Toward an Understanding of the Mechanisms of Classical Conditioning of Antibody Responses

Mice of different ages were subjected to repeated exposure to cyclophosphamide:saccharin (conditioned), or cyclophosphamide:saccharin followed by saccharin only (extinguished). Only young animals in the former group showed a decreased IgG antibody-forming-cell (AFC) response after challenge with sheep erythrocytes (SRBC) in the presence of saccharin. When irradiated conditioned young animals were used as recipients of antigen-challenged spleen cells from nonconditioned mice they were found to support a greater immune response than nonconditioned recipients. Similarly, cells from conditioned young mice gave a greater immune response in naive recipients than did cells from nonconditioned mice. Only when cells from conditioned young mice rather than conditioned "aged " mice were studied in irradiated conditioned young recipients was immunosuppression observed. These data are most consistent with a specific host celhenvironment interaction being responsible for the conditioned immunosuppression observed in young mice. A deficit in both cellslenvironment apparently occurs during aging. At least one of these deficiencies seems related to loss of a suppressor T-cell population with age in conditioned mice. THERE are a number of studies which indicate that im-mune responses are susceptible to regulation by classical conditioning techniques, as originally outlined by Pavlo