Author response: Tuberculosis-associated IFN-I induces Siglec-1 on tunneling nanotubes and favors HIV-1 spread in macrophages

Article Figures and data Abstract Introduction Results Discussion Materials and methods Data availability References Decision letter Author response Article and author information Metrics Abstract While tuberculosis (TB) is a risk factor in HIV-1-infected individuals, the mechanisms by which Mycobacterium tuberculosis (Mtb) worsens HIV-1 pathogenesis remain scarce. We showed that HIV-1 infection is exacerbated in macrophages exposed to TB-associated microenvironments due to tunneling nanotube (TNT) formation. To identify molecular factors associated with TNT function, we performed a transcriptomic analysis in these macrophages, and revealed the up-regulation of Siglec-1 receptor. Siglec-1 expression depends on Mtb-induced production of type I interferon (IFN-I). In co-infected non-human primates, Siglec-1 is highly expressed by alveolar macrophages, whose abundance correlates with pathology and activation of IFN-I/STAT1 pathway. Siglec-1 localizes mainly on microtubule-containing TNT that are long and carry HIV-1 cargo. Siglec-1 depletion decreases TNT length, diminishes HIV-1 capture and cell-to-cell transfer, and abrogates the exacerbation of HIV-1 infection induced by Mtb. Altogether, we uncover a deleterious role for Siglec-1 in TB-HIV-1 co-infection and open new avenues to understand TNT biology. Introduction Co-infection with Mycobacterium tuberculosis (Mtb) and the human immunodeficiency virus (HIV-1), the agents of tuberculosis (TB) and acquired immunodeficiency syndrome (AIDS), respectively, is a major health issue. Indeed, TB is the most common illness in HIV-1-infected individuals, about 55% of TB notified patients are also infected with HIV-1, and about a fifth of the TB death toll occurs in HIV-1 co-infected individuals (WHO health report 2017). Clinical studies evidence a synergy between these two pathogens, which is associated with a spectrum of aberration in immune function (Esmail et al., 2018). Yet, while progress has been made towards understanding how HIV-1 enhances Mtb growth and spread, the mechanisms by which Mtb exacerbates HIV-1 infection require further investigation (Bell and Noursadeghi, 2018; Deffur et al., 2013; Diedrich and Flynn, 2011). Besides CD4+ T cells, macrophages are infected by HIV-1 in humans and by the simian immunodeficiency virus (SIV), the most closely related lentivirus to HIV, in non-human primates (NHP) (Cribbs et al., 2015; Rodrigues et al., 2017). Recently, using a humanized mouse model, macrophages were shown to sustain HIV-1 infection and replication, even in the absence of T cells (Honeycutt et al., 2017; Honeycutt et al., 2016). This is in line with several studies characterizing tissue macrophages, such as alveolar, microglia and gut macrophages, as reservoirs in HIV-1 patients undergoing antiretroviral therapy (Ganor et al., 2019; Jambo et al., 2014; Mathews et al., 2019; Sattentau and Stevenson, 2016). Macrophages are key host cells for Mtb (O'Garra et al., 2013; VanderVen et al., 2016). We recently reported the importance of macrophages in HIV-1 exacerbation within the TB co-infection context (Souriant et al., 2019). Using relevant in vitro and in vivo models, we showed that TB-associated microenvironments activate macrophages towards an M(IL-10) profile, distinguished by a CD16+CD163+MerTK+ phenotype. Acquisition of this phenotype is dependent on the IL-10/STAT3 signaling pathway (Lastrucci et al., 2015). M(IL-10) macrophages are highly susceptible not only to Mtb infection (Lastrucci et al., 2015), but also to HIV-1 infection and spread (Souriant et al., 2019). At the functional level, we demonstrated that TB-associated microenvironments stimulate the formation of tunneling nanotubes (TNT), membranous channels connecting two or more cells over short to long distances above substrate. TNT are subdivided in two classes based on their thickness and cytoskeleton composition: ‘thin’ TNT (<0.7 μm in diameter) containing F-actin, and ‘thick’ TNT (>0.7 μm in diameter) are enriched in F-actin and microtubules (MT) (Souriant et al., 2019). Thick TNT are functionally distinguished by the transfer of large organelles, such as lysosomes and mitochondria (Dupont et al., 2018; Eugenin et al., 2009; Hashimoto et al., 2016). While the contribution for each TNT class to HIV-1 pathogenesis has not been explored (Dupont et al., 2018; Eugenin et al., 2009; Hashimoto et al., 2016), we reported that total inhibition of TNT formation in M(IL-10) macrophages resulted in the abrogation of HIV-1 exacerbation induced by Mtb (Souriant et al., 2019). Factors influencing TNT function in M(IL-10) macrophages remain unknown at large. In this study, global mapping of the M(IL-10) macrophage transcriptome revealed Siglec-1 (CD169, or sialoadhesin) as a potential factor responsible for HIV-1 dissemination in the co-infection context with TB. As a type-I transmembrane lectin receptor, Siglec-1 possesses a large extracellular domain composed of 17 immunoglobulin-like domains, including the N-terminal V-set domain, which allows the trans recognition of terminal α2,3-linked sialic acid residues in O- and N-linked glycans and glycolipids, such as those surface-exposed in HIV-1 and SIV particles (Izquierdo-Useros et al., 2012a; Puryear et al., 2012). While Siglec-1 has yet to be implicated in the TB context, it is clearly involved in the pathogenesis of HIV-1, SIV and other retroviruses (Martinez-Picado et al., 2017). Siglec-1 is mainly expressed in myeloid cells (e.g. macrophages and dendritic cells) and participates in HIV-1 transfer from myeloid cells to T cells, as well as in the initiation of virus-containing compartment (VCC) formation in macrophages (Izquierdo-Useros et al., 2012a; Izquierdo-Useros et al., 2012b; Puryear et al., 2013; Puryear et al., 2012), and in the viral dissemination in vivo (Akiyama et al., 2017; Izquierdo-Useros et al., 2012a; Sewald et al., 2015). Indeed, HIV-1 and other retroviruses have evolved the capacity to hijack the immune surveillance and housekeeping immunoregulatory functions of Siglec-1 (Izquierdo-Useros et al., 2014; O'Neill et al., 2013). Here, we investigate how Siglec-1 expression is induced by TB, and the role it has in the capture and transfer of HIV-1 by TB-induced M(IL-10) macrophages, in particular in the context of TNT. Results Tuberculosis-associated microenvironments induce Siglec-1 in macrophages TB-induced M(IL-10) macrophages are highly susceptible to HIV-1 infection and spread (Souriant et al., 2019). To assess the global gene expression landscape in these cells, we performed a genome-wide transcriptome analysis (GEO submission GSE139511). To this end, we employed our published in vitro model (Lastrucci et al., 2015), which relies on the use of conditioned medium from either mock- (cmCTR) or Mtb-infected (cmMTB) human macrophages. As we described and observed before and herein, cmMTB-treated cells were positive for the M(IL-10) markers (CD16+CD163+MerTK+ and phosphorylated STAT3), and displayed a high rate of HIV-1 infection, as compared to those treated with cmCTR (Lastrucci et al., 2015). A distinct 60 gene-transcript signature was defined in cmMTB-treated cells, using a combination of the expression level, statistical filters and hierarchical clustering; 51 genes were up-regulated and nine genes were down-regulated in cmMTB- compared to cmCTR-treated cells (Figure 1A). We compared expression data of cmMTB- and cmCTR-treated cells to public genesets available from MSigDB (Broad Institute) using the gene set enrichment analysis (GSEA) algorithm (Subramanian et al., 2005). As shown in Figure 1—figure supplement 1A, a significant fraction of genes that were up-regulated in response to interferon (IFN) type I (e.g. IFNα) and II (i.e. IFNγ), were also found, as a group, significantly up-regulated in cmMTB-treated cells in comparison to control samples (FDR q-value:<10-3). IFN-stimulated genes (ISG) usually exert antiviral activities (McNab et al., 2015; Schneider et al., 2014) and cannot be inferred as obvious candidates to facilitate HIV-1 infection. However, among this ISG signature, the up-regulation of Siglec-1 (7.4-fold, adjusted p-value of 0.0162) in cmMTB-treated cells captured our attention due to its known role in HIV-1 pathogenesis (Izquierdo-Useros et al., 2014; O'Neill et al., 2013). We confirmed a high Siglec-1 expression in cmMTB-treated macrophages at the mRNA (Figure 1B), intracellular and cell-surface protein (Figure 1C and Figure 1—figure supplement 1B–D) levels. This effect was superior to the level obtained in HIV-1-infected cells (Figure 1—figure supplement 1E). Particularly, cmMTB-treated macrophages displayed high density of Siglec-1 surface expression applying a quantitative FACS assay that determines the absolute number of Siglec-1 antibody binding sites per cell (Figure 1D). Figure 1 with 2 supplements see all Download asset Open asset Tuberculosis-associated microenvironments induce Siglec-1 expression in macrophages. (A–D) For 3 days, human monocytes were differentiated into macrophages with cmCTR (white) or cmMTB (black) supernatants. (A) Heatmap from a transcriptomic analysis (GEO submission GSE139511) illustrating the top 60 differentially expressed genes (DEGs) between cmCTR- or cmMTB-cells. Selection of the top DEGs was performed using an adjusted p-value ≤ 0.05, a fold change of at least 2, and a minimal expression of 6 in a log2 scale. Hierarchical clustering was performed using the complete linkage method and the Pearson correlation metric with Morpheus (Broad Institute). Interferon-stimulated genes (ISG) are labelled with an asterisk and Siglec-1 is indicated in red. (B–D) Validation of Siglec-1 expression in cmMTB-treated macrophages. Vertical scatter plots showing the relative abundance to mRNA (B), median fluorescent intensity (MFI) (C), and mean number of Siglec-1 antibody binding sites per cell (D). Each circle represents a single donor and histograms median values. (E) Representative immunohistochemical images of Siglec-1 staining (brown) in lung biopsies of healthy, SIV infected (SIV), active TB (ATB), and co-infected (ATB-SIV) non-human primates (NHP). Scale bar, 100 µm. Insets are 2x zoom. (F) Vertical Box and Whisker plot indicating the distribution of the percentage of Siglec-1+ alveolar macrophages in lung biopsies from the indicated NHP groups. Quantification analysis from n = 800 alveolar macrophages grouped from three independent animals per NHP group. (G) Vertical scatter plots displaying the number of cells that are positive for Siglec-1 per mm² of lung biopsies from the indicated NHP groups. Each symbol represents a single animal per NHP group. (H) Correlation between Siglec-1+ cells per mm² of lung tissue and the pathological score for healthy (white circle), SIV+ (white triangles), latent (black circle) or active (black square) TB, and SIV+ with latent (grey circle) or active (grey square) TB. Each symbol represents a single animal per NHP group. Mean value is represented as a black line. Statistical analyses: Two-tailed, Wilcoxon signed-rank test (B–D), Mann-Whitney unpaired test (F–G), Spearman correlation (H). *p<0.05, p<0.01, *p<0.001, ****p<0.0001. ns: not significant. See Figure 1—source data 1. Figure 1—source data 1 Raw data and statistical analyses supporting Siglec-1 expression in human and non-human primate macrophages exposed to TB-associated microenvironment. https://cdn.elifesciences.org/articles/52535/elife-52535-fig1-data1-v2.xlsx Download elife-52535-fig1-data1-v2.xlsx These data indicate that Siglec-1 is highly expressed in human macrophages exposed to TB-associated microenvironments and potentially in the context of TB-HIV co-infection. Siglec-1+ alveolar macrophage abundance correlates with pathology in co-infected primates NHP has been an invaluable in vivo model to better understand the role of macrophages in SIV/HIV pathogenesis (Merino et al., 2017). Considering Siglec-1 binds sialylated lipids present in the envelop of HIV-1 and SIV (Izquierdo-Useros et al., 2012a; Puryear et al., 2012), we examined the presence of Siglec-1 positive alveolar macrophages in lung biopsies obtained from different NHP groups: (i) co-infected with Mtb (active or latent TB) and SIV, (ii) mono-infected with Mtb (active or latent TB), (iii) mono-infected with SIV, and (iv) healthy (Supplementary file 1-Table S1, Figure 1—figure supplement 2A; Cai et al., 2015; Kuroda et al., 2018; Souriant et al., 2019). Histological immuno-staining confirmed the presence of Siglec-1+ alveolar macrophages in the lungs of healthy NHP (Figure 1E–F and Figure 1—figure supplement 2A), and revealed its significant increase in NHP mono-infected with either Mtb or SIV (Figure 1E–F and Figure 1—figure supplement 2A). Strikingly, we noticed a massive abundance of these cells in co-infected NHP (Figure 1E–F and Figure 1—figure supplement 2A). Concerning the overall abundance of Siglec-1+ leukocytes in lungs, we observed a significant increase in all infected NHP in comparison to healthy, with a higher tendency in active TB or co-infected NHP (Figure 1G and Figure 1—figure supplement 2A). In fact, the number of Siglec-1+ leukocytes correlated positively with the severity of NHP pathology (Figure 1H, Supplementary file 1-Table S2). Based on their cell morphology, localization in alveoli, and co-expression with the macrophage marker CD163 (Figure 1—figure supplement 2A–C), Siglec-1+ cells were identified as alveolar macrophages. Collectively, these data show that Siglec-1 is up-regulated in alveolar macrophages in the context of a retroviral co-infection with active TB. Siglec-1 expression is dependent on Mtb-induced type I IFN signaling Siglec-1 is an ISG whose expression is induced by IFN-I in myeloid cells (Hartnell et al., 2001). In addition to viral infection, IFN-I is also induced in TB and known to mainly play a detrimental role (McNab et al., 2015; Moreira-Teixeira et al., 2018). Siglec-1 expression has not been described in the TB context or in co-infection with retroviruses such as SIV or HIV-1, therefore we assessed whether IFN-I stimulates Siglec-1 expression in TB-associated microenvironments. First, we found that cmMTB contains high amounts of IFN-I compared to cmCTR (Figure 2A). Next, we showed that recombinant IFN-β significantly increased Siglec-1 cell-surface expression in macrophages, close to the level induced by cmMTB (Figure 2B). Interestingly, we observed a modest, albeit significant, induction of Siglec-1 expression in cells treated with interleukin 10 (IL-10), a cytokine we have previously shown to be abundant in cmMTB (Lastrucci et al., 2015) and that renders macrophages highly susceptible to HIV-1 infection (Souriant et al., 2019). However, IL-10 depletion had no effect on Siglec-1 expression by cmMTB-treated cells (Figure 2C). By contrast, blocking the IFN-I receptor (IFNAR-2) during cmMTB treatment fully abolished the expression of Siglec-1 (Figure 2D and Figure 1—figure supplement 1D), indicating that IFN-I is the responsible factor for Siglec-1 up-regulation in cmMTB-treated cells. Figure 2 Download asset Open asset Siglec-1 expression is dependent on Mtb-induced type I IFN signaling. (A) Vertical scatter plot showing the relative abundance of IFN-I in cmCTR (white) and cmMTB (black) media, as measured indirectly after 24 hr exposure to the HEK-Blue IFN-α/β reporter cell line yielding reporter activity in units (U) per mL. (B–D) Vertical scatter plots displaying the median fluorescent intensity (MFI) of Siglec-1 cell-surface expression after three days of monocyte differentiation into macrophages either with cmMTB (black) or cmCTR (white), the indicated recombinant cytokines (B), the presence of an IL-10 depletion (α-IL-10) or a control (α-IgG) antibodies (C), or the presence of an IFNAR-2 blocking (α-IFNAR) or control (α-IgG) antibodies (D). (E) Representative serial immunohistochemical images of lung biopsies of a co-infected (ATB-SIV) NHP stained for Siglec-1 (brown, top) and pSTAT1 (brown, bottom). Scale bar, 250 µm. Insets are 10x zooms. (F) Correlation of the percentage of cells positive for Siglec-1 and pSTAT1, as measured per mm2 of lung tissue from the indicated NHP groups. Mean value is represented as a black line. (G) Representative immunohistochemical images of lung biopsies from the indicated NHP group stained for pSTAT1 (brown). Arrowheads show pSTAT1-positive nuclei. Scale bar, 500 µm. (H) Upper panel: Vertical Box and Whisker plot illustrating the percentage of pSTAT1+ alveolar macrophages in lung biopsies from the indicated NHP groups. Quantification analysis from n = 600 alveolar macrophages grouped from three independent animals per NHP group. Lower panel: Correlation of the percentage of alveolar macrophages positive for Siglec-1 and pSTAT1, from the indicated NHP groups. Mean value is represented as a black line. (A–D) Each circle within vertical scatter plots represents a single donor and histograms median value. Statistical analyses: Two-tailed, Wilcoxon signed-rank test (A–D), Spearman correlation (F, H lower panel), and Mann-Whitney unpaired test (H, upper panel). *p<0.05, p<0.01, *p<0.001, ****p<0.0001. ns: not significant. See Figure 2—source data 1. Figure 2—source data 1 Raw data and statistical analyses supporting that IFN-I induced by M. tuberculosis is responsible for Siglec-1 expression in human and non-human primate macrophages. https://cdn.elifesciences.org/articles/52535/elife-52535-fig2-data1-v2.xlsx Download elife-52535-fig2-data1-v2.xlsx IFN-I binding to IFNAR leads to the phosphorylation and nuclear translocation of the transcription factor STAT1, whose role is essential for transcription of ISG (Ivashkiv and Donlin, 2014). We thus examined the status of STAT1 activation in co-infected NHP lung tissue. Histological staining of serial sections of co-infected lungs revealed that zones rich in Siglec-1+ leukocytes also exhibited positivity for nuclear phosphorylated STAT1 (pSTAT1) (Figure 2E), and the abundance of these two markers strongly correlated with the active status of TB in the different NHP groups (Figure 2F). Moreover, we found that the majority of Siglec-1+ alveolar macrophages were also positive for nuclear pSTAT1 in the infected NHP groups compared to healthy (Figure 2E and G). In fact, there was a higher number of pSTAT1+ alveolar macrophages in TB-SIV co-infected lungs when compared to those from mono-infected NHP and this number directly correlates with the number of Siglec-1+ alveolar macrophages (Figure 2G–H). Altogether, these data demonstrate that Siglec-1 expression in human macrophages is controlled by IFN-I in a TB-associated microenvironment, and suggest the involvement of the IFN-I/STAT1/Siglec-1 axis in the pathogenesis of TB and co-infection with retroviruses. Siglec-1 localization on thick TNT is associated with their length and HIV-1 cargo TNT formation is responsible for the increase in HIV-1 spread between human macrophages in TB-associated microenvironments (Souriant et al., 2019). To investigate whether Siglec-1 expression is involved in this process, we first examined its localization in the context of TNT formed by cmMTB-treated cells infected by HIV-1. We observed that Siglec-1 is localized mainly on microtubule (MT)-positive thick TNT, and not on thin TNT (Figure 3A and Figure 3—video 1). Semi-automatic quantification of hundreds of TNT showed that about 50% of thick TNT were positive for Siglec-1 (Figure 3B and Figure 3—figure supplement 1A). These TNT exhibited a greater length compared to those lacking Siglec-1 (Figure 3C). Importantly, unlike thin TNT, HIV-1 viral proteins are found mainly inside Siglec-1+ thick TNT (Figure 3D–E and Figure 3—video 2). In addition, these thick TNT also contained large organelles such as mitochondria (Figure 3F and Figure 3—figure supplement 1B), another characteristic distinguishing thick from thin TNT (Dupont et al., 2018; Onfelt et al., 2006). In general, we also noticed that the incidence of Siglec-1+ thick TNT between HIV-1 infected macrophages persisted for more than one week upon HIV-1 infection (Figure 3—figure supplement 1C), suggesting a high degree of stability for these TNT. Figure 3 with 3 supplements see all Download asset Open asset Siglec-1 localization on thick TNT is associated with their length and HIV-1/mitochondria cargo. (A–F) Human monocytes were differentiated into macrophages with cmMTB for 3 days, and then infected with HIV-1-ADA strain (unless indicated otherwise) and fixed 3 days post-infection. (A) Representative immunofluorescence images of cmMTB-treated macrophages infected with HIV-1-ADA, and stained for extracellular Siglec-1 (red), intracellular tubulin (MT, green) and Wheat Germ Agglutinin (WGA, blue). Inserts are 3x zooms. Red arrowheads show Siglec-1 localization on TNT. Scale bar, 20 µm. (B) Vertical bar plot showing the semi-automatic quantification of Siglec-1+ TNT (black) and Siglec-1- TNT (white) in thick (WGA+, MT+) and thin (WGA+, MT-) TNT. 400 TNT were analyzed from two independent donors. (C) Siglec-1+ TNT exhibit a larger length index. Violin plots displaying the semi-automatic quantification of TNT length (in μm) for thin (WGA+, MT-), and thick TNT (WGA+, MT+) expressing Siglec-1 or not. 400 TNT were analyzed per condition from two independent donors. (D) Representative immunofluorescence images of cmMTB-treated macrophages 3 day post-infection with HIV-1-NLAD8-VSVG strain, and stained for extracellular Siglec-1 (red), intracellular HIV-1Gag (green) and WGA (grey). Scale bar, 10 µm. (E) Vertical bar plots indicating the quantification of presence (dark grey) or absence (light grey) of HIV-1Gag in thick TNT (WGA+, MT+) expressing Siglec-1 or not. 120 TNT in at least 1000 cells were analyzed from four independent donors. (F) Representative immunofluorescence images of cmMTB-treated macrophages infected with HIV-1-ADA loaded with and stained for extracellular Siglec-1 and WGA (grey). Inserts are 3x zooms. arrowheads show mitochondria inside TNT. Scale bar, 10 µm. Statistical analyses: the presence of Siglec-1 in thin and thick TNT (B), and Mann-Whitney unpaired test TNT length (C) and the presence of HIV-1 in TNT *p<0.05, ****p<0.0001. See Figure data 1. Figure data 1 Raw data and statistical analyses supporting Siglec-1 expression on thick TNT and its correlation with TNT Download These a localization of Siglec-1 on thick TNT that correlates positively with a greater length and high cargo of HIV-1 or for a functional capacity of Siglec-1+ TNT to transfer to cells over long Mtb-induced exacerbation of HIV-1 infection and spread in macrophages Siglec-1 To a functional role for Siglec-1 in the of macrophages to HIV-1 infection and spread induced by TB, Siglec-1 was in cmMTB-treated cells by gene (Figure and Figure supplement 1A). While this depletion not the total number of thick TNT (Figure and Figure supplement 1B), we observed a of thick TNT in cells lacking Siglec-1 when compared to control cells (Figure we performed a viral assay in these cells using particles lacking the viral but sialylated lipids that with Siglec-1 on myeloid cells (Izquierdo-Useros et al., 2012b; Puryear et al., 2013). We observed binding of Siglec-1+ thick TNT (Figure supplement Yet, in the absence of we noticed a significant of binding in comparison to control cells (Figure supplement 1D). We confirmed this functional using a blocking antibody showing that this receptor is involved in HIV-1 binding in cmMTB-treated cells (Figure supplement 1E). Figure with 1 supplement see all Download asset Open asset exacerbation of HIV-1 infection and spread in macrophages treated with cmMTB (A) from healthy were with of Siglec-1 or not A day monocytes were differentiated into macrophages with cmMTB for 3 were then infected with HIV-1-ADA to the formation (B) and length (C) of TNT at day or assess HIV-1 production and cell formation at day In cells were either infected with or labelled with to the transfer of HIV-1 (D) or mitochondria (B) plots showing the percentage of cells thick TNT (C) Violin plots displaying the semi-automatic quantification of TNT length (in μm) for thick (WGA+, MT+) TNT were analyzed per condition from two independent donors. plots indicating the percentage of cells (D) or cells (E) among cells after 24 hr (F) Representative immunofluorescence images of cells treated with days infection. were stained for intracellular HIV-1Gag F-actin and Scale bar, 500 µm. (G) Vertical scatter plots showing in cell and percentage of at day infection in cells represented in and Each circle represents a single donor and histograms median value. Statistical analyses: lower or Wilcoxon signed-rank test upper panel). *p<0.05, p<0.01, **p<0.0001. See Figure data 1. Figure data 1 Raw data and statistical analyses supporting a role for Siglec-1 in TNT length, HIV-1 and cell-to-cell and exacerbation of HIV-1 infection. Download We then assessed the role of Siglec-1 in HIV-1 transfer between macrophages, as this receptor is also for the transfer of the virus to CD4+ T cells (Akiyama et al., 2015; Izquierdo-Useros et al., 2012a; Puryear et al., 2013). We an between cmMTB-treated macrophages that allows the transfer of the viral protein from infected to green) cells over 24 hr (Souriant et al., 2019; Figure supplement Siglec-1 the infection of macrophages et al., we to effect on HIV-1 we the viral was in cells at the of the the of Siglec-1 (Figure supplement depletion of Siglec-1 significantly the capacity of cmMTB-treated macrophages to transfer HIV-1 to cells (Figure indicating that this receptor is involved in the viral spread (Souriant et al., 2019). there was a tendency for the capacity of cmMTB-treated macrophages to transfer mitochondria to cells compared to (Figure and Figure supplement to a in mechanisms involved in transfer including thick TNT et al., 2016). using HIV-1 strain (Figure we showed that Siglec-1 expression in cmMTB-treated cells abolished the exacerbation of HIV-1 infection and as well as the formation of cells (Figure which are pathological of HIV-1 infection of macrophages et al., 2015; et al., These that TB-induced Siglec-1 expression a key in HIV-1 and cell-to-cell transfer, in the exacerbation of HIV-1 infection and production in M(IL-10) macrophages. Discussion In this study, we potential mechanisms by which Mtb exacerbates HIV-1 infection in macrophages, and a deleterious role for Siglec-1 in this These have different to our understanding of this receptor in the synergy between Mtb and distinct retroviral and also for TNT in global transcriptomic revealed the up-regulation of as of an in macrophages exposed to a TB-associated microenvironment. active TB has been as an et al., et al., 2015; Moreira-Teixeira et al., there are no report in the about a role for Siglec-1 in TB or in Mtb co-infection with retroviruses. of Siglec-1 is to myeloid cells monocytes et al., and is by IFN-I et al., 2013; et al., and during HIV-1 infection et al., 2015). In addition, human alveolar macrophages are distinguished from lung macrophages by Siglec-1 expression et al., 2016). In this study, we that IFN-I present in TB-associated is responsible for Siglec-1