Causes of rheumatoid arthritis. Rheumatoid arthritis is an autoimmune condition, which means it is caused by the body’s immune system attacking itself. However, it is not yet known what triggers this.Normally, your immune system makes antibodies that attack bacteria and viruses, helping fight infection.auses of rheumatoid arthritis. Rheumatoid arthritis is an autoimmune condition, which means it is caused by the body’s immune system attacking itself. However, it is not yet known what triggers this.