Induction and specificity of delayed hypersensitivity to Staphylococcus aureus in mice

The induction and specificity of delayed hypersensitivity (DH) to Staphylococcus aureus in mice was evaluated in vivo by the footpad (FP) assay and in vitro by spleen cell stimulation. Repeated infections result in a biphasic DH response. The first DH response, observed following three subcutaneous injections, was route and antigen specific, required viable organisms, and could not be enhanced by the incorporation of bacteria in adjuvants. Footpad reactivity was transferred to non-injected recipients by spleen cells but not serum and was inhibited by anti-thymocyte serum but not by cyclophosphamide. Spleen cell stimulation was maximal with homologous antigen, but, some cross reactivity was observed when cells were stimulated with hererologous gram-positive antigens. No cross reactivity was observed when antigens from gram-negative bacteria were used to stimulate spleen cells. The FP reactivity to homologous antigen following 7 injections, the second DH response, is of longer duration than that following 3 injections. Mice given seven injections exhibit a greater degree of cross reactivity to heterologous gram-positive but not gram-negative bacterial antigens. Similar results were observed when spleen cells from mice receiving 7 injections were simulated with gram-positive antigens. Furthermore, the degree of spleen cell stimulation following three of seven injections could be increased by elicitation prior to the vitro experiments.