MIR337-3p Enhances Mycobacterial Pathogenicity Involving TLR4/MYD88 and STAT3 Signals, Impairing VDR Antimicrobial Response and Fast-Acting Immunity

IFNγ-secreting T cells that highly express IL-2 potently inhibit the growth of intracellular M. tuberculosis in macrophages

Cytokine of interferon-gamma (IFNγ) plays a vital role in the immune response against Mycobacteria tuberculosis (Mtb) infection, yet the specific function of T cells producing IFNγ in this process remains unclear. In this study, we first isolated IFNγ+CD3+ T cells induced by Mtb antigens using surface staining assays. which showed a strong ability to inhibit the growth of intracellular mycobacteria in macrophages. Peripheral blood mononuclear cells (PBMCs) from healthy individuals were then challenged with Bacillus Calmette-Guérin (BCG) or Mtb, respectively, to sort IFNγ-secreting T cells for mRNA sequencing to analyze the gene expression patterns. The results of the integrated data analysis revealed distinct patterns of gene expression between IFNγ+CD3+ T cells induced by the BCG vaccine and those induced by Mtb pathogens. Further, unlike Mtb-induced cells, BCG-induced IFNγ+CD3+ T cells expressed high levels of interleukin-2 (IL-2), which increased the frequencies of these cells and the production of effector cytokines IFNγ and IL-2. Our findings suggested that IFNγ+CD3+ T cells with high IL-2 expression presented potent effector functions to inhibit intracellular Mtb growth, while Mtb infection impaired IL-2 expression in IFNγ+CD3+ T cells.

LncRNA SNHG16 Inhibits Intracellular M. tuberculosis Growth Involving Cathelicidin Pathway, Autophagy, and Effector Cytokines Production

Long noncoding small nucleolar RNA (LncRNA) host gene 16 (SNHG16) is associated with certain diseases, including cancers. However, its role and mechanism in Mycobacterium tuberculosis (Mtb) infection remain unclear. Here, we demonstrated that SNHG16 expression levels were suppressed in peripheral blood mononuclear cells (PBMCs) and CD14+ monocytes of tuberculosis (TB) patients. SNHG16 was up-regulated by acute Mtb infection of PBMCs from healthy control (HC) subjects. Such TB suppression of SNHG16 was consistent with an immunosuppressive-like state driven by IL-10 signaling as seen in TB patients. Notably, SNHG16 limited Mtb growth in macrophages/monocytes through autophagy and vitamin D receptor (VDR)-dependent cathelicidin (CAMP) antimicrobial pathways. Concurrently, SNHG16 was highly expressed in lymphocytes, including CD8+ and Vγ2 Vδ2 T-cell subsets in HCs. SNHG16 overexpression in lymphocytes allowed them to control Mtb infection in macrophages, and SNHG16 epigenetically increased the expression of anti-Mtb effector cytokines in lymphocytes by developing more accessible chromatin states in gene loci encoding IFN-γ, TNF-α, and Granzyme B. Furthermore, the adoptive transfer of SNHG16-overexpressing human PBMCs into Mtb-infected SCID mice conferred protective immunity against Mtb infection. Thus, SNHG16 drove the induction of pleiotropic effector functions that inhibited intracellular Mtb growth in vitro and in vivo, serving as an immunotherapy target in TB.

CD137 expression and signal function drive pleiotropic γδ T-cell effector functions that inhibit intracellular M. tuberculosis growth

Co-activation signal that induces/sustains pleiotropic effector functions of antigen-specific γδ T cells remains unknown. Here, Mycobacteria tuberculosis (Mtb) tuberculin administration during tuberculosis (TB) skin test resulted in rapid expression of co-activation signal molecules CD137 and CD107a by fast-acting Vγ2Vδ2 T cells in TB-resistant subjects (Resisters), but not patients with active TB. And, anti-CD137 agonistic antibody treatment experiments showed that CD137 signaling enabled Vγ2Vδ2 T cells to produce more effector cytokines and inhibit intracellular Mtb growth in macrophages (Mɸ). Consistently, Mtb antigen (Ag) HMBPP stimulation induced sustainable high-level CD137 expression in fresh and activated Vγ2Vδ2 T cells from uninfected subjects, but not TB patients. CD137+Vγ2Vδ2 T-cell subtype predominantly displayed central memory phenotype and mounted better proliferative responses than CD137-Vγ2Vδ2 T-cells. In response to HMBPP, CD137+Vγ2Vδ2 T-cell subtype rapidly differentiated into greater numbers of pleiotropic effector cells producing anti-Mtb cytokines compared to CD137-Vγ2Vδ2 T subtype, with the non-canonical NF-κB pathway involved. CD137 expression in Vγ2Vδ2 T cells appeared to signal anti-Mtb effector functions leading to intracellular Mtb growth inhibition in Mɸ, and active TB disrupted such CD137-driven anti-Mtb effector functions. CD137+Vγ2Vδ2 T-cells subtype exhibited an epigenetic-driven high-level expression of GM-CSF and de novo production of GM-CSF critical for Vγ2Vδ2 T-cell controlling of Mtb growth in Mϕ. Concurrently, exosomes produced by CD137+Vγ2Vδ2 T cells potently inhibited intracellular mycobacterial growth. Furthermore, adoptive transfer of human CD137+Vγ2Vδ2 T cells to Mtb-infected SCID mice conferred protective immunity against Mtb infection. Thus, our data suggest that CD137 expression/signaling drives pleiotropic γδ T-cell effector functions that inhibit intracellular Mtb growth.

Mycobacterium tuberculosis infection depressed cytotoxic T cells activity owing to decreasing NKG2C and increasing NKG2A expression

Cytotoxic T lymphocytes (CTLs) play protective roles in immunity against tuberculosis (TB) infection by strongly inhibiting intracellular mycobacterial growth. In TB infection, the impairing mechanism of CTLs function remains unclear. In this study, we identified that the cytotoxic granule molecules expression levels of perforin (PRF) and granulysin (GNLY) in CD3+ and CD8+ CTL cells were significantly depressed in TB patients compared to those in healthy donors. The frequencies of T-CTLs, co-expressing granzyme B (GZMB), PRF and GNLY, were obviously decreased in TB patients. Moreover, NKG2C highly expressed in T-CTLs, was an effective activator of cytotoxic activity of CD3+ T cells. And, NKG2C+CD3+ T cells potently inhibited intracellular mycobacterial growth. The proportions of NKG2C+ cells in CD3+ and CD8+ T cells were dramatically decreased in TB patients. Contrarily, NKG2A, an inhibitor of T cells cytotoxic activities, was highly expressed in T-CTLs of CD3+ and CD8+ T cells in TB patients. Here, we successfully discovered that depressed CTLs activities in TB patients were attributed to low expression of cytotoxic granule molecules and high expression of inhibitory NKG2A receptor, suppression of agonist receptor NKG2C. Thus, NKG2 receptors were potential targets for immunotherapy of tuberculosis, especially for multidrug-resistant tuberculosis.

Circular RNA circTRAPPC6B Enhances IL-6 and IL-1β Expression and Repolarizes Mycobacteria Induced Macrophages from M2- to M1-Like Phenotype by Targeting miR-892c-3p

Mycobacterium tuberculosis (Mtb) infection elicits macrophage polarization into M2 phenotype to block the host's protective immune response. However, it remains unclear how Mtb regulates macrophage polarization. Recent studies have suggested that noncoding RNA may play a role in macrophage polarization. In this study, we investigated the potential involvement of circTRAPPC6B, a circular RNA that is downregulated in tuberculosis (TB) patients, in regulating macrophage polarization. We found that Mtb infection downregulated M1-related IL-6 and IL-1β while highly expressed M2-related CCL22 and CD163. Overexpressed circTRAPPC6B had switched Mtb-infected macrophages from M2- to M1-like phenotype, accompanied by upregulation of IL-6 and IL-1β. Meanwhile overexpressed circTRAPPC6B significantly inhibited Mtb growth in macrophages. Our findings suggest that circTRAPPC6B may regulate macrophage polarization by targeting miR-892c-3p, which is highly expressed in TB patients and M2-like macrophages. And miR-892c-3p inhibitor decreased intracellular Mtb growth in macrophages. Thus, TB-inhibited circTRAPPC6B could specifically induce IL-6 and IL-1β expression to switch/antagonize Mtb-induced macrophage polarization from M2- to M1-like phenotype by targeting miR-892c-3p, leading to enhanced host clearance of Mtb. Our results reveal a potential role for circTRAPPC6B in regulating macrophage polarization during Mtb infection and provide new insights into the molecular mechanisms underlying host defense against Mtb.

Dimethyl itaconate is effective in host-directed antimicrobial responses against mycobacterial infections through multifaceted innate immune pathways

BACKGROUND

Itaconate, a crucial immunometabolite, plays a critical role in linking immune and metabolic functions to influence host defense and inflammation. Due to its polar structure, the esterified cell-permeable derivatives of itaconate are being developed to provide therapeutic opportunities in infectious and inflammatory diseases. Yet, it remains largely uncharacterized whether itaconate derivatives have potentials in promoting host-directed therapeutics (HDT) against mycobacterial infections. Here, we report dimethyl itaconate (DMI) as the promising candidate for HDT against both Mycobacterium tuberculosis (Mtb) and nontuberculous mycobacteria by orchestrating multiple innate immune programs.

RESULTS

DMI per se has low bactericidal activity against Mtb, M. bovis Bacillus Calmette-Guérin (BCG), and M. avium (Mav). However, DMI robustly activated intracellular elimination of multiple mycobacterial strains (Mtb, BCG, Mav, and even to multidrug-resistant Mtb) in macrophages and in vivo. DMI significantly suppressed the production of interleukin-6 and -10, whereas it enhanced autophagy and phagosomal maturation, during Mtb infection. DMI-mediated autophagy partly contributed to antimicrobial host defenses in macrophages. Moreover, DMI significantly downregulated the activation of signal transducer and activator of transcription 3 signaling during infection with Mtb, BCG, and Mav.

CONCLUSION

Together, DMI has potent anti-mycobacterial activities in macrophages and in vivo through promoting multifaceted ways for innate host defenses. DMI may bring light to new candidate for HDT against Mtb and nontuberculous mycobacteria, both of which infections are often intractable with antibiotic resistance.

Immune regulation and emerging roles of noncoding RNAs in Mycobacterium tuberculosis infection

Tuberculosis, caused by Mycobacterium tuberculosis, engenders an onerous burden on public hygiene. Congenital and adaptive immunity in the human body act as robust defenses against the pathogens. However, in coevolution with humans, this microbe has gained multiple lines of mechanisms to circumvent the immune response to sustain its intracellular persistence and long-term survival inside a host. Moreover, emerging evidence has revealed that this stealthy bacterium can alter the expression of demic noncoding RNAs (ncRNAs), leading to dysregulated biological processes subsequently, which may be the rationale behind the pathogenesis of tuberculosis. Meanwhile, the differential accumulation in clinical samples endows them with the capacity to be indicators in the time of tuberculosis suffering. In this article, we reviewed the nearest insights into the impact of ncRNAs during Mycobacterium tuberculosis infection as realized via immune response modulation and their potential as biomarkers for the diagnosis, drug resistance identification, treatment evaluation, and adverse drug reaction prediction of tuberculosis, aiming to inspire novel and precise therapy development to combat this pathogen in the future.