Two types of deposits, hyaline droplets and eosinophilic bodies, associated with α(2u)-globulin accumulation in the rat kidney

Alpha(2u)-globulin is an adult male rat-specific protein that accumulates spontaneously or inductively in the renal proximal tubular epithelium and forms microscopically observable deposits, which are generally referred to as “hyaline droplets,” whereas a specific type of deposits is referred to as “eosinophilic bodies” by Japanese toxicologic pathologists. We compared hyaline droplets and eosinophilic bodies using special stains including immunostaining for α(2u)-globulin and lysosome-associated membrane protein in spontaneously occurring and d-limonene-induced cases. Eosinophilic bodies appeared simultaneously and increased in parallel with the hyaline droplets in the induced case. In both of the spontaneous and induced cases, hyaline droplets and eosinophilic bodies were associated with α(2u)-globulin and lysosomes, although there were differences in the forms and staining properties that probably reflected the purity or density of α(2u)-globulin. According to the results, it is not necessary for eosinophilic bodies to be strictly distinguished from hyaline droplets, and it is reasonable to identify eosinophilic bodies as hyaline droplets in α(2u)-globulin nephropathy in routine toxicity studies, as they have been recognized to be a sequence of changes associated with accumulation of α(2u)-globulin.