The peripheral naive T cell pool is fairly stable in number, diversity and functional competence in the absence of vigorous immune responses. However, this apparent tranquillity is not an intrinsic property of T cells but involves continuous tuning of the T cell pool composition by homeostatic signals. In the past decade, studies have revealed that naive T cells rely on combinatorial signals from self-peptide-MHC complexes and interleukin-7 for their physical and functional maintenance. Competition for these factors dictates T cell 'space'. In addition, recent studies show that these and other homeostatic factors are offered to T cells on stromal cell networks, which also serve to guide T cell trafficking in secondary lymphoid organs. Such findings suggest the importance of 'place' in the perception and integration of homeostatic cues for the maintenance and functional tuning of the naive T cell pool.
Bibliographical noteFunding Information:
We thank the members of the Jameson and Hogquist laboratories for suggestions and comments. This work was supported by grants from the NIH (S.C.J.) and Japan Society for the Promotion of Science (K.T.).