Mycobacterium tuberculosis Membrane Vesicles Inhibit T Cell Activation

Abstract

Mycobacterium tuberculosis utilizes multiple mechanisms to evade host immune responses, and inhibition of effector CD4+ T cell responses by M. tuberculosis may contribute to immune evasion. T cell receptor signaling is inhibited by M. tuberculosis cell envelope lipoglycans, such as lipoarabinomannan and lipomannan, but a mechanism for lipoglycans to traffic from M. tuberculosis within infected macrophages to reach T cells is unknown. In these studies, we found that membrane vesicles produced by M. tuberculosis and released from infected macrophages inhibited the activation of CD4+ T cells, as indicated by reduced production of interleukin-2 and reduced T cell proliferation. Flow cytometry and western blot demonstrated that lipoglycans from M. tuberculosis-derived bacterial vesicles (BVs) are transferred to T cells, where they inhibit T cell responses. Stimulation of CD4+ T cells in the presence of BVs induced expression of GRAIL, a marker of T cell anergy; upon restimulation, these T cells showed reduced ability to proliferate, confirming a state of T cell anergy. Furthermore, lipoarabinomannan was associated with T cells after their incubation with infected macrophages in vitro and when T cells were isolated from lungs of M. tuberculosis-infected mice, confirming the occurrence of lipoarabinomannan trafficking to T cells in vivo. These studies demonstrate a novel mechanism for the direct regulation of CD4+ T cells by M. tuberculosis lipoglycans conveyed by BVs that are produced by M. tuberculosis and released from infected macrophages. These lipoglycans are transferred to T cells to inhibit T cell responses, providing a mechanism that may promote immune evasion.

Proteomics and Network Analyses Reveal Inhibition of Akt‐mTOR Signaling in CD4+ T Cells by Mycobacterium tuberculosis Mannose‐Capped Lipoarabinomannan

“…Overall, these proteomic findings combined with our functional studies in human CD4 + T cells and in vivo studies in murine Mtb infection support a model in which ManLAM as Mtb bacterial membrane vesicles can travel beyond the immediate environment of infected cells, that is, the granuloma, to interact with CD4 + T cells and likely others . For CD4 + T cells, this interaction results in inhibition of TCR–CD3 and CD28 signaling with a downstream effect on the Akt‐mTOR signaling pathway, resulting in T‐cell inhibition and anergy.…”

“…We demonstrated direct and indirect inhibition of CD4 + T‐cell activation by different Mtb molecules, including lipoproteins LpqH, LprA, and LprG, and more recently glycolipid mannose‐capped lipoarabinomannan (ManLAM) . ManLAM is abundant in the Mtb cell wall, found in membrane vesicles produced by Mtb, in Mtb granulomas, and most recently in CD4 + T cells from lungs of Mtb‐infected mice . ManLAM interferes with T‐cell receptor (TCR) proximal signaling by downregulating phosphorylation of Lck, CD3ζ, ZAP70, and LAT, and can induce T‐cell anergy, and thus potentially a major modulator of host T cells response to Mtb …”

Dynamin-like proteins are essential for vesicle biogenesis inMycobacterium tuberculosis

“…Previous studies have shown that bacteria-derived EV are released by Mtb -infected mouse macrophages and can act as potent immunomodulators of uninfected cells (5, 6). To determine whether Mtb cells require DLPs to produce EV in macrophages, we compared the abundance of vesicles containing bacterial components released into the culture medium from THP-1 macrophages 24 hours after infection with different Mtb strains: WT, iniA∷hyg , or iniA∷hyg complemented with iniBAC.…”

“…Mtb -produced EV ( Mtb -EV) contain many immunologically active lipoproteins and glycolipids (3, 4) and are enriched in polar lipids consistent with a cytoplasmic membrane origin (3). Mtb -EV mediate transfer of bacterial components into immune cells (5, 6) and aid in acquisition of nutritional iron (Fe) by mediating export and uptake of the hydrophobic siderophore, mycobactin (7). Furthermore, Mtb -EV contain protective antigens; immunization with isolated EV elicits a protective immune response against TB in mice that is comparable to BCG vaccination (8).…”

Mechanisms of M. tuberculosis Immune Evasion as Challenges to TB Vaccine Design

“…Whether this mechanism contributes to the inability of T cell responses to eliminate M. tuberculosis in vivo has not been established, but man-LAM and other mycobacterial lipoglycans can be acquired by T cells via bacterial membrane vesicles, and man-LAM can be detected on T cells isolated from lungs of M. tuberculosis-infected mice (Athman et al, 2017). …”