Localization of calpain immunoreactivity in senile plaques and in neurones undergoing neurofibrillary degeneration in Alzheimer's disease.

An antibody raised against the calcium activated neutral protease (calpain) was used to investigate the possible involvement of this enzyme in the formation of plaques and tangles in Alzheimer-type dementia (ATD) brain. Our results revealed the presence of a number of strongly stained calpain positive neurones in the normal human cerebral cortex and a loss of calpain positive cells in ATD brain. Furthermore, double staining experiments revealed that calpain immunoreactivity was present in cells undergoing tangle formation, and was also present in senile plaques. These data suggest that activation of calpain may be an important factor in the abnormal proteolysis underlying the accumulation of plaques and tangles in ATD.