Abstract
Mycobacterium abscessus (Mab) is a fast-growing, antibiotic-resistant mycobacterium that causes severe lung infections, particularly in patients with cystic fibrosis. In general, inhalation of aerosols containing the infectious bacilli causes Mycobacterium infection. Adhesion of the bacilli to the surface of macrophages via specific receptors leads to phagocytosis and the underlying immunological events. However, the exact mechanism of Mab uptake by host cells remains poorly understood. During my thesis, I investigated the role of the large extracellular loop (LEL) of CD81, a novel human receptor belonging to the tetraspanin family, and its associated mycobacterial ligands in Mab internalization by macrophages and pneumocytes. My findings showed that deletion of CD81LEL, antibodies blocking surface-exposed CD81, and pre-incubation of bacilli with recombinant GST-CD81LEL protein or synthetic peptides mimicking a small portion of CD81LEL significantly reduced mycobacterial uptake by host cells. Furthermore, pull-down experiments revealed, among other interactant proteins, a mycobacterial ligand, Alkylhydroperoxidase C or AhpC (Mab_4408c) belonging to the bacterial antioxidant system, interacting with CD81LEL. Interestingly, soluble AhpC saturating macrophages reduces bacterial internalization, however when overproduced in mycobacteria, AhpC promotes bacilli internalization. Moreover, pre-incubation of macrophages with anti-CD81LEL antibodies completely inhibited phagocytosis of AhpC-coated fluorescent beads, indicating a direct interaction between the CD81LEL receptor and the mycobacterial adhesin AhpC. Finally, conditional knock-down of AhpC in Mab led to a decrease in mycobacterial invasion, in correlation with our previous data. In conclusion, my thesis project describes a novel mechanism of invasion of pathogenic Mab within the host, which could pave the way for future translational applications to reduce or inhibit mycobacterial infections.