Pitfalls in the quantitative estimation of beta-amyloid immunoreactivity in human brain tissue.

The duration of formic acid (FA) pretreatment clearly influences the extent of beta-amyloid immunoreactivity in brain tissue and consequently also the results of quantitative analysis. All of the parameters studied (area fraction, density, and mean size of beta-amyloid deposits) significantly increased with pretreatment of up to 6 h with beta-amyloid antibody obtained from Dako. Longer exposure to FA only marginally increased the mean size of the single deposits, whereas the area fraction and the density of beta-amyloid deposits slightly decreased. Optimal 6-h pretreatment (or even longer) did not reveal any beta-amyloid aggregates in those cases where none was seen with shorter durations of FA pretreatment. Similar results were obtained with beta-amyloid antibody 4G8 obtained from Senetek, whereas beta-amyloid antibody 6E10 was shown to be less dependent upon FA pretreatment. In conclusion, we recommend that the FA pretreatment time should be studied and optimized for each antibody used and always be described when the quantitative analysis of beta-amyloid load is reported.