[Mucosal immune responses against influenza virus]

The respiratory tract-mucosa is the site of either contact with influenza virus or defense against the virus. Such a defense is mediated by immune competent cells. The precursors of IgA-producing B cells and immune T cells are first induced in the mucosal inductive sites such as nasal-associated lymphoid tissues (NALT) or bronchus-associated lymphoid tissues (BALT). They are disseminated to mucosal effector sites for the development of immune responses, where IgA-producing cells in the lamina propria produce polymeric IgA, which are secreted through the epithelial cell into the external. The secretory IgA and serum IgG are mainly involved in protection against influenza in the upper respiratory tract and pneumonia in the lower respiratory tract, respectively. CD8+ cytotoxic T cells and Th1 cells are involved in recovery from influenza.