Background and Purpose: Females exhibit a more robust immune response in many disease models, yet sex differences in the inflammatory response to ischemia remain largely unexplored. We conducted flow cytometry and RNA sequencing of blood from ischemic stroke patients, with follow-up studies in mice.
Hypothesis: We assessed the hypothesis that there are sex differences in the acute immune response to ischemic stroke.
Methods: Patient samples were drawn at 24 hours post-stroke for flow cytometry (n=6) and RNA sequencing Analysis (n=40). For murine studies, male and ovariectomized (OVX) female animals (n=14) were subjected to 90-minute middle cerebral artery occlusion or sham surgery and sacrificed at 24 hours. Murine blood was stained for leukocyte markers and CD62L (L-selectin). Results were analyzed by student T-test and two-way ANOVA.
Results: RNA sequencing revealed that 24 hours after ischemic stroke, female patients had 79 significantly upregulated genes, compared to male patients with 6 significantly upregulated genes. Human flow cytometry revealed that male stroke patients had a significantly higher percentage of monocytes (p=.026), while females had a greater percentage of CD8+ T-cells (p=.023). Murine flow cytometry showed a post-stroke increase in peripheral myeloid cells at 24 hours in male mice only (p=.0046), whereas female mice had a higher CD8/CD4 T cell ratio (p=.0027). Neutrophils from male sham animals displayed greater L-selectin positivity, with stroke-induced shedding of L-selectin seen only in males (sex/stroke p=.0266). Male monocytes and lymphocytes also displayed higher L-selectin positivity (p=.0079, p=.0004).
Conclusion: These results suggest that the immune response to ischemic stroke is different in male and female patients, a phenomenon that can be recapitulated in a mouse model of experimental stroke. Female immune cells exhibit a higher level of baseline activation (reduced L-selectin expression) and post-stroke activity, which may enable a quicker and more robust response to immune challenges. Understanding sex differences in the acute immune response is crucial to developing future immunomodulatory drugs for the safe and effective treatment of ischemic stroke in both sexes.