Inflammatory genes TNFα and IL6 display no signs of increased H3K4me3 in circulating monocytes from untreated rheumatoid arthritis patients

Innate immune cells, such as monocytes, can adopt a long-lasting pro-inflammatory phenotype, a phenomenon called 'trained immunity'. In trained immunity, increased cytokine levels of genes, like interleukin (IL)-6 and tumor necrosis factor (TNF)-α, are observed, which are associated with increased histone 3 lysine 4 trimethylation (H3K4me3) in the promoter region. As systemic IL6 and TNFα levels are increased in rheumatoid arthritis (RA) patients and monocytes are known to be the primary producers of TNFα and IL6, we hypothesized that 'trained immunity' signals may be observed at these genes in monocytes from RA patients. CD14+ monocytes were isolated from untreated RA patients and paired age-matched healthy controls. H3K4me3, mRNA, protein and serum levels of IL6 and TNFα were evaluated by chromatin immunoprecipitation, reverse-transcription quantitative PCR and enzyme-linked immunosorbent assays. Despite elevated serum levels of TNFα and IL6 in the tested RA patients (P<0.05), ex vivo isolated monocytes displayed similar H3K4me3 levels to healthy controls in the promoter region of TNFα and IL6. Concordantly, mRNA and protein levels of IL6 and TNFα were similar before and after lipopolysaccharide stimulation between patients and controls. Together, with the current number of individuals tested we have not detected enhanced trained immunity signals in circulating monocytes from untreated RA patients, despite increased IL6 and TNFα serum levels.