Antibody combinations for optimized staining of macrophages in human lung tumours

The analysis of tumour-associated macrophages (TAMs) has a high potential to predict cancer recurrence and response to immunotherapy. However, the heterogeneity of TAMs poses a challenge for quantitative and qualitative measurements. Here, we critically evaluated by immunohistochemistry and flow cytometry two commonly used pan-macrophage markers (CD14 and CD68) as well as some suggested markers for tumour-promoting M2 macrophages (CD163, CD204, CD206 and CD209) in human non-small cell lung cancer (NSCLC). Tumour, non-cancerous lung tissue and blood were investigated. For immunohistochemistry, CD68 was confirmed to be a useful pan-macrophage marker although careful selection of antibody was found to be critical. The widely used anti-CD68 antibody clone KP-1 stains both macrophages and neutrophils, which is problematic for TAM quantification because lung tumours contain many neutrophils. For TAM counting in tumour sections, we recommend combined labelling of CD68 with a cell membrane marker such as CD14, CD163 or CD206. In flow cytometry, the commonly used combination of CD14 and HLA-DR was found to not be optimal because some TAMs do not express CD14. Instead, combined staining of CD68 and HLA-DR is preferable to gate all TAMs. Concerning macrophage phenotypic markers, the scavenger receptor CD163 was found to be expressed by a substantial fraction (50%-86%) of TAMs with a large patient-to-patient variation. Approximately 50% of TAMs were positive for CD206. Surprisingly, there was no clear overlap between CD163 and CD206 positivity, and three distinct TAM sub-populations were identified in NSCLC tumours: CD163⁺ CD206⁺ , CD163⁺ CD206^- and CD163^- CD206^- . This work should help develop macrophage-based prognostic tools for cancer.

Soluble CD14, Ischemic Stroke, and Coronary Heart Disease Risk in a Prospective Study: The REGARDS Cohort

Background

Soluble CD14 (sCD14), a circulating pattern recognition receptor, has been suggested as a cardiovascular disease risk factor. Prospective studies evaluating sCD14 with incident cardiovascular disease events are limited, particularly among racially diverse populations.

Methods and Results

Between 2003 and 2007, the REGARDS (Reasons for Geographic and Racial Differences in Stroke) study recruited 30 239 black and white participants across the United States. In a nested case–cohort study, sCD14 was measured in baseline serum from 548 cases of incident ischemic stroke, 612 cases of incident coronary heart disease (CHD), and a cohort random sample (n=1039). Cox models estimated hazards ratios (HR) of incident ischemic stroke or CHD per 1 SD higher sCD14, adjusting for cardiovascular disease risk factors. There was a differential association of sCD14 with ischemic stroke and CHD risk by race. Among blacks, the adjusted HR of stroke per SD increment of sCD14 was 1.42 (95% CI: 1.12, 1.80), with no association among whites (HR 1.02 [95% CI: 0.82, 1.27]). Higher sCD14 was associated with increased CHD risk in blacks but not whites, and relationships between sCD14 and CHD were stronger at younger ages. Adjusted for risk factors, the HR of CHD per SD higher sCD14 among blacks at age 45 years was 2.30 (95% CI: 1.45, 3.65) compared with 1.56 (95% CI: 0.94, 2.57) among whites. At age 65 years, the CHD HR was 1.51 (95% CI: 1.20, 1.91) among blacks and 1.02 (95% CI: 0.80, 1.31) among whites.

Conclusions

sCD14 may be a race‐specific stroke and CHD risk marker.

Elevated Plasma Soluble CD14 Levels Correlate with the Monocyte Response Status During Hantaan Virus Infection in Humans

Hantaan virus (HTNV) infection can cause severe hemorrhagic fever with renal syndrome (HFRS) in humans. CD14, a pattern recognition receptor recognizing lipopolysaccharide, is highly expressed on monocytes and can be shed as soluble CD14 (sCD14) upon monocyte activation. To understand the role of sCD14 in HFRS, the sCD14 plasma concentrations from 45 HFRS patients were quantified, and the relationships between the plasma sCD14 level and the monocyte response status and clinical parameters were analyzed. The plasma sCD14 levels were significantly higher in the HFRS patients and they correlated with monocyte expansion and activation, which were characterized by increased blood monocyte counts, the proportion of CD14(++)CD16(+) intermediate monocytes, as well as elevated plasma tumor necrosis factor-α (TNF-α) and soluble CD163 (sCD163) levels. Additionally, the high plasma sCD14 levels positively correlated with white blood cell counts and blood urea nitrogen levels and negatively correlated with platelet counts in the HFRS patients. Taken together, our data indicate that elevated plasma sCD14 levels are associated with the monocyte response status during HTNV infection in humans.

Soluble hemojuvelin is released by proprotein convertase-mediated cleavage at a conserved polybasic RNRR site

As the principal iron-regulatory hormone, hepcidin plays an important role in systemic iron homeostasis. The regulation of hepcidin expression by iron loading appears to be unexpectedly complex and has attracted much interest. The GPI-linked membrane protein hemojuvelin (GPI-hemojuvelin) is an essential upstream regulator of hepcidin expression. A soluble form of hemojuvelin (s-hemojuvelin) exists in blood and acts as antagonist of GPI-hemojuvelin to downregulate hepcidin expression. The release of s-hemojuvelin is negatively regulated by both transferrin-bound iron (holo-Tf) and non-transferrin-bound iron (FAC), indicating s-hemojuvelin could be one of the mediators of hepcidin regulation by iron. In this report, we investigate the proteinase involved in the release of s-hemojuvelin and show that s-hemojuvelin is released by a proprotein convertase through the cleavage at a conserved polybasic RNRR site.

Engagement of CD14 mediates the inflammatory potential of monosodium urate crystals

Phagocyte ingestion of monosodium urate (MSU) crystals can induce proinflammatory responses and trigger acute gouty inflammation. Alternatively, the uptake of MSU crystals by mature macrophages can be noninflammatory and promote resolution of gouty inflammation. Macrophage activation by extracellular MSU crystals involves apparent recognition and ingestion mediated by TLR2 and TLR4, with subsequent intracellular recognition linked to caspase-1 activation and IL-1beta processing driven by the NACHT-LRR-PYD-containing protein-3 inflammasome. In this study, we examined the potential role in gouty inflammation of CD14, a phagocyte-expressed pattern recognition receptor that functionally interacts with both TLR2 and TLR4. MSU crystals, but not latex beads, directly bound recombinant soluble (s) CD14 in vitro. CD14(-/-) bone marrow-derived macrophages (BMDMs) demonstrated unimpaired phagocytosis of MSU crystals but reduced p38 phosphorylation and approximately 90% less IL-1beta and CXCL1 release. Attenuated MSU crystal-induced IL-1beta release in CD14(-/-) BMDMs was mediated by decreased pro-IL-1beta protein expression and additionally by decreased caspase-1 activation and IL-1beta processing consistent with diminished NACHT-LRR-PYD-containing protein-3 inflammasome activation. Coating of MSU crystals with sCD14, but not sTLR2 or sTLR4, restored IL-1beta and CXCL1 production in CD14(-/-) BMDMs in vitro. Gain of function of CD14 directly enhanced TLR4-mediated signaling in response to MSU crystals in transfected Chinese hamster ovary cells in vitro. Last, MSU crystal-induced leukocyte influx at 6 h was reduced by approximately 75%, and local induction of IL-1beta decreased by >80% in CD14(-/-) mouse s.c. air pouches in vivo. We conclude that engagement of CD14 is a central determinant of the inflammatory potential of MSU crystals.

Surfactant protein-D regulates soluble CD14 through matrix metalloproteinase-12

Surfactant protein D (SP-D) and CD14 are important innate immune defense molecules that mediate clearance of pathogens and apoptotic cells from the lung. To test whether CD14 expression and function were influenced by SP-D, the surface expression of CD14 was assessed on alveolar macrophages from SP-D-/- mice. CD14 was reduced on alveolar macrophages from SP-D-/- mice and was associated with reduced uptake of LPS and decreased production of TNF-alpha after LPS stimulation. CD14 is proteolytically cleaved from the cell surface to form a soluble peptide. Soluble CD14 (sCD14) was increased in the bronchoalveolar lavage fluid from SP-D-/- mice. Because matrix metalloproteinase (MMP)-9 and -12 activities were increased in the lungs of SP-D-/- mice, the role of these metalloproteases in the production of sCD14 was assessed. sCD14 was decreased in both MMP(9-/-)/SP-D-/- and MMP12(-/-)/SP-D-/- mice demonstrating MMP-9 and MMP-12 contribute to proteolytic shedding of CD14. The increased sCD14 seen in SP-D-/- mice was dependent upon the activation of MMP-12 via an MMP-9-dependent mechanism. Supporting this observation, MMP-12 caused the release of sCD14 from RAW 264.7 cells in vitro. In conclusion, SP-D influences innate host defense, in part, by regulating sCD14 in a process mediated by MMP-9 and MMP-12.

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.