Murine and Human T Cell Factors that Induce the Differentiation of Normal Mouse Lymphocytes into Cytotoxic Cells Copurify with Interleukin 2

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Abstract
Fetal calf serum (FCS)‐specific T promoter cell lines (line 12), clones, or lymphomas produce lymphocyte promoter factors (LPF). These factors are defined as T‐cell supernatant activities that induce polyclonal differentiation of normal experimentally unprimed mouse lymphocytes into antibody‐forming cells (B‐LPF) or into cytotoxic cells (T‐LPF). The cytotoxic cells thus induced lysed a broad range of target cells including syngeneic and allogeneic tumour cells and lymphoblasts. We have investigated whether T cell tumours (mouse or human) other than FCS‐specific T promoter cell lines (line 12), clones, or lymphomas produce T‐LPF activity, and whether T‐LPF activity is related to interleukin 2 (IL‐2) activity. We found that the EL4 thymoma cells were high producers of T‐LPF and IL‐2 activity. When EL4 cells and T‐LPF + line 12 lymphomas were cloned, all T‐LPF high‐producer clones were also high IL‐2 producers. In addition, the human Jurkat T tumour cells produced both T‐LPF and IL‐2 activity which could he detected on both mouse and human lymphocytes. By using biochemical fractionation (size fractionation or chromatofocusing fractionation) and absorption techniques, we could not separate T‐LPF and IL‐2 activity. Thus, the present data may indicate that the T‐LPF and IL‐2 activities studied in the present systems are borne by the same molceule(s) (=IL‐2?). These results are discussed in relation to current hypotheses on the cellular and molecular requirements for the generation of cytotoxic T cells.