Nucleoprotein (NP) and matrix protein (M1) of influenza virus are conserved structural influenza antigens, to which antibody response is induced after natural infection. These antibodies, however, do not display a considerable effect on protection against influenza infection [22] . On the other hand, NP, M1 and other inner influenza antigens play important role in the cellular immune response. It was demonstrated that NP-or M1-specific Th cells could augment protective antibody response, aiding the B cells to produce antibodies specific to hemagglutinin [71] .