Various types of plaques. Various types of plaques stained with HE (a-d) and immunohistochemical labeling with mAb F99/97.6.1 (e-h). Unicentric (a and e) and multicentric (b-d and f-h) cores of plaques (arrows) in the white matter of the thalamus (a-c and e-g) and in the deep cortical area of the frontal lobe (d and h). The inset in the lower left corner of (e) shows an amyloid plaque detected by Congo red staining in the serial section; it shows birefringence under polarized light. Scale bars = 20 μm.