Monocytes are a heterogeneous cell population with subset-specific functions and phenotypes. The differential expression of CD14 and CD16 distinguishes classical CD14⁺⁺CD16⁻, intermediate CD14⁺⁺CD16⁺, and nonclassical CD14⁺CD16⁺⁺ monocytes. Current knowledge on human monocyte heterogeneity is still incomplete: while it is increasingly acknowledged that CD14⁺⁺CD16⁺ monocytes are of outstanding significance in 2 global health issues, namely HIV-1 infection and atherosclerosis, CD14⁺⁺CD16⁺ monocytes remain the most poorly characterized subset so far. We therefore developed a method to purify the 3 monocyte subsets from human blood and analyzed their transcriptomes using SuperSAGE in combination with high-throughput sequencing. Analysis of 5 487 603 tags revealed unique identifiers of CD14⁺⁺CD16⁺ monocytes, delineating these cells from the 2 other monocyte subsets. Gene Ontology (GO) enrichment analysis suggests diverse immunologic functions, linking CD14⁺⁺CD16⁺ monocytes to Ag processing and presentation (eg, CD74, HLA-DR, IFI30, CTSB), to inflammation and monocyte activation (eg, TGFB1, AIF1, PTPN6), and to angiogenesis (eg, TIE2, CD105). In conclusion, we provide genetic evidence for a distinct role of CD14⁺⁺CD16⁺ monocytes in human immunity. After CD14⁺⁺CD16⁺ monocytes have earlier been discussed as a potential therapeutic target in inflammatory diseases, we are hopeful that our data will spur further research in the field of monocyte heterogeneity.

Patients with chronic kidney disease (CKD) pose a worldwide growing burden to health care systems due to accelerated atherosclerosis and subsequent high cardiovascular (CV) morbidity. Atherogenesis is prominently driven by monocytes and monocyte-derived macrophages. The expression of CD14 and CD16 characterizes three monocyte subsets: CD14⁺⁺CD16⁻, CD14⁺⁺CD16⁺, and CD14⁽⁺⁾CD16⁺ cells; the latter two are often denoted as ‘proinflammatory’ CD16⁺ monocytes. Despite an association between CD16⁺ monocyte counts and higher CV risk in cross-sectional cohorts, the prognostic impact of elevated CD16⁺ monocyte counts is poorly understood. We assessed monocyte heterogeneity using flow cytometry in 119 patients with non-dialysis CKD, who were prospectively followed for a median of 4.9 (inter-quartile range 4.8–5.0) years for the occurrence of CV events. In addition, we assessed expression of chemokine receptors on monocyte subsets. CD14⁺⁺CD16⁺ monocyte were independently associated with CV events [hazard ratio (for an increase of 10 cells/μL) 1.26 (confidence interval: 1.04–1.52; P = 0.018)] after adjustment for variables that significantly affected CD14⁺⁺CD16⁺ cell counts at baseline. Across the spectrum of CKD, CD14⁺⁺CD16⁺ monocytes selectively expressed CCR5. We found that CD14⁺⁺CD16⁺ monocytes were independently associated with CV events in non-dialysis CKD patients. Our results support the notion that CD16⁺ monocytes rather than CD16⁻ monocytes are involved in human atherosclerosis.

Monocytes and monocyte-derived macrophages have been recognised as the cellular hallmark of atherosclerosis decades ago. Recently, they have also been shown to play a pivotal role in obesity. Monocytes display immunophenotypic heterogeneity with functionally distinct subpopulations. We initiated the I LIKE HOMe study to examine monocyte heterogeneity in obesity and subclinical atherosclerosis. We assessed carotid intima media thickness (IMT), body mass index (BMI), and other cardiovascular risk factors in 622 healthy volunteers. Using flow-cytometry, we differentiated monocytes into CD14⁺⁺CD16⁻ and CD16⁺ cells, which we further subdivided into CD14⁺⁺CD16⁺ and CD14⁽⁺⁾CD16⁺ cells. Body mass index was significantly correlated with carotid IMT. High CD16⁺ monocyte counts were significantly associated with both higher BMI and increased carotid IMT. Adjustment for CD16⁺ monocyte counts weakened the correlation between BMI and carotid IMT, suggesting that the increase in CD16⁺ monocyte numbers in obesity may partly explain the association between obesity and IMT. Our results reveal a significant univariate association between CD16⁺ monocytes and both obesity and subclinical atherosclerosis in low-risk individuals. They are in line with recent observations that CD16⁺ monocytes show high endothelial affinity and a potent capacity to invade vascular lesions and to transform into pro-inflammatory cytokine producing macrophages.

A decreased expression of the fibroblast growth factor (FGF)-23 coreceptor Klotho was postulated as an early alteration in chronic kidney disease mineral and bone disorder, resulting in a compensatory increase in plasma FGF-23 levels. Klotho exists in both membrane-bound and secreted (sKlotho) forms, the latter of which may exert vasculoprotective effects. Here we analyzed plasma sKlotho levels in a large cohort of 312 patients with stage 2–4 chronic kidney disease, and assessed plasma levels of FGF-23, sKlotho, parathyroid hormone, and urinary fractional phosphate excretion. Patients were prospectively followed for an average of 2.2 years for the occurrence of death or initiation of renal replacement therapy. The levels of sKlotho were significantly associated with age, but not with the glomerular filtration rate or other parameters of calcium-phosphate metabolism. Moreover, while patients with high FGF-23 levels faced worst outcome even after adjustment for confounders, we found no prognostic impact of sKlotho. Thus, plasma levels of sKlotho were not related to kidney function and did not predict adverse outcome in patients with chronic kidney disease. Future studies are needed to understand how tissue expression, urinary excretion, and plasma levels of Klotho diverge in progressive chronic kidney disease.

Background and objectives CKD–mineral and bone disorders (CKD-MBD) measures contribute to cardiovascular morbidity in patients with CKD. Among these, fibroblast growth factor (FGF)-23 and its coreceptor Klotho may exert direct effects on vascular and myocardial tissues. Klotho exists in a membrane-bound and a soluble form (sKlotho). Recent experimental evidence suggests sKlotho has vasculoprotective functions. Design, settings, participants, & measurements Traditional and novel CKD-MBD variables were measured among 444 patients with CKD stages 2–4 recruited between September 2008 and November 2012 into the ongoing CARE FOR HOMe study. Across tertiles of baseline sKlotho and FGF-23, the incidence of two distinct combined end points was analyzed: (1) the first occurrence of an atherosclerotic event or death from any cause and (2) the time until hospital admission for decompensated heart failure or death from any cause. Results Patients were followed for 2.6 (interquartile range, 1.4–3.6) years. sKlotho tertiles predicted neither atherosclerotic events/death (fully adjusted Cox regression analysis: hazard ratio [HR] for third versus first sKlotho tertile, 0.75 [95% confidence interval (95% CI), 0.43–1.30]; P=0.30) nor the occurrence of decompensated heart failure/death (HR for third versus first sKlotho tertile, 0.81 [95% CI, 0.39–1.66]; P=0.56). In contrast, patients in the highest FGF-23 tertile had higher risk for both end points in univariate analysis. Adjustment for kidney function attenuated the association between FGF-23 and atherosclerotic events/death (HR for third versus first FGF-23 tertile, 1.23 [95% CI, 0.58–2.61]; P=0.59), whereas the association between FGF-23 and decompensated heart failure/death remained significant after adjustment for confounders (HR for third versus first FGF-23 tertile, 4.51 [95% CI, 1.33–15.21]; P=0.02). Conclusions In this prospective observational study of limited sample size, sKlotho was not significantly related to cardiovascular outcomes. FGF-23 was significantly associated with future decompensated heart failure but not incident atherosclerotic events.