The immune response of aged mice to influenza: diminished T-cell proliferation, interleukin 2 production and cytotoxicity.

In view of the fact that T lymphocytes play a key role in the recovery from viral infections, and that many immune functions involving T cells show a decline in aged individuals, we examined the ability of old mice to mount a T-cell response to influenza virus. Both primary and secondary cytotoxic T-lymphocyte (CTL) responses following in vivo immunization with influenza virus were minimal in old mice at the time point of peak response in young mice. Analysis of CTL activity generated in an in vitro microculture system revealed both a diminished proliferative response and a decrease in Interleukin 2 (IL-2) production in "old" compared to "young" cultures following stimulation with virus. Furthermore, addition of exogenous IL-2 at the initiation of the culture period augmented both subtype-specific and A-strain cross-reactive CTL activity of old spleen cells. Finally, exogenous IL-2 increased the lower proliferative response of the old cultures. These findings, if also true for elderly humans, might have broad clinical relevance to the problem of suitable prophylactic approaches to influenza infection in the elderly.