ULTRASTRUCTURAL-STUDY OF MACROPHAGES OF THE RAT THYMUS AFTER CYCLOSPORINE TREATMENT

Young adult male Wistar rats were given 30 mg per kg of cyclosporin (C S) for 21 consecutive days. After CS treatment thymic medulla virtuall y disappears and the thymus is almost entirely composed of cortical ti ssue. Macrophages are scattered throughout the thymic cortex. These ce lls are very large, rounded, with inconspicuous prolongations and euch romatic nucleus with prominent nucleoli. These cells are loaded with l ipid bodies and vacuolar cytoplasmic inclusions of different size and diverse content, but very rarely contain phagocytosed lymphocyte remna nts. The cytoplasm between inclusions has very active aspect with abun dance of polyribosomes, granular endoplasmic reticulum and vesicles. M itoses of lymphocytes in the vicinity of macrophages are frequently se en. We discuss the morphological similarity between cortical macrophag es of CS-treated thymus and macrophages of cortico-medullary zone (CMZ ) of the normal rat thymus, as well as functional significance of desc ribed morphological characteristics of this type of thymic macrophages , which probably reflect the metabolism of arachidonic acid.