Inflammatory cytokines as a third signal for T cell activation

Abstract

CD8 T cells require a third signal, along with Ag and costimulation, to make a productive response and avoid death and/or tolerance induction. Recent studies indicate that IL-12 and Type I IFN (IFNalpha/beta) are the major sources of signal 3 in a variety of responses, and that the two cytokines stimulate a common regulatory program involving altered expression of about 350 genes. Signal 3-driven chromatin remodeling is likely to play a major role in this regulation. Although less well studied, there is emerging evidence that CD4 T cells may also require a 'third signal' for a productive response and that IL-1 can provide this signal. Signal 3 cytokines can replace adjuvants in supporting in vivo T cell responses to peptide and protein antigens, and a better understanding of their activities and mechanisms should contribute to more rational design of vaccines.

Figure 1. Activation of naïve CD8 T cells requires three signals: Ag, costimulation and either IL-12 or IFNα/β

Stimulation with Ag and B7-1 results in extensive proliferation, but survival is compromised and development of effector functions is suboptimal. The small numbers of cells that survive long term are anergic. When either IL-12 or IFNα/β are present, proliferation is comparable but survival is increased, the cells develop strong effector functions, and a protective memory population is formed.