Localization of alpha 2u-globulin within protein droplets of male rat kidney: immunohistochemistry using perfusion-fixed, GMA-embedded tissue sections.

We investigated the light microscopic subcellular localization and quantitation of alpha 2u-globulin (alpha 2uG) in male rat kidney after 2,2,4-trimethylpentane exposure using a monoclonal antibody to alpha 2uG. Slices of perfusion-fixed kidney were cold-processed in glycolmethacrylate and the antigen localized after an avidin-biotin-horseradish peroxidase procedure with Hanker-Yates reagent as the chromagen. Light microscopic examination revealed resolution comparable to low-magnification electron microscopy, with excellent morphological detail of tissue architecture, including subcellular localization of alpha 2uG within lysosomes of P2 segment cells of the proximal tubule epithelium. The anatomical relationship between alpha 2uG and TMP-induced protein droplets observed after staining with Lee's methylene blue-basic fuchsin was studied using serial sections. Image analysis of selected P2 segments in treated and control rats revealed a high correlation between subcellular localization of alpha 2uG and protein droplet deposition in the cytoplasm of P2 segment cells of the proximal tubule epithelium. Quantitative morphometry of alpha 2uG-stained proximal tubule epithelium 72 hr after treatment with 50 mg/kg 2,2,4-trimethylpentane p.o. demonstrated a 1.5- to 2-fold increase in staining area of tubules from treated rats compared with controls. Similar increases of Lee's methylene blue-basic fuchsin-stained protein droplets were also observed, but quantitative morphometry of the protein droplets was technically more difficult owing to a lower staining contrast between droplets and the surrounding cytoplasm. This immunohistochemical procedure provides a valuable technique for further studies on the pathological role of alpha 2uG in protein droplet nephropathy of male rats induced by many environmental chemicals, and demonstrates the value of cold glycolmethacrylate processing to improve morphological detail.