Immunohistochemical study of constituents other than β-protein in canine senile plaques and cerebral amyloid angiopathy

To clarify the significance of the constituents of canine senile plaques (SPs) or cerebrovascular amyloid deposits, paraffin and cryostat sections of canine brains were examined by immunohistochemistry using antibodies against cathepsin B (CB), cathepsin D (CD), cystatin C (CC), α-1-antichymotrypsin (ACT), heat shock protein 70 (HSP70), ubiquitin (Ubq), and apolipoprotein E (Apo E). On the cryostat sections, all types of canine SPs and cerebrovascular amyloid deposits in both arterioles and capillaries were positive for Apo E. On paraffin sections, the Apo E immunoreactivity of diffuse plaques was weak and varied according to the method of fixation or pretreatment before immunostaining. Moreover, amyloid plaques were found to contain several elements that were positive for CC, ACT, CD, and Ubq, and a subset of vascular amyloid deposits around cortical capillaries showed significant immunoreactivity for CD, CC, and ACT. In addition, vascular amyloid deposits in the arterioles showed moderate CD immunoreactivity and were intensely Apo E positive. No significant labeling of canine SPs or vascular amyloid deposits was detected when the antibodies against CB and HSP 70 were applied to the cryostat and paraffin sections. These results indicated that, of the constituents examined, Apo E might be most closely related to canine β-amyloidosis in the early stage of this brain disorder.