Specific antibodies are responsible for the low dose suppression of the immune response to thymus-independent antigens.

Animals primed to the thymus-independent antigen native dextran B512 could not respond to the FITC hapten after immunization with native FITC-dextran. The degree of suppression of the anti-FITC response paralleled the increase of the anti-alpha1-6 PFC after priming with different doses of dextran. Suppression could be passively transferred with serum from dextran primed animals. Young animals that are very low-or non-responders to the alpha1-6 epitope of dextran B512, failed to suppress the anti FITC PFC response after priming with native dextran. We conclude that antibodies against the dextran carrier were responsible for the suppressed response to the FITC epitope in FITC-dextran immunized animals that had been primed with low doses of the dextran carrier.