XK and influenza: T-cell responses to natural influenza infections are mainly directed against common epitopes on the nucleoprotein, PB2 and M1 but also, to a lesser degree, against the highly variable hemagglutinin and the neuraminidase [2] and thus, in contrast to the generally type-specific protection of antibodies against HA and NA, have the potential to provide broad, heterosubtypic protection.