Mucosal immunology and oral vaccination

Abstract

Mucosal surfaces are exposed to a wide variety of antigens and represent the major access route for pathogens. The immune system at the distinct mucosal compartments is highly specialized and regulated as it has to distinguish between inoffensive antigens and potential pathogens. Mucosal vaccines offer important advantages over the widely used parenteral ones since they constitute the best strategy to stimulate protective immune responses at the mucosal-invading pathogen routes, which have been evidenced with the oral polio vaccine or other replicating vaccines. However, the development of mucosal vaccines, particularly subunit vaccines, has showed limited success because eliciting effective immune responses represents a significant challenge because the vaccine has to overcome the complex mucosal environment and also deal with the immune regulation mechanisms that maintain the homeostasis. Fortunately, advances in the knowledge of the organization and function of the mucosal immune system, which is basically divided into inductive and effector sites, have provided important clues for the design of mucosal vaccines. Particularly, the oral immunization route is still considered the safest route, and plant-based vaccines may represent a promising strategy to overcome obstacles related to the administration of antigens by this route since plant biomass possesses characteristics that influence the efficiency of delivery at the mucosal inductive sites as well as compounds that may serve as adjuvants to mount effective mucosal immune responses.