To establish and evaluate an animal model of rheumatoid arthritis (RA) comorbid with depression.

A rat model of RA comorbid with depression was established based on a model of type II collagen-induced arthritis (CIA) combined with chronic unpredictable mild stress. Evaluation of mice behavior was performed by the Open-field test and sucrose preference test. Serum IL-27, IL-17, and IL-10 levels were determined by ELISA. One-way ANOVA and LSD-t test were used for the overall comparison between groups.

The ankle joints of rats in the model group were swollen and deformed, accompanied with retardation of movement and lack of pleasure. On the 28th day after modeling, the body mass of rats in the depression alone group [(63.6±2.5) g vs (179.5±3.7) g, F=7.64] and comorbidity group [(152.2±3.2) g vs (179.5±3.7) g, F=12.37] was significantly lower than that of the normal control group (t=-2.383, P=0.019; t=-3.887, P=0.010). On the 22nd day after chronic stress stimulation, the intake of sugar water in the depression alone group [(19.8±0.3) g vs (31.7±0.8) g] and comorbidity group [(18.9±0.1) g vs (31.7±0.8) g, F=26.71] was significantly lower than that of the normal control group (t=6.71, P=0.016; t=5.12, P=0.023). The horizontal score [(54.41±6.42) points vs (98.34±4.83) points] and vertical score [(19.83±2.31) points vs (36.03±2.75) points] in the depression alone group after stimulation were significantly lower than those of the normal control group (t=5.31, P=0.023; t=2.34, P=0.042). The horizontal score [(38.35±3.28) points vs (98.34±4.83) points] and the vertical score [(12.73±3.42) points vs (36.03±2.75) points, F=7.31] of the comorbidity group were significantly lower than those of the normal control group (t=3.96, P=0.032; t=3.26, P=0.035). The levels of IL-27, IL-17, and IL-10 in the model group [(297.97±34.23) ng/L vs (212.43±14.52) ng/L; (184.62±33.71) ng/L vs (109.40±9.81) ng/L; (162.74±25.38) ng/L vs (131.51±20.43) ng/L] were significantly higher than those in the control group (t=4.78, P=0.0291; t=2.57, P=0.032; t=5.33, P=0.023).

The comorbidity group rats showed typical characteristics of arthritis and depression, such as ankle swelling, deformity, and lack of pleasure. The above symptoms are consistent with the clinical characteristics of patients with RA comorbid with depression. The model has high reproducibility and is easy to operate, and it is an ideal model for the study of RA combined with depression.