Depression by Pseudomonas aeruginosa of two T-cell-mediated responses, anti-Listeria immunity and delayed-type hypersensitivity to sheep erythrocytes.

Pseudomonas aeruginosa was studied for its effects on T-cell-mediated responses in mice, as exemplified by anti-Listeria immunity and delayed-type hypersensitivity to sheep erythrocytes. Immunity to Listeria monocytogenes was measured by quantitation of bacteria in spleens and mortality; delayed hypersensitivity to sheep erythrocytes was tested by the footpad reaction. Three different preparations of P. aeruginosa were used: the supernatant of a heat-killed culture, living bacteria, and heat-killed organisms. Similar results were obtained with the three preparations. Administration of P. aeruginosa 24 h before Listeria infection reduced the resistance to the secondary challenge, as measured by increased bacterial multiplication in the spleen and rate of mortality. Cell transfer experiments showed that pretreatment of normal recipient mice with P. aeruginosa prevented them from being adoptively immunized against a Listeria challenge infection with spleen cells from immune donors. They also showed that treatment of donors with P. aeruginosa before immunization affected the capacity of their spleen cells to protect normal recipients against Listeria. Furthermore, spleen and peritoneal exudate cells obtained from mice given P. aeruginosa were capable of preventing immunization of normal recipients against Listeria. Similar results were obtained when the delayed hypersensitivity response to sheep erythrocytes was studied. The suppressive activity of P. aeruginosa-treated spleen cells was lost by removing adherent cells. Conversely, the adherent, heat-killed, anti-immunoglobulin-treated spleen cells exerted a suppressor effect. It thus appears that P. aeruginosa injection changes macrophage and T-lymphocyte activities and results in the development of adherent, macrophage-like suppressor cells in the spleen and peritoneal cavity.