[Role of IgG plasma cells in the change of protein C system in ulcerative colitis]

The present study is designed to explore the role of plasma cells in the change of protein C system (PCS) in ulcerative colitis (UC). Dextran sulfate sodium (DSS, 4% in concentration) was used to induce mouse UC model. The plasma cells and the type of immune complex in colon were observed by immunofluorescence. The amount and type of plasma cells separated from colonic mucosal lamina propria were detected by flow cytometry using anti-CD54⁺CD38⁺ and IgA/M/G antibodies, respectively. After stimulation of macrophages by IgG type immune complex, TNF-α and IL-6 levels were evaluated by ELISA. After co-incubation of microvascular endothelial cells with TNF-α or IL-6, the expressions of endothelial protein C receptor (EPCR) and thrombomodulin (TM), and the activity of activated protein C (APC) were examined. As the results showed, the IgG type plasma cells infiltration and the quantity of IgG type immune complex were increased in DSS group in comparison with control group. After incubation with IgG type immune complex, the levels of TNF-α and IL-6 in the supernatant of macrophages were increased (P < 0.01) in a concentration-dependent manner. Meanwhile, after incubation with TNF-α or IL-6, the expressions of EPCR and TM in the microvascular endothelial cells were decreased (P < 0.05 or P < 0.01), while the activity of APC was reduced (P < 0.05 or P < 0.01). These results suggested that the quantity of IgG type plasma cells increases in UC and forms immune complexes, which affect the secretion of cytokines from macrophage, thereby affecting the function of endothelial cells and finally inhibiting PCS in UC. Therefore, plasma cell may be a novel target for the treatment of UC.