Pain and Swelling of Rheumatoid Arthritis
As it happens, when the immune system becomes de-regulated, you see the joint capital has a lining of tissues called the synovium.
The Synovium makes fluid that keeps joint lubricated, when you have Rheumatoid Arthritis, your immune system send antibodies to Synovium and causes inflammation.
This causes pain and joint damage, especially in small joints, in finger and wrist. But it can effect any joint.