E. coli may spark immune reaction in bowel disease

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E. coli may spark immune reaction in bowel disease

By Merritt McKinney

NEW YORK, Feb 05 (Reuters Health) - A common type of bacterium may be

involved in some cases of inflammatory bowel disease, new research

suggests.

Infection with E. coli seems to kick off an immune response that could

lead to the inflammation that occurs in Crohn's disease and other types

of inflammatory bowel disease, according to scientists in France.

Crohn's disease symptoms include pain, abdominal cramps, diarrhea,

bleeding and weight loss. Drugs called corticosteroids and surgery to

remove the portion of the intestine affected by the disease may relieve

symptoms, but there is no cure.

Scientists recently identified a gene defect linked to Crohn's, although

the mutation is thought to account for only a small percentage of cases.

People with Crohn's are often infected with a diarrhea-causing strain of

E. coli bacteria. Since Crohn's and other types of inflammatory bowel

disease occur when the immune system wages an attack on the body's own

tissue, Dr. Antoine Toubert, of the Hopital Saint-Louis in Paris, and

colleagues took a close look at what happens when this strain of E. coli

infects intestinal cells.

The investigators found that when E. coli infects the gut, levels of a

molecule called MICA rise rapidly in the cells lining the intestine. The

surge in MICA molecules sets off a chain reaction, causing " natural

killer " immune cells to release an immune-stimulating protein called

gamma interferon.

The research suggests that the interplay between E. coli and the cells

it infects " could activate multiple pathways of the immune system, "

Toubert told Reuters Health. He noted that MICA molecules seem to play

an important role in the so-called innate immune system.

By activating MICA molecules, infection with E. coli could trigger

autoimmune diseases such as Crohn's in some susceptible people, he

explained.

The research was conducted on cells in the lab, so Toubert and his

colleagues measured MICA levels in colon tissue samples from patients

with Crohn's and a " control " group of healthy people. In support of the

idea that rising MICA levels kick off an immune response, the

researchers found that Crohn's patients had higher levels of MICA than

controls.

The findings are published online in the Proceedings of the National

Academy of Sciences Early Edition.

A potential practical application of the research, according to Toubert,

might be to see whether treating E. coli infection with antibiotics

would be beneficial to people with active Crohn's disease. He stressed,

though, that the study is still on a basic science level and that much

more research needs to be done.

The findings may have implications for the study of cancer, Toubert and

his colleagues suggest in their report. They note that MICA molecules

are expressed in a variety of tumors. Though the possible role of E.

coli in cancer is uncertain, the researchers note that E. coli infection

in the colon has been associated with colorectal cancer.

SOURCE: Proceedings of the National Academy of Sciences Early Edition

2002;10.1073.