T lymphocytes need IL-7 but not IL-4 or IL-6 to survive in vivo.

The role of IL-4, -6 and -7 in the survival of T lymphocytes was studied in vivo. The decay of polyclonal populations of CD4(+) and CD8(+) T cells was monitored in thymectomized anti-cytokine receptor mAb-treated and/or cytokine-deficient mice. The lack of IL-4 or -6 did not have any detectable effect on T cell survival, but IL-7 played an important role in the survival of the naive T cell compartment, especially of naive CD4(+) T cells.