Caveolin-1 Controls Vesicular TLR2 Expression, p38 Signaling and T Cell Suppression in BCG Infected Murine Monocytic Myeloid-Derived Suppressor Cells

Abstract

Monocytic myeloid-derived suppressor cells (M-MDSCs) and granulocytic MDSCs (G-MDSCs) have been found to be massively induced in TB patients as well in murine Mtb infection models. However, the interaction of mycobacteria with MDSCs and its role in TB infection is not well studied. Here, we investigated the role of Cav-1 for MDSCs infected with Mycobacterium bovis Bacille-Calmette-Guerín (BCG). MDSCs that were generated from murine bone marrow (MDSCs) of wild-type (WT) or Cav1−/− mice upregulated Cav-1, TLR4 and TLR2 expression after BCG infection on the cell surface. However, Cav-1 deficiency resulted in a selective defect of intracellular TLR2 levels predominantly in the M-MDSC subset. Further analysis indicated no difference in the phagocytosis of BCG by M-MDSCs from WT and Cav1−/− mice or caveosome formation, but a reduced capacity to up-regulate surface markers, to secrete various cytokines, to induce iNOS and NO production required for suppression of T cell proliferation, whereas Arg-1 was not affected. Among the signaling pathways affected by Cav-1 deficiency, we found lower phosphorylation of the p38 mitogen-activated protein kinase (MAPK). Together, our findings implicate that (i) Cav-1 is dispensable for the internalization of BCG, (ii) vesicular TLR2 signaling in M-MDSCs is a major signaling pathway induced by BCG, (iii) vesicular TLR2 signals are controlled by Cav-1, (iv) vesicular TLR2/Cav-1 signaling is required for T cell suppressor functions.

Mycobacterium tuberculosis and myeloid-derived suppressor cells: Insights into caveolin rich lipid rafts

“…Among the signaling pathways affected by Cav-1 deficiency, we found lower phosphorylation of the p38 mitogen-activated protein kinase (MAPK). Our findings reveal major differences to macrophages and dendritic cells (DCs) and implicate that Cav-1 is dispensable for the internalization of BCG, but that vesicular TLR2 signaling in M-MDSC is a major signaling pathway induced by BCG, controlled by Cav-1, and lastly, that vesicular TLR2/Cav-1 signaling is required for T cell suppressor functions [97].…”

Monocytic myeloid-derived suppressor cells reflect tuberculosis severity and are influenced by cyclooxygenase-2 inhibitors

“…Since M‐MDSCs internalize both Mtb 21 and M.bovis 35 and like Mtb , M.bovis induce suppressive MDSCs, 35 we used a MDSC‐ mycobacterial infection model 36 that does not require biosafety level‐3 containment, to assess the impact of COX‐2i in mycobacterial replication control upon MDSC internalization. PBMCs from the ScreenTB cohort were thawed and enriched for HLADR − and CD33 + using MACS magnetic bead separation (Miltenyi Biotec, Bergisch, Germany), rested in a 37°C incubator (with 5% CO 2 ) prior to infection.…”

“…Since M-MDSCs internalize both Mtb 21 and M.bovis 35 and like Mtb, M.bovis induce suppressive MDSCs, 35 we used a MDSC-mycobacterial infection model 36 Culture supernatants were collected after 3 h infection and new media containing COX-2i was replaced to continue the culture for 24 h. Supernatants were collected for Luminex analysis and enriched M-MDSCs were subjected to CFU measurements. Lower out of range values (OOR <) were set to zero.…”

Immune Correlates of Non-Necrotic and Necrotic Granulomas in Pulmonary Tuberculosis: A Pilot Study

“…Furthermore, MDSCs suppress lymphocyte proliferation through the production of NO for both in vitro and aerosol Mtb infections [32]. BCG studies further indicate that the NO release and suppressor function depend on TLR/caveolin-1 signals [41]. However, studies that correlate ARG1 or NOS2 expression with MDSC the mediated suppression of immune response in TB patients have not been conclusive.…”