Smoking has a direct effect on inflammation in the intestines, say Korean researchers. Their study, published in the journal Frontiers in Immunology, found that exposing mice to cigarette smoke as adults caused an inflammation of the colon that resembled Crohn's disease.

Previous studies had indicated that smoking increased the risk of Crohn's disease, a chronic disease that produces inflammation of the digestive system, but the mechanism was unknown. The new study identified a specific white blood cell and inflammatory protein that was responsible.

"The airways and the intestinal system have a lot in common," said Hyunsu Bae of Kyung Hee University in South Korea. "Interestingly, in Traditional Korean Medicine, a connection between the lung and the large intestine has long been emphasized.

"Crohn's disease is more likely to occur in people with airway diseases, suggesting that inflammation in the lungs is linked with inflammation in the gut."

It was no surprise that mice exposed to cigarette smoke showed significant inflammation in their lungs compared to those exposed to clean air. But they also suffered from a type of colitis resembling Crohn's disease.

The researchers found increased levels of mucus and inflammation in the colon, and blood in the feces of the smoke-exposed mice. They also found increased levels of CD4+ T cells, a type of white blood cell, which were releasing a pro-inflammatory protein called interferon-gamma.

Further research found that mice who had few CD4+ T cells and those that couldn't produce interferon-gamma didn't develop inflammation in their lungs when exposed to cigarette smoke. In addition, researchers took CD4+ T cells from tissue near their lungs and injected it into mice that had never been exposed to smoke. Surprisingly, the injected cells migrated to the colon, and the non-smoke-exposed mice developed colitis.

"Our results suggest that cigarette smoking activates specific white blood cells in the lung, which might later move to the colon, triggering bowel inflammation," explained researcher Jinju Kim.  

"Smokers, especially those who also have bowel disease, should reduce their smoking." The findings could also help scientists to develop new treatments for Crohn's disease.

Recent research also found a that a bout of food poisoning increases the risk of developing Crohn's disease. A study by Canada's McMaster University found that the bacteria that cause food poisoning increases growth of adherent-invasive E. coli (AIEC) in the gut. Levels of AIEC, a pathogenic form of E. coli, are associated with the development of Crohn's disease. AIEC promotes inflammation, and levels remain high even after food poisoning is cured.