SEMIQUANTITATIVE POSTEMBEDDING CHARACTERIZATION OF INTERMEDIATE FILAMENTS IN CENTRAL-NERVOUS-SYSTEM LESIONS USING IMMUNOELECTRON MICROSCOPY

Standardized postembedding immunoelectron microscopy was performed to demonstrate glial fibrillary acidic protein (GFAP) and vimentin in ind ividual intermediate filaments to determine the diagnostic value of de monstrating ultrastructural and immunophenotypic characteristics of in termediate filaments in routine brain biopsy specimens. Dual expressio n of GFAP and vimentin was observed in the astroblastoma and astrocyte s of Alexander's disease. The antigen availability for vimentin, howev er, was too low to allow reliable assessment of the GFAP:vimentin rati o in individual intermediate filaments and/or filament bundles. In men ingioma, only vimentin positive intermediate filaments were found. GFA P positive intermediate filaments were present in all other specimens except the oligodendroglial components of the mixed glioma, which were devoid of intermediate filaments. GFAP positivity in the filamentous periphery and electron-dense core of Rosenthal fibers was demonstrated , Technical and tissue processing factors had a significant effect on particle density values obtained for individual specimens. Although th e number, distribution, and density of glial intermediate filaments va ries in different astroglial entities, correlation of particle density values determined by immunoelectron microscopy with relative GFAP con centrations in different lesions requires utmost caution. Nevertheless , application of the postembedding approach to routinely fixed biopsy specimens indicated an association of different entities with the excl usive presence of GFAP and/or vimentin in individual intermediate fila ments, thus emphasizing the diagnostic value of intermediate filament typing for pathological characterization.