Another arm of the adaptive immune system, that of HLA class I restricted, CD8 positive, cytotoxic T cells (CTL), specifically survey the internal metabolism of our cells and detect intracellular pathogens such as viruses Although this does not prevent the influenza virus from infecting the mucosal target cells, it does allow for a cytotoxic immune response, which can abort the transmission of infectious influenza virus from one host cell to the next thereby aiding in the recovery from the infection. This evidence concerns the gene CD8A and infection.