Mucosal immunity and viral infections.
The mucosal surfaces are the first portals of entry for most infectious agents, among which respiratory and intestinal viruses are of greatest epidemiological importance. To combat these infections, the immune system uses unspecific and specific mechanisms. Unspecific responses include the production of virus-induced cytokines, such as type 1 interferons and natural killer (NK) cell activity, while specific immune responses mainly depend on cytotoxic T cells, which are important especially in the early course of a viral infection, and on antibodies. At the mucosal sites, antiviral secretory IgA antibodies play a major role in clearing viral infections and preventing or modifying disease after re-exposure. Passive transfer of virus-specific antibodies has been used in experimental and clinical settings to prevent or treat viral mucosal infections. In the future, the development of new mucosal vaccines promises to have the strongest impact on the epidemiology of viral infections.