Helen Williams

Background: Dyslipidaemia promotes atherosclerotic plaque formation. Plaques that are vulnerable to rupture have a higher proportion of inflammatory (M1:CD86) macrophages in their cap. Many plaque macrophages are derived from blood monocytes which have been exposed to elevated blood lipid levels. Here, we explored whether the inflammatory state of monocyte-derived macrophages is associated with blood lipid levels and assessed whether oxidised low-density lipoprotein (oxLDL) directly induces some of the observed changes. Method: Blood was collected from 20 individuals. Lipid profiles were measured, and monocytes differentiated into macrophages. Macrophage inflammatory state was assessed by flow cytometry for phenotypic markers (e.g., CD86 and CD163) and cytokine production: TNF, IL-1β, and IL-6. Furthermore, monocytes were isolated from 6 normo-lipidaemic individuals and cultured with oxLDL, followed by stimulation with LPS/IFNγ and assessment of the cytokine response. Results: The inflammatory phenotype acquired by macrophages (ex vivo) was related to levels of in vivo circulating lipids. Correlations for CD86/CD163 were found with CVD risk markers; most strongly with triglycerides (TG) and TG/HDL-C, but also with cholesterol/HDL-C and ApoB/ApoA1 and inversely with LDL particle size. Functionally, macrophage production of inflammatory cytokines (TNF and IL-1β) correlated with oxLDL levels and inversely with ApoA1. Macrophages differentiated from monocytes cultured with oxLDL produced significantly higher IL-1β but lower IL-10 (in response to LPS/IFNγ), compared to control cells. Conclusions: Monocyte-derived macrophages adopt an inflammatory phenotype relative to the levels of circulating lipid factors that are characteristic of atherogenic dyslipidaemia (such as high TG, TG/HDL-C and low LDL particle size), but not LDL-C.

The three subsets of human monocytes, classical, intermediate, and nonclassical, show phenotypic heterogeneity, particularly in their expression of CD14 and CD16. This has enabled researchers to delve into the functions of each subset in the steady state as well as in disease. Studies have revealed that monocyte heterogeneity is multi-dimensional. In addition, that their phenotype and function differ between subsets is well established. However, it is becoming evident that heterogeneity also exists within each subset, between health and disease (current or past) states, and even between individuals. This realisation casts long shadows, impacting how we identify and classify the subsets, the functions we assign to them, and how they are examined for alterations in disease. Perhaps the most fascinating is evidence that, even in relative health, interindividual differences in monocyte subsets exist. It is proposed that the individual’s microenvironment could cause long-lasting or irreversible changes to monocyte precursors that echo to monocytes and through to their derived macrophages. Here, we will discuss the types of heterogeneity recognised in monocytes, the implications of these for monocyte research, and most importantly, the relevance of this heterogeneity for health and disease.

Monocytes play a key role in cardiovascular disease (CVD) as their influx into the vessel wall is necessary for the development of an atherosclerotic plaque. Monocytes are, however, heterogeneous differentiating from classical monocytes through the intermediate subset to the nonclassical subset. While it is recognized that the percentage of intermediate and nonclassical monocytes are higher in individuals with CVD, accompanying changes in inflammatory markers suggest a functional impact on disease development that goes beyond the increased proportion of these ‘inflammatory’ monocyte subsets. Furthermore, emerging evidence indicates that changes in monocyte proportion and function arise in dyslipidemia, with lipid lowering medication having some effect on reversing these changes. This review explores the nature and number of monocyte subsets in CVD addressing what they are, when they arise, the effect of lipid lowering treatment, and the possible implications for plaque development. Understanding these associations will deepen our understanding of the clinical significance of monocytes in CVD.

Hypertrophic scars (HTS) remain a common outcome of burn injury, particularly in children. They can arise from variations in the wound healing stages, such as an excessive inflammatory response or inefficient remodelling. Of the cells contributing to these healing stages, macrophages and fibrocytes are crucial. Specifically, the inflammatory phase is dominated by M1 macrophages, the proliferation/remodelling stages by M2 macrophages, and scar tissue contains numerous fibrocytes. As the progenitors to these cells, monocytes, can also exhibit M1‐ and M2‐skewing, we proposed that their profile, or circulating fibrocyte counts, could be used to predict poor healing outcomes. To investigate this, we obtained blood samples from paediatric controls and burns patients, which were then divided into HTS and NoHTS groups upon scar assessment at 12 months. The samples were assessed by whole blood flow cytometry to quantify fibrocytes and monocyte subset proportions and to determine monocyte levels of M1 (CD86, CD120b, CD319) and M2 (CD93, CD163, CD200R) markers. Both burns groups had higher proportions of classical monocytes compared to controls, indicating increased cell turnover and/or entry of other subsets into the wound. In burns patients who took more than 21 days to heal, the HTS group had lower M2 (CD200R) expression with the ratio of M1/M2 (CD86/CD200R) being significantly higher. These results suggest an elevated early inflammatory monocyte response contributes to development of HTS. Correlations of marker expression with remaining healing time revealed a significant positive correlation with M1 (CD120b) and M1/M2 (CD120b/CD200R), suggesting a potential role for CD120b as an indicator of healing delay. Fibrocytes did not significantly differ between the groups. In conclusion, increased monocyte inflammation likely contributes to slower healing and development of scarring, but further studies are needed to determine the predictive power of monocyte inflammatory profile.

Background: While many risk factors for preeclampsia, such as increased body mass index, advanced maternal age, chronic hypertension, diabetes, are now established in clinical practice, maternal lipid profile has not been included in the risk assessment for preeclampsia. We aim to characterize the serum levels of Total Cholesterol (TC), High density lipoprotein (HDL), Low density lipoprotein (LDL), Triglycerides (TG), Apolipoprotein A1, Apolipoprotein B and their ratios TC/HDL and ApoB/ApoA1 in the maternal and fetal circulations of normal pregnancy, preeclampsia (PE), fetal growth restriction (FGR) and PE + FGR. Methods: A prospective cross-sectional case control study was conducted measuring maternal and fetal lipid levels by enzymatic analysis and immune-turbidimetric enzymatic assays. FGR was defined by elevated umbilical artery Doppler resistance in association with estimated fetal weight < 10%. Kruskal Wallis non-parametric analysis of variance was used to test for homogeneity across the clinical groups for each of the variables, Mann-Whitney tests for pairwise comparisons and Spearman rank correlation were used to quantify gestational age-related changes. Results: (1) TG levels were elevated in maternal PE and cord blood PE + FGR groups compared to normal pregnancies. (2) A statistically significant elevation of fetal ApoB levels was observed in PE, FGR and PE + FGR compared to normal pregnancies. Apolipoprotein levels A1 and B were not different between maternal groups. (3) TC, HDL, LDL and TC/HDL levels did not show any significant gestational variation or between clinical groups in the maternal or fetal circulation. Conclusions: Elevation in maternal TG levels may have a role in the pathogenesis of PE. The implications of elevated maternal and fetal TG levels and elevated fetal Apolipoprotein B levels deserves further exploration of their role in long term cardiovascular risk in the mother as well as the offspring.

Background: There is little available data on fetal monocyte phenotype and function. A prospective cross-sectional pilot study was conducted to describe the cord blood monocyte subset phenotype in preeclampsia (PE) and fetal growth restriction (FGR) as compared to normal pregnancy and maternal circulation. Methods: Maternal and cord blood samples from 27 pregnancies were collected at delivery from normal pregnancy, PE, FGR and PE+FGR. The distribution of fetal monocyte subtypes was characterized by CD14 and CD16 expression using flow cytometry and compared for each clinical group using a classification of classical, intermediate and non-classical subsets. Results: The intermediate monocytes were the dominant monocyte subset in the cord blood of PE and PE+FGR with an increase in the combined inflammatory monocyte subsets intermediate and non-classical in PE compared to normal pregnancy. The non-classical monocyte subset proportion was elevated in all pathological groups PE, FGR and PE+FGR. A significant reduction in the non-classical monocyte subset was observed in the cord blood of the normal pregnancy group as compared to the maternal circulation. Conclusion: This study describes for the first time in the fetal circulation, dominant monocyte intermediate subsets and increased inflammatory subsets in PE as well as increased non-classical subsets in PE and FGR compared to normal pregnancy.

Monocytes are key contributors in various inflammatory disorders and alterations to these cells, including their subset proportions and functions, can have pathological significance. An ideal method for examining alterations to monocytes is whole blood flow cytometry as the minimal handling of samples by this method limits artifactual cell activation. However, many different approaches are taken to gate the monocyte subsets leading to inconsistent identification of the subsets between studies. Here we demonstrate a method using whole blood flow cytometry to identify and characterize human monocyte subsets (classical, intermediate, and non-classical). We outline how to prepare the blood samples for flow cytometry, gate the subsets (ensure contaminating cells have been removed), and determine monocyte subset expression of surface markers — in this example M1 and M2 markers. This protocol can be extended to other studies that require a standard gating method for assessing monocyte subset proportions and monocyte subset expression of other functional markers.

Aim: Monocytes are likely to play a significant role in the pathogenesis of preeclampsia (PE) and intrauterine fetal growth restriction (IUGR), given their role in homeostasis and tissue repair. Our aim was to study the gestational changes in monocytes in normal pregnancy and to determine whether monocyte subsets and phenotype are altered in pregnancy complications, such as PE and IUGR.Methods: A prospective cross‐sectional case–control study was conducted. Pregnant women between 24 and 40 weeks of gestation (n = 54) were recruited and classified into four clinical groups of normal pregnancy, PE, IUGR and PE + IUGR. The maternal monocyte subsets classical, intermediate and nonclassical were compared for each clinical group. Monocyte polarization towards M1 (inflammatory) and M2 (repair) phenotypes was assessed by surface expression of CD86 and CD163 ratio, using flow cytometry.Results: The classical monocytes were reduced and intermediate monocyte elevated compared to normal pregnancy in PE, IUGR and PE + IUGR in gestations <37 weeks and IUGR in 26–40 weeks. CD163 expression was increased and CD86/CD163 ratio decreased in IUGR compared to normal pregnancy for all subsets. Nonclassical monocyte counts and CD163 expression increased with advancing gestation in normal pregnancy.Conclusion: These results show for the first time, a shift towards increased intermediate maternal monocyte subtype in IUGR and in preterm PE as well as skewing of maternal peripheral monocytes (all subsets) towards M2 phenotype in pregnancies complicated by IUGR.