Immunoprecipitation of PS1 in human CSF. (A) Ventricular post-mortem CSF was immunoprecipitated with the anti-PS1 98/1 antibody, and precipitated proteins (IP) were immunoblotted with PS1-NTF (Calbiochem) or PS1-CTF antibodies (00/2). Precipitated proteins (IP) were immunoblotted with the PS2-CTF antibody 00/12. (B) Lumbar ante-mortem CSF was immunoprecipitated with NTF-PS1 antibody 98/1 or with antibody from Thermo Scientific, and precipitated proteins (IP) detected with an NTF-PS1 antibody from Calbiochem. (C) Extracts from SH-SY5Y cells over-expressing PS1 (+) and extracted in the presence of 1% Nonidet P-40/0.5% Triton X-100 were run in parallel with post mortem CSF samples from non-diseased control subjects. The presence of a ~43 kDa PS1 holoprotein in membrane extracts was detected with the NTF-PS1 antibody from Calbiochem. Comparison of the immunoreactive bands indicates that this 50-kDa band is not the PS1 holoprotein. (D) PS1-precipitated proteins (PS1-IP) were also immunoblotted with anti APH-1, PEN-2 or nicastrin antibodies. APH-1 and PEN-2, but not nicastrin were detected in PS1 immunoprecipitates. Extracts incubated with protein A-Sepharose with an irrelevant rabbit IgG (Bound IgG), were analyzed in parallel as negative controls.