In vitro T cell-mediated killing of Pseudomonas aeruginosa. I. Evidence that a lymphokine mediates killing

Previous studies have demonstrated in vivo that T cells can provide protective immunity, in the absence of antibody, against infection with the extracellular Gram-negative bacterium Immunotype 1 (IT-1) Pseudomonas aeruginosa. We established an in vitro system in which immune T cells, after reexposure to bacterial antigens and to macrophages, secrete a product that kills the bacteria. Although macrophages are required for in vitro killing, they function neither as antigen-presenting nor as phagocytic cells in this system. T cells from animals immunized against a different P. aeruginosa immunotype will not kill IT-1 organisms; but the supernatants produced by IT-1 immune T cells after exposure to macrophages and IT-1 P. aeruginosa organisms are nonspecifically effective in killing unrelated bacteria. Because the supernatants from immune T cells lose their bactericidal properties upon minimal dilution, we conclude that if this mechanism is active in vivo, it must play a role in local immunity.