Inhibition of in vitro Autosensitization by a Thymic Humoral Factor

WE have recently reported 1 that mouse lymphoid cells sensitized in vitro , according to the method of Ginsburg 2 , against either syngeneic tumour cells or syngeneic fibroblasts could mediate specific killing when tested in the microcytotoxicity assay devised by Takasugi and Klein 3 . We also found that the presence of a thymic humoral factor (THF) during in vitro sensitization against syngeneic tumour cells markedly increased lymphoid competence to destroy their target cells (C. C., D. I., I. Brook, and N. T., unpublished). It was therefore of interest to test whether THF would also affect autosensitization of spleen cells cultured on syngeneic fibroblast monolayers.