CD169/SIGLEC1 is expressed on circulating monocytes in COVID-19 and expression levels are associated with disease severity.

Coronavirus disease 2019 (COVID-19) is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Type I interferons are important in the defense of viral infections. Recently, neutralizing IgG auto-antibodies against type I interferons were found in patients with severe COVID-19 infection. Here, we analyzed expression of CD169/SIGLEC1, a well described downstream molecule in interferon signaling, and found increased monocytic CD169/SIGLEC1 expression levels in patients with mild, acute COVID-19, compared to patients with severe disease. We recommend further clinical studies to evaluate the value of CD169/SIGLEC1 expression in patients with COVID-19 with or without auto-antibodies against type I interferons.

Decreased expression of a phagocytic receptor Siglec-1 on alveolar macrophages in chronic obstructive pulmonary disease.

BACKGROUND: Alveolar macrophages are professional phagocytes that remove microbial pathogens inhaled into the lung. The phagocytic ability is compromised in chronic obstructive pulmonary disease (COPD). However, the molecular mechanisms underlying this defect in phagocytosis are not clearly defined. MATERIALS AND METHODS: Cell suspensions were collected from lung tissues of patients undergoing lung resection. Alveolar macrophages were detected as FSChi/ SSChi/CD45+/CD206+ cells in the isolated cell suspension by flow-cytometry. The cell surface expression of plasma membrane-bound phagocytic receptors (Fcγ receptor I (FcγRI), a complement receptor CD11b, macrophage scavenger receptor-1 (MSR-1), CD36 and Siglec-1) was determined on the alveolar macrophages. Correlations between the expression levels of the phagocytic receptors and disease severity were analysed. Phagocytosis of fluorescence-tagged bacteria by human alveolar macrophages was evaluated. RESULTS: The flow-cytometry analyses revealed that FcγRI, CD11b, MSR-1 and Siglec-1, but not CD36, were expressed on human alveolar macrophages. Among these receptors, Siglec-1 expression was significantly decreased on alveolar macrophages in COPD ex-smokers (n = 11), compared to control never-smokers (n = 11) or control ex-smokers (n = 9). The Siglec-1 expression on alveolar macrophages was significantly correlated with lung function (forced expiratory volume in 1 s) and with the severity of emphysema. Treatment of human alveolar macrophages with an anti-Siglec1 blocking antibody decreased phagocytosis of non-typeable Haemophilus influenzae (NTHi). CONCLUSION: Our findings demonstrated reduced expression of Siglec-1 on alveolar macrophages in COPD, which is involved in engulfment of NTHi.

Maf expression in human macrophages and lymph node sinus macrophages in patients with esophageal cancer.

The large Maf transcription factors are expressed in immune cells including macrophages and lymphocytes. To investigate the distribution of Maf expression in human organs, immunostaining for Maf was performed using sections of several human organs. High Maf expression was seen in the nucleus of macrophages in the gastrointestinal tract and lymph node sinus macrophages (LySMs). Then, we assessed whether Maf expression in LySMs was correlated with CD169 expression and the clinical prognosis in patients with esophageal cancer. Maf expression was associated with CD169 expression, but Maf expression in LySMs was not associated with the clinical course in patients with esophageal cancer. We determined which cytokines stimulate Maf expression using cultured macrophages. Immunocytochemistry showed that Maf expression was significantly elevated by interferon-γ. These results are the first report of Maf expression in human samples. Maf expression may be a marker for the macrophage population in humans.

Constitutive Siglec-1 expression confers susceptibility to HIV-1 infection of human dendritic cell precursors.

The human dendritic cell (DC) lineage has recently been unraveled by high-dimensional mapping, revealing the existence of a discrete new population of blood circulating DC precursors (pre-DCs). Whether this new DC population possesses specific functional features as compared to the other blood DC subset upon pathogen encounter remained to be evaluated. A unique feature of pre-DCs among blood DCs is their constitutive expression of the viral adhesion receptor Siglec-1. Here, we show that pre-DCs, but not other blood DC subsets, are susceptible to infection by HIV-1 in a Siglec-1-dependent manner. Siglec-1 mediates pre-DC infection of CCR5- and CXCR4-tropic strains. Infection of pre-DCs is further enhanced in the presence of HIV-2/SIVmac Vpx, indicating that Siglec-1 does not counteract restriction factors such as SAMHD1. Instead, Siglec-1 promotes attachment and fusion of viral particles. HIV-1-infected pre-DCs produce new infectious viral particles that accumulate in intracellular compartments reminiscent of the virus-containing compartment of macrophages. Pre-DC activation by toll-like receptor (TLR) ligands induces an antiviral state that inhibits HIV-1 fusion and infection, but Siglec-1 remains functional and mediates replication-independent transfer of HIV-1 to activated primary T lymphocytes. Altogether, Siglec-1-mediated susceptibility to HIV-1 infection of pre-DCs constitutes a unique functional feature that might represent a preferential relationship of this emerging cell type with viruses.

High CD169 expression in lymph node macrophages predicts a favorable clinical course in patients with esophageal cancer.

Recent findings indicate CD169-positive lymph node sinus macrophages (LySMs) in the regional lymph nodes (RLNs) play an important role in anti-cancer immunity. In the present study, we investigated the correlation between CD169 expression in RLNs and clinicopathologic factors. Higher CD169 expression in LySMs was significantly associated with longer cancer-specific survival (CSS). The density of tumor-infiltrating lymphocytes (TILs) in the cancer nest and CD169 expression on LySMs were positively associated in patients who underwent pretreatment. As CD169 expression is thought to reflect a high interferon signature in RLNs, we tried to identify immunity-related genes that are up-regulated by interferon in macrophages as well as CD169. Indoleamine 2,3-dioxygenase (IDO1) was found to be elevated by interferon, and expression of IDO1 was tested using immunohistochemistry. IDO1 expression on LySMs was positively correlated with CD169 expression; however, there was no significant correlation between IDO1 and clinicopathologic factors. These results suggest that high expression of CD169 in LySMs reflects a high potential for anti-cancer immune responses in esophageal cancer patients and that monitoring CD169 expression would be useful for evaluating the potential of anti-cancer immune reactions.

Reduced number of CD169+ macrophages in pre-metastatic regional lymph nodes is associated with subsequent metastatic disease in an animal model and with poor outcome in prostate cancer patients.

BACKGROUND: Tumor-derived antigens are captured by CD169+ (SIGLEC1+ ) sinus macrophages in regional lymph nodes (LNs), and are presented to effector cells inducing an anti-tumor immune response. Reduced CD169 expression in pre-metastatic regional LNs is associated with subsequent metastatic disease and a poor outcome in several tumor types, but if this is the case in prostate cancer has not been explored. METHODS: CD169 expression was measured with immunohistochemistry in metastasis-free regional LNs from 109 prostate cancer patients treated with prostatectomy (January 1996 to April 2002). Possible associations of CD169 expression with PSA-relapse, prostate cancer death, Gleason score, and other clinical data were assessed using Kaplan-Meier survival- and Cox regression analysis. In addition, the Dunning rat prostate tumor model was used to examine CD169 expression in pre-metastatic LNs draining either highly metastatic MatLyLu- or poorly metastatic AT1-tumors. RESULTS: In patients with low CD169 immunostaining in metastasis-free regional LNs, 8 of the 27 patients died from prostate cancer compared with only three of the 82 patients with high immunostaining (P < 0.001). CD169 expression in regional LNs was not associated with PSA-relapse. Rats with highly metastatic tumors had decreased CD169 immunoreactivity in pre-metastatic regional LNs compared with rats with poorly metastatic tumors. CONCLUSION: Low expression of CD169 in metastasis-free regional LNs indicates a reduced anti-tumor immune response. If verified in other studies, CD169 expression in regional LNs could, in combination with other factors, potentially be used as a marker of prostate cancer aggressiveness.

Type I IFN-Inducible Downregulation of MicroRNA-27a Feedback Inhibits Antiviral Innate Response by Upregulating Siglec1/TRIM27.

Upon recognition of viral components by pattern recognition receptors, including TLRs and retinoic acid-inducible gene I-like helicases, cells are activated to produce type I IFN, which plays key roles in host antiviral innate immune response. However, excessive IFN production may induce immune disorders, and the mechanisms responsible for the regulation of type I IFN production have attracted much attention. Furthermore, type I IFN activates the downstream IFN/JAK/STAT pathway to modulate expression of a set of genes against viral infection, but whether these genes can feedback regulate type I IFN production is poorly understood. In this study, by screening the microRNAs modulated by viral infection in macrophages, we identified that microRNA (miR)-27a was significantly downregulated via the IFN/JAK/STAT1/runt-related transcription factor 1 pathway. Inducible downregulation of miR-27a, in turn, negatively regulated vesicular stomatitis virus-triggered type I IFN production, thus promoting vesicular stomatitis virus replication in macrophages. Mechanistically, we found that miR-27a directly targeted sialic acid-binding Ig-like lectin (Siglec)1 and E3 ubiquitin ligase tripartite motif-containing protein 27 (TRIM27), both of which were previously verified as negative regulators of type I IFN production. Furthermore, we constructed "Sponge" transgenic mice against miR-27a expression and found that Siglec1 and TRIM27 expression were elevated whereas type I IFN production was inhibited and viral replication was aggregated in vivo. Therefore, type I IFN-induced downregulation of miR-27a can upregulate Siglec1 and TRIM27 expression, feedback inhibiting type I IFN production in antiviral innate response. Our study outlines a new negative way to feedback regulate type I IFN production.

HIV-1 immune activation induces Siglec-1 expression and enhances viral trans-infection in blood and tissue myeloid cells.

BACKGROUND: Myeloid cells are key players in the recognition and response of the host against invading viruses. Paradoxically, upon HIV-1 infection, myeloid cells might also promote viral pathogenesis through trans-infection, a mechanism that promotes HIV-1 transmission to target cells via viral capture and storage. The receptor Siglec-1 (CD169) potently enhances HIV-1 trans-infection and is regulated by immune activating signals present throughout the course of HIV-1 infection, such as interferon α (IFNα). RESULTS: Here we show that IFNα-activated dendritic cells, monocytes and macrophages have an enhanced ability to capture and trans-infect HIV-1 via Siglec-1 recognition of viral membrane gangliosides. Monocytes from untreated HIV-1-infected individuals trans-infect HIV-1 via Siglec-1, but this capacity diminishes after effective antiretroviral treatment. Furthermore, Siglec-1 is expressed on myeloid cells residing in lymphoid tissues, where it can mediate viral trans-infection. CONCLUSIONS: Siglec-1 on myeloid cells could fuel novel CD4(+) T-cell infections and contribute to HIV-1 dissemination in vivo.

Transforming growth factor beta 1 up-regulates CD169 (sialoadhesin) expression on monocyte-derived dendritic cells: role in HIV sexual transmission.

OBJECTIVE: Recent data describe CD169 (also called sialoadhesin or Siglec-1) as the main HIV-1 receptor expressed by mucosal dendritic cells involved in the capture of the virus and its transmission to target cells. In this study, we investigated the effect of transforming growth factor beta 1 (TGF-ß1), a cytokine found in abundance in semen, on the expression of CD169 on dendritic cells in order to characterize its potential role in the capture of HIV-1 particles by these antigen-presenting cells. METHODS: Monocyte-derived dendritic cells (MDDCs) were cultured in the presence of lipopolysaccharide, pro-inflammatory cytokines [interleukin (IL)-1ß and tumor necrosis factor alpha (TNF-α)] or different concentrations of TGF-ß1, and analyzed for maturation marker and Siglec expression. The ability of MDDCs to capture HIV particles following the different treatments was also analyzed. RESULTS: TGF-ß1 treatment promotes a significant increase of CD169 expression on MDDCs. This effect was specific since neither DC-SIGN nor other Siglec expressions were changed. The CD169 increase was due to a de-novo synthesis as evidenced by Western blot experiment. This up-regulation was well correlated to the concentration of TGF-ß1 and associated with an increase of the MDDC ability to bind HIV particles. Interestingly, this phenomenon was independent of the maturation status of MDDCs. CONCLUSION: This study demonstrates that the most abundant cytokine present in semen (TGF-ß1) is able to enhance specifically the expression of an important molecule (CD169) involved in the capture and transmission of HIV-1 particles from the mucosal lumen to the submucosal compartment. Our results suggest that this mechanism may play a relevant role in sexual HIV transmission.

Partial recovery of the damaged rat blood-brain barrier is mediated by adherens junction complexes, extracellular matrix remodeling and macrophage infiltration following focal astrocyte loss.

Blood-brain barrier (BBB) dysfunction is a feature of many neurodegenerative disorders. The mechanisms and interactions between astrocytes, extracellular matrix and vascular endothelial cells in regulating the mature BBB are poorly understood. We have previously shown that transitory glial fibrillary acidic protein (GFAP)-astrocyte loss, induced by the systemic administration of 3-chloropropanediol, leads to reversible disruption of tight junction complexes and BBB integrity to a range of markers. However, early restoration of BBB integrity to dextran (10-70 kDa) and fibrinogen was seen in the absence of paracellular tight junction proteins claudin-5 and occludin. In the present study we show that in the GFAP-astrocyte-lesioned rat inferior colliculus, paracellular expression of adherens junction proteins (vascular endothelial (VE)-cadherin and ß-catenin) was maintained in vascular endothelial cells that lacked paracellular claudin-5 expression and which showed reversible post-translational occludin modification. Claudin-1 expression paralleled the loss and recovery of claudin-5, while claudin-3 or -12 immunoreactivity was not detected. In addition, the extracellular matrix, as visualized by laminin and fibronectin, underwent extensive reversible remodeling and perivascular CD169 macrophages become abundant throughout the lesioned inferior colliculus. At a time that GFAP-astrocytes repopulated the lesion area and tight junction proteins were returned to paracellular domains, the extracellular matrix and leukocyte profiles normalized and resembled profiles seen in control tissue. This study supports the hypothesis that a combination of paracellular adherens junctional proteins, remodeled basement membrane and the presence of perivascular leukocytes provide a temporary barrier to limit the extravasation of macromolecules and potentially neurotoxic substances into the brain parenchyma until tight junction proteins are restored to paracellular domains.

Sialoadhesin ligand expression identifies a subset of CD4+Foxp3- T cells with a distinct activation and glycosylation profile.

Sialoadhesin (Sn) is a sialic acid-binding Ig-like lectin expressed selectively on macrophage subsets. In a model of experimental autoimmune encephalomyelitis, Sn interacted with sialylated ligands expressed selectively on CD4(+)Foxp3(+) regulatory T cells (Tregs) and inhibited their proliferation. In this study, we examined the induction of Sn ligands (SnL) on all splenic CD4(+) T cells following in vitro activation. Most CD4(+) Tregs strongly upregulated SnL, whereas only a small subset of ~20% CD4(+)Foxp3(-) T cells (effector T cells [Teffs]) upregulated SnL. SnL(+) Teffs displayed higher levels of activation markers CD25 and CD69, exhibited increased proliferation, and produced higher amounts of IL-2 and IFN-γ than corresponding SnL(-) Teffs. Coculture of activated Teffs with Sn(+) macrophages or Sn(+) Chinese hamster ovary cells resulted in increased cell death, suggesting a regulatory role for Sn-SnL interactions. The key importance of α2,3-sialylation in SnL expression was demonstrated by increased binding of α2,3-linkage-specific Maackia amurensis lectin, increased expression of α2,3-sialyltransferase ST3GalVI, and loss of SnL following treatment with an α2,3-linkage-specific sialidase. The induction of SnL on activated CD4(+) T cells was dependent on N-glycan rather than O-glycan biosynthesis and independent of the mucin-like molecules CD43 and P-selectin glycoprotein ligand-1, previously implicated in Sn interactions. Induction of ligands on CD4(+)Foxp3(-) Teffs was also observed in vivo using the New Zealand Black × New Zealand White F1 murine model of spontaneous lupus and SnL levels on Teffs correlated strongly with the degree of proteinuria. Collectively, these data indicate that SnL is a novel marker of activated CD4(+) Teffs that are implicated in the pathogenesis of autoimmune diseases.

Trafficking and replication patterns reveal splenic macrophages as major targets of dengue virus in mice.

Human postmortem studies of natural dengue virus (DENV) infection have reported systemically distributed viral antigen. Although it is widely accepted that DENV infects mononuclear phagocytes, the sequence in which specific tissues and cell types are targeted remains uncharacterized. We previously reported that mice lacking alpha/beta and gamma interferon receptors permit high levels of DENV replication and show signs of systemic disease (T. R. Prestwood et al., J. Virol. 82:8411-8421, 2008). Here we demonstrate that within 6 h, DENV traffics to and replicates in both CD169(+) and SIGN-R1(+) macrophages of the splenic marginal zone or draining lymph node, respectively, following intravenous or intrafootpad inoculation. Subsequently, high levels of replication are detected in F4/80(+) splenic red pulp macrophages and in the bone marrow, lymph nodes, and Peyer's patches. Intravenously inoculated mice begin to succumb to dengue disease 72 h after infection, at which time viral replication occurs systemically, except in lymphoid tissues. In particular, high levels of replication occur in CD68(+) macrophages of the kidneys, heart, thymus, and gastrointestinal tract. Over the course of infection, proportionately large quantities of DENV traffic to the liver and spleen. However, late during infection, viral trafficking to the spleen decreases, while trafficking to the liver, thymus, and kidneys increases. The present study demonstrates that macrophage populations, initially in the spleen and other lymphoid tissues and later in nonlymphoid tissues, are major targets of DENV infection in vivo.