Rheumatic diseases, such as rheumatoid arthritis (RA), lupus and multiple sclerosis, are caused by autoimmune responses. While in immune deficiency disorders the immune system fails to elicit the appropriate immune responses, in autoimmune disorders the immune system overresponds against one’s own antigens. This failure to distinguish between self and nonself antigens arises from breach of immune tolerance, the preventative mechanisms the immune system has in place to prevent attacking itself.1 Autoimmunity could affect specific tissues or it could be systemic (lupus). Some diseases such as ankylosing spondylosis are considered both autoimmune as well as inflammatory arthritic diseases.
Examples of rheumatic diseases investigated in clinical research
Rheumatoid arthritis (RA) is an autoimmune disorder characterized by inflammation and damage of the joints throughout the body, including hands and feet and affects about 0.5–1% of the population, being more common among women than men in the United States.2
Systemic lupus erythematosus (SLE) is a chronic inflammatory autoimmune disease. It affects multiple organ systems, such as the skin, kidneys, lungs and the central nervous system, by producing autoantibodies.3
Ankylosing spondylosis (AS) is a chronic, progressive inflammatory rheumatic disease of the axial musculoskeletal system caused by multiple genes.4
Rheumatoid Arthritis
Types of RA
RA could be divided into two categories:
- Anti-citrullination protein antibodies (ACPA) positive
- ACPA negative
During inflammation, the amino acid arginine is converted into citrulline by peptidylarginine deaminase (PAD). This process, called citrullination, elicits formation of antibodies, which are almost certain indicators of development of RA within a few years.5 The ACAP positive type is more aggressive than the ACPA negative type.6
