Rituximab targets a protein on B cells, which are part of the immune system (the body’s defense against infections and other harmful substances). B cells produce antibodies, proteins that allow the body to remove infectious or other dangerous particles. B cells also produce chemicals that help other parts of the immune system do their jobs. However, people with rheumatoid arthritis and vasculitis make B cells that do not work the way they should. These abnormal B cells do not interact properly with other parts of the immune system and can attack a person’s own body even if there is no infection (which is called an autoimmune response).
The autoimmune response can result in a number of different symptoms, including inflammation of the joints (arthritis), with symptoms of joint pain, swelling and stiffness. The autoimmune response can also affect blood vessels and cause inflammation, resulting in multiple problems in many parts of the body, including the skin, sinuses, lungs, and kidney. By temporarily removing the harmful B cells, rituximab can help control the arthritis, and can help control inflammation of blood vessels.