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Type I IFN (IFN-I or IFN-αβ) plays an important role in the innate immune response against viral infection. Here we report that a potent inducer of IFN-αβ, polyinosinic-polycytidylic acid [poly(I:C)], led to the depletion of T cells in young, but not aged mice, and that this depletion was limited to central memory, but not effector memory, T cells. Although early activation of T cells in vivo by poly(I:C), as demonstrated by CD69, was not impaired with aging, the expression of active caspase-3 was higher in young compared with aged mice. This depletion of T cells and induction of active caspase-3 in young mice and of CD69 in both young and aged mice by poly(I:C) were blocked by anti-IFN-αβ Ab. Although poly(I:C) stimulated lower circulating levels of IFN-αβ in aged mice, administration of IFN-αβ after poly(I:C) did not induce depletion of T cells in aged mice. These results indicate that IFN-αβ plays a critical role in the depletion of T cells of young mice, and further suggest that the lower level of functional IFN-αβ and decreased induction of active caspase-3 in T cells of aged mice after poly(I:C) may be responsible for the increased resistance of T cells of aged mice to depletion.

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