Induction of interleukin 1 by Legionella pneumophila antigens in mouse macrophage and human mononuclear leukocyte cultures.

Exposure to Legionella pneumophila antigens has been reported to result in both an adjuvant effect and pathophysiological changes such as fever, headache, myalgia and arthralgias. Immunoenhancement and inflammatory changes have been associated with the production of interleukin 1, and we, therefore, sought an involvement of interleukin production in the alteration of biological responsiveness following exposure to Legionella pneumophila antigens. Killed Legionella pneumophila cells, incubated with mouse splenocytes, induced the formation of a soluble substance which enhanced splenocyte antibody production to heterologous antigen. The immunoenhancing substance was also produced by mouse peritoneal macrophages and supernatants from these cultures were demonstrated to also contain thymocyte co-mitogenic activity. Following gel filtration, this co-mitogenic activity eluted in the 15,000 molecular weight range suggesting an involvement of interleukin 1. Experiments with Legionella pneumophila cells, and cell extracts containing endotoxin, and purified endotoxin suggested that the interleukin 1 activity was induced by both endotoxin and non-endotoxin antigens. The Legionella pneumophila antigens were also found to be potent inducers of interleukin 1 activity in human peripheral blood mononuclear cell cultures. These results suggest that Legionella pneumophila antigens are potent inducers of interleukin 1 in both mouse and human cells. The induction of this monokine may partially account for both the immunoenhancing property of this bacterial species and the associated pathophysiological changes following infection with this microorganism.