There was a marked enhancement of the immune response to keyhole limpet hemocyanin administered at the time of inoculation with Listeria monocytogenes. Such enhancement was best seen if the antigen was given close to the time of inoculation with Listeria monocytogenes. Such enhancement was best seen if the antigen was given close to the time of inoculation with the bacteria. Bacterial filtrates also produced an adjuvant effect. Peritoneal exudate cells harvested a few days after Listeria

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... on contained large activated macrophages. Such macrophages had a greater uptake of 125I-labeled hemocyanin. Metabolic studies indicated that the percentage of hemocyanin retained on the membrane or released from macrophages was increased in activated cells. Hemocyanin bound to activated macrophages was slightly more immunogenic. Activated macrophages (without antigen) did not transfer adjuvant effects. We conclude that the adjuvant effect was not associated with the presence of activated macrophages.