Type I interferons keep activated T cells alive

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