Suppression of the delayed-type hypersensitivity and cell-mediated immune responses to Listeria monocytogenes induced by Pseudomonas aeruginosa.

Pseudomonas aeruginosa-mediated suppression of the immune response to Listeria monocytogenes was investigated in mice. Because delayed-type hypersensitivity (DTH) footpad swelling to L. monocytogenes was suppressed equally in lipopolysaccharide-responsive and -hyporesponsive mouse strains, the lipopolysaccharide component of P. aeruginosa could not have been the suppressive agent. Mucoid P. aeruginosa cells were no more suppressive than their nonmucoid revertants; therefore, mucoid coating was not an additional immunosuppressive element. Interleukin-1 and macrophage inhibitory factor production to L. monocytogenes and clearance of L. monocytogenes from mouse spleens were all decreased by prior Pseudomonas infection, indicating that cell-mediated immunity, as well as DTH, was decreased to a sublethal Listeria dose. The timing of Pseudomonas exposure relative to Listeria sensitization was varied. P. aeruginosa injected 24 or 6 h before or at the same time as L. monocytogenes depressed DTH to Listeria challenge 7 days later. Animals treated in this way could not respond to reinfection with L. monocytogenes at 13 days. P. aeruginosa administered to L. monocytogenes-sensitized mice at the time of footpad challenge was suppressive, but these mice responded normally upon reinfection. It appears that P. aeruginosa induced two types of suppression to L. monocytogenes: a transient suppression, affecting DTH challenge but not resensitization, and a longer lasting suppression that did not permit mice exposed to P. aeruginosa at the time of Listeria sensitization to respond to subsequent Listeria exposure.