Immunohistochemical analysis of htt cleavage. A, Htt552 immunostaining of frontal cortex from control brain showing Htt552 immunoreactivity in many but not all pyramidal cortical neurons. B, Control panel for Htt552 immunostaining on the same control brain showing no immunoreactivity in the absence of primary antibody. Scale bar, 100 μm.C–H, High-power magnification of Htt552 immunostaining on frontal cortex from the grade I homozygote HDB171, showing the punctate, predominately cytoplasmic staining evident in cortical projection neurons. Scale bars: (in C) C–E,G, H, 20 μm; F, 10 μm.I, Htt552 immunostaining of frontal cortex from a 32-year-old presymptomatic patient (HDB Emory) showing the presence of cleaved htt in some neurons in layers II and III. J, Htt552 staining of frontal cortex from the same presymptomatic patient (HDB Emory) showing abundant immunoreactivity in pyramidal cortical neurons of layers V and VI. K, Htt552 immunostaining on striatum from the same presymptomatic patient, showing that some striatal neurons contain caspase-cleaved htt. Scale bar, 100 μm.