This study suggested significant difference in the mRNA level of C1QC, C1QB, C4BPA, CR1, C9, C6, C4A, CLU, CD59, SERPING1, C1S, C1R, C3AR1, C3 and C5AR1 among AD patients when compared with healthy people through single cell RNA-seq analysis. Here, C3 is linked to Alzheimer disease.