Cell-mediated immunity and delayed-type hypersensitivity in Pseudomonas aeruginosa-infected mice

In mice repeated systemic injections of Pseudomonas aeruginosa viable cells were able to induce a specific delayed-type hypersensitivity, which was evaluated as increase both in footpad swelling and in the weight of popliteal lymph nodes, after a challenge in the footpad. Unfractionated spleen cells or T lymphocyte-enriched spleen cells from sensitized donors were able to specifically transfer the delayed-type hypersensitivity to syngeneic recipients but failed to protect them against a lethal challenge with P. aeruginosa. In contrast, serum or B lymphocyte and macrophage-enriched spleen cells from the same donors were capable of transferring protective immunity but failed to induce any delayed-type hypersensitivity reaction in the recipients. These results clearly show that in systemic P. aeruginosa infections a dissociation between delayed-type hypersensitivity and acquired cellular resistance occurs.