Fig. 3.

Aβ immunohistochemistry and 6-CN-PiB histofluorescence: qualitative differences. Adjacent paraffin sections of the frontal cortex from the [C-11]PiB(−) case (a, b) and the [C-11]PiB(+) case (c, d) processed for Aβ immunohistochemistry with hematoxylin counter-staining (a, c) and 6-CN-PiB histofluorescence (b, d). a, b In the [C-11]PiB(−) case, diffuse plaques are poorly labeled with 6-CN-PiB (large empty arrows) except for minor portions which have 6-CN-PiB fluorescence comparable to primitive plaques (thin arrows) and halo of a classic plaque. c, d In the [C-11]PiB(+) case, two cored plaques (small empty arrows), CAA (asterisk), and a primitive plaque (thin arrow) have prominent 6-CN-PiB fluorescence. Scale bar 100 μm. e The graph shows correlation analyses of Aβ immunoreactive (6E10) and 6-CN-PiB labeled plaque loads (percent area) in 16 brain areas from the [C-11]PiB(−) case (triangles) and the [C-11]PiB(+) case (circles). The inset is an expansion of the [C-11]PiB(−) data showing no increase in 6-CN-PiB labeling in the same brain regions with up to 1.8% area occupied by Aβ immunoreactive deposits