MAPT and Alzheimer disease: To further validate GT-38 selectivity, we performed co-immunofluorescent (co-IFC) staining with GT-38 and 3R- or 4R-tau specific antibodies since AD-tau NFTs are comprised of all six human tau isoforms, including both 3R- and 4R- tau, while PiD aggregates are comprised primarily of 3R-tau and CBD and PSP are comprised of primarily 4R-tau.