Clarified temporal cortical homogenates (low-speed supernatants) from 7 end-stage AD cases and 7 aged squirrel monkeys, normalized to 60 μg total protein, were electrophoretically separated in SDS by molecular weight on a Tris-Tricine 10-20% gel and immunoblotted with anti-Aβ antibodies 6E10 (top) and 4G8 (bottom). (A) Immunoblotting with antibody 6E10 revealed strong bands migrating at approximately 4 kDa in all extracts, which correspond to monomeric Aβ40 and Aβ42. Dimeric and trimeric Aβ species were also detected in some AD and squirrel monkey samples, particularly in the cases shown to have higher levels of Aβ by ELISA (see Table 1). (B) The 4G8 antibody detected strong bands of Aβ monomers in nearly all AD and squirrel monkey extracts. 4G8-immunoreactive bands corresponding to Aβ dimers and trimers were substantially stronger in most AD samples than in squirrel monkeys with comparable levels of total Aβ as shown by ELISA. Both antibodies bound to a band migrating around 105KDa, or full-length APP, in all samples. In the last lane, 100ng of fibrillar synthetic Aβ42 was run as a positive control. AD: Human Alzheimer's disease cases, Ss: Squirrel monkey (Saimiri sciureus); each lane represents a separate case.