Unique Cell Population Involved In Granuloma Formation In The Intestine

Infection with some microbes (such as the microbe that causes tuberculosis) and some cases of tissue damage (such as occurs in Crohn disease) result in a localized chronic inflammatory response that causes the formation of granulomas (small cellular nodules).

Although the cellular content of granulomas is reasonably well characterized, epitheloid cells (probably immune cells known as macrophages) surrounded by immune cells known as lymphocytes, the mechanisms of granuloma formation are not well defined.In a study that appears online in advance of publication in the March print issue of the Journal of Clinical Investigation, Atsushi Mizoguchi and colleagues from Massachusetts General Hospital, Boston, identify a unique cell population that promotes intestinal granuloma formation in mice. This cell population was defined by expression of the dendritic cell (DC) marker CD11c and the macrophage marker F4/80 and by production of the soluble factor IL-23. These DC-like cells were unable to induce granuloma formation in the presence of IL-4 and IgG and if microbes were absent from the gut, indicating that both host and environmental factors can modulate granuloma formation induced by these cells. This study therefore identifies a population of cells that is crucial for granuloma formation under Th1 conditions. As others have recently identified a similar population of cells in the lungs of mice infected with the agent that causes tuberculosis it seems probable that these cells will have a role in granuloma formation in other tissues.(Source: Journal of Clinical Investigation : Harvard Medical School : March 2007.)