages and in a heterologous gene expression model to demonstrate that Hb is effectively endocytosed by CD163 in the absence of Hp. Additionally, the authors have considered Hb-based oxygen carriers (HBOCs) administration as a unique situation during which direct CD163 uptake may be relevant as a mechanism of clearance. However, the nature of chemical modifications introduced onto the Hb molecule and/or oxidative changes induced in the protein appear to influence the extent of CD163 interaction and cellular uptake. Here, an overview and novel insights into the role of CD163 in Hb redox inactivation and clearance are provided.

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    • "It has been reported that GVHD can be divided into 3 subtypes based on the number of macrophages and T lymphocytes infiltrated in the skin, and that GVHD with many CD163+ macrophages was refractory with poor prognosis and a therapeutic challenge [5]. However, those macrophages were CD163 positive, a member of the scavenger receptor cysteine-rich superfamily, which was one of anti-inflammatory macrophage markers [6]. Thus, the pathogenesis between macrophage infiltration and refractory GVHD is currently unclear. "
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    ABSTRACT: Macrophage infiltration of skin GVHD lesions correlates directly with disease severity, but the mechanisms underlying this relationship remain unclear and GVHD with many macrophages is a therapeutic challenge. Here, we characterize the macrophages involved in GVHD and report that dexamethasone palmitate (DP), a liposteroid, can ameliorate such GVHD by inhibiting macrophage functions. We found that host-derived macrophages could exacerbate GVHD in a mouse model through expression of higher levels of pro-inflammatory TNF-α and IFN-γ, and lower levels of anti-inflammatory IL-10 than resident macrophages in mice without GVHD. DP significantly decreased the viability and migration capacity of primary mouse macrophages compared to conventional dexamethasone in vitro. DP treatment on day 7 and day 14 decreased macrophage number, and attenuated GVHD score and subsequent mortality in a murine model. This is the first study to provide evidence that therapy for GVHD should be changed on the basis of infiltrating cell type.
    PLoS ONE 05/2014; 9(5):e96252. DOI:10.1371/journal.pone.0096252 · 3.23 Impact Factor
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    • "It is a glycoprotein belonging to class B of the scavenger receptor cysteine rich superfamily. It functions as a membrane bound scavenger receptor for clearing extracellular haptoglobin-hemoglobin (Hp-Hb) complexes [35]. It is also able to recognize and bind Gram-negative and Gram-positive bacteria, and may have a role to play in host defense [36]. "
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    ABSTRACT: Microglial activation is a pathological feature common to both Alzheimer's and Parkinson's diseases (AD and PD). The classical activation involves release of pro-inflammatory cytokines and reactive oxygen species. This is necessary for maintenance of tissue homeostasis and host defense, but can cause bystander damage when the activation is sustained and uncontrolled. In recent years the heterogeneous nature of microglial activation states in neurodegenerative diseases has become clear and the focus has shifted to alternative activation states that promote tissue maintenance and repair. We studied the distribution of CD163, a membrane-bound scavenger receptor found on perivascular macrophages. CD163 has an immunoregulatory function, and has been found in the parenchyma in other inflammatory diseases e.g. HIV-encephalitis and multiple sclerosis. In this study, we used immunohistochemistry to compare CD163 immunoreactivity in 31 AD cases, 27 PD cases, and 16 control cases. Associations of microglia with pathological hallmarks of AD and PD were investigated using double immunofluorescence. Parenchymal microglia were found to be immunoreactive for CD163 in all of the AD cases, and to a lesser extent in PD cases. There was prominent staining of CD163 immunoreactive microglia in the frontal and occipital cortices of AD cases, and in the brainstem of PD cases. Many of them were associated with Ass plaques in both diseases, and double staining with CD68 demonstrates their phagocytic capability. Leakage of fibrinogen was observed around compromised blood vessels, raising the possibility these microglia might have originated from the periphery. Increase in microglia's CD163 immunoreactivity was more significant in AD than PD, and association of CD163 immunoreactive microglia with Abeta plaques indicate microglia's attraction towards extracellular protein pathology, i.e. extracellular aggregates of Abeta as compared to intracellular Lewy Bodies in PD. Double staining with CD163 and CD68 might point towards their natural inclination to phagocytose plaques. Fibrinogen leakage and compromise of the blood brain barrier raise the possibility that these are not resident microglia, but systemic macrophages infiltrating the brain.
    02/2014; 2(1):21. DOI:10.1186/2051-5960-2-21
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    • "Other more recently recognised functions of CD163 include anti-inflammatory scavenger receptor for the tumour necrosis factor-like weak inducer of apoptosis (TWEAK) [12], an erythroblast receptor, promoting their survival and differentiation [13], and a receptor functioning as an innate immune sensor for both Gram positive and negative bacteria [14]. CD163 expressing macrophages are also involved in resolution of inflammation by limiting free hemoglobin associated damage [11] and secreting anti-inflammatory cytokines in response to inflammation [15], [16]. However, the immune effects of CD163 are complicated and may not be limited to down-regulating inflammation as CD163 stimulation has also been reported to induce pro-inflammatory cytokine production from rat macrophages [17]. "
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    ABSTRACT: 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.
    PLoS ONE 05/2011; 6(5):e19968. DOI:10.1371/journal.pone.0019968 · 3.23 Impact Factor
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