Background/Purpose: Adult-onset Still’s disease (AOSD) is a systemic autoinflammatory disorder characterized by spiking fever, transient rash, arthritis and leukocytosis. Macrophage and neutrophil activation is a hallmark of AOSD. No specific laboratory tests have been known in AOSD. A few serological markers, such as ferritin, CRP, and IL-18, have been used in the clinical settings but their specificity is limited. Although a line of evidence has suggested a genetic contribution to AOSD, the pathogenesis of the disease is still unclear. Non-genetic factors, such as environment, infection and epigenetics, may play pivotal roles in the pathogenesis. Epigenetic mechanisms including posttranslational histone modifications are known to regulate gene expression without altering the genomic sequence. Histone modifications in major rheumatic diseases, such as rheumatoid arthritis, have been investigated, while studies on those in AOSD are limited. From the functional point of view, it is important to analyze the difference of histone modifications in each functional subset of peripheral blood nucleated cells. To examine the pathological condition-specific histone modifications of peripheral white blood cells (WBCs) in AOSD, We have established a novel method for analyzing histone methylation in each subset defined by the surface markers using fluorescence-activated cell sorting (FACS).

Methods: Peripheral WBCs were obtained from patients with active and inactive AOSD and healthy controls (HC). Nine immune cell types were stained with antibodies against surface markers and classified as below: CD4+ T cells, CD8+ T cells, γδT cells, neutrophils, regulatory T cells, B cells, CD14++CD16- monocytes, CD14++CD16+ monocytes and CD14+CD16++ monocytes. All samples were analyzed with a FACSCanto II cytometer. As a quantitative measure of H3K4me3 and H3K27me3, mean fluorescence intensity (MFI) was used. We quantified the serum levels of 10 cytokines (IFN-α, IFN-γ, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12p70, IL-17A and TNF-α) using multiplex bead array assays and IL-18 using ELISA. The correlation between the level of histone methylation and CRP, ferritin and 11 cytokine levels was examined.

Results: The distinction in H3K27me3 and H3K4me3 MFI levels were observed in several WBC subsets when comparing HC and AOSD. Particularly, histone methylation in neutrophils, B cells, and CD14++CD16- monocytes correlated with the disease activity of AOSD. The levels of serum ferritin, CRP, IFN-γ, IL-2, IL-6 and IL-18 were significantly higher in active AOSD than in inactive AOSD. Histone methylation levels in neutrophils, B cells, or CD14++CD16- monocytes correlated with the levels of either CRP, IFN-γ, IL-2 or IL-18. However, there was no significant correlation between serum ferritin and histone methylation. Focusing on CD14++CD16- monocytes, H3K4me3 MFI levels negatively correlated with the levels of IL-18.

Conclusion: Differences in histone modifications were detected by FACS in different subsets of peripheral WBCs in AOSD patients. Aberrant histone methylations in CD14++CD16- monocytes were associated with the disease activity of AOSD. It is indicated that histone methylation could be a novel biomarker for AOSD.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/aberration-of-histone-lysine-methylation-in-adult-onset-stills-disease-are-novel-biomarker-candidates-associated-with-the-disease-activity/