MAPT and Alzheimer disease: Finally, and of clinical relevance, we found that the increase in p-tau181 and p-tau231 (7, 8) was statistically significant in the plasma of the grafted amyloid mice but not in control grafted or nongrafted mice (Fig. 1, J and K), reflecting increased secretion of soluble p-tau biomarkers into the bloodstream in response to amyloid pathology, as in human AD.