THE ROLE OF ADP-RIBOSYLATION AND G(M1)-BINDING ACTIVITY IN THE MUCOSAL IMMUNOGENICITY AND ADJUVANTICITY OF THE ESCHERICHIA-COLI HEAT-LABILEENTEROTOXIN AND VIBRIO-CHOLERAE CHOLERA-TOXIN

The mucosal route of vaccination has attracted a great deal of attenti on recently. Not only is mucosal application of vaccines, for example, orally or intranasally, particularly convenient, it also offers the p ossibility to induce locally produced and secreted S-IgA antibodies in addition to systemic IgG antibodies. These IgA antibodies are known t o play a key role in protection against pathogens that invade the host through mucosal surfaces. Induction of such responses is not readily achieved by currently used vaccination strategies, which generally inv olve intramuscular or subcutaneous injection with inactivated pathogen s or antigens thereof. For the induction of a mucosal immune response, the vaccine needs to be applied locally. However, local vaccination w ith non-replicating antigens is usually ineffective and may result in tolerance unless a mucosal immunoadjuvant is included. The most potent mucosal immunoadjuvants known to date are probably cholera toxin (CT) and the closely related Escherichia coli heat-labile enterotoxin (LT) . Although CT and LT have become standard adjuvants for experimental m ucosal vaccines, the intrinsic toxicity has thus far precluded their u se as adjuvants for human vaccine formulations. In the present review, the mucosal immunogenic and adjuvant properties of LT and CT are desc ribed, with special emphasis on the functional role of the individual subunits on their immune-stimulatory properties.