Graft-Versus-Host and Cytotoxic Activity of Rat Thoracic Duct Lymphocytes Fractionated by Zonal Centrifugation after Culture on Allogeneic Fibroblasts

Abstract

Large cytotoxic lymphocytes were generated by culturing syngeneic rat thoracic duct lymphocytes on a monolayer of allogeneic fibroblasts. Lymphocytes removed from culture at 5 days were fractionated by zonal centrifugation, and as expected, cytotoxicity was found to be a property of the large cells. At the same time, graft-vs-host activity of the small lymphocytes purified by zonal centrifugation was assayed by a quantitative method. Activities similar to controls were found in both specific (Ag-B-identical to those of fibroblasts) and nonspecific (Ag-B-different from those of fibroblasts) semiallogeneic F₁ hybrids. Cultures were also terminated after 3 and 4 days, and graft-vs-host assays were performed on small lymphocytes purified by zonal centrifugation. The activities also did not differ markedly from the controls. Hence, large cytotoxic lymphocytes are not generated at the expense of small lymphocytes capable of specific graft-vs-host activity; various possibilities for this finding are discussed.