How a young T cell is educated may dictate its future function, according to a new report by Li et al. (page 2145).
Young T cells receive survival signals through their T cell receptors during development. These signals are normally provided by epithelial cells in the thymus. But recent reports show that CD4+ thymocytes also signal to each other.
When stimulated by antigen, epithelium-educated CD4+ thymocytes can become helper T cells of all varieties—T helper (Th)-1, Th2, or Th17 cells—depending largely on the surrounding cytokines. But self-educated thymocytes, Li et al. now find, fail to make this lineage choice. These cells rapidly generated both interferon (IFN)-γ and interleukin (IL)-4, even when stimulated under conditions that normally inhibit IL-4 production. A ready-to-fire IL-4 locus and preformed IL-4 mRNA in the developing cells explained their tendency to continue synthesizing IL-4.
Mice whose thymocytes were...
