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Studies on Restoration of Sensitivity of Thymectomized Rats to Viral Leukemia¹

Department of Pathology, College of Physicians and Surgeons, Columbia University, and Francis Delafield Hospital, New York, New York, and Department of Pathology, University of Pennsylvania Medical School, Philadelphia, Pennsylvania

Thymectomy at 3–4 days of age prevented the induction of leukemia by virus in WF rats; grafts of neonatal thymus corrected this deficiency. Multiple thymus grafts were much more effective than single ones. Similarly, thymectomy in rats caused a lasting reduction of lymphocyte levels and the capacity to produce hemagglutinins; these deficiencies were also corrected by thymus grafts. In restoring susceptibility to leukemia and the lymphocyte levels, 5 thymuses were more effective than a single thymus, and 10 thymuses were more effective than 5 thymuses. In restoring immunologic capacity, 5 and 10 thymuses were more effective than a single thymus.

Transplantation assays of the induced lymphomas for genetic and histocompatibility factors suggested that the induced lymphoma cells were of 3 types: (a) those which possessed the transplantation pattern of the host; (b) those which had the transplantation pattern of the donor cells; and (c) those which were immunologically altered. This alteration is indicated by lack of transplantability in adult rats with transplantability in young rats and/or by regression of tumors in adult hosts.

Electron micrographs revealed the presence of replicating virus in all 3 lymphomas arising in thymus grafts that were examined. The mechanism by which the thymus and the virus bring about neoplastic transformation of normal lymphoid cells remains conjectural.

¹ This work was supported by Grants CA-06215 and CA-3562 from the National Cancer Institute, NIH.

² Permanent address: The First Department of Internal Medicine, Nagoya University School of Medicine, Nagoya, Japan.

³ Address reprint requests to: Dr. Jacob Furth, Department of Pathology, Francis Delafield Hospital, 99 Fort Washington Ave., New York, N. Y. (10032).

Received 5/17/65.

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