Tumor-promoting macrophages induce the expression of the macrophage-specific receptor CD163 in malignant cells.

Tumor-associated macrophages (TAMs) represent a distinct malignancy-promoting phenotype suggested to play a key role in tumor formation and metastasis. We aimed to investigate the expression of the monocyte/macrophage-restricted receptor CD163 in bladder tumor biopsies and assess the potential mechanism inducing the CD163 expression in tumor cells. A high CD163 mRNA expression (n = 87) was significantly associated with a poor 13-year overall survival (log-rank test, χ(2) = 8.931; p = 0.0028). Moreover, CD163 mRNA expression was significantly increased in muscle invasive (T2-T4), p = 0.017, and aggressive (grade III/IV) cancers (p = 0.015). The expression strongly correlated with local expression of IL-6 (r = 0.72; p <0.0001) and IL-10 (r = 0.75; p <0.0001), mediators known to induce CD163 expression in vitro. CD163 immunostaining (n = 46) confirmed the association between dense TAM infiltration and histologically advanced disease. In 39% of the biopsies, CD163 immunoreactivity was also observed in tumor cells, and CD163-expressing metastatic cells were identified in lymph node biopsies (n = 8). Bladder cancer cell lines did not express CD163; however, when cocultured with macrophages the bladder cancer cell expression of CD163 was significantly induced in an IL-6/IL-10 independent manner. In conclusion, we show a strong association between CD163 mRNA expression in bladder cancer biopsies and poor patient outcome. CD163 expression was not confined to the infiltrating TAMs, but was also expressed by a significant portion of the malignant cells in both tumors and lymph nodes. CD163 expressing tumor cells may constitute a subpopulation of tumor cells with a phenotypic shift associated with epithelial-to-mesenchymal transition (EMT) and increased metastatic activity induced by TAMs.

Impaired CD163-mediated hemoglobin-scavenging and severe toxic symptoms in patients treated with gemtuzumab ozogamicin.

We describe a novel syndrome of severe toxic symptoms during intravascular hemolysis due to impaired hemoglobin scavenging in 2 children with acute myeloid leukemia undergoing CD33-directed therapy with the immunotoxin gemtuzumab ozogamicin (GO). A simultaneous high plasma hemoglobin, haptoglobin, and low bilirubin after septicemia-induced intravascular hemolysis indicated abrogated clearance of haptoglobin-hemoglobin complexes. This was further supported by low levels of plasma soluble CD163 and a concordant low number of CD163-expressing monocytes. We show that CD163 positive monocytes and macrophages from liver, spleen, and bone marrow coexpress CD33, thus suggesting that the GO-induced cellular cytotoxicity of CD33 positive cells eradicates a significant part of the CD163 positive monocytes and macrophages. The risk of severe toxic symptoms from plasma hemoglobin should be considered after CD33-targeted chemotherapy when the disease is complicated by a pathologic intravascular hemolysis. Furthermore, the cases provide further circumstantial evidence of a key role of (CD163-expressing) monocytes/macrophages in plasma hemoglobin clearance in vivo.

CD163 positive subsets of blood dendritic cells: the scavenging macrophage receptors CD163 and CD91 are coexpressed on human dendritic cells and monocytes.

CD163 and CD91 are scavenging receptors with highly increased expression during the differentiation of monocytes into the anti-inflammatory macrophage phenotype. In addition, CD91 is expressed in monocyte-derived dendritic cells (MoDCs), where the receptor is suggested to be important for internalization of CD91-targeted antigens to be presented on the dendritic cell surface for T-cell stimulation. Despite their overlap in functionality, the expression of CD91 and CD163 has never been compared and the expression of CD163 in the monocyte-dendritic cell lineage is not yet characterized. CD163 expression in dendritic cells (DCs) was investigated using multicolor flow cytometry in peripheral blood from 31 healthy donors and 15 HIV-1 patients in addition to umbilical cord blood from 5 newborn infants. Total RNA was isolated from MACS purified DCs and CD163 mRNA was determined with real-time reverse transcriptase polymerase chain reaction. The effect of glucocorticoid and phorbol ester stimulation on monocyte and dendritic cell CD163 and CD91 expression was investigated in cell culture of mononuclear cells using multicolor flow cytometry. We identified two CD163+ subsets in human blood with dendritic cell characteristics, CD163lo and CD163hi, together constituting a substantial fraction of DCs. Both subsets were characterized as [lin]- CD4+ ILT3+ HLA-DR+ CD11c+ by flow cytometry, and CD163 mRNA was readily detectable in MACS purified human DCs. CD163 on DCs was upregulated by glucocorticoid, and treatment by phorbol ester significantly decreased surface expression. Overall, the expression of CD163 on DCs was significantly increased in HIV-1 patients (19.3% [95% CI: 14.7-26.3%]) compared to healthy patients (10.5% [95% CI: 8.0-12.5]) p < 0.001. The CD163lo subset was CD16+, whereas the CD163hi subset was CD16-. Both subsets were CD91+, thereby constituting a subfraction of the recently described CD91+ CD11c+ dendritic cell subset. Coexpression of CD163 and CD91 was also demonstrated on human monocytes, which upon glucocorticoid treatment exhibited an increase in both CD163 and CD91 expression. We have now shown that CD163 and CD91 are coexpressed and coregulated on human monocytes. In addition, two subsets of CD163+ DCs constituting a fraction of the recently described CD91+ CD11c+ dendritic cell subset have been identified. The CD163 expression pattern suggests that if antigens are targeted to CD163 they may induce an immunostimulatory response like that of CD91-targeted antigens.

Elevated platelet expression of CD36 may contribute to increased risk of thrombo-embolism in active inflammatory bowel disease.

CONTEXT: Inflammatory bowel disease (IBD) induces increased risk of thrombo-embolism. CD36 is involved in platelet activation, glucose metabolism and inflammation. OBJECTIVE: The relationship between CD36 expression on platelets and monocytes, plasma sCD36, and CD36-positive platelet-derived microparticles (PDMPs) and inflammation in both active IBD and after one week of anti-tumour necrosis alpha antibody (anti-TNF) treatment was investigated. MATERIAL AND METHODS: Patients with exacerbation of Crohn's disease (n = 8) or ulcerative colitis (n = 5) and 13 healthy controls were enrolled. Seven patients underwent anti-TNF treatment for one week. Platelet, monocyte, and PDMP-CD36 were measured by flow-cytometry. RESULTS: Platelet CD36 expression was 34% higher in patients, and correlated with insulin resistance and fasting glucose. sCD36 was 37% lower and restored after anti-TNF treatment. CONCLUSION: Elevated platelet CD36 expression may contribute to increased risk of thrombo-embolism in active IBD. This may not entirely be attributed to inflammation and secondary insulin resistance may play a role.

Efficient intracellular drug-targeting of macrophages using stealth liposomes directed to the hemoglobin scavenger receptor CD163.

The hemoglobin scavenger receptor CD163 is exclusively expressed in the monocytic lineage and preferentially in tissue resident macrophages of the M2 phenotype and in macrophages in sites of inflammation and tumor growth. In the present study we have designed liposomes specifically targeting CD163 by hydrophobic linkage of CD163-binding monoclonal antibodies to polyethylene glycol-coated liposomes ('stealth liposomes'). Targeting to the endocytic CD163 protein greatly increased the uptake of liposomes in CD163 transfected cells and macrophages as visualized by confocal microscopy and flow cytometry of cells exposed to CD163 targeting liposomes loaded with calcein. Strong cytotoxic effects were seen in CD163-expressing human monocytes by using the chemotherapeutic agent doxorubicin as cargo of the liposomes. In conclusion, the use of stealth liposomes modified to recognize CD163 is a potential way to target drugs to macrophages that support inflammatory and malignant processes.

Comparative assessment of the recognition of domain-specific CD163 monoclonal antibodies in human monocytes explains wide discrepancy in reported levels of cellular surface CD163 expression.

BACKGROUND: CD163 is expressed exclusively on cells of the monocyte/macrophage lineage and is widely used as a marker of human macrophages. Further, it has been suggested as a diagnostic marker of monocyte/macrophage activity in inflammatory conditions and as a therapeutic target. However, studies continue to exhibit great discrepancy in the measured percentage of CD163-expressing blood monocytes in healthy individuals. In this study we sought to clarify this inconsistency in reported levels of CD163 surface expression by a detailed analysis of a panel of CD163 antibodies used in previous studies. MATERIALS AND METHODS: The cellular distribution of CD163 on human peripheral blood monocytes in freshly drawn blood and peripheral blood mononuclear cells isolated from buffy-coats was investigated by flow cytometry using CD163 monoclonal antibodies recognizing scavenger receptor cysteine-rich (SRCR) domain 1 (MAC2-158), domain 4 (R-20), domain 7 (GHI/61), and domain 9 (RM3/1). The CD163 monoclonal antibodies were characterized in binding and endocytosis experiments in human macrophages and CD163-transfected Flp-In CHO cells. Calcium-dependent ligand binding was assessed using surface plasmon resonance, and the specificity of the CD163 monoclonal antibodies was analyzed by western blotting. RESULTS AND DISCUSSION: Flow cytometric analysis revealed that the estimated proportion of CD163-expressing human peripheral blood monocytes increased when using CD163 monoclonal antibodies recognizing epitopes in the N-terminal part of CD163, remote from the membrane surface. Moreover, the proportion of CD163 positive monocytes observed was highly dependent on free calcium. GHI/61 did not exhibit CD163 binding in the presence of calcium as measured by surface plasmon resonance, which was in agreement with the concordant loss of binding in heparin-stabilized whole blood observed by flow cytometry. In contrast, RM3/1 exhibited weak binding to CD163 in the absence of calcium but high affinity binding to CD163 in the presence of calcium. R-20 and MAC2-158 were unaffected by extracellular calcium levels. The latter SRCR domain 1mAb consistently recognized more than 80% CD163-positive monocytes in human peripheral blood. CONCLUSION: Epitope accessibility and extracellular calcium dependence elucidate discrepancies in reported levels of monocytic CD163 expression. Utilizing monoclonal antibodies to the N-terminal part of CD163 more than 80% monocytes in human peripheral blood could be identified as CD163 positive, indicating that most, and conceivably all, human peripheral blood monocytes do express CD163.

Soluble macrophage-derived CD163: a homogenous ectodomain protein with a dissociable haptoglobin-hemoglobin binding.

BACKGROUND: The soluble form of the haptoglobin-hemoglobin (Hp-Hb) scavenger receptor (sCD163) is a specific plasma/serum marker for macrophage activity. Here, we have characterized molecular forms in serum and investigated a role of sCD163 as a binder of Hp-Hb complexes. METHODS: The sCD163 species in serum (from 50 healthy subjects and 29 patients) were measured with domain-specific ELISAs, purified from serum (from 6 individuals) by affinity chromatography and identified by western blotting and MALDI-TOF/TOF mass spectrometry. Binding to Hp-Hb complexes was investigated by gel-chromatography, surface plasmon resonance (SPR) analyses, and inhibition of Hp-Hb endocytosis in CD163-transfected Chinese hamster ovary (CHO) cells. RESULTS: By using C- and N-terminal-specific ELISAs, no sCD163 concentration differences in plasma were seen, thus indicating a homogenous sCD163 species. Affinity-purified sCD163 from serum migrated as a single band of 130kDa, and spanned at least 945 amino acids (94%) of the total extra-cellular part of CD163. In solution sCD163 only weakly competed for Hp-Hb uptake in CD163-expressing cells, and Hp-Hb saturation of sCD163 in serum was only seen with large excess of Hp-Hb complexes. However, upon immobilisation, recombinant sCD163 bound Hp-Hb with high affinity. This suggests that Hp-Hb is less dissociable when bound to the membrane form of CD163, presumably because of the di- or multivalent nature of Hp-Hp complexes in terms of CD163 binding. CONCLUSIONS: Serum sCD163 is a homogenous protein covering more than 94% of the CD163 ectodomain including the Hp-Hb-binding region. However, CD163 is a poor competitor of Hp-Hb uptake, probably because of its soluble nature, where Hp-Hb cannot take advantage of receptor cross-linkage.

Tumor necrosis factor α-converting enzyme (TACE/ADAM17) mediates ectodomain shedding of the scavenger receptor CD163.

CD163 is expressed specifically in the monocyte/macrophage lineage, where it mediates uptake of haptoglobin-hemoglobin complexes, leading to metabolism of the oxidative heme molecule. Shedding of the CD163 ectodomain from the cell surface produces a sCD163 plasma protein, and a positive correlation is seen between the sCD163 plasma level and the severity of various infectious and inflammatory diseases. In the present analysis of the phorbol ester-induced shedding of sCD163 in CD163 cDNA-transfected HEK293 cells, we used metalloproteinase inhibitors and siRNA-mediated inhibition of metalloproteinases to identify TACE/ADAM17 as an enzyme responsible for PMA-induced cleavage of the membrane-proximal region of CD163. As TACE/ADAM17-mediated shedding of TNF-α is up-regulated in macrophages subjected to inflammatory stimuli, the present results now provide a likely explanation for the strong empirical relationship between the sCD163 plasma level and infectious/inflammatory diseases relating to macrophage activity.

Macrophage markers in serum and tumor have prognostic impact in American Joint Committee on Cancer stage I/II melanoma.

PURPOSE: To evaluate the prognostic role of soluble CD163 (sCD163) in serum and macrophage infiltration in primary melanomas from patients with American Joint Committee on Cancer (AJCC) stage I/II melanoma. The scavenger receptor CD163 is associated with anti-inflammatory macrophages, and it is shed from their surface. PATIENTS AND METHODS: Serum samples from 227 patients with stage I/II melanoma obtained before definitive surgery (baseline) and during 5 years of follow-up were analyzed for sCD163 by enzyme-linked immunosorbent assay. Excised formalin-fixed, paraffin-embedded primary melanomas from 190 patients were available for immunohistochemical analyzes of CD163(+) and CD68(+) macrophage infiltration. They were estimated semiquantitatively in three different tumor compartments: tumor nests, tumor stroma, and at the invasive front of the tumor. RESULTS: Serum sCD163 treated as an updated continuous covariate as well as the baseline value were analyzed together with the covariate's ulceration and thickness in a Cox proportional hazards model. sCD163 was an independent prognostic factor for overall survival (baseline, hazard ratio [HR] = 1.4; 95% CI, 1.1 to 1.7; P = .01; and updated, HR = 1.4; 95% CI, 1.1 to 1.8; P = .003). Melanomas with dense CD163(+) macrophage infiltration in tumor stroma and CD68(+) macrophage infiltration at the invasive front were associated with poor overall survival (CD163, HR = 2.7; 95% CI, 0.8 to 9.3; P = .11; and CD68, HR = 2.8; 95% CI, 1.2 to 6.8; P = .02) independent (borderline for CD163) of thickness and ulceration. CONCLUSION: Both serum levels of sCD163 and the presence of CD68(+) macrophage infiltration at the tumor invasive front are independent predictors of survival in AJCC stage I/II melanoma. CD163(+) cell infiltration in tumor stroma may be predictive of survival.