The specific suppressing activity of passively administered antibody on 7S antibody synthesis against sheep and chicken red blood cells has been investigated at the cellular level using the indirect hemolytic agar-plaque technique. 7S antibody production was found to be sensitive to antibody-induced suppression. No inhibitory effect of transferred antibody was seen until 48 to 72 hr after administration. This indicates that the action of antibody is not by direct suppression of synthesis of already committed cells but rather by removal from the system of the stimulus for maintenance of 7S synthesis. The sensitivity of the 7S system to inhibition decreases with time after immunization but significant specific suppression could still be obtained if transfer of antibody was delayed until 40 days after immunization. The present findings emphasize the role of antibody as a feedback factor during a substantial postpeak period of 7S antibody synthesis and suggest an important role of antigen in stabilizing the 7S antibody production.

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