HISTOPATHOLOGY AND ULTRASTRUCTURE OF THE THYMUS IN OP OP RATS WITH SPECIAL FOCUS ON THYMIC MACROPHAGES - EFFECT OF BONE-MARROW TRANSPLANTATION/

The thymi of op/op rats were investigated before and after bone marrow graft. Normal littermates were used as controls. The thymic involutio n and atrophy in nontreated op/op rats was characterized by the presen ce of pyknotic thymocytes (apoptosis) and numerous lipid-laden macroph ages containing pleiomorphic lysosomes. This thymic atrophy is histolo gically very similar to the thymic involution induced by glucocorticoi ds or by stress in normal rats. In treated new born op/op rats, the os teopetrotic process began to be reversed 2 weeks after the graft. The thymus of treated op/op recovered a normal weight and its histology an d ultrastructure were quite similar to that of normal littermates. The se findings are discussed in relation to the defective macrophage func tion and cellular immunity impairment reported in osteopetrosis.