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Delayed-type hypersensitivity and acquired cellular resistance in mice immunized with killed Listeria monocytogenes and adjuvants.

Delayed-type hypersensitivity (DH) and acquired cellular resistance (ARC) to Listeria monocytogenes in mice was studied following immunization with killed bacteria in combination with Freund's complete adjuvant or the adjuvant dimethyldioctadecylammonium bromide (DDA). Intracutaneous or intraperitoneal injections of killed listeria mixed with Freund's complete adjuvant did neither result in DH nor in ACR. Intracutaneous injections of killed listeria and DDA resulted in an antigen-dose dependent DH but not in ACR. Intraperitoneal injections of listeria and DDA, however, induced ACR but no DH. Optimal conditions for the induction of ACR were simultaneous intraperitoneal injection of 15 mg DDA/kg body weight and 10(7) or 10(8) listeria. The optimal interval between immunization and challenge was 7 days. No protection was found against challenge with a lethal dose of Salmonella enteritidis, suggesting that the protection is specific. Intraperitoneal injection of mice with DDA resulted in inhibition of phagosome-lysosome fusion in macrophages harvested 24 h later. Interference with macrophage activity is discussed as one of the possible mechanisms for the adjuvant effect of DDA.