Pathogenic mechanism of miR-21 in autoimmune lymphoid hyperplasia syndrome.

miR-21 plays an important role in immune responses and inflammatory diseases, but the mechanism of action of miR-21 in autoimmune lymphoid hyperplasia syndrome still remains unclear. The aim of the present study was to assess the mechanism of miR-21 in autoimmune disease, particularly, the autoimmune lymphoid hyperplasia syndrome. The pathology and immunity-related phenotypes of miR-21 transgenic mice, and the lymphocyte subsets were analyzed. The related T cell subsets and germinal center B (GCB) cells generated at the germinal center were detected with flow cytometry. The target genes of miR-21 were evaluated with the luciferase reporter gene method. The homeostatic proliferation of the lymphocytes was detected with the EdU incorporation assay. Inflammatory infiltration occurred to the lung and liver of the transgenic mice at 8 weeks. The frequency of the regulatory helper T cells decreased slightly. Significantly increased double negative T cells were observed in the spleen of the transgenic mice (P<0.05). The immunoglobulins IgG1, IgG2a, IgG2b, and IgG3 in the serum of the transgenic mice aged 8 weeks were significantly higher than those in the wild-type mice aged 8 weeks (P<0.05). The percentages of the GCB cells in the peripheral lymphoid organs such as lymph nodes, mesenteric lymph nodes, PP and spleen in the transgenic mice aged 8-52 weeks increased significantly (P<0.05). The percentage (26.32%) of the newly-formed GCB cells derived from transgenic mice was significantly higher than that (3.87%) of the GCB cells derived from the wild-type mice. miR-21 played a role of negative feedback regulation by inhibiting the NF-κB signal pathway. The highly-expressed miR-21 B cells promoted homeostatic proliferation of the T cells. miR-21 can promote homeostatic proliferation of lymphocytes by inhibiting the NF-κB signal pathway.