Minimal growth requirements of mature T lymphocytes: interleukin (IL)-1 and IL-6 increase growth rate but not plating efficiency of CD4 cells stimulated with anti-CD3 and IL-2

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Abstract
We show that interleukin (IL)‐2 is necessary and sufficient for the proliferation of both CD4 and CD8 subsets of peripheral murine T cells activated by plastic‐bound anti‐CD3 monoclonal antibodies (mAb). The frequency of proliferating cells (f) was 0.32 for CD4 cells and 0.63 for CD8 cells. These frequencies were not increased by the addition of IL‐1 or IL‐6, alone or in combination. These cytokines were unable to induce responsiveness to IL‐2 in T cells confirming that they cannot substitute for the signal delivered via the TcR/CD3 complex. On the other hand, IL‐1 and IL‐6 increase the growth rate of CD4 cells. The addition of IL‐6 significantly lowered the mean doubling time (dt) of CD4 cells (dt: 26 h vs. 38 h in the presence of IL‐2 alone, p < 0.01), while the addition of IL‐1, ineffective by itself, combined with IL‐6 further increased the growth rate of CD4 cells (dt: 23 h, p < 0.001). The growth rate of CD8 cells stimulated with anti‐CD3 and IL‐2, was markedly faster than that of CD4 cells (dt: 18 h vs. 38 h, p < 0.001) and was not significantly influenced by addition of IL‐1 and/or IL‐6.