CD8+ T cells and NK cells protect from viral infections by killing virally infected cells and secreting interferon-γ. Several inhibitory receptors limit the magnitude and duration of these anti-viral responses. NKG2A, which is encoded byKlrc1, is a lectin-like inhibitory receptor that is expressed as a heterodimer with CD94 on NK cells and activated CD8+ T cells. Previous studies on the impact of CD94/NKG2A heterodimers on anti-viral responses have yielded contrasting results and the in vivo function of NKG2A remains unclear. Here, we generatedKlrc1–/– mice and found that NKG2A is selectively required for resistance to ectromelia virus (ECTV). NKG2A functions intrinsically within ECTV-specific CD8+ T cells to limit excessive activation, prevent apoptosis, and preserve the specific CD8+ T cell response. Thus, although inhibitory receptors often cause T cell exhaustion and viral spreading during chronic viral infections, NKG2A optimizes CD8+ T cell responses during an acute poxvirus infection.
NK cells and T cells express a variety of inhibitory receptors that differentially regulate cell survival and effector functions. Here, Colonna and colleagues demonstrate that NKG2A limits excessive activation and apoptosis of CD8+ T cells in vivo and that this function is required to resist infection with ectromelia virus.