PREIMMUNE RESISTANCE TO TOXOPLASMA-GONDII IN AGED AND YOUNG-ADULT MICE

Aged individuals are more susceptible to certain infections than are y oung adults. To investigate the relative resistance capabilities of ag ed and young adult mice, responses that are induced within the first w eek of a Toxoplasma gondii infection, which are known to be involved i n preimmune resistance, were compared in young adult and aged mice. Ag ed mice did not differ reproducibly from young adults in numbers of in duced Thy-1(+) CD4(-) CD8(-) cells or interferon-gamma levels. Numbers of induced CD4(+) and CD8(+) T cells, associated with acquired immuni ty, were as high in aged mice as in young adults. Natural killer cell activity, although induced to a high level, was lower in aged mice. Ag ed mice thus are capable of inducing a mechanism of preimmune resistan ce to T. gondii and presumably other infectious agents. Nonetheless, a ged mice died within 8-12 days after intraperitoneal or peroral inocul ation of 500 T. gondii cysts, whereas young adult mice survived. Cause s other than an age-related impairment in preimmune resistance mechani sms are apparently responsible for the increased susceptibility of age d mice to T. gondii infection.