A previously unknown network of immune cells has been discovered in the mammalian gastrointestinal system by a research group based in the Center for the Study of Inflammatory Bowel Diseases at Massachusetts General Hospital (MGH). The finding, reported in the January 14 issue of Science, could lead to better understanding of how the immune system recognizes and responds to dangerous bacteria and viruses and to new approaches to immunization and infectious disease treatment.

"We found an extensive system of immune cells throughout the intestinal tract that take up bacteria and other antigens, giving us a new target for understanding the immune response," says Hans-Christian Reinecker, MD, of the MGH Gastrointestinal Unit, the study's senior author.

The investigation focused on dendritic cells which are found in tissues in direct contact with the external environment, such as the skin, lungs and digestive system. Characterized by long extensions called dendrites, dendritic cells continually sample their environment for bacteria and viruses. When dendritic cells encounter pathogens, they ingest them, break them down and then transport protein fragments to the cellular membrane. On the cells' surface the fragments are displayed to other immune system cells, which will recognize the proteins as antigens to be destroyed.

Exactly how dendritic cells monitor intestinal contents and recognize harmful organisms was unknown, and learning more about that process was a goal of the current study. The researchers conducted several experiments using genetically altered mice in which one or both copies of a gene required for cell migration and dendrite formation was replaced with a gene that produces a fluorescent protein. Examination of the animals' tissues revealed populations of dendritic cells throughout the small intestine in a layer just below the epithelial lining. It previously had been believed that gastrointestinal dendritic cells were
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Contact: Sue McGreevey
smcgreevey@partners.org
617-724-2764
Massachusetts General Hospital
13-Jan-2005

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