Phenotypic and functional heterogeneity of human intermediate monocytes based on HLA-DR expression.

Human blood monocytes are subclassified as classical, intermediate and nonclassical. In this study, it was shown that conventionally defined human intermediate monocytes can be divided into two distinct subpopulations with mid- and high-level surface expression of HLA-DR (referred to as DRmid and DRhi intermediate monocytes). These IM subpopulations were phenotypically and functionally characterized in healthy adult blood by flow cytometry, migration assays and lipoprotein uptake assays. Their absolute numbers and proportions were then compared in blood samples from obese and nonobese adults. DRmid and DRhi intermediate monocytes differentially expressed several proteins including CD62L, CD11a, CX3CR1 and CCR2. Overall, the DRmid intermediate monocytes surface profile more closely resembled that of classical monocytes while DRhi intermediate monocytes were more similar to nonclassical. However, in contrast to classical monocytes, DRmid intermediate monocytes migrated weakly to CCL2, had reduced intracellular calcium flux following CCR2 ligation and favored adherence to TNFα-activated endothelium over transmigration. In lipid uptake assays, DRmid intermediate monocytes demonstrated greater internalization of oxidized and acetylated low-density lipoprotein than DRhi intermediate monocytes. In obese compared to nonobese adults, proportions and absolute numbers of DRmid , but not DRhi intermediate monocytes, were increased in blood. The results are consistent with phenotypic and functional heterogeneity within the intermediate monocytes subset that may be of specific relevance to lipoprotein scavenging and metabolic health.

Chronic Kidney Disease Severity Is Associated With Selective Expansion of a Distinctive Intermediate Monocyte Subpopulation.

Chronic kidney disease (CKD) affects 11-13% of the world's population and greatly increases risk of atherosclerotic cardiovascular disease (ASCVD) and death. It is characterized by systemic inflammation and disturbances in the blood leukocytes that remain incompletely understood. In particular, abnormalities in the numbers and relative proportions of the three major monocyte subsets-classical, intermediate, and non-classical-are described in CKD and end-stage renal disease. In this study, we characterized absolute numbers of blood leukocyte subtypes in adults with renal function varying from normal to advanced CKD. The primary aim was to identify monocyte subpopulations that associated most closely with current estimated glomerular filtration rate (eGFR) and subsequent rate of eGFR decline. Leucocyte and monocyte populations were enumerated by multi-color flow cytometry of whole blood and peripheral blood mononuclear cell (PBMC) samples from adults with CKD stage 1-5 (n = 154) and healthy adults (n = 33). Multiple-linear regression analyses were performed to identify associations between numbers of leucocyte and monocyte populations and clinical characteristics including eGFR and rate of eGFR decline with adjustment for age and gender. In whole blood, total monocyte and neutrophil, but not lymphocyte, numbers were higher in adults with CKD 1-5 compared to no CKD and were significantly associated with current eGFR even following correction for age. In PBMC, classical and intermediate monocyte numbers were higher in CKD 1-5 but only intermediate monocyte numbers were significantly associated with current eGFR in an age-corrected analysis. When intermediate monocytes were further sub-divided into those with mid- and high-level expression of class II MHC (HLA-DRmid and HLA-DRhi intermediate monocytes) it was found that only DRhi intermediate monocytes were increased in number in CKD 1-5 compared to no CKD and were significantly associated with eGFR independently of age among the total (No CKD + CKD 1-5) study cohort as well as those with established CKD (CKD 1-5 only). Furthermore, blood number of DRhi intermediate monocytes alone proved to be significantly associated with subsequent rate of renal functional decline. Together, our data confirm neutrophil and monocyte subset dysregulation in CKD and identify a distinct subpopulation of intermediate monocytes that is associated with higher rate of loss of kidney function.

Infliximab Selectively Modulates the Circulating Blood Monocyte Repertoire in Crohn's Disease.

BACKGROUND: Infliximab (IFX), an anti-tumour necrosis factor alpha (TNFα) monoclonal antibody, provides clinical benefits in treating Crohn's disease (CD) but its mechanisms of action are not fully elucidated. This study investigated blood monocyte repertoires and the acute effects of IFX infusion on monocyte subset phenotype and function in IFX-treated patients with CD. METHODS: Monocytes and monocyte subsets were enumerated and phenotypically characterized by multicolor flow cytometry in freshly isolated blood from healthy controls (n = 21) and patients with CD treated with (IFX, n = 24) and without (non-IFX, n = 20) IFX. For the IFX-CD group, blood was sampled immediately before (tough-IFX) and after (peak-IFX) infusion. Monocyte responses to lipopolysaccharide were analyzed by whole-blood intracellular cytokine staining. RESULTS: Non-IFX and IFX-CD patients had increased numbers of intermediate (CD14CD16) monocytes compared with healthy controls, whereas classical (CD14CD16) and nonclassical (CD14CD16) monocytes were numerically reduced in the IFX-CD group alone. In all groups, monocyte subsets expressed high surface levels of transmembrane (tm)TNFα. After IFX infusion, a significant reduction in monocyte numbers occurred. Post-IFX monocytopenia was proportionately greatest for classical and intermediate subsets, correlated with postinfusion IFX levels and was not associated with monocyte apoptosis. In contrast, lipopolysaccharide-induced production of TNFα and IL-12 by monocytes was significantly reduced in peak-IFX compared with trough-IFX blood samples. CONCLUSIONS: Actively managed CD is associated with monocyte repertoire skewing suggestive of chronic inflammatory stimulation. Infused IFX acutely targets monocytes, likely by binding to tmTNFα, resulting in a non-apoptosis-related decline in circulating monocyte numbers and blunting of the inflammatory response of monocytes remaining in the blood.