A polarizing view on posttraumatic brain injury inflammatory response.

Area of Science:

• Neuroscience
• Immunology
• Pathology

Background:

• Traumatic brain injury (TBI) induces a complex inflammatory response involving numerous pro- and anti-inflammatory molecules.
• Current neurotrauma research often simplifies this response using *in vitro* macrophage polarization phenotypes (M1 and M2).
• This binary classification may not accurately reflect the *in vivo* inflammatory milieu following TBI.

Purpose of the Study:

• To review and evaluate research on the complexity of inflammatory responses after TBI.
• To assess the adequacy of the M1/M2 macrophage polarization paradigm in characterizing TBI-induced neuroinflammation.
• To highlight the limitations of binary classification in complex biological systems.

Main Methods:

• Literature review of studies investigating inflammatory responses in TBI.
• Analysis of research examining macrophage/microglia polarization markers post-TBI.
• Synthesis of findings regarding the heterogeneity of the inflammatory landscape.

Main Results:

• TBI induces a broad spectrum of simultaneous pro- and anti-inflammatory reactions.
• A heterogeneous parenchymal landscape is observed in TBI.
• Concurrent expression of M1 and M2 markers on microglia/macrophages indicates limitations of strict binary polarization.

Conclusions:

• The M1/M2 macrophage polarization model is insufficient to fully define the inflammatory profile following TBI.
• Microglia/macrophages in TBI contexts do not exhibit strictly polarized M1-only or M2-only phenotypes.
• Complex signaling events necessitate a more nuanced approach to understanding TBI-induced neuroinflammation.