Enhanced Antigen Retrieval of Amyloid β Immunohistochemistry: Re-evaluation of Amyloid β Pathology in Alzheimer Disease and Its Mouse Model

Senile plaques, extracellular deposits of amyloid beta peptide (A beta), are one of the pathological hallmarks of Alzheimer disease (AD). As the standard immunohistochemical detection method for A beta deposits, anti-A beta immunohistochemistry combined with antigen retrieval (AR) by formic acid (FA) has been generally used. Here, we present a more efficient AR for A beta antigen. On brain sections of AD and its mouse model, a double combination of either autoclave heating in EDTA buffer or digestion with proteinase K plus FA treatment reinforced A beta immunoreactivity. A further triple combination of digestion with proteinase K (P), autoclave heating in EDTA buffer (A), and FA treatment (F), when employed in this order, gave a more enhanced immunoreactivity. Our PAF method prominently visualized various forms of A beta deposits in AD that have not been clearly detected previously and revealed numerous minute-sized plaques both in AD and the mouse model. Quantification of A beta loads showed that the AR effect by the PAF method was 1.86-fold (in the aged human brain) and 4.64-fold (in the mouse brain) higher than that by the FA method. Thus, the PAF method could have the potential to be the most sensitive tool so far to study A beta pathology in AD and its mouse model. (J Histochem Cytochem 60:761-769, 2012)