PS1 stable complexes are increased in AD post-mortem CSF. (A) Representative blot of NTF-PS1 in post-mortem CSF samples from 10 AD (open circles) and 7 NDC controls (closed circles). The densitometric quantification of the accumulative immunoreactivity from the sum of the higher molecular mass PS1 complex (100 + 150 kDa) is shown. (B) Immunodetection and densitometric quantification of higher molecular mass PS1 complex (100 + 150 kDa) from CSF samples blotted with an anti-CTF-PS1 antibody. Dashed lines represent arbitrary cutoffs that maximally discriminated between AD and NDC groups. (C) PS1 complexes in 4 (of 7) NDC (closed circles) and 8 (of 10) AD CSF samples (open circles) were fractionated on 5-20% sucrose density gradients. The fractions (collected from the top of each tube) were immunoblotted for NTF-PS1 under denaturing conditions with the antibody from Calbiochem. Enzymes of known sedimentation coefficient, β-galactosidase (G, 16.0S; ~540 kDa), catalase (C, 11.4S; ~232 kDa) and alkaline phosphatase (P, 6.1S; ~140-160 kDa) were used as internal markers. Representative blots are shown. A quotient between highly stable complexes (100 + 150 kDa immunoreactive bands sediment closer to alkaline phosphatase, fractions 2-7) and unstable complexes (50-kDa immunoreactive bands sediment closer to catalase, fractions 8-12) was defined and represented. Dashed lines represent an arbitrary cutoff that maximally discriminated between AD and NDC groups. The data represent the means (in arbitrary units) ± SEM. *Significantly different (p < 0.05) from the NDC group, as assessed by the Mann-Whitney U test.