Monomeric and polymeric forms of alpha-1 antichymotrypsin in sera from patients with probable late onset Alzheimer's disease.

Patients with probable late-onset Alzheimer's disease (l-AD) had higher levels of serum alpha 1-antichymotrypsin (alpha 1-ACT) than those found in patients with vascular dementia (VD) and healthy elderly controls, when assessed by a competitive enzyme-linked immune assay. Serum alpha 1-ACT was also characterized by SDS PAGE electrophoresis. Western blot and computer-assisted optical density reading (OD). Using a polyclonal affinity-purified antibody specific for human alpha 1-ACT, one band with the apparent MW of 60 and another with 180 kD in sera from all subjects were clearly detectable. OD of both alpha 1-ACT bands from patients with l-AD was higher than that from VD patients, the 180-kD form being 2.65 times higher than that observed from patients with VD. Serum levels of other acute phase proteins from l-AD were comparable to those observed in VD patients. A slight but nonstatistical increment of serum IL-6 was noted in patients with l-AD. Serum alpha 1-ACT was purified from 3 of these l-AD patients by a two-step affinity chromatography technique. After Western blot, purified alpha 1-ACT showed two or three different bands which immune-reacted with an antibody specific for alpha 1-ACT. The apparent MWs were 60, 120 and 180 kD. In human sera the serpin was present mainly in a monomeric form, but it could also form SDS stable dimers and trimers. Both monomeric and SDS stable polymeric forms of alpha 1-ACT appeared to be increased in sera from patients with l-AD.