Histological observations on thymus grafts placed under the renal capsule in mice, with special reference to the occurrence of lymphoid nodules.

Recently several studies have been made concerning morphological and functional aspects of thymus grafts in mice (METCALF, 1963, 1964; DUKOR, MILLER, HOUSE and ALLEN, 1965; LEUCHARS, CROSS and DUKOR, 1965; MILLER et al., 1966). In these studies, thymuses from neonatal donor mice were usually grafted under the renal capsule of recipients, because grafting at that site offered many advantages as compared with other sites. It is generally accepted that following grafting the grafts rapidly regenerate, restore normal structure and develop autonomously at the same rate as the normal thymus of corresponding age (METCALF, 1963; METCALF, WAKONIG-VAARTAJA and BRADLEY, 1965). Cytological and histological events during the regeneration and development of thymus grafts were observed in detail by the previous investigators. Nevertheless, the previous observations were limited to thymus grafts studied at relatively short intervals after grafting. In this study, systematic examination was undertaken for a long period of time after grafting. Of particular interest was the finding that thymus grafts frequently contained lymphoid nodules with germinal centers. It is well known that the thymus, unlike other lymphoid organs, has no lyphoid nodules, but that under certain pathological conditions lymphoid nodules with germinal centers appear in the thymus (MACKEY, 1966). No report has described the occurrence of lymphoid nodules in thymus grafts.