CD8+ T cells with an intraepithelial phenotype upregulate cytotoxic function upon influenza infection in human lung

The human lung T cell compartment contains many CD8(+) T cells specific for respiratory viruses, suggesting that the lung is protected from recurring respiratory infections by a resident T cell pool. The entry site for respiratory viruses is the epithelium, in which a subset of lung CD8(+) T cells expressing CD 103 (alpha E integrin) resides. Here, we determined the specificity and function of CD103(+)CD8(+) T cells in protecting human lung against viral infection. Mononuclear cells were isolated from human blood and lung resection samples. Variable numbers of CD103(+)CD8(+) T cells were retrieved from the lung tissue. Interestingly, expression of CD103 was seen only in lung CD8(+) T cells specific for influenza but not in those specific for EBV or CMV.CD103(+) and influenza-reactive cells preferentially expressed NKG2A, an inhibitor of CD8(+) T cell cytotoxic function. In contrast to CD103(-)CD8(+) T cells, most CD103(+)CD8(+) cells did not contain perforin or granzyme B. However, they could quickly upregulate these cytotoxic mediators when exposed to a type IIFN milieu or via contact with their specific antigen. This mechanism may provide a rapid and efficient response to influenza infection, without inducing cytotoxic damage to the delicate epithelial barrier.