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IFN-gamma primes macrophage responses to bacterial DNA
M J Sweet1, K J Stacey, D K Kakuda
1Centre for Molecular and Cellular Biology, Department of Microbiology, University of Queensland, Brisbane, Australia.
Abstract:
Macrophages recognize and are activated by unmethylated CpG motifs in bacterial DNA. Here we demonstrate that production of nitric oxide (NO) from murine RAW 264 macrophages and bone marrow-derived macrophages (BMM) in response to bacterial DNA is absolutely dependent on interferon-gamma (IFN-gamma) priming. Similarly, arginine uptake and expression of the inducible nitric oxide synthase (iNOS) gene in response to bacterial DNA in BMM occurred only after IFN-gamma priming. In contrast, mRNA for the cationic amino acid transporter, CAT2, was induced by plasmid DNA alone, and priming with IFN-gamma had no effect on this response. Tumor necrosis factor-alpha (TNF-alpha) release from RAW 264 and BMM in response to bacterial DNA was augmented by IFN-gamma pretreatment. In a stably transfected HIV-1 long terminal repeat (LTR) luciferase RAW 264 cell line, IFN-gamma and bacterial DNA synergized in activation of the HIV-1 LTR. Bacterial DNA has been shown to induce IFN-gamma production in vivo as an indirect consequence of interleukin-12 (IL-12) and TNF-alpha production from macrophages. The results herein suggest the existence of a self-amplifying loop that may have implications for therapeutic applications of bacterial DNA.
Insights
Bacterial DNA activates macrophages, but nitric oxide (NO) production requires interferon-gamma (IFN-gamma) priming. This points to a self-amplifying immune loop with potential therapeutic uses for bacterial DNA.
Area of Science:
- Immunology
- Molecular Biology
Background:
- Macrophages recognize unmethylated CpG motifs in bacterial DNA.
- Bacterial DNA can activate immune responses, including cytokine production.
Purpose of the Study:
- To investigate the role of interferon-gamma (IFN-gamma) in macrophage activation by bacterial DNA.
- To elucidate the mechanisms of nitric oxide (NO) and cytokine production in response to bacterial DNA.
Main Methods:
- Murine RAW 264 macrophages and bone marrow-derived macrophages (BMM) were used.
- Assays included nitric oxide (NO) production, arginine uptake, gene expression (iNOS, CAT2), and tumor necrosis factor-alpha (TNF-alpha) release.
- A stably transfected HIV-1 LTR luciferase cell line was used to assess gene activation.
Main Results:
- Nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) gene expression required IFN-gamma priming.
- Cationic amino acid transporter 2 (CAT2) mRNA induction by plasmid DNA was independent of IFN-gamma.
- IFN-gamma augmented TNF-alpha release and synergized with bacterial DNA to activate the HIV-1 LTR.
Conclusions:
- Macrophage activation by bacterial DNA, particularly NO production, is critically dependent on IFN-gamma priming.
- A potential self-amplifying immune loop involving bacterial DNA, IFN-gamma, and macrophage activation exists.
- These findings suggest therapeutic applications for bacterial DNA in modulating immune responses.