Causes:

Researchers do not know the exact causes of inflammatory bowel disease. IBD appears to be due to an interaction of many complex factors including genetics, impaired immune system response, and environmental triggers. The result is an abnormal immune system reaction, which in turn causes an inflammatory response in the bodyâ ' s intestinal regions.

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 turn against the body's own cells.
• TH cells also secrete or stimulate the production of powerful immune factors called cytokines. 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.

Helper T cells are further categorized as TH1 and TH2. An imbalance in these two types appears to occur in IBD, although each disorder has a different balance.

Genetic Factors

Although the exact causes of inflammatory bowel disease are not yet known, genetic factors certainly play some role. Between 10 - 20% of people with ulcerative colitis have family members with the disease. Several identified genes and chromosome locations play a role in the development of ulcerative colitis, Crohn's disease, or both. Genetic factors appear to be more important in Crohn's disease, although there is evidence that both forms of inflammatory bowel disease have common genetic defects.

The first important genetic discovery for Crohnâ ' s disease was the identification of the genetic variant CARD15 (also called NOD2), which alters the immune system so that it launches an over-reaction in response to bacteria, causing inflammation. However, this genetic factor only affects a small percentage of Crohnâ ' s disease cases and is not involved with ulcerative colitis.

In recent years, scientists have made significant genetic research breakthroughs including identifying variants in interleukin-23 receptor (IL23R), which appears to be linked to increased or decreased risk for both Crohnâ ' s disease and ulcerative colitis. Other genetic risk factors are also being investigated.

Infections

Measles. Some studies have reported that children with IBD may have had more and earlier childhood infections. The measles virus has been of particular interest. According to the U.S. Centers for Disease Control, and many studies, the measles virus does not cause Crohnâ ' s or IBD.

Much publicity has centered on whether the vaccine for measles, mumps, and rubella (the MMR vaccine) causes conditions such as autism and Crohnâ ' s disease. This theory has been rigorously reviewed and refuted in many well-conducted studies. The evidence clearly indicates that the MMR vaccine does not increase the risk of Crohnâ ' s disease, other inflammatory bowel disease, or autism.

Dietary Factors

Inflammatory bowel disease is much more prevalent in industrialized nations and in higher-income groups. However, there is no strong evidence that diet or particular types of food cause Crohnâ ' s disease or ulcerative colitis.