Nature Immunology pp 1199 - 1205

Everyone has suffered, at one time or another, from swollen glands or lymph nodes. In the December issue of Nature Immunology, scientists have finally discovered which signals induce this uncomfortable state, in which T cells accumulate in lymph nodes.

Lymph nodes usually swell during microbial infection as a result of T cell entrapment. As such, lymph nodes are the epicenter of the immune system, because certain cells within these structures switch on the T cells and direct them to commence fighting infection. Soman Abraham and colleagues now report that mice with no mast cells (the cells famous for releasing histamine during allergy attacks) did not suffer from swollen lymph nodes when infected with bacteria. When these mice were injected with mast cells, their lymph nodes could swell. Researchers found that mast cells needed be able to produce the immune modulator tumor necrosis factor (TNF). Injection of a chemical compound that activates mast cells also induced lymph node swelling through production of TNF, a swelling accompanied by recruitment of T cells to the lymph node. These results highlight the two-faced nature of mast cells: critical to jump-start our fight against infection, but responsible for our misery during an allergic reaction.