[Cholera immunology and the molecular biology of cholera toxin. Recent progress and future prospects]

Cholera toxin (CT) and the analogous heat-labile enterotoxin (LT) from Escherichia coli have several immunomodulating effects that might explain their adjuvant action in stimulating secretory mucosal IgA after oral immunization. In mice experimental model, these effects include: enhanced antigen presentation by macrophages and other cell types; promotion of isotype differentiation in B cells leading to increased IgA formation; and other important effects on T cell proliferation and lymphokine production. The adjuvant activity is linked to the ADP-ribosylating action of CT with increased cyclic AMP formation in the affected cell, and thus it may be difficult to eliminate the enterotoxic activity without loss of adjuvanticity. However, both CT and its non-toxic B subunit moiety (CTB) have been shown to enhance the mucosal immune response to various epitopes or antigens covalently linked to these molecules. This now give promise that those antigens could become a useful vehicle to facilitate the induction of specific secretory IgA response to a broad range of antigens for human vaccination against cholera and other enteric infections.