Transcriptome-based network analysis reveals a spectrum model of human macrophage activation

Area of Science:

• Immunology
• Transcriptomics
• Systems Biology

Background:

• Macrophage activation involves significant transcriptional changes.
• Current models (M1/M2) inadequately describe the full spectrum of macrophage polarization and function.
• Transcriptional programs governing macrophage activation are not fully understood.

Purpose of the Study:

• To characterize the transcriptional landscape of human macrophage activation.
• To identify key transcriptional regulators of macrophage activation.
• To investigate macrophage transcriptional states in chronic obstructive pulmonary disease (COPD).

Main Methods:

• Stimulation of human macrophages with diverse signals to generate 299 transcriptomes.
• Network analysis to identify central and stimulus-specific transcriptional regulators.
• Application of identified programs to alveolar macrophages from healthy donors, smokers, and COPD patients.
• Integration with murine data (ImmGen) for cross-species comparison.

Main Results:

• A spectrum of macrophage activation states was identified, expanding the M1/M2 paradigm.
• Central transcriptional regulators common to all activation states and stimulus-specific regulators were discovered.
• COPD patients exhibited an unexpected decrease in inflammatory signatures in alveolar macrophages.
• A refined, activation-independent core signature for human and murine macrophages was proposed.

Conclusions:

• Macrophage activation is more complex than the M1/M2 model suggests, encompassing a continuous spectrum.
• This work provides a valuable resource for understanding macrophage regulation in health and disease.
• The findings offer new insights into immune dysregulation in COPD.