What is the latest understanding for the cause of autoimmune disease (rheumatoid arthritis)?

Nobody Knows: We are not sure what gets the ball rolling, but autoimmune disease in general is a case of "misprogramming" in which the immune system begins to incorrectly recognize the body's own tissues (joints in the case of ra) as though they were foreign. It then attacks them as it would any invading substance. Smoking definitely raises the risk of ra, though we don't know why!