Vaccine antigens coupled to an antibody (green) that binds to carbohydrates on M cells (right) induce a stronger immune response than when coupled to lectins (red).
In mucosal tissues such as the airways and digestive tract, immune responses are only weakly stimulated by injected vaccines, which are taken up by circulating cells that boost systemic immunity. Local immunity is more effectively generated by ingested or inhaled vaccines that can be taken up directly by lymphoid tissues in the gut and airway. These tissues are lined by microvilli-bearing M cells that soak up the vaccines and pass them along to the immunity-inducing dendritic cells and macrophages lurking in the tissue below.
In past attempts to get vaccines to M cells, vaccine antigens were hitched to lectins that bind to carbohydrates on the M cells. But since these carbohydrates are also present on nonabsorbent mucosal cells, the antigen becomes diluted.
Nochi et al. now identify a mouse antibody that gets around this problem. The new antibody recognizes part of a carbohydrate that is found only on M cells. Mice fed this antibody coupled to a bacterial toxin remained healthy even when later given a 104 higher dose of the toxin than would normally cause disease. Whether the human antibody will be just as effective remains to be seen. 
