Molecular basis of the mucosal immune system: from fundamental concepts to advances in liposome-based vaccines

The mucosal immune system, the primary portal for entry of most prevalent and devastating pathogens, is guarded by the special lymphoid tissues (mucosally associated lymphoid tissues) for immunity. Mucosal immune infection results in induction of IgA-manifested humoral immunity. Cell-mediated immunity may also be generated, marked by the presence of CD4(+) Th1 and CD8(+) cells. Furthermore, the immunity generated at the mucosal site is transported to the distal mucosal site as well as to systemic tissues. An understanding of the molecular basis of the mucosal immune system provides a unique platform for designing a mucosal vaccine. Coadministration of immunostimulatory molecules further accelerates functioning of the immune system. Mimicking receptor-mediated binding of the pathogen may be achieved by direct conjugation of antigen with an immunostimulatory molecule or encapsulation in a carrier followed by anchoring of a ligand having affinity to the cells of the mucosal immune system. Nanotechnology has played a significant role in mucosal vaccine development and among the available options liposomes are the most promising. Liposomes are phospholipid bilayered vesicles that can encapsulate protein as well as DNA-based vaccines and offer coencapsulation of adjuvant along with the antigen. At the same, time ligand-conjugated liposomes augment interaction of antigen with the cells of the mucosal immune system and thereby serve as suitable candidates for the mucosal delivery of vaccines. This article exhaustively explores strategies involved in the generation of mucosal immunity and also provides an insight to the progress that has been made in the development of liposome-based mucosal vaccine.