TREM2 and Alzheimer disease: Although a recent report has revealed that TREM2 KO, or expression of human R47H TREM2 on a mouse TREM2 null background, results in exacerbation of NP tau pathology after AD-tau injection of APP/PS1 mice [28], we extend these studies by comparing the effects of both TREM2−/− and TREM2−/+ microglia in AD-tau-injected 5XFAD mice.