Failure of thymic grafts to stimulate resorption of bone in the Fatty/Orl-op rat.

An infusion of compatible normal bone marrow stimulated bone resorption in both unthymectomized and thymectomized Fatty/Orl-op osteopetrotic rats. Bone resorption was not stimulated by compatible normal thymic grafts in either unthymectomized or thymectomized mutants. It is concluded that the thymus is not fundamental in the cure of osteopetrosis in this strain of osteopetrotic rat and that the defect lies in myeloid rather than thymic regulation of osteoclastic function.