CD33 and Alzheimer disease: For the significant causal associations with FDR < 0.05, rs2949661 and rs9916257 associated with CD247 and SLFN12L impacted CD3 on CM CD4+ and NK AC leading to a decreased risk of ALS; CD33 could influence different CD33+ ICTs to enhance the risk of AD under rs3865444 and rs2455069, while rs3087456‐CIITA could reduce AD risk by impacting HLA DR+ CD8br AC.