Growth of Legionella pneumophila in a human macrophage-like (U937) cell line.
We established a model of the bacteria-macrophage interaction to study the cellular basis of Legionella pneumophila pathogenesis and to characterize avirulent L. pneumophila. We found that U937 cells, which are derived from a human histiocytic lymphoma cell line, support intracellular growth of L. pneumophila with a doubling time of 6 h, and that sustained intracellular growth is associated with a cytopathic effect (CPE) that can be detected by microscopic examination and quantified with the vital stain 3-(4,5-dimethyl thiazol-2-yl)-2,5,-diphenyl tetrazolium bromide (MTT). An L. pneumophila isolate obtained directly from infected guinea-pig spleens can grow and produce CPE in these cells, destroying most of the cell layer after 72 h of growth. Only 10(6) organisms of this strain are required to kill 50% of guinea-pigs inoculated by the intraperitoneal route. In contrast, an avirulent isolate derived by 203 successive plate passages of the same strain can neither kill guinea-pigs at an intraperitoneal inoculum of 10(7) nor grow or produce CPE in U937 cells. Since the cells were able to differentiate between a virulent and an avirulent strain of L. pneumophila, we conclude that U937 cells are an appropriate model system for study of the bacteria-macrophage interaction.
Pearlman
E
E
Department of Microbiology, University of Michigan, Ann Arbor 48109-0620.
Jiwa
A H
AH
Engleberg
N C
NC
Eisenstein
B I
BI
D000818:Animals; D002460:Cell Line; D002470:Cell Survival; D006168:Guinea Pigs; D007875:Legionella / Q000254:growth & development* / Q000472:pathogenicity; D008264:Macrophages / Q000382:microbiology*; D014774:Virulence