Objective To explore the mechanism of Xiaowugui Decoction（XWGD

小乌桂汤） for the treatment of rheumatoid arthritis. Methods Sixty male DBA/1 mice were randomly divided into normal group（n=8） and model group（n=52）. To establish mice model of collagen-induced arthritis（CIA）

chicken type Ⅱ collagen emulsion was intracutaneously injected into the tail root and back of the mice at 3 points. Forty successful CIA model mice were randomly divided into model group

methotrexate group

XWGD low

medium

and high-dose groups

with 8 mice per group. The mice in methotrexate group were given 0.1 mg/ml methotrexate once a week

and the mice in XWGD low

medium and high-dose groups were respectively given 19.5

39

75 g/（kg·d） XWGD once a day. The mice in the normal group and model group were administered with 0.2 ml/10 g normal saline once a day. All the interventions were given by gavage for 4 weeks. The arthritis index score

thickness of the diseased paws and the histopathology of the ankle joint were evaluated. The ratio of helper T cell 17（Th17） and regulatory T cell（Treg） in spleens

and the expression levels of tumor necrosis factor-α（TNF-α）

interleukin-6（IL-6）

interleukin-17（IL-17）

interleukin-1β（IL-1β） and interleukin-10（IL-10） in plasma were detected. Results Compared to model group

the methotrexate group and XWGD medium and high-dose groups significantly decreased the arthritis index score

the thickness of the diseased paws

the ratio of Th17

the expression levels of plasma TNF-α

IL-6

IL-17

and IL-1β

the total ankle joint pathology score

and the pannus-bone destruction score

as well as increased the ratio of Treg; the methotrexate group and XWGD high-dose group significantly decreased the ratio of Th17/Treg and the synovitis score（P<0.05 or P<0.01）. Compared to methotrexate group

XWGD low-dose group had significantly higher Th17 and Th17/Treg in spleen as well as higher total ankle joint pathology score and pannus-bone destruction score; the XWGD low and medium-dose groups had significantly lower ratio of Treg（P<0.05 or P<0.01）. Compared to XWGD low-dose group

the Th17 and Th17/Treg ratio in the medium and high groups significantly reduced

Treg level increased; the total ankle joint pathology score and the pannus-bone destruction score in the high-dose group also significantly decreased（P<0.05 or P<0.01）. The level of Treg in XWGD high-dose group was significantly higher than that of medium-dose group（P<0.01）. Conclusion XWGD has anti-inflammatory and immune regulation effects on CIA model mice

and the high-dose works best. It may reduce the joint inflammation by regulating the balance of Th17/Treg and inhibiting the expression of TNF-α

IL-6

IL-17

and IL-1β.