Determination of amyloid beta protein precursors harboring active form of proteinase inhibitor domains in cerebrospinal fluid of Alzheimer's disease patients by trypsin-antibody sandwich ELISA.

beta-Amyloid protein precursors (APP) having proteinase inhibitor domains (APPI) were quantified by a new sandwich enzyme linked immunosorbent assay for detection of active (free) form of proteinase inhibitors by using trypsin in place of the first antibody and by denaturation of APPI-trypsin complex in the microtiterplate. The concentration of APPs having APPI in cerebrospinal fluid of Alzheimer's disease patients was found, by this method, to be significantly elevated compared with those of multi-infarct dementia.