The use of formic acid to embellish amyloid plaque detection in Alzheimer's disease tissues misguides key observations

We compared our heat pretreatment method to the widely used formic acid pretreatment technique to immunohistochemically detect amyloid in control and Alzheimer's disease brain tissues. Both methods detected amyloid in plaques, neurons, ependymal cells, circulating monocytes, vascular smooth muscle and endothelial cells. Although there were no observable differences in the intensity of the amyloid labeling in these cell types using both pretreatment methods, there were considerable differences in the intensity of amyloid immunolabeling in the plaques. The formic acid produced much more intense amyloid labeling in the plaques than the heat method. With the heat method, the intensity of the amyloid labeling in the plaques was similar to that detected in nearby neurons suggesting a neuronal origin of plaques. Conversely, the intensity of the amyloid in nearby neurons and plaques was drastically different using the formic acid suggesting unique origins of amyloid. The obvious benefits of formic acid for increasing the sensitivity of amyloid plaque immunolabeling may artifactually emphasize plaques over amyloid-containing cells during analyses.