Reactivity of thymic metallophilic cells during the regeneration after the application of cyclophosphamide.

Metallophilic cells, which had dendritic morphology in vivo, were localized almost exclusively in the cortico-medullary zone of the control rat thymus. The patterns of thymic regeneration after a single (300 mg/kg) or consecutive injections (5 X 60 mg/kg) of Cyclophosphamide were well correlated with the changes in the number and topographical distribution of the metallophilic cell population. The specific staining with aldehyde fuchsin of metallophilic cells diffusely distributed throughout the cortex during the regeneration clearly demonstrated that these cells were identical with aldehyde fuchsin-positive metallophilic cells in the cortico-medullary zone of the normal rat thymus. The results presented suggest that metallophilic cells play some role in the process of normal thymocytopoiesis and represent a hitherto undescribed component of the thymic microenvironment.