Inability of interleukin-12 to modulate T-helper 0 effectors to T-helper 1effectors: a possible distinct subset of T cells

Interleukin-12 (IL-12) strongly favours the development of T-helper 1 (Th1) -type cells through its ability to induce interferon-gamma (IFN-gamma) prod uction by natural killer cells and T cells. In the present work we analysed the effects of IL-12 on the synthesis and secretion of IFN-gamma and IL-4 by human T-cell clones. Several previously described human T-cell clones ex hibiting Th1, Th2 or Th0 phenotypes were used for these analyses. We demons trated, by enzyme-linked immunosorbent assay (ELISA) and intracytoplasmic s taining, that, in Th0 clones, IL-12 up-regulated the production of both IFN -gamma and IL-4 and was unable to modulate these cells to Th1-type. The up- regulation of cytokine gene expression was transcriptionally regulated and was not due to differences in mRNA stability. In Th1 cells. IL-12 up-regula ted only IFN-gamma and not IL-4. However, in Th cells, both IFN-gamma and I L-4 were up-regulated by IL-12. This suggests that Th2 cells may be less st able than Th1 cells. We also observed that human Th2 cells expressed the IL -12 beta 2 receptor, in contrast to murine Th2, which lacks this receptor. The observed differences in the effects of IL-12 on the three T-cell subset s may have important ramifications for IL-12-based therapies.