When compared with that of several autoimmune diseases, the percentage of CD27+ memory B cells remained higher in SP (42.7±11.6% for SP patients, 29.4±11.3% for NoP controls, 29.9±19.8% for patients with rheumatoid arthritis (n = 52), 24.9±19.9% for patients with primary Sjögren’s syndrome (n = 48) and 40.2± 21.8% for patients with SLE (n = 50), personal data). Here, CD27 is linked to rheumatoid arthritis.