bAmyloid 1-42 was measured with a 1-step sandwich enzyme-linked immunoabsorbent assay (ELISA) (IGEN International Inc) using a polyclonal antibody specific for b-amyloid 1-42 (catalog No. 44-344; QCB Division of BioSource International) as the capture antibody and a monoclonal antibody, 4G8, (Senetek now Signet)used as the detection antibody. This assay is designed specifically to measure the human b-amyloid 1-42 peptide in CSF in a 10 × excess background of 1-40.
Tau was measured using a commercial enzyme immunoassay (Innotest Inc, Ghent, Belgium). In this assay, the wells of polystyrene microtiter plates were coated with the solid phase anti–human tau monoclonal antibody (AT120). The test samples were incubated in these wells along with 2 separate biotinylated tau monoclonal antibodies H57 and BT2 that recognize different tau epitopes.