The precise causes of psoriasis are unknown. It is generally believed to be caused by damage to factors in the immune system, enzymes, and other materials that control skin cell division. This prompts an abnormal immune response, which causes inflammation and rapid production of immature skin cells.
Inflammatory Response and Autoimmunity
The Normal Immune System Response. The inflammatory process is the result of the body's immune response, which fights infection and heals wounds and injuries:
- When an injury or infection occurs, white blood cells are mobilized to rid the body of any foreign invaders, such as bacteria or viruses.
- The masses of blood cells that gather at the injured or infected site produce factors to repair wounds, clot the blood, and fight infections.
- In the process, the surrounding area becomes inflamed (red and swollen), and some healthy tissue is injured.
The Infection Fighters. The primary infection-fighting units are two types of white blood cells: lymphocytes and leukocytes.
Lymphocytes are a type of white blood cell designed to recognize foreign substances (antigens) and launch an offensive or defensive action against them. Lymphocytes include two subtypes known as T cells and B cells:
- B cells produce antibodies, which are designed to attack the antigens. Antibodies can either ride along with a B cell or travel on their own.
- T cells have special receptors attached to their surface that recognize the specific antigen.
A type of T cell called a helper T cell stimulates B cells and other white blood cells to attack a foreign substance. In psoriasis, however, the helper T cell appears to direct the B cells to produce autoantibodies ("self" antibodies), which attack skin cells. In psoriatic arthritis, cells in the joints also come under attack.
Review Date: 10/21/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.