Aging and antimicrobial immunity. Impaired production of mediator T cells as a basis for the decreased resistance of senescent mice to listeriosis.

Immunity to infection of mice with the facultative, intracellular pathogen Listeria monocytogenes was employed as a model system to investigate the immunological basis for the age-associated decline in anti-microbial immunity. In response to a sublethal immunizing infection, aged (24-mo old or more) mice displayed a smaller increase in spleen weight, spleen cellularity, and splenic T cell content than young (3- to 4-mo-old) mice. Aged mice also generated a smaller number of anti-Listeria protective T cells at the time of a peak response, in that their spleen cells were 1,000-fold less protective than equivalent numbers of spleen cells from the young donors, even when enriched T cell populations were employed. These results suggest that the impaired ability of aged mice to produce protective T cells is mainly responsible for decreased resistance of these mice to infection with Listeria.