In the arthritis model, Robo4-deficient (Robo4−/−) and wild-type (Robo4+/+) mice were subcutaneously injected with type II collagen with Freund’s complete adjuvant twice, and their rheumatoid arthritis scores were subsequently assessed according to the evaluation criteria (Fig. 6a and Table S4). This evidence concerns the gene ROBO4 and rheumatoid arthritis.