[Thymus morphology in Down's syndrome]

Changes in the thymus considered to be the morphological substrate of immune deficiency in Down's syndrome are described. Most typical changes include elimination of lymphocytes from the cortical and medullar substances, formation of giant cystic thymic bodies with necrosis and calcinosis, hyper- or hypoplasia of reticuloepithelium. In some observations these changes may be regarded as the primary immunodeficient condition associated with the reticuloepithelial pathology, in others they appear to be manifestations of a perverted course of accidental involution.