Conditioned suppression of a thymus-independent antibody response.

An illness-induced taste aversion was conditioned in mice by pairing cyclophosphamide, an immunosuppressive drug, with the consumption of saccharin, a novel drinking solution. Two weeks 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 a significant attenuation of their anti-TNP antibody response. In a second experiment, the conditioned stimulus (CS) consisted of the novel saccharin drinking solution plus the noxious internal effects of an injection of LiCl. Conditioned animals reexposed to the CS again showed the lowest antibody titers, but differed significantly from only one of the control groups. Taken together, the results of these experiments confirm previous reports of conditioned immunosuppression and suggest that the effects of conditioning on a primary humoral antibody response can be observed in response to a T-cell independent antigen in the mouse.