The organisation of carbohydrates on the surface of Mycobacterium tuberculosis facilitates infection

The pathogenic bacterium Mycobacterium tuberculosis binds DC-SIGN, a receptor expressed on the surface of dendritic cells and specialized in the recognition of carbohydrate molecules, and thereby induces an immune response favorable to its multiplication within the body. Surprisingly, the bacterial species closest to M. tuberculosis are unable to bind DC-SIGN even though they express the same carbohydrate molecules on their surface, potential ligands of the receptor.
In this study, the scientists showed, notably through the use of a molecular imaging technique with nanometric resolution, that the carbohydrate molecules on the surface of the M. tuberculosis complex species, contrary to species of the same bacterial genus, are organized in large domains that constitute platforms of strong interaction with the DC-SIGN receptor, itself organized in clusters.
These results constitute a conceptual advance in the understanding of the functioning of receptors specialized in the recognition of carbohydrate molecules, demonstrating that the organization of ligands at the surface of microorganisms is a key parameter. Moreover, they change our perception of the surface of bacterial envelopes, by suggesting the presence of functional domains. Finally, they open the way to the development of new anti-tuberculosis approaches using immunomodulation.