Background/Purpose: Behcet’s disease (BD) is systemic inflammatory vasculitis with unknown etiology. As a critical compartment in innate immunity, macrophages may play a role in BD. According to the phenotype and cytokine expression, macrophages can be classified into 2 subtypes, the pro-inflammatory classically activated macrophages (M1) and the anti-inflammatory alternatively activated macrophages (M2). However, the mechanism of how macrophage polarization is involved in BD is yet unidentified. Here we aim to investigate the effect of the BD serum on the phenotype and the functions of macrophages.

Methods: Thirty treatment-naïve active BD patients from our center and 30 gender- and age-matched healthy controls (HC) were included in this study. The monocytes of HC were isolated from PBMCs through CD14⁺ microbeads and further cultured into M0 macrophages. Then the macrophages were polarized to M1 macrophages with LPS and IFNγ, and to M2 macrophages with IL4. Serum from BD patients and HC was applied to the human monocyte-derived macrophages (HMDM). The cell surface markers and the cytokines in the supernatant were detected and compared to the phenotypes of M1 and M2 macrophages. The phagocytosis of different HMDMs was determined by the cellular uptake of Dextran. In order to investigate the effect of different HMDMs on the differentiation of Th1 and Th17 cells, HMDMs were co-cultured with naïve CD4⁺ T cells and the intracellular cytokines as well as the nuclear transcription factor were detected by FACS. Western-blot analysis was performed to detect the expression of JAK1, STAT1 and their phosphorylated forms in the HMDMs when stimulated with BD serum.

Results: Compared to M0 macrophages, BD serum stimulated HMDM had an increased expression of CD86 (p=0.024) and a decreased CD163 expression (p=0.009). The secretion of IL12 (p=0.019) and TNFα (p=0.0295) was also increased. The HC serum stimulated HMDM, however, had a similar phenotype with M0 macrophage. All these observations suggested BD serum could promote M1 polarization. BD serum also led to a significant increase in macrophage phagocytosis (p=0.011), which was similar with M1 phenotype (p=0.014). Moreover, M1 phenotype macrophages and BD serum treated macrophages can both promote naïve CD4⁺ T cells to differentiate into Th1 cells, characterized by increased IFNγ and T-bet (IFNγ: M1 p=0.037; M_BD p=0.048. T-bet: M1 p=0.0009; M_BD p=0.0121). No significant increase of IL17A was noted in both M1 phenotype macrophages as well as BD serum treated macrophages. After stimulating HMDM with BD serum for 5 minutes, the expressions of phosphorylated JAK1 and phosphorylated STAT1 were both elevated (p_JAK1=0.0228, p_STAT1=0.0101), indicating a role if JAK1-STAT1 pathway in the BD serum treated macrophage polarization and the pathogenesis of BD.

Conclusion: Serum from patients with BD could promote M1 macrophage polarization via the JAK1-STAT1 pathway, and could also increase the macrophage phagocytosis and drive Th1 differentiation.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/aberrant-m1-polarization-of-macrophages-in-behcets-disease/