Is IL-7 from dendritic cells essential for the homeostasis of CD4+ T cells?
To the Editor: In an article published in the February 2009 issue of Nature Immunology1, Guimond et al. offered an interesting explanation for the slower interleukin 7 (IL-7)-driven homeostatic proliferation of naive CD4+ T cells than of CD8+ T cells1, 2. Guimond et al. concluded that CD4+ T cells can respond efficiently only to IL-7 expressed by dendritic cells but not to IL-7 expressed by stromal cells, which are the main IL-7 producers3, 4. As direct evidence of their hypothesis, Guimond et al. showed that polyclonal CD4+ T cells and CD4+ T cells transgenic for the Marilyn T cell antigen receptor (TCR) proliferated abundantly in bone marrow chimeras in which IL-7 was expressed only by bone marrow–derived cells (IL-7-deficient (Il7−/−) hosts given bone marrow from mice deficient in recombination-activating gene 1 (Rag1−/−)).
