Jerne (1) has proposed that the immune system functions as an interacting network of inducible elements that normally exist in a steady state. In this network, the immune response is regulated by idiotype-anti-idiotype interactions. Antigen administration stimulates some elements of the network, and the subsequent alterations to restore the perturbed steady-state condition represent the cellular and molecular reactions that occur during the immune response.In many experimental systems that examine idiotype-anti-idiotype interactions, the anti-idiotypic antibodies have been induced in species other than the one in which the idiotype was produced (2-6). Induction of isologous anti-idiotypic antibodies has also been achieved (4-12). Spontaneous, autologous anti-idiotypic-antibody and (or) anti-receptor-antibody production during the course of an immune response has been described for haptens (13-16), sheep erythrocytes (SRBC) 1 (i 5, 16), and alloantigens (16)(17)(18)(19). In addition, the decrease in binding affinity of anti-tobacco mosaic virus antibodies has been attributed to the appearance, during the course of the immune response, of lymphocytes bearing auto-anti-idiotypic receptors (20).Although cyclic changes in serum-antibody levels and affinity have been observed during the immune response to many antigens, they have generally been attributed to variations in the degree of masking, by serum antibody, of antigenic determinants on persisting antigen (21,22). Nevertheless, a rapid decrease in affinity of individual plaque-forming cells (PFC) (23) or serum antibody (20, 24) cannot be convincingly explained in this manner. Urbain (25) has suggested that an auto-anti-idiotypic

In the accompanying paper (1), we have shown that after day 4 of the immune response of AKR/J mice to 2,4,6-trinitrophenyl-lys-Ficoll (TNP-F) 1, the addition of free hapten to a plaque-forming-cell (PFC) assay increased the number of observed splenic anti-trinitrophenol (TNP) PFC. Immune spleen cells, taken 7 d after immunization, transferred this property of the immune response to normal recipients; spleen cells from such recipients, assayed 4 d after cell transfer and TNP-F injection, manifested an exaggerated form of this phenomenon. It was hypothesized that the increase in PFC was the result of the displacement, by hapten, of auto-anti-idiotypic antibodies that were synthesized during the course of the normal immune response. If this hypothesis were correct, it should be possible to obtain auto-anti-idiotypic antibodies by hapten elution from appropriate immune spleen cells. Results in the accompanying paper (1) also suggested that the putative auto-anti-idiotypic-antibody response was involved in the downward regulation of the immune response of AKR/ J mice to TNP-F. One might, therefore, expect to find auto-anti-idiotypic antibody in the serum of AKR/J mice immediately after the abrupt decrease in the number of detectable splenic PFC: i.e., 7 d after antigen injection.In the present paper, evidence is presented to support these hypotheses in that hapten-reversible inhibition of PFC in vitro can be demonstrated with hapten eluates from immune cells and with immune serum. The factor responsible for inhibition has immunoglobulin-like determinants, lacks anti-TNP-antibody activity, and is absorbable by an AKR/J anti-TNP-antibody immunoadsorbent. Hapten-reversible inhibition of PFC represents a simple in vitro assay for anti-idiotypic antibody. In this

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).

We have previously shown that old mice produce more hapten-augmentable plaque-forming cells (PFC) than do young animals, suggesting a greater auto-antiidiotype antibody (auto anti-Id) component in their immune response. In the present studies this is confirmed serologically. The marked auto-anti-Id response of aged mice can be transferred to lethally irradiated young recipients with spleen but not bone marrow cells from old donors, suggesting that it is an intrinsic property of their peripheral B cell population and that the distribution of Id arising from the bone marrow of old and young mice is similar. In contrast with young mice the auto-anti-Id response of old animals is relatively T cell-independent and old donors do not show an increase in their ability to transfer an auto-anti-Id response after priming with TNP-F. These observations suggest that old mice behave as if already primed for auto-anti-Id production. Irradiated mice reconstituted with bone marrow cells from either young or old donors together with splenic T cells from old donors generate a relatively large auto-anti-Id response, whereas mice reconstituted with bone marrow from either young or old donors together with splenic T cells from young donors produce few hapten-augmentable PFC. It is suggested that differences in Id expression and auto-anti-Id production are the consequences of the interaction of Id (and anti-Id) arising from the marrow with anti-Id (and Id) present in the peripheral T cell population which serves as a repository of information about shifts in Id distribution, resulting from lifelong interactions with environmental and self-antigens.

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