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Published on: July 6, 2016
Mouse resident peritoneal macrophages partially control in vitro infection with Coxiella burnetii phase II
Dario S Zamboni1, Renato A Mortara, Edna Freymuller
1Departamento de Microbiologia, Imunologia e Parasitologia, Disciplina de Parasitologia, Escola Paulista de Medicina, UNIFESP, Rua Botucatu 862, 6o andar, São Paulo, Brazil.
Abstract:
Coxiella burnetii, the agent of Q fever in man and of coxiellosis in other species, is a small, dimorphic, obligate intracellular bacterium, sheltered within large, acidified, and hydrolase-rich phagosomes. Although several primary and established cell lines, macrophage-like cells, and primary macrophages from other species have been infected with C. burnetii, the infection of mouse primary macrophages has not been sufficiently characterized. In this report quantification of DAPI (4', 6-diamino-2-phenylindole) fluorescence images acquired by confocal microscopy, and transmission electron microscopy were used to compare the infection of three mouse-derived cells, L929 fibroblasts, J774 macrophage-like cells, and resident peritoneal macrophages, with a phase II clone of C. burnetii known to be non-virulent for mammals. Infected peritoneal phagocytes differed from L929 or J774 cells in that: (a) large vacuoles took longer to appear (3-5 d instead of 2), and were only found in a subset (20-30%) of macrophages, as opposed to in more than 70% of the other cells; (b) total and vacuole-associated relative bacterial loads in L929 and J774 cells were several-fold higher than in peritoneal macrophages; (c) estimated doubling times of the bacteria were about 68 h in the primary macrophages, 18 h in J774 and 22 h in L929 cells. Thus, mouse resident peritoneal macrophages control both the formation of the large vacuoles and the intracellular proliferation of C. burnetii phase II.
Insights
Mouse macrophages control Coxiella burnetii infection by limiting vacuole formation and bacterial growth. This study characterizes C. burnetii infection in different mouse cell types, revealing macrophages
Area of Science:
- Microbiology
- Cell Biology
- Immunology
Background:
- Coxiella burnetii causes Q fever and coxiellosis.
- It resides in acidified phagosomes within host cells.
- Infection dynamics in mouse primary macrophages remain poorly understood.
Purpose of the Study:
- To characterize the infection of mouse primary macrophages by C. burnetii.
- To compare C. burnetii infection in primary macrophages versus cell lines.
- To investigate bacterial replication and vacuole formation.
Main Methods:
- Confocal microscopy with DAPI staining for bacterial quantification.
- Transmission electron microscopy for ultrastructural analysis.
- Infection of L929 fibroblasts, J774 macrophage-like cells, and resident peritoneal macrophages.
Main Results:
- Resident peritoneal macrophages showed delayed vacuole formation (3-5 days vs. 2 days) and lower bacterial loads compared to L929 and J774 cells.
- Vacuoles formed in only 20-30% of macrophages, versus >70% of L929/J774 cells.
- Bacterial doubling times were significantly longer in primary macrophages (68h) than in J774 (18h) or L929 (22h) cells.
Conclusions:
- Mouse resident peritoneal macrophages effectively control C. burnetii phase II.
- Macrophages limit both the development of large vacuoles and intracellular bacterial proliferation.
- This suggests a robust innate immune control mechanism in primary macrophages.
