Causes of Crohn's Disease

Causes

Inflammatory bowel disease has many different causes. It is due in many cases to a genetic susceptibility that enables an organism such as a virus or bacteria to trigger an abnormal immune reaction, which in turn, causes an inflammatory response in the intestines. Although Crohn's disease has features that resemble an autoimmune disease (in which the body's immune system attacks its own cells), some researchers think that it may be due to initial immune deficiencies.

The Inflammatory Response

The Immune System's Infection Fighters. The primary infection-fighting units are two types of white blood cells: lymphocytes and leukocytes.

Lymphocytes include two subtypes known as T cells and B cells. Both types of cells are designed to recognize foreign invaders (antigens) and to launch an offensive or defensive action against them:

• B cells produce antibodies, which are separate substances that can either ride along with a B cell or travel on their own to attack the antigen.
• T cells have special receptors attached to their surface that recognize the specific antigen.

T cells are further categorized as killer T cells or helper T cells.

• Killer T cells directly attack antigens that occur in any cells that contain a nucleus.
• Helper T cells also recognize antigens, but their role is two fold. They stimulate B cells and other white cells to attack the antigen. They also produce cytokines, powerful immune factors that have an important role in the inflammatory process.

Helper T cells and Inflammatory Bowel Disease. The actions of the helper T cells (TH cells) are of special interest in inflammatory bowel disease:

• TH cells stimulate other white blood cells called B cells to produce antibodies. In this case, however, they appear to direct the B cells to produce autoantibodies, which are directed against the body's own cells.
• TH cells also secrete or stimulate the production of powerful immune factors called cytokines. In small amounts, cytokines are indispensable for healing. If overproduced, however, they can cause serious damage, including inflammation and cellular injury. Cytokines, particularly specific ones known as tumor necrosis factor, interferon-gamma, and interleukins, cause intestinal inflammation and damage, which, in a vicious cycle, attract even more helper T cells.