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Updated: Mar 27, 2026
Three-dimensional Confocal Analysis of Microglia/macrophage Markers of Polarization in Experimental Brain Injury
Published on: September 4, 2013
Interleukin-4 Is Essential for Microglia/Macrophage M2 Polarization and Long-Term Recovery After Cerebral Ischemia
Xiangrong Liu1, Jia Liu1, Shangfeng Zhao1
1From the Department of Neurology, University of Pittsburgh School of Medicine, PA (X.L., S.Z., H.Z., W.C., J.C., X.H.); Cerebrovascular Diseases Research Institute, Xuanwu Hospital of Capital Medical University, Beijing, P.R. China (X.L., X.J.); State Key Laboratory of Medical Neurobiology, Institute of Brain Sciences, Fudan University, Shanghai, China (J.L., M.C., Y.G., J.C., X.H.); Division of Pharmaceutical Sciences, Duquesne University, Pittsburgh, PA (R.K.L.); and Geriatric Research, Educational and Clinical Center, Veterans Affairs Pittsburgh Health Care System, PA (J.C., X.H.).
Background And Purpose:
Interleukin-4 (IL-4) is a unique cytokine that may contribute to brain repair by regulating microglia/macrophage functions. Thus, we examined the effect of IL-4 on long-term recovery and microglia/macrophage polarization in 2 well-established stroke models.
Methods:
Transient middle cerebral artery occlusion or permanent distal middle cerebral artery occlusion was induced in wild-type and IL-4 knockout C57/BL6 mice. In a separate cohort of wild-type animals, IL-4 (60 ng/d for 7 days) or vehicle was infused into the cerebroventricle after transient middle cerebral artery occlusion. Behavioral outcomes were assessed by the Rotarod, corner, foot fault, and Morris water maze tests. Neuronal tissue loss was verified by 2 independent neuron markers. Markers of classically activated (M1) and alternatively activated (M2) microglia were assessed by real-time polymerase chain reaction, immunofluorescence, and flow cytometry.
Results:
Loss of IL-4 exacerbated sensorimotor deficits and impaired cognitive functions ≤21 days post injury. In contrast to the delayed deterioration of neurological functions, IL-4 deficiency increased neuronal tissue loss only in the acute phase (5 days) after stroke and had no impact on neuronal tissue loss 14 or 21 days post injury. Loss of IL-4 promoted expression of M1 microglia/macrophage markers and impaired expression of M2 markers at 5 and 14 days post injury. Administration of IL-4 into the ischemic brain also enhanced long-term functional recovery.
Conclusions:
The cytokine IL-4 improves long-term neurological outcomes after stroke, perhaps through M2 phenotype induction in microglia/macrophages. These results are the first to suggest that immunomodulation with IL-4 is a promising approach to promote long-term functional recovery after stroke.
Insights
Interleukin-4 (IL-4) enhances brain repair after stroke by promoting M2 microglia/macrophage function. This cytokine improves long-term neurological recovery and functional outcomes in stroke models.
Area of Science:
- Neuroscience
- Immunology
- Stroke Research
Background:
- Interleukin-4 (IL-4) is a cytokine with potential roles in brain repair.
- Microglia and macrophages are key immune cells in the central nervous system that can be modulated by IL-4.
- Understanding IL-4's effect on these cells is crucial for developing stroke therapies.
Purpose of the Study:
- To investigate the impact of IL-4 on long-term recovery following stroke.
- To examine how IL-4 influences microglia/macrophage polarization in stroke models.
- To determine if IL-4 administration can promote functional recovery after ischemic injury.
Main Methods:
- Two established stroke models were used: transient and permanent middle cerebral artery occlusion in mice.
- Behavioral tests (Rotarod, corner, foot fault, Morris water maze) assessed functional recovery.
- Neuronal tissue loss was quantified, and microglia/macrophage polarization (M1/M2 markers) was analyzed using molecular and cellular techniques.
Main Results:
- IL-4 deficiency worsened sensorimotor and cognitive deficits post-stroke.
- Loss of IL-4 increased acute neuronal tissue loss and skewed microglia towards an M1 phenotype.
- IL-4 administration improved long-term functional recovery and promoted M2 microglia/macrophage markers.
Conclusions:
- Interleukin-4 (IL-4) significantly improves long-term neurological outcomes after stroke.
- IL-4 may promote recovery by inducing an M2 phenotype in microglia/macrophages.
- Immunomodulation with IL-4 represents a promising therapeutic strategy for stroke recovery.
