C5AR1 and Alzheimer disease: To understand the effects of C5a–C5aR1 signaling on gene expression in AD, changes in expression of genes found in the current bulk RNA analysis were compared to our previous reports of microglia isolated from combined cortex and hippocampus from Arc and ArcC5aR1KO at the same ages [18], to those known to be associated with AD pathology progression in the 5xFAD mice model [36], and to human AD genes, such as Cd33, Trem2, Tyrobp, Inpp5d, and S100a6 [41–44] (Fig. 2C, right and Additional file 1: Fig S5B).