γ chain required for naive CD4+ T cell survival but not for antigen proliferation

Lymphoid homeostasis is required to ensure immune responsiveness and to prevent immunodeficiency, As such, the immune system must maintain distinct populations of naive T cells that are able to respond to new antigens as well as memory T cells specific to those antigens it has already encountered,Though both naive and memory T cells reside in and traffic through secondary lymphoid organs, there is growing evidence that the two populations may be regulated differently,We show here that naive T cell survival and memory T cell survival have different requirements for cytokines (including the interleukins IL-2, IL-4, IL-7, IL-9 and IL-15) that use the common cytokine receptor gamma chain (gamma(c)). Using monoclonal populations of antigen-specific CD4(+) T cells, we found that naive T cells cannot survive without gamma(c), whereas memory T cells show no such requirement. In contrast, neither naive nor gamma(c)-deficient memory T cells were impaired in their ability to proliferate and produce cytokines in response to in vivo antigenic stimulation,These data call into question the physiological role of gamma(c)-dependent cytokines as T cell growth factors and show that naive and memory CD4(+)T cell survival is maintained by distinct mechanisms.