Interaction of cytokines and alveolar cells with Pneumocystis carinii in vitro.

Although deficient cellular immune function is a major predisposing factor in the development of Pneumocystis carinii pneumonia, the mechanisms involved in cellular immune surveillance against P. carinii have not been defined. When P. carinii were separated from rat cells by a semipermeable membrane, alveolar macrophages secreted substances lethal to P. carinii only when the macrophages were activated by interferon-gamma; normal macrophages were ineffective. Type II alveolar epithelial cells caused death of P. carinii whether or not interferon-gamma was present. The effects of soluble mediators also were tested; recombinant human tumor necrosis factor-alpha (TNF) but not recombinant rat interferon-gamma or endotoxin was directly lethal to P. carinii. These lethal effects were prevented when antiserum to TNF or antioxidants (catalase and superoxide dismutase) were included. These data suggest that TNF may be a major mediator involved in the killing activity of activated macrophages against P. carinii and that TNF's activity against P. carinii is related to induction of oxidative stresses.