Immunodetection of protein composition in cerebral amyloid extracts in Alzheimer's disease: enrichment of retinol-binding protein.

The protein profile of amyloid-enriched extracts from Alzheimer brain tissue was studied by enzyme immunoassay using antisera to 37 different antigens including neurofilament protein, the proteins of the prealbumin complex, immunoglobulins, light chains, and amyloid A and P components. The results demonstrate a significant enrichment of retinol-binding protein in Alzheimer brain extracts, but not in control extracts from non-Alzheimer brains or amyloid extracts from cases of amyloid A (secondary) or lambda light chain (primary) amyloidosis. The retinol-binding protein was enriched in the extracts from all four Alzheimer brains. In contrast, no enrichment of prealbumin, immunoglobulins or amyloid P component was observed. Two of the 4 different Alzheimer amyloid extracts showed significant accumulation of neurofilament protein. In addition, slightly increased amounts of free light chains were observed. The results suggest that retinol-binding protein may be involved in the pathogenesis of the amyloid deposits in Alzheimer's disease.