OBJECTIVETo explore the mechanism of Qingluo Tongbi formula for regulating "immune-bone erosion" in rheumatoid arthritis (RA).METHODSSixty-four RA patients were randomized into two groups to receive treatment with oral methotrexate or Qingluo Tongbi Formula for 12 weeks. Flow cytometry was used to analyze the changes in the percentages of CD3-CD19+, CD19+CD27 and CD19+BAFFR+B cell subpopulations in peripheral blood of the patients, and serum levels of B cell activating factor (BAFF), RANKL, RANK and osteoprotegerin (OPG) levels were detected using ELISA. Before and after the treatment, serum levels of β-CTX, TRACP-5b, BGP, BALP, and PINP were measured with ELISA, and bone mineral density was determined with DXEA dual-energy X-ray absorptiometry. In the cell experiment, RAW264.7 cells were induced to differentiated into osteoclasts and treated with Qingluo Tongbi Formula at low-, moderate and high doses (125, 250 and 500 μg/mL, respectively) or with methotrexate (2 μg/mL) for 48 h, and the changes in the expre