Interleukin-10 stimulates Coxiella burnetii replication in human monocytes through tumor necrosis factor down-modulation: role in microbicidal defect of Q fever - PubMed (original) (raw)

Interleukin-10 stimulates Coxiella burnetii replication in human monocytes through tumor necrosis factor down-modulation: role in microbicidal defect of Q fever

E Ghigo et al. Infect Immun. 2001 Apr.

Abstract

Coxiella burnetii, an obligate intracellular bacterium, is the agent of Q fever. The chronic form of the disease is associated with the overproduction of interleukin-10 and deficient C. burnetii killing by monocytes. We hypothesized that the replication of C. burnetii inside monocytes requires a macrophage-deactivating cytokine such as interleukin-10. In the absence of interleukin-10, C. burnetii survived but did not replicate in monocytes. C. burnetii replication (measured 15 days) was induced in interleukin-10-treated monocytes. This effect of interleukin-10 is specific since transforming growth factor beta1 had no effect on bacterial replication. C. burnetii replication involves the down-modulation of tumor necrosis factor (TNF) release. First, interleukin-10 suppressed C. burnetii-stimulated production of TNF. Second, the addition of recombinant TNF to interleukin-10-treated monocytes inhibited bacterial replication. Third, the incubation of infected monocytes with neutralizing anti-TNF antibodies favored C. burnetii replication. On the other hand, deficient C. burnetii killing by monocytes from patients with chronic Q fever involves interleukin-10. Indeed, C. burnetii replication was observed in monocytes from patients with Q fever endocarditis, but not in those from patients with acute Q fever. Bacterial replication was inhibited by neutralizing anti-interleukin-10 antibodies. As monocytes from patients with endocarditis overproduced interleukin-10, the defective bacterial killing is likely related to endogenous interleukin-10. These results suggest that interleukin-10 enables monocytes to support C. burnetii replication and to favor the development of chronic Q fever.

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Figures

FIG. 1

FIG. 1

Effect of IL-10 on C. burnetii replication. (A) Monocytes were pretreated with IL-10 or TGF-β1 (5 ng/ml) for 24 h and then infected with C. burnetii at a bacterium-to-cell ratio of 200:1 for 24 h (designated day 0). Bacteria were revealed with rabbit immune serum and fluorescein isothiocyanate-conjugated anti-rabbit F(ab′)2 Ab. The infection index was measured every 3 days; the results are expressed as the mean ± SE of five experiments. (B) Monocytes were pretreated with different doses of IL-10 and infected with C. burnetii as described above. The infection index was measured after 12 days; the results are expressed as the mean ± SE of three experiments. (C) Infected monocytes were sonicated and dilutions of homogenates containing bacteria were added to HEL cell monolayers. Bacteria were revealed by indirect immunofluorescence. Results are expressed as the mean number ± SE of fluorescent vacuoles per shell vial and represent three experiments conducted in triplicate.

FIG. 2

FIG. 2

Effect of C. burnetii uptake on bacterial replication. (A) Monocytes were infected with C. burnetii at a bacterium-to-cell ratio of 200:1 for 24 h (designated day 0) and then treated with IL-10 at 5 ng/ml. Infection was determined as described in the Fig. 1A legend; the results are the mean ± SE of four experiments. (B) IL-10-pretreated monocytes were infected with C. burnetii at different bacterium-to-cell ratios for 24 h. The infection index was determined after 12 days; the results represent the mean ± SE of three experiments.

FIG. 3

FIG. 3

Effect of IL-10 and TGF-β1 on TNF production. (A and B) Monocytes were pretreated with IL-10 or TGF-β1 (5 ng/ml) and then incubated in the absence (A) or the presence (B) of C. burnetii (bacterium-to-cell ratio, 200:1) for 4 h. Total RNA was extracted and transcribed in cDNA. After amplification, PCR products were analyzed by agarose gel electrophoresis and ethidium bromide staining. The figure is representative of three experiments. (C) Monocytes were pretreated with IL-10 or TGF-β1 for 24 h and then infected with C. burnetii. Supernatants were assayed for the presence of TNF by ELISA after different times. The results are expressed as the mean ± SE of three experiments.

FIG. 4

FIG. 4

Effect of immunoregulatory cytokines on the production of IL-1ra and TNF-RII. Monocytes were pretreated with IL-10 or TGF-β1 (5 ng/ml) for 24 h and then stimulated with C. burnetii (bacterium-to-cell ratio, 200:1) for 24 h. Supernatants were assayed for the presence of IL-1ra (A) and soluble TNF-RII (B) by ELISA after different times. The results are expressed as the mean ± SE of three experiments.

FIG. 5

FIG. 5

Effect of anti-TNF Abs and exogenous TNF on monocyte infection. (A) Monocytes were infected with C. burnetii (bacterium-to-cell ratio, 200:1) and cultured for 12 days in the presence of neutralizing anti-TNF Abs. (B) Monocytes were treated with IL-10 for 24 h, incubated with C. burnetii for 24 h, and cultured for 12 days in the presence of TNF. The infection index at day 12 was expressed relative to day 0. Results are the mean ± SE of four experiments.

FIG. 6

FIG. 6

Effect of IL-10 on C. burnetii replication in Q fever endocarditis. (A) Monocytes from patients with acute Q fever or ongoing Q fever endocarditis were incubated with C. burnetii at a bacterium-to-cell ratio of 200:1, and the infection index was assessed at days 0, 6, and 12 as described in the legend to Fig. 1A. (B and C) Infected monocytes from patients with acute Q fever (B) or from patients with Q fever endocarditis (C) were cultured in the presence of neutralizing anti-IL-10 Abs or control serum (10 μg/ml), and the infection index was determined after 6 and 12 days relative to day 0.

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