A polarizing question: do M1 and M2 microglia exist?

Area of Science:

• Neuroscience
• Immunology
• Cell Biology

Background:

• Microglial research is rapidly advancing with new technologies like transcriptomics and advanced imaging.
• The field has widely used macrophage polarization terms (M1/M2) to describe microglia.
• This terminology was adopted to simplify interpretation when microglial function was less understood.

Purpose of the Study:

• To critically evaluate the established use of macrophage polarization terminology in microglial research.
• To argue for the discontinuation of the M1/M2 microglial polarization schema.

Main Methods:

• Review of current microglial research literature and methodologies.
• Analysis of the historical context and rationale for adopting macrophage polarization terms.
• Discussion of emerging technologies and their impact on microglial understanding.

Main Results:

• Microglial polarization into distinct M1 and M2 phenotypes is not empirically established by research findings.
• The M1/M2 schema was an oversimplification for interpreting early microglial data.
• Current advanced research methods reveal a more complex microglial landscape.

Conclusions:

• The terminology of microglial polarization (M1/M2) lacks scientific validation.
• Continuing to use this outdated schema impedes rather than advances microglial research.
• Researchers should discard the M1/M2 polarization terminology for more accurate descriptions of microglial states.