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Growth of Legionella pneumophila in a human macrophage-like (U937) cell line
E Pearlman1, A H Jiwa, N C Engleberg
1Department of Microbiology, University of Michigan, Ann Arbor 48109-0620.
Abstract:
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.
Insights
This study developed a U937 cell model to investigate Legionella pneumophila pathogenesis. The model effectively differentiates virulent and avirulent bacterial strains, aiding in understanding host-pathogen interactions.
Area of Science:
- Microbiology
- Cell Biology
- Pathogenesis Research
Background:
- Legionella pneumophila is a significant human pathogen.
- Understanding the bacteria-macrophage interaction is crucial for studying L. pneumophila pathogenesis.
- Existing models may not fully capture the nuances of virulent vs. avirulent strains.
Purpose of the Study:
- To establish and validate a cell-based model for studying L. pneumophila pathogenesis.
- To characterize the interaction between L. pneumophila and U937 cells.
- To differentiate between virulent and avirulent L. pneumophila strains using a cellular model.
Main Methods:
- Utilized U937 cells, a human histiocytic lymphoma cell line.
- Monitored intracellular growth of L. pneumophila using doubling time and vital stain MTT.
- Assessed cytopathic effect (CPE) via microscopy.
- Correlated in vitro findings with in vivo virulence in guinea pigs.
Main Results:
- U937 cells supported intracellular growth of virulent L. pneumophila (6h doubling time) with significant CPE.
- Virulent L. pneumophila induced cell layer destruction and was lethal to guinea pigs at low doses.
- Avirulent L. pneumophila, derived through serial passage, failed to grow, induce CPE in U937 cells, or cause mortality in guinea pigs.
Conclusions:
- U937 cells provide a suitable in vitro model for studying bacteria-macrophage interactions in L. pneumophila pathogenesis.
- The model effectively distinguishes between virulent and avirulent strains of L. pneumophila.
- This system facilitates research into the cellular basis of L. pneumophila virulence.