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Different Toll-like receptor agonists induce distinct macrophage responses
B W Jones1, T K Means, K A Heldwein
1The Pulmonary Center, Boston University School of Medicine, Boston, Massachusetts, USA.
Journal of Leukocyte Biology
|June 19, 2001
Summary
Toll-like receptor (TLR) agonists lipopolysaccharide (LPS), lipoarabinomannan (LAM), and soluble tuberculosis factor (STF) activate similar signaling pathways. However, these TLR agonists induce distinct cellular responses, highlighting unique downstream effects despite shared initial activation.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Gram-negative bacterial lipopolysaccharide (LPS) signals via Toll-like receptor (TLR) 4.
- Mycobacterial lipoarabinomannan (LAM) signals via TLR2.
- Soluble tuberculosis factor (STF) is a secreted TLR2 agonist from Mycobacterium tuberculosis.
Purpose of the Study:
- To identify the active component in STF.
- To investigate the signaling pathways activated by STF and its components.
- To compare the cellular responses induced by different TLR agonists.
Main Methods:
- Stimulation of RAW 264.7 macrophages with LPS, LAM, STF, and purified phosphatidylinositol (PIM).
- Analysis of nuclear factor-kappaB (NF-κB), activator protein-1 (AP-1), and mitogen-activated protein (MAP) kinase activation.
- Measurement of cytokine (tumor necrosis factor alpha, interleukin-1beta) and nitric oxide secretion.
Main Results:
- Purified PIM, a component of STF, exhibits TLR2 agonist activity.
- LPS, LAM, STF, and PIM all activated NF-κB, AP-1, and MAP kinases.
- All tested TLR agonists induced tumor necrosis factor alpha secretion.
- Only LPS induced interleukin-1beta and nitric oxide secretion.
Conclusions:
- Mannosylated phosphatidylinositol (PIM) is a TLR2 agonist present in STF.
- Distinct TLR agonists can elicit similar early signaling events (NF-κB, AP-1, MAP kinases).
- Despite shared signaling, different TLRs or agonists can trigger unique downstream cellular outcomes.