Type I Interferons Keep Activated T Cells Alive

Antigen injection into animals causes antigen-specific T cells to become activated and, rapidly thereafter, die. This antigen-induced death is inhibited by inflammation. To find out how inflammation has this effect, various cytokines were tested for their ability to interfere with the rapid death of activated T cells. T cells were activated in vivo, isolated, and cultured with the test reagents. Two groups of cytokines were active, members of the interleukin 2 family and the interferons (IFNs) α and β. This activity of IFN-α/β has not been described previously. It was due to direct effects of the IFNs on the T cells and was not mediated by induction of a second cytokine such as interleukin 15. IFN-γ did not slow the death of activated T cells, and therefore the activity of IFN-α/β was not mediated only by activation of Stat 1, a protein that is affected by both classes of IFN. IFN-α/β did not raise the levels of Bcl-2 or Bcl-_XL in T cells. Therefore, their activity was distinct from that of members of the interleukin 2 family or CD28 engagement. Since IFN-α/β are very efficiently generated in response to viral and bacterial infections, these molecules may be among the signals that the immune system uses to prevent activated T cell death during infections.