MAPT and frontotemporal dementia: Previous post-mortem FTLD-tau studies reported evidence of microglial activation in combined subtypes of FTLD-tau using semi-quantitative analyses16 or smaller cohorts of PiD (CD68, n = 6)51 or PSP cases (HLA-DR, n = 5).52 One recent post-mortem study investigating microglia in a range of FTLD, reported absence of CD68 and Iba1 expression in PSP and FTLD-MAPT but increased expression in PiD,15 in contrast to our findings, perhaps explained by the limited number of FTD-tau cases (n = 5) in that study.