Electronmicroscopic observation of amyloid deposits in the vascular walls of the choroid plexus in systemic amyloidosis

Human choroid plexus is an uniquely involved area of the brain in amyloidosis: a histochemical, immunohistochemical and ultrastructural study

To better understand the characteristics of amyloid deposition in the choroid plexus, we examined autopsied brain by routine histology, immunohistochemistry, and electron microscopy in three group of patients: primary systemic amyloidosis (n = 7), cerebral amyloid angiopathy (CAA, n = 6), and controls (n = 3). Three of the CAA patients had Alzheimer's disease. Congophilic, birefringent amyloid deposits of the choroid plexus were seen in six of the seven cases of systemic light chain amyloidosis. Immunohistochemistry revealed that the deposited amyloids had reactivity for immunoglobulin light chain and amyloid P component. Accumulation of macrophages labeled with monoclonal antibodies against CD 68 and major histocompatibility complex class II antigens were observed around the massive amyloid deposits. The presence of approximately 10 nm amyloid fibrils along the epithelial basement membrane as well as in the vascular walls was ascertained by electron microscopy. In CAA, Congo red-positive amyloid deposits were consistently present in meningeal blood vessels and were often found in senile plaques of the cerebral parenchyma; congophilic amyloid deposits were absent in the choroid plexus. Choroid plexus epithelial cells exhibited immunostaining for beta amyloid precursor protein (APP) with N-terminal- and C-terminal-specific antibodies; in particular, consistent staining was obtained for the latter antibody. Immunoreactivity for amyloid beta protein (A beta) with monoclonal antibodies (6E10, 4G8) was often found in choroid plexus epithelial cells. These findings suggest that amyloid deposition of the choroid plexus depends on the major component protein in amyloidosis, and that the choroid plexus may produce APP and A beta protein although A beta amyloidosis is not evident in the choroid plexus.

Cerebral vascular amyloid deposition in rabbits with induced thyroglobulin immunity

Cerebral amyloid angiopathy (CAA) occurs in humans along with the neuritic amyloid plaques in Alzheimer's disease, in several familial (inherited) syndromes, and in a sporadic form that increases in prevalence with age to attain a rate of about 60% after age 90. In the non-Alzheimer conditions, it is often accompanied by cerebral hemorrhage and sometimes also by dementia. We report here the experimental induction of cerebrovascular amyloid (CVA) in thyroglobulin (Tg)-immunized rabbits. The vascular deposits in these rabbits are comparable to that seen in humans in that they primarily involve arterioles, venules, and capillaries and exhibit microscopic and ultrastructural characteristics similar to the human lesion. Prominent congophilic vascular lesions in the brain were seen in three out of six Tg-immunized rabbits, whereas less striking basement membrane thickening was evident in three other experimental animals, probably reflecting individual variations in vascular responses to actively induced Tg immunity. Occasional primitive amyloid plaques were also encountered adjacent to vascular lesions. These observations are of particular interest since in other experimental models, cerebral vascular amyloid deposits have not been observed, thus suggesting that immunopathogenic events induced by active Tg immunization may be unique in their effects on the cerebral vasculature.