IL-21 and TNF had a synergistic effect on DNA synthesis.

(A) OH-2 cells were incubated with increasing concentrations of IL-21 either alone, with IL-6 (1 ng/mL), or with TNF (10 ng/mL) for 72 hours. ³H-thymidine incorporation was measured. Similar results were obtained in the cell line IH-1, and the experiment was repeated twice. (B) A patient sample (patient 5 in Table 1) was incubated for 72 hours with IL-21 (40 ng/mL), IL-6 (1 ng/mL), or TNF (10 ng/mL), and ³H-thymidine incorporation was measured. Error bars in both panels represent ± 1 SD of triplicate data.