Immunological characterization of the ~55- and the ~15- kDa, 6E10-immunoreactive proteins in CSF.

(A) A series of antibodies directed against various epitopes of Aβ were used to immunoprecipitate target proteins from CSF, and blots were probed with biotinylated- 6E10 or 82E1. Capture antibodies are indicated by the labels above each lane. Top panels show short exposure (30 sec), and bottom panels show longer exposure (3 min). Note that the ~55-kDa proteins (arrowheads) were immunoprecipitated by monoclonal antibodies targeting the N-terminal region (6E10 and 42–5), mid-region (4G8) and the C-terminal end of Aβ (anti-Aβx-40/42); whereas the ~15-kDa proteins (arrows) were only immunoprecipitated by monoclonal antibodies targeting the N-terminal region of Aβ. (B) A series of antibodies directed against various epitopes of APP were used to immunoprecipitate target proteins from CSF, and blots were probed with biotinylated 6E10. Capture antibodies are indicated by the labels above each lane. Both the ~55- and the ~15- kDa species were immunoprecipitated by monoclonal antibody 1G6 directed against an APP epitope N-terminally adjacent to Aβ, but not by antibodies directed against the N- (“NT”) or C- (“CT”) termini of APP. Mouse and rabbit IgGs (msIgG, rbtIgG) served as negative control capture reagents. * = non-specific bands.