Correlation analysis of 22 immune cells showed that the number and proportion of immune cells in the hippocampus of AD patients were more abundant than those in healthy individuals, suggesting that core immune cells, such as regulatory T cells, neutrophils, plasma cells, activated mast cells, T follicular helper cells, CD8 T cells, resting memory CD4 T cells, and M1 macrophages, are involved in promoting AD progression. The gene discussed is CD8A; the disease is Alzheimer disease.