MAPT and Alzheimer disease: As the target epitopes for these antibodies have all been reported to be present in AD brain samples, absence of immunoreactivity with AD brain Tau for these reagents may suggest that: (i) the antibody does not detect the target Tau species by WB, under the experimental conditions employed here; or, alternatively, (ii) that the target epitopes were present at low levels below the detection limit of the techniques employed here.