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 recovery 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 in 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 CD8αβ⁺CD3⁺TCRαβ⁺ and a proportion of these cells also expressed the NK cell-associated Ly49 receptors. Interestingly, 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-γ after viral peptide stimulation. Moreover, these cells were distinct from conventional NKT cells as they were also found at increased numbers in influenza-infected CD1(-/-) mice. These results demonstrate that a significant proportion of CD8⁺ T cells acquire NK1.1 and other NK cell-associated molecules, and suggests that these receptors may possibly regulate CD8⁺ T cell effector functions during viral infection.