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Zheng et al. Neuroimmunol Neuroinflammation 2019;6:1 I http://dx.doi.org/10.20517/2347-8659.2018.52 Page 9 of 12

reverse the M1-like pro-inflammatory effect after SAH. Clinical trials are essential to provide the advanced
evidence for their therapeutic effect. With the expanding investigation of microglial polarization and function,
the treatment that targets microglial phenotype switching may be an efficient approach for SAH therapy.

CONCLUSION
Microglial activation is an important pathological mechanism in the progression of SAH. Microglia undergo
polarization into mainly M1 and M2 phenotypes contributing differently to neuroinflammation after SAH.
These results indicate the presence of M1-related pro-inflammatory state early after SAH. While microglia
polarize to M2 phenotype gradually on delayed phase. Although the dynamics of microglial polarization
specifically after SAH remain to be defined, modulation of microglial activation is expected to enhance the
tissue repair and functional recovery. The transition from M1 to M2 polarization is thought to be a target
concerning the amelioration of the pro-inflammatory response. The investigation on the applications of
microglia-targeted treatments is expected to improve our understanding of the pathogenesis of SAH and
lead to potential therapeutic strategies for affected patients.

DECLARATIONS
Authors’ contributions
Formulation of the key concepts and manuscript framework, literature research, manuscript draft and
editing: Zheng ZV
Formulation of the key concepts and manuscript framework, manuscript revision: Wong GKC

Availability of data and materials
Not applicable.

Financial support and sponsorship
None.

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Copyright
© The Author(s) 2019.

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