Combating mycobacterial diseases: investigating the interplay between Dectin-1 and TLRs in the recognition and killing of Mycobacterium avium
This report regards the travel grant MycoCombat with the title "Combating mycobacterial diseases: the interplay of C-type lectins and Toll-like receptors in shaping host-responses to mycobacteria". The study took place in Dr. Trude Flo's lab at the Norwegian Centre of Excellence: Centre of Molecular Inflammation Research and at Dr. David Underhill's lab at Cedars-Sinai Medical Center, Los Angeles. The travel grant funded my stay in Dr. Underhills lab for 6 months from November 2014 until April 2015. Mycobaterial infections are a global health problem that caused the death of approximately 1.3 million people in 2012. Despite recent advances in the field of innate immunity we still lack a complete understanding of how mycobacteria evades detection by the immune system. Mycobacterium avium is an opportunistic pathogen that cause non-tuberculosis pulmonary diseases in addition to disseminated disease in AIDS patients that are not undergoing anti-retroviral therapy. It has been shown that autophagy is induced in M. tuberculosis infected macrophages and involved in cellular host defense. The aim of this study was to address the following hypotheses: - Dectin-1 is involved in the induction of LC3-associated phagocytosis (LAP) and autophagy during M. avium infection in macrophages - Dectin-1 interacts with TLR2 in phagocytosis and induction of LAP and reduces the survival of M. avium during infection Autophagy was measured by western blot and confocal microscopy of LC3 and p62 punctates. We found that human and mouse primary macrophages showed increased levels of autophagy during M. avium infection. Inhibition of autophagy increased the survival of M. avium. Knock-down or inhibition of Toll-like receptor 2 (TLR2) reduced the number of LC3 punctates induced by infection. Knock-down or inhibition of Dectin-1 did not affect the ability of M. avium to induce autophagy in primary macrophages. Dectin-1 signals through Syk but inhibition of this pathway did not affect the level of autophagy in infected macrophages. These results were in accordance with results obtained from Dectin-1 knock-out mice. Furthermore we found that removal or inhibition of Dectin-1 did not have an effect on the inflammation response of the host cells. These results indicate that TLR2 but not Dectin-1 is involved in the induction of autophagy observed in primary macrophages during M. avium infection. The results from this study were presented as a poster at the Keystone Symposia in Innate Immunity and Determinants of Microbial Pathogenesis in Olympic Valley, California, April 2015.
Mycobacterial infections constitute a global health problem. Treatment is generally complicated and requires a combination of medications for months or years. The rapid emergence of antibiotic resistance has made treatment even more difficult. Our current understanding of the role of various pattern recognition receptors (PRRs) in recognition and killing of mycobacterial pathogens is lacking. The host immune system elicit a tailored response to the various mycobacterial pathogens, such as M. tuberculosis, M. marinum, M. avium and others. It is therefore of great importance to understand the interactions between the pathogens and the host immune system. Basic research on these interactions has the potential to point to new treatment strategies and development of vaccines.