Emergence of CD8(+) T cells expressing NK cell receptors in influenza A virus-infected mice

Both innate and adaptive immune responses play an important role in the rec overy of the host from viral infections. In the present report, a subset of cells coexpressing CD8 and NKR-P1C (NK1.1) was found in the lungs of mice infected with influenza A virus. These cells were detected at low numbers i n the lungs of uninfected mice, but represented up to 10% of the total CD8( +) T cell population at day 10 postinfection, Almost all of the CD8(+)NK1.1 (+) cells were CD8 alpha beta (+)CD3(+)TCR alpha beta (+) and a proportion of these cells also expressed the NK cell-associated Ly49 receptors, Intere stingly, up to 30% of these cells were virus-specific T cells as determined by MHC class I tetramer staining and by intracellular staining of IFN-gamm a after viral peptide stimulation. Moreover, these cells were distinct from conventional NKT cells as they were also found at increased numbers in inf luenza-infected CD1(-/-) mice. These results demonstrate that a significant proportion of CD8(+) T cells acquire NK1.1 and other NK cell-associated mo lecules, and suggests that these receptors may possibly regulate CD8(+) T c ell effector functions during viral infection.