Restoration of immune responses of aging hamsters by treatment with isoprinosine.

Immune competence declines with advanced age in hamsters, as in other laboratory mammals and in humans. We found significant alterations in the functional parameters of different populations of immunocytes (natural killer cells, T cells, monocytes, and suppressor cells) in aging hamsters, beginning at approximately 14 mo of age. Natural killer cytotoxicity, phytohemagglutinin-induced lymphocyte stimulation, and monocyte chemotaxis were decreased in aging Lak:LvG(Syr) outbred hamsters. When old hamsters were given a single injection (5 mg/kg body wt) of isoprinosine, a chemical immune potentiator, these three immune parameters increased almost to the levels found in young adult hamsters but returned to pretreatment levels after 7 d. Suppressor cell activity for the lymphocyte response to phytohemagglutinin, which increased with age, was decreased after treatment. In old hamsters treated with weekly injections of isoprinosine, these four immunological parameters remained at or near the levels found in young adults.