Background/Purpose: Behcet’s disease (BD) is a chronic recurrent, multisystem inflammatory disorder. The phenotypic characteristics include oral aphtha, genital ulcers, uveitis and skin lesions. No specific laboratory tests have been known in BD. Reported in BD have been an increased number of γδ T cells in the peripheral blood and hyperactivity of neutrophils. Although a line of evidence has suggested genetic contributions to the disease, etiopathogenesis of BD is still unclear and non-genetic factors, like environment, infection or 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. The association of specific histone modifications with gene expression is very well defined, such as H3K27me3, which may be characteristics of repressed genes, or H3K4me3, which may present in many active genes. Histone modifications in major rheumatic diseases, such as rheumatoid arthritis, have been investigated, while studies on histone modifications in BD are limited. From the functional point of view, it is important to analyze differences of histone modifications in each functional subclass of the entire peripheral blood nucleated cells. To examine the histone modifications of peripheral white blood cells (WBCs) in BD, we have established a novel method analyzing histone methylation in each subset defined by the surface markers using fluorescence-activated cell sorting (FACS).

Methods: WBCs were obtained from patients with active and inactive BD and healthy controls (HC). Six immune cell types were stained with antibodies against surface markers and classified as below : CD4+ T cells, CD8+ T cells, γδ T cells, CD16+CD66b+ neutrophils, CD4+CD25+Foxp3+ Tregs, and CD19+ B cells. All samples were analyzed with a FACSCanto II cytometer. As a quantitative measure of H3K4me3 and H3K27me3, mean fluorescence intensity (MFI) was used and normalized using isotype controls.

Results: H3K27me3 MFI levels of BD in CD4+T cells, CD8+T cells and γδT cells were significantly decreased, compared with HC. H3K27me3 MFI levels of BD in neutrophils were significantly increased. In contrast, H3K4me3 MFI levels of BD in CD4+T cells, CD8+T cells, γδ T cells and Tregs were significantly decreased, compared with those of HC. H3K4me3/H3K27me3 MFI ratio of BD was significantly lower in neutrophils and Tregs, and higher in γδ T cells of BD than that of HC. H3K27me3 MFI of active BD were significantly decreased in γδ T cells as compared to inactive BD. H3K4me3/H3K27me3 MFI ratio of active BD was significantly higher in γδ T cells than in inactive BD.In addition, the similar result was also observed between active and inactive phasesin the same patients. Preliminary observations suggest IL-17 secretion on γδ T cells in BD.

Conclusion: Differences in histone modifications could be detected by FACS in peripheral WBCs in BD patients. Aberrant histone methylation in γδ T cells may be associated with the pathogenesis of BD. It is suggested that histone methylation could be a new candidate-biomarker for BD and that γδ T cells might be a possible therapeutic target in BD.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/histone-methylation-in-%ce%b3%ce%b4-t-cells-as-a-biomarker-of-behcets-disease-activity/