Expansion of inflammatory monocytes in periphery and infiltrated into thyroid tissue in Graves' disease

Abstract

Monocytes are important mediators of immune system and are reported to be altered in autoimmune disorders. Little is known about the pathological role of monocytes in Graves' disease (GD). Thus, we investigated monocytes in periphery and thyroid tissue in GD. Untreated GD patients were enrolled and followed up until remission. Monocytes were significantly increased and positively correlated with anti-thyrotropin receptor antibody (TRAb) in untreated GD (r_counts = 0.269, P < 0.001; r_percentage = 0.338, P < 0.001). Flow cytometry showed CD14++ CD16+ monocytes were increased and CD14++ CD16- monocytes were decreased in untreated GD (both P < 0.001). Skewed monocyte subsets were recovered in GD with remission. Serum B cell-activating factor (BAFF) was positively correlated with TRAb (r = 0.384 and P = 0.001). CD14++ CD16+ monocytes expressed higher level of BAFF in untreated GD (P < 0.05). The frequency of CD14+ monocytes and CD14+ CD16+ monocytes were significantly higher in GD thyroid tissue than in normal thyroid tissue (both P < 0.001). Our study suggested CD14++ CD16+ monocytes were significantly expanded and involved in the production of TRAb via secreting a higher level of BAFF in periphery. Besides, monocytes infiltrated into thyroid tissue and thus could serve as an important participant in GD pathogenesis.

Figure 1

B cell activating factor (BAFF) expression in monocytes and serum and its correlation with TRAb. (a), BAFF mRNA expression in the monocytes of healthy controls (n = 10), patients with untreated GD (n = 24) and patients with negative TRAb GD in remission (n = 6) using real-time PCR; (b), ELISA assay for BAFF expression in the serum of healthy controls (n = 14), patients with untreated GD (n = 56) and GD patients in remission (n = 12); (c), correlation analysis of TRAb and serum BAFF levels in patients with untreated GD; **P < 0.001.

Figure 2

Characterization of the monocyte subsets in healthy controls and patients with Graves’ disease. (a,b) showed the gating strategy for monocytes, (c–e) representative dot plots of CD14 and CD16 expression on monocytes from healthy controls, untreated GD patients and GD patients in remission; (f) showed the percentages of CD14+ CD16+ monocytes (non-classical monocytes), (g) showed the percentages of CD14++ CD16+ monocytes (intermediate monocytes) and (h) showed the percentages of CD14++ CD16- monocytes (classical monocytes) from healthy control subjects (n = 10), untreated GD (n = 24) and negative TRAb GD in remission (n = 6), (i) showed the mean fluorescence intensity (MFI) of BAFF on different monocytes subsets; *P < 0.05, **P < 0.001.

Figure 3

CD14 and CD16 expressing monocytes in the thyroid tissues of patients with Graves’ disease. Immunofluorescence staining was carried out using the samples of the normal thyroid tissues of patients with thyroid nodules (a–d) and patients with Graves’ disease (e–h). The scale was 100 μm. Cells that co-express CD14 (green) and CD16 (red) markers in a similar location were yellow in color. The frequency of CD14+ , CD16+ and CD14+ CD16+ cells were calculated per high power field (HPF, × 400) in multiple samples: NC (n = 3, 15 sections) and GD (n = 6, 30 sections) were shown in (i–k), respectively; **P < 0.001.