Cytokine requirements for acute and basal homeostatic proliferation of naive and memory CD8+ T cells

Both naive arid memory T cells undergo antigen-independent proliferation after transfer into a T cell-depleted environment (acute homeostatic proliferation), whereas only memory T cells slowly divide in a full T cell compartment (basal proliferation). We show, first, that naive and memory CD8(+) T cells have different cytokine requirements for acute homeostatic proliferation, Interleukin (IL)-7 receptor(R)alpha-mediated signals were obligatory for proliferation of naive T cells in lymphopenic hosts, whereas IL-15 did not influence their division. Memory T cells. on the other hand, could use either IL-7Ralpha- or IL-15-mediated signals for acute homeostatic proliferation: their proliferation was delayed when either IL-7Ralpha was blocked or IL-15 removed, but only, when both signals were absent was proliferation ablated. Second, the cytokine requirements for basal and acute homeostatic proliferation of CD8(+) memory T cells differ. as basal division of memory T cells was blocked completely in IL-15-deficient hosts. These data suggest a possible mechanism for the dearth of memory CD8(+) T cells in IL-15- arid IL-15Ralpha-deficient mice is their impaired basal proliferation. Our results show that naive and memory T lymphocytes differ in their cytokine dependence for acute homeostatic proliferation and that memory T lymphocytes have distinct requirements for proliferation in full versus empty compartments.