Antibody-mediated suppression of the in vitro immune response to polymerized flagellin of Salmonella adelaide and to sheep erythrocytes was studied at the cellular level. Normal mouse spleen cells, preincubated in vitro with mixtures of antigen and antibody for short periods of time before being washed, did not respond to an optimal antigenic challenge in vitro, whereas similar cells treated with antibody alone gave a normal response. The degree of immune suppression was found to depend on the time of preincubation. Significant immune suppression could be induced in as short a time as 15 min, whereas profound suppression (90%) required the incubation of cells with mixtures of antigen and antibody for 4–6 hr. Mouse spleen cells treated similarly were also unable to respond subsequently to the antigen upon transfer to lethally irradiated hosts, as measured at both the level of the antigen-reactive cell and that of serum antibody production. These results were taken as evidence that in vitro an effect of antibody-mediated suppression occurred at the level of the immunocompetent cell.

Similarities between immune tolerance and antibody-mediated suppression in vitro were described, and the significance of the findings discussed in the light of current concepts of the mechanism of antibody-mediated suppression.

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