FURTHER STUDIES ON THE RELATIONSHIP OF THE THYMUS TO HEMOPOIESIS1

Abstract

Thymocytes of parental (P) type did not augment hemopoiesis in irradiated hybrid (F1) recipients of P marrow when (1) implanted i.p. in Millipore diffusion chambers as cell suspensions or as tissue slices; (2) disrupted by freezing and thawing or by sonification; or (3) used as saline extracts. These results suggest strongly that a humoral factor is not responsible for the augmenting effect. The augmentation of early marrow growth in P → F1 chimeras, produced by a standard number of P thymocytes, was dependent on age of thymus donor (within the limits of 1–13 weeks in this study). The effectiveness of thymoeytes from donors of different ages was related inversely to cell yield. The ability of thymocytes to augment marrow growth was found in transplantation situations other than the particular P → F1 poor growth cases previously studied so extensively; these include the allogenic A.SW → B6D2F1 and xenogenic Sprague-Dawley rat → B6D2F1 combinations. Ninety-day mortality data from several P → F1 and allogenic marrow plus thymocyte transplantation experiments showed that thymus of marrow donor type, either P or allogenic to F1 recipients, decreased survival of chimeras by accelerating graft-versus-host (GVH) disease. However, all long-term survivors of this constitution, although few in number, retained marrow grafts, whereas those that had been given either host-type or no thymocetes occasionally reverted to host-type red cells.