Generation of a haptoglobin-hemoglobin complex-specific Fab antibody blocking the binding of the complex to CD163

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.

Survey of the year 2003 commercial optical biosensor literature

In the year 2003 there was a 17% increase in the number of publications citing work performed using optical biosensor technology compared with the previous year. We collated the 962 total papers for 2003, identified the geographical regions where the work was performed, highlighted the instrument types on which it was carried out, and segregated the papers by biological system. In this overview, we spotlight 13 papers that should be on everyone's 'must read' list for 2003 and provide examples of how to identify and interpret high-quality biosensor data. Although we still find that the literature is replete with poorly performed experiments, over-interpreted results and a general lack of understanding of data analysis, we are optimistic that these shortcomings will be addressed as biosensor technology continues to mature.

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.

CD163: a regulated hemoglobin scavenger receptor with a role in the anti-inflammatory response

CD163 is a hemoglobin scavenger receptor exclusively expressed in the monocyte-macrophage system. A particularly high expression is seen in macrophages of the 'alternative activation' phenotype playing a major role in dampening the inflammatory response and in scavenging components of damaged cells. CD163-mediated endocytosis of haptoglobin-hemoglobin complexes formed upon red blood cell hemolysis leads to lysosomal degradation of the ligand protein and metabolism of heme by cytosolic heme oxygenase. In accordance with a stimulated expression of haptoglobin, CD163 and heme oxygenase-1 during the acute phase response, there is evidence that this metabolic pathway regulates inflammation by at least two ways. First, CD163 is reported to directly induce intracellular signaling leading to secretion of anti-inflammatory cytokines. Second and perhaps even more important, the CD163-mediated delivery of hemoglobin to the macrophage may fuel an anti-inflammatory response because heme metabolites have potent anti-inflammatory effects. In addition to being present on the macrophage surface, continuous shedding of the extracellular domain of CD163 leads to substantial amounts of soluble receptor in plasma. An increased shedding is due to inflammatory stimuli, and a role for soluble CD163 in immune suppression has been proposed. Furthermore, recent data indicate that soluble CD163 may be a valuable diagnostic parameter for monitoring macrophage activation in inflammatory conditions.