Recently (1) we have shown that, with age, there are changes in B cell clonal expression as manifested by differences in the idiotypes (Id) produced and an increase in the magnitude of the auto-anti-Id response. The increased auto-antiId response can be transferred to young recipients with splenic lymphoid cells from aged animals (2). However, lethally irradiated mice reconstituted with bone marrow (BM) from aged donors behave like young mice in that they manifest only modest auto-anti-Id responses (2), suggesting that the BM of old and young animals is similar. Furthermore, it has been shown that splenic T cells obtained from old mice modify the response of BM-reconstituted irradiated mice to behave in a manner typical of old animals with respect to auto-anti-Id production (2). On the basis of these observations we have proposed the hypothesis that the changes in Id expression and auto-anti-Id production in old animals are due to shifts in clonal distribution among the long-lived peripheral T cells, as a consequence of life-long interactions with internal and environmental antigens. This hypothesis predicts that if the peripheral lymphoid system of an old animal is acutely depleted of cells while the BM is left intact (e.g., irradiation with BM shielding) and the animals are allowed to repopulate their peripheral lymphoid system from their own marrow, they should behave like young mice with respect to auto-anti-Id production and it should be possible to influence this pattern of recovery transfer of peripheral T cells from donors of different ages. These predictions are borne out by the present results.
Materials and MethodsAnimals, Irradiation, and Cell Transfer. C57BL/6J male mice were used. Old animals were 18 mo old, or older, while young mice were 8 wk old. Mice were anesthesized with tribromo ethanol, and placed in a lead shield that protected the bone marrow of their rear legs, head, and part of their spinal column, while permitting irradiation of their This work was supported in part by grants AG00842, Aii i 694, AG04860, AG00541, and AG00239 from the National Institutes of Health. J. Exe. MEt).