Characterization of N-terminal polyclonal PS1 antibodies by Western blot analysis. (A) Western blot analysis of endogenous and overexpressed human PS1. Lanes: 1, cell extract of Jurkat cells; 2, cell extract of HEp-2 cells transfected with full-size PS1 cDNA (Vector pcDNA3; Invitrogen); 3, cell extract of untransfected HEp-2 cells. (B) Western blot analysis of endogenous PS1 of mouse brain. Lanes: 1, brain extract of wild-type PS1(+/+) mice antibodies; 2, brain extract of PS1 knockout (−/−) mice.