Cell-mediated immune responses to the hemagglutinin and neuraminidase antigens of influenza A virus after immunization in humans.

Humoral and cell-mediated immunity (CMI) were evaluated in groups of school children after immunization with inactivated influenza virus vaccines. A conventional biphasic strain (H3ChN2Ch) of Port Chalmers influenza virus (X-41), a recombinant influenza virus specific for the neuraminidase antigen (Heq1N2Ch) of Port Chambers influenza A virus (X-42), and a placebo were employed for immunization. The techniques of hemagglutination inhibition and neuraminidase inhibition were used to determine serum antibody titers. The CMI responses were evaluated by the in vitro lymphocyte transformation assay employing HavN2Ch, Heq1Neq1, H3ChNeq1, and H3ChN2Ch influenza A virus strains as stimulants. Specific HAI antibody and CMI responses to H3Ch were observed in X-41 but not in X-42 vaccinees. Specific anti-neuraminidase antibodies and CMI responses to N2Ch were manifested by both X-41 and X-42 vaccinees. Immunization with the placebo resulted in no influenza-specific immune responses. The CMI response was first detectable 10 days after immunization and then declined. These observations demonstrate the induction of CMI responses to the HA and NA influenza surface antigens after immunization. These responses may be important in antiviral immunity and the recovery from influenza infection.