Glowing mouse shows how immune alarm rallies troops against invasion

In the body, dendritic and other antigen-presenting cells initially handle all infections in the body. The dendritic cells lurk in the skin, lungs, gut, and other tissues. On sentry duty, they continually snack on things around them, which might include a pathogenic bacterium. When a dendritic cell has gobbled a germ, it stops snacking and races to the nearest lymph node to alert the T cells, which command the more complex immune responses. Scientists believed that the dendritic cell arrived in the lymph node with the antigen complex in full view, like a peacock with all its feathers on display. There, many varieties of T cell swarmed around until the right one came along, since each T cell senses a different kind of germ antigen. Or so the story went. Now it appears that dendritic cells may save most of their antigen cargo for the right T cells. Time-lapse video produced in two Harvard Medical School labs shows the way captured antigen fragments may progress to the surface of live dendritic cells. The study was published in the Aug. 29, 2002 issue of the journal Nature.