MAPT and Alzheimer disease: To investigate whether α-synuclein fibrils promote tau aggregation through cross-seeding, we first immunoprecipitated (IP) α-synuclein from AD-DLB postmortem brain tissue (BA20) and validated the immunoprecipitated fraction using total α-synuclein (for IP) and tau5 (for Co-IP) antibodies on a Western blot (Fig. 2G).