Differential expression of intercellular adhesion molecule-1 (ICAM-1) in the Aβ-containing lesions in brains of patients with dementia of the Alzheimer type

Inflammatory processes have been implicated in the formation of senile plaques in the cerebral cortex of patients with dementia of the Alzheimer type (DAT), since several inflammation-induced proteins are present within these plaques. The relation between inflammatory components and other amyloid β protein (Aβ)-containing lesions of the DAT brain [cerebrovascular amyloidosis (CA) and cerebellar senile plaques] is unclear. We studied the distribution of the inflammation-inducible protein intercellular adhesion molecule-1 (ICAM-1) in CA and in senile plaques of the cerebellum, using an immunohistochemical approach. We observed striking differences in ICAM-1 reactivity between the different types of Aβ-containing lesions. ICAM-1 was only expressed in classic senile plaques in the granular and Purkinje cell layer of the cerebellum, and not in diffuse senile plaques of the molecular layer. Also, ICAM-1 was not associated with CA; only when the vascular amyloid extended into the neuropil (dyshoric angiopathy) was perivascular ICAM-1 reactivity observed. This is in contrast to the putative primary involvement of inflammation in the formation of cerebrocortical classic and diffuse senile plaques. Our findings indicate that ICAM-1 expression, which may be an indicator of an inflammatory reaction, is induced in the neuropil depending on the specific site of Aβ production.