ABSTRACT
The first productive interaction between most infectious agents and the host is with mucosal surfaces, specially, the nasal, oropharyngeal, respiratory, genitourinary, and gastrointestinal mucosa. Conventional vaccine strategies that involve parenteral immunization with inactivated viruses, bacteria or subunits of relevant virulence determinants of those pathogens do not prevent initial interactions. Infact, traditional vaccine strategies do not prevent infection but instead resolve infection before disease ensues. Moreover, many bacterial toxins bind to and interact with mucosal epithelial cells, in which case significant damage to the host may ensue before serum antibodies can play a role in protection. The mucosal surfaces of the gastrointestinal and respiratory tracts represent the main portals of entry for most human pathogens. Sexual contact is another mucosal mode of transmission of infection. Direct inoculation of pathogens into the bloodstream is other important route of infection. Most external mucosal surfaces are replete with organized follicles and scattered antigen-reactive or sensitized lymphoid elements, including B cells, T lymphocytes, T-cell subsets, plasma cells, and a variety of other cellular elements involved in the induction and maintenance of immune response. The mucosal surfaces encompass a critical component of the mammalian immunologic repertoire.
