Stimulation with mycobacterial glycolipids and PPD reveals different innate immune response profiles in active and latent TB

Upon infection with Mycobacterium tuberculosis (Mtb) the host immune response might clear the bacteria, control its growth leading to latent tuberculosis (LTB), or fail to control its growth resulting in active TB (ATB). There is however no clear understanding of the features underlying a more or less effective response. Mtb glycolipids are abundant in the bacterial cell envelope and modulate the immune response to Mtb, but the patterns of response to glycolipids are still underexplored. To identify the CD45+ leukocyte activation landscape induced by Mtb glycolipids in peripheral blood of ATB and LTB, we performed a detailed assessment of the immune response of PBMCs to the Mtb glycolipids lipoarabinomannan (LAM) and its biosynthetic precursor phosphatidyl-inositol mannoside (PIM), and PPD. At 24 h and 5 days of stimulation, cell profiling and secretome analysis was done using mass cytometry and high-multiplex immunoassay. PIM mainly affected antigen-presenting cells to produce both proinflammatory (IL-2, IL-6, IL-17A, TNF- and GM-CSF), and IL-4 and IL-10 cytokines, but not IFN-{gamma}. LAM triggered a similar, albeit weaker, response. By contrast, PPD induced an increase in IFN-{gamma}-producing cells. Moreover, PPD also led to increased numbers of IL-2, IL-6, IL-10, IL-17A, TNF- and GrzB-producing cells. Treatment with an anti-TLR2 antibody led to partial inhibition of PIM-induced IL-6 production in myeloid cells, suggesting that PIM induces IL-6 production through TLR2. Expansion of monocyte subsets in response to PIM or LAM was reduced in both ATB and LTB as compared to healthy controls, suggesting a hyporesponsive/tolerance pattern in Mtb-infected individuals.