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Pneumolysin, a protein toxin of Streptococcus pneumoniae, induces nitric oxide production from macrophages
1Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA. johann.braun@stjude.org
Abstract:
Nitric oxide (NO) production by inducible NO synthase (iNOS) during inflammation is an essential element of antimicrobial immunity but can also contribute to host-induced tissue damage. Under conditions of bacterial sepsis, large amounts of NO are produced, causing hypotension, a critical pathological feature of septic shock. In sepsis caused by gram-positive organisms, the bacterial factors contributing to host NO production are poorly characterized. We show that a soluble toxin of Streptococcus pneumoniae, pneumolysin (Pln), is a key component initiating NO production from macrophages. In contrast to wild-type bacteria, a mutant of S. pneumoniae lacking Pln failed to elicit NO production from murine macrophages. Purified recombinant Pln induced NO production at low concentrations and independently of exogenous gamma interferon (IFN-gamma) priming of RAW 264.7 macrophages. However, IFN-gamma was essential for Pln-induced NO production, since primary macrophages from mice lacking the IFN-gamma receptor or interferon regulatory factor 1, a transcription factor essential for iNOS expression, failed to produce NO when stimulated with Pln. In addition, Pln acts as an agonist of tumor necrosis factor alpha and interleukin 6 production in macrophages. The properties of Pln, previously identified as a pore-forming hemolysin, also include a role as a general inflammatory agonist.
Insights
Pneumolysin, a toxin from Streptococcus pneumoniae, triggers nitric oxide (NO) production in macrophages, contributing to inflammation during sepsis. This finding highlights pneumolysin
Area of Science:
- Immunology
- Microbiology
- Pathology
Background:
- Nitric oxide (NO) synthase (iNOS) produces NO during inflammation, crucial for immunity but potentially harmful.
- Sepsis involves high NO levels, leading to hypotension and septic shock.
- Bacterial factors driving NO production in gram-positive sepsis are not well understood.
Purpose of the Study:
- To investigate the role of Streptococcus pneumoniae toxins in initiating NO production by macrophages.
- To elucidate the inflammatory mechanisms of pneumolysin (Pln) in the context of sepsis.
Main Methods:
- Comparison of NO production by murine macrophages stimulated with wild-type S. pneumoniae versus a Pln-deficient mutant.
- Stimulation of macrophages with purified recombinant Pln.
- Assessment of NO production in macrophages from mice lacking key inflammatory signaling components (IFN-gamma receptor, IRF1).
- Measurement of tumor necrosis factor alpha and interleukin 6 production.
Main Results:
- A mutant S. pneumoniae lacking Pln failed to induce NO production in macrophages.
- Purified Pln induced NO production in macrophages, even without gamma interferon (IFN-gamma) priming.
- IFN-gamma signaling was essential for Pln-induced NO production in primary macrophages.
- Pln also stimulated the production of tumor necrosis factor alpha and interleukin 6.
Conclusions:
- Pneumolysin (Pln) is a key bacterial factor initiating macrophage nitric oxide (NO) production during S. pneumoniae infection.
- Pln acts as a potent inflammatory agonist, inducing NO, TNF-alpha, and IL-6 production.
- Understanding Pln's role provides insights into gram-positive sepsis pathogenesis and potential therapeutic targets.