Histochemistry of the acutely involved thymus in nickel chloride-treated rats

Young adult male Wistar rats received a single injection of nickel chloride (0.5 mmol per kg) and were killed 72 h later. Histological examination showed that numerous, large, vacuolated cells appeared in the thymic cortex, which was almost totally depleted of lymphocytes. Enzyme histochemistry revealed that these cells were strongly acid phosphatase-positive macrophages. They contained aldehyde fuchsin-positive granules of varying size. Histochemical tests showed that these macrophages contained products of lipid peroxidation. According to the enzyme and histochemical characteristics, the macrophages which appeared in the thymic cortex during nickel-induced acute involution were identical to the special type of macrophage found in the cortico-medullary zone of the normal rat thymus.