LIGHT AND ELECTRON-MICROSCOPY IMMUNOHISTOCHEMICAL CHARACTERIZATION OFAMYLOID DEPOSITS

The present study reports our optimized fixation and processing method s for the light and electron microscopic immunohistochemical character ization of tissue amyloid. The study involved a series of 25 abdominal fat aspirates and of 11 tissue biopsy samples from different organs f rom 36 patients. We tested a short fixation and processing method and a series of enzymatic, acidic and physical (microwave oven) pretreatme nts on paraffin slides for light microscopy, Congo red stain and immun ohistochemistry. Microwave antigen retrieval provided the highest enha ncement for both Congo red stain and immunohistochemical reactions wit h all tested antibodies; formic acid also gave good results, but tissu e morphology may have been altered. Immunoelectron microscopy provided evidence of fibril accumulation and immunoreactivity in both mixed (d ouble immunoreactivity) and non-mixed forms, along with information on the relative amount of immunoreaction for the two components in mixed amyloid deposits; the technique also yielded details on spatial fibri l arrangement, which differs, at least for beta(2)-microglobulin and T TR, from that of AL amyloid deposits.