Conditioned Suppression of a Thymus-Independent Antibody Response*

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Abstract
An illness-induced taste aversion was conditioned in mice by pairing cyclophosphamide, an immunosuppressive drug, with consumption of saccharin, a novel drinking solution. Two wk after conditioning, animals were injected with the hapten trinitrophenyl (TNP) coupled to the thymus-independent carrier, lipopolysaccharide. Serum antibodies to TNP were titered 6 days later by passive hemagglutination. Relative to control groups, conditioned animals provided with saccharin at the time of antigenic stimulation and again 3 days later showed significant attenuation of their anti-TNP antibody response. In a 2nd experiment, the conditioned stimulus (CS) consisted of the novel saccharin drinking solution plus the noxious internal effects of an injection of LiCl. Conditioned animals re-exposed to the CS again showed the lowest antibody titers, but differed significantly from only 1 of the control groups. Previous reports of conditioned immunosuppression were confirmed and the effects of conditioning on a primary humoral antibody response could be observed in response to a T [thymus-derived] cell independent antigen in the mouse.