IL-4 Is Required for Sex Differences in Vulnerability to Focal Ischemia in Mice

Abstract

Background and Purpose IL-4 protects from middle cerebral artery occlusion (MCAO) in male mice. Females generally show less injury in response to the same ischemic challenge, but the underlying mechanisms are not fully understood. We tested the importance of IL-4 in female protection using IL-4 knockout (KO) mice. Methods IL-4KO and wild-type mice of both sexes were subjected to MCAO. Infarct volume was assessed by triphenyltetrazolium chloride staining and neurobehavioral outcome by neuroscore. T cell proliferation was assessed after ConA exposure. Ischemic brain immune cell populations were analyzed by FACS and immunostaining. Results Infarction in WT-females during estrus and proestrus phases was significantly smaller than in males; neurological score was better. Infarction volume was larger and neurological score worse in IL-4KO compared with WT in both sexes, with no sex difference. Proliferation of T cells was inhibited in WT-females with higher proliferation and no sex difference in IL-4KO. Macrophage numbers and total T cells in the ischemic hemisphere were lower in WT-females, and monocytes increased markedly in IL-4KOs with no sex difference. The reduced macrophage infiltration in WT-females was predominantly M2. Loss of IL-4 increased CD68+ and iNOS+ cells and reduced YM1+ and Arg1+ cells in both sexes. Conclusions IL-4 is required for female neuroprotection during the estrus phase of the estrus cycle. Protected WT-females show a predominance of M2 activated microglia/macrophages and reduced inflammatory infiltration. Increasing macrophage M2 polarization, with or without added inhibition of infiltration, may be a new approach to stroke treatment.

Interleukin-4 Is Essential for Microglia/Macrophage M2 Polarization and Long-Term Recovery After Cerebral Ischemia

“…Interestingly, recent studies support the importance of IL-4 in sex differences in stroke models. 12, 29 IL-4 is critical for neuroprotection during the estrus phase of the estrous cycle in females. 12 Furthermore, microglia isolated from female mice after MCAO express higher levels of the IL-4 receptor upon further inflammatory stimulation.…”

“…12, 29 IL-4 is critical for neuroprotection during the estrus phase of the estrous cycle in females. 12 Furthermore, microglia isolated from female mice after MCAO express higher levels of the IL-4 receptor upon further inflammatory stimulation. 29 Therefore, the effect of IL-4 on long-term outcomes after stroke in female warrants further investigation.…”

“…In patients, serum levels of IL-4 increase significantly several hours after stroke onset. 10 IL-4 deficiency exacerbates brain injury and worsens neurological outcomes 24h after transient middle cerebral artery occlusion (tMCAO) in animal models of stroke, 11, 12 suggesting that IL-4 serves as an early endogenous neuroprotective mechanism soon after stroke onset. The effect of IL-4 on long-term recovery after stroke has not yet been explored although persistent recovery is more important for clinical translation.…”

Sex differences and the role of PPAR alpha in experimental stroke

“…For instance, the spleen and IL-4 are needed to observe sex difference in infarct size after stroke, and without either the spleen or IL-4, infarct sex difference is lost (Dotson et al 2015; Xiong et al 2015). Additionally, higher levels of IL-10 after stroke have been associated with poor acute and long-term outcomes in females (Conway et al 2015).…”

Sex differences in the immune response to experimental stroke: Implications for translational research

“…IL-4 has also been shown to be important for neuroprotection of young female mice after stroke. Loss of IL-4 in female mice exacerbated infarct and increased inflammatory cells in the brain, thus eliminating sex difference after experimental stroke (Xiong et al, 2015). M2 microglia are reduced in the brains of female IL-4 KO mice but not males, supporting the neuroprotective role of IL-4 in females (Xiong et al, 2015).…”