Nature of the Delayed Graft-Versus-Host Reactivity of Fetal Liver Cell Transplants in Mice

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Abstract
Experiments were designed to determine which actual differences in the cellular composition between fetal liver and bone marrow account for the distinct types of graft-versus-host (GvH) disease. The assay of reactive lymphocytes (by in vitro mitogenic stimulation) in fetal liver transplants in mice, the purification of hemopoietic stem cells (HSC) of the transplants, and the quantitation of HSC numbers in the grafts traced the basis for the distinctly weak type of GvH disease after fetal liver cell grafts. It was found that transplantation of purified HSC concentrates did not modify the severity of GvH mortality. The moderate character of the delayed GvH disease was shown to depend on the presence of an HSC population in fetal liver with different qualities and not on numerical differences between the HSC in fetal liver and bone marrow. Data collected also demonstrated that when GvH disease occurred in the recipients of transplants of fetal liver, it shared the characteristic histologic features of the bone marrow GvH syndrome. The recovery of mitogen responsiveness of spleen cells may have been delayed in fetal liver allotransplantation as compared to syngeneic grafting. By supportive infusion of lymphoid cells, it was suggested that the immunodeficiency coinciding with GvH disease represented a secondary manifestation of the disease rather than a primary impairment in lymphoid differentiation.