The mucosal surfaces are the largest areas within the body in contact with the external environment and thus are major sites of antigen exposure. Discrimination between pathogenic antigens, towards which a protective immune response has to be established and harmless antigens such as food, airborne antigens or the commensal microflora that should be ignored is the most challenging task of the mucosal immune system. A normal mucosal immune responses relies heavily on a number of factors: strong physical barrier, mucosal colonization with commensal microflora, generation of antimicrobial molecules, production of an antibody (secretory immunoglobulin A) and unique way of antigen presentation. Since the majority of pathogens enter the body by crossing mucosal surfaces, there is great interest in developing vaccines which induce protective immune responses at mucosae as well as systemically.