When the RA patients were divided into the low-disease activity (DAS28<3.2), moderate-disease activity (3.2≦DAS28≦5.1) and high-disease activity (DAS28>5.1) groups, a significant elevation in serum sCD4 levels was noted in the high-disease activity group compared with the low-disease activity group (Fig. 4B and Table 2). Here, SCD5 is linked to rheumatoid arthritis.