[Characteristics of immunity in influenza]

Immunity in influenza is a complex phenomenon that depends upon numerous factors whose importance is not yet sufficiently known. The following mechanisms of defence are triggered by infection with the influenza virus: (a) The immune secretory system: -- IgA antibodies, --immune response in terms of the vaccinating dose, previous immunologic experience and time (appraised according to the moment in which infection started). (b) Serum antibodies: -- to the soluble antigen, -- to surface particulate antigens (hemagglutinin and neuraminidase), --antihemagglutinin and antineuraminidase antibodies, indicating the degree of protection. (c) Cellular immunity: -- influenza virus inducing the proliferation of lymphocytes in vitro and activating the inhibitory factor of mononuclear migration, -- mediated immunity. These problems of immunity have not yet been fully elucidated.