The present study was undertaken in the hope of obtaining a clear picture of relative importance of delayed-type hypersensitivity (DTH) reaction on the resistance of mice to Salmonella typhimurium and of examining some of properties of antigen in immune responses.
Mice were immunized subcutaneously with 100 μg of egg albumin(OVA) in complete Freund adjuvant and were challenged i. p. with 10μg or 100μg of OVA in saline 8 days after- OVA immunization. Immunized and challenged mice and control mice were infected i. p. with 1 x 1G3 S. typhimurium at 2hr after OVA challenge, and the total bacterial growth in the spleens, livers and kidneys was assessed at predetermined intervals. In addition, the effect of concanavalin A-induced lymphokine on the resistance of mice to S. typhimurium was investigated. Immune mice which exhibited systemic DTH reaction to OVA immunization and challenge demonstrated resistance to S. typhimurium without primary infection or vaccination with Salmonella. The number of bacteria in the injections of lymphokine before or after Salmonella infection was similar to that of control mice which received only control supernatant.
Trinitrochlorobenzene (TNCB) was used to sensitize for and elicit contact sensitivity (CS) reactions. It was found that 2- and 4-hr CS reactions to TNCB in infected mice and uninfected control mice were of similar magnitude. However, 24 hr-CS reactions in infected mice were depressed as compared with that in counterpart.
DTH reactions to protein obtained from sonically disrupted S. typhimurium which was measured by footpad swelling reaction, serum antibody titers to S. typhimurium which were determined by passive hemagglutination and recovery of S. typhimurium from spleens and kidneys were examined in S. typhimurium- infected mice that were previously immunized 3 times with 3 antigens such as living vaccine, protein vaccine or formalin-killed vaccines of S. typhimurium. Immunized mice and unimmunized control mice were infected is p. with 3x10´ S. typhimurium. Manifestations of typical DTH to bacterial protein were found to be present in mice immunized with respective antigens employed in this experiment. Mice immunized with living bacteria showed more prominent DTH reactions at 8 days after infection than mice immunized with other two immunogens. In contrast, mice immunized with formalin-killed bacteria showed higher antibody titers than mice immunized with living bacteria and protein derived from Salmonella. The number of S. typhimurium recovered from the spleens and kidneys of mice immunized with living vaccine was dramatically decreased at 6 and 9 days after infection as compared with that of control and of mice immunized with formalin-killed vaccine or bacterial protein.
Interrelationships of recovery of S., typhimurium from spleens, DTH reaction and serum antibody titers to S. typhimurium were attempted to three antigens as in above experiment. The number of bacteria recovered from spleens of mice immunized with formalin-killed vaccine, protein vaccine or living vaccine was decreased at a time which DTH reaction in the some mice was increased and the number of bacteria recovered from spleens of immunized mice was increased at a time which DTH reaction in the some mice was decreased, indicating the existence of correlation between DTH react )n and emergence of antibacterial protective immunity. The correlation between DTH reaction and protective immunity was more pronounced in mice immunized with living bacteria than in mice immunized with other antigens. Serum antibody titers showed such correlation.
These overall results provide further evidence that systemic DTH reactions demonstrated enhanced resistance to SS typhimurium without primary infection or vaccination with Salmonella species and that cellular immune response plays more decisive role in antibacterial immunity to facultative intracellular bacteria infection and a close correlation ship exists between the development of DTH reaction and the appearance of effective protective immunity.
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