Although the immune system is constantly patrolling for foreign invaders, it attacks neither the bacteria in the gut nor those intestinal cells exposed to the bacteria. Researchers at Dana-Farber Cancer Institute this year announced that a previously unrecognized population of cells in the lymph nodes signals the immune system to tolerate conditions that would normally prompt an attack.
Immunologists already knew that a population of cells called dendritic cells can teach T lymphocytes, also called T cells—key instigators of an immune response—how to react to a particular protein. When the dendritic cells are in a calm environment, they communicate tolerance to T cells. If the dendritic cells are in an environment with microbes or tissue inflammation, they tell the T cells to start an immune system attack. That paradigm left no explanation for how T cells learn to tolerate the conditions in the gut, where cells are constantly in the ...
