Theta-Bearing Cells in the Bone Marrow of Thymus-Deprived Mice

Theta-bearing cells in lymphomyeloid tissues of thymus-deprived and normal mice have been studied by the use of anti-theta. antisenun and cytotoxicity tests in addition to functional tests, In contrast to the findings in peripheral lymphoid tissues, increased percentages and numbers of theta-bearing cells were found in the bone marrow of neonatally thymectomized and nude mice as compared with normal and sham-thymectomized mice. In adult thymectomized mice, percentages comparable to those in sham-perated littermates were found. The findings were not due to irrelevant antibodies in the anti-theta antiserum, and neonatally thymectomized mice grafted with a thymic lobe showed percentages of theta-positive cells in the bone marrow comparable to those of sham-operated animals. Adrenalectomy did not lead to diminished percentages of theta-positive cells in the bone marrow of neonatally thymectomized mice, and the serum levels of hydrocortisone and corticosterone were within normal ranges in thymus-deprived mice. The mitogen responses and graft-versus-host activity of bone marrow cells from neonatally thymectomized mice suggest that most theta-positive cells in the bone marrow of these mice are functionally immature cells.