Immunohistochemical Visualization of Amyloid-β Protein Precursor and Amyloid-β in Extra- and Intracellular Compartments in the Human Brain

Amyloid-beta (A beta) peptide, a cleavage product of the amyloid-beta protein precursor (A beta PP), has been reported to be detected in the intracellular compartment. Most studies reporting the presence of intracellular A beta are based on the use of immunohistochemistry. In this study, the presence of A beta PP and A beta was assessed by applying immunohistochemistry in postmortem human brain tissue samples obtained from 10 neurologically intact subjects, the youngest being 2 years of age, one aged with mild cognitive impairment, 14 neurologically diseased, and in one brain biopsy sample obtained from a subject with normal pressure hydrocephalus. Intracellular immunoreactivity was detected in all ages independent of the disease state or existence of extracellular A beta aggregates with all antibodies directed to A beta PP, with three A beta antibodies (4G8, 6E10, and 82E1), clones that are unable to distinguish A beta from A beta PP. These results suggest that it is A beta PP rather than A beta that is detected intracellularly when using the antibodies listed above. Furthermore, the staining results varied when different pretreatment strategies were applied. Interestingly intracellular A beta was detected with antibodies directed to the C-terminus of A beta (neoepitope) in subjects with Alzheimer's disease. The lack of intracellular immunoreactivity in unimpaired subjects, when using antibodies against neoepitopes, may be due to a lack or a low level of the protein that is thus undetectable at light microscopic level by immunohistochemistry method. The staining results and conclusions depended strongly on the chosen antibody and the pretreatment strategy and thus multiple antibodies must be used when assessing the intracellular accumulation of A beta.