Immune cells and ischemic stroke: A bidirectional Mendelian randomization analysis

Ischemic stroke (IS) is a leading cause of morbidity and mortality worldwide, with emerging evidence suggesting that immune cell characteristics may play a crucial role in its pathogenesis. This study aimed to investigate the causal relationship between 731 immune cell signatures and IS via a two-sample Mendelian randomization approach, thereby elucidating the potential immunological mechanisms underlying IS. We conducted a two-sample Mendelian randomization analysis using genome-wide association study summary statistics for IS and immune traits. Instrumental variables were selected based on stringent criteria, including genome-wide significance thresholds and quality control measures. Causal estimates were derived via inverse-variance weighted regression, supplemented by sensitivity analyses to assess robustness and address potential pleiotropy. Our findings indicate that IS may causally influence the activation of immune cells, specifically increasing absolute counts and relative proportions of CD86+ plasmacytoid dendritic cells and increasing B-cell activating factor receptor expression on CD20-CD38- B cells. Conversely, we identified 6 immunophenotypes associated with reduced IS risk, including elevated CD62L-HLA-DR+ monocyte counts and decreased CD28 expression on regulatory T cells. Sensitivity analyses confirmed the robustness of these associations, with no evidence of horizontal pleiotropy. This study provides compelling evidence for the causal roles of specific immune cell characteristics in the pathogenesis of IS. These findings suggest that immune modulation, particularly through the CD86 and B-cell activating factor receptor signaling pathways, may influence IS risk and highlight the potential for targeted immunotherapeutic strategies in stroke prevention. Future research should further explore these mechanisms and their implications for clinical practice.