CD4 and Alzheimer disease: We found that the frequency of CD4+CD25+Foxp3+ Tregs in the spleens of AD+IIV mice after ATRA treatment (IIV+ATRA) was significantly higher than that in the vehicle (IIV+Vehicle) and AD+IIV groups (Fig. 6a, b), but no significant alterations in other CD4+ T cell subsets, such as Th1 (IFN-γ+CD4+), Th2 (IL-4+CD4+) and Th17 (IL-17A+CD4+) cells (Fig. S3A-C), or CD8+ T cells were observed in the spleen of AD+IIV mice (Fig. S4).