To complement and extend the ELISA/MSD screening for antibody binding to pathological tau fractions (see Methods), we characterized C5.2 binding by Western and dot blots in brain samples isolated from tau transgenic mice (rTg4510 mice overexpressing human tau with P301L mutation) and non-transgenic littermates, as well as from Alzheimer’s disease patients and healthy control subjects. This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.