generated from their direct precursor C99 in independent cell clones. Aβ42 and Aβ40 were immunoprecipitated from conditioned media of SH-SY5Y cells, overexpressing C99, using specific antibodies for Aβ42 and Aβ40. Both Aβ species were detected by Western blotting using antibody W02. C99 is intracellularly cleaved, generating different amounts of Aβ42 and Aβ40 in C99I45F and C99V50F. C99I45F generates more Aβ42 than Aβ40, whereas C99V50F generates more Aβ40 than Aβ42.