Human Monocyte-Derived Macrophages Acquire an Inflammatory Phenotype Relative to Risk Factors Typical of Atherogenic Dyslipidaemia

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.