Role Of Siglec-1 Research Articles

When Dendritic Cells Go Viral: The Role of Siglec-1 in Host Defense and Dissemination of Enveloped Viruses.

Dendritic cells (DCs) are among the first cells that recognize incoming viruses at the mucosal portals of entry. Initial interaction between DCs and viruses facilitates cell activation and migration to secondary lymphoid tissues, where these antigen presenting cells (APCs) prime specific adaptive immune responses. Some viruses, however, have evolved strategies to subvert the migratory capacity of DCs as a way to disseminate infection systemically. Here we focus on the role of Siglec-1, a sialic acid-binding type I lectin receptor potently upregulated by type I interferons on DCs, that acts as a double edge sword, containing viral replication through the induction of antiviral immunity, but also favoring viral spread within tissues. Such is the case for distant enveloped viruses like human immunodeficiency virus (HIV)-1 or Ebola virus (EBOV), which incorporate sialic acid-containing gangliosides on their viral membrane and are effectively recognized by Siglec-1. Here we review how Siglec-1 is highly induced on the surface of human DCs upon viral infection, the way this impacts different antigen presentation pathways, and how enveloped viruses have evolved to exploit these APC functions as a potent dissemination strategy in different anatomical compartments.

The role of Siglec-1 in HIV-1/macrophage interaction

Although CD4 T-cells are a major target for HIV, recent work has demonstrated the ability of macrophages despite expressing relatively low levels of CD4, to be a target of the virus. Our recent study has found that the presence of growth factors not only play a role in the phenotype of these monocyte-derived-macrophages, but also are an important aspect of the permissiveness of these cells to infection. The work utilized cellular and biophysical methods to examine Siglec-1 on macrophages as a primary receptor in HIV-1 infection. These findings support the notion that Siglec-1 and macrophages and their interactions with the HIV-1 envelope should be considered in HIV-1 vaccine development.

The role of Siglec-1 in chemokines secretion and phagocytosis of oxidized low-density lipoprotein on macrophages

Objective By in vitro culture of mouse macrophage cell line RAW264. 7 and primary mouse bone marrow macrophages, the expression of Siglec-1 when stimulated by ox-LDL was observed. Meanwhile, Siglec-1 was up-regulated by M-CSF and down-regulated by small interference RNA targeting Siglec-1 ( si-RNA-Siglec-1) , and the expression of chemokines and lipid uptake ability by macrophages were observed, to explore the role of Siglec-1 on macrophages in atherosclerosis. Methods LDL was oxidized by copper. According to preliminary experiment results, ox-LDL 100 μg/ml was selected as a stimulus. There were 6 experimental groups:normal control group,ox-LDL 100 μg/ml group, ox-LDL 100 μg/ml + si-RNA 2509 2 ng/ml group,ox-LDL 100 μg/ml + si-RNA 3618 2 ng/ml group,ox-LDL 100 μg/ml + M-CSF 5 ng/ml group and ox-LDL 100 μg/ml + M-CSF 10 ng/ml group. si-RNA-Siglec-1 was transfected into macrophage to inhibit the expression of Siglec-1, whereas M-CSF 10 ng/ml or 5 ng/ml were added into the culture medium to enhance the expression of Siglec-1. Quantitative real-time polymerase chain reaction ( qRT-PCR) was used to determine the interfere efficiency of si-RNA-Siglec-1 or M-CSF. After stimulation with ox-LDL for 48 h, cell culture supernatants were collected to determine MIP-1 alpha, MCP-1 and IL-8 concentration by ELISA (n =3 for each group) to evaluate the activation of macrophages. Internalization of lipid particles by macrophages was analyzed by oil red 0 staining. Results Observed by fluorescence microscope, si-RNA-Siglec-1 could be effectively transfected into macrophages with a transfection efficiency about 90% ;PCR results showed that si-RNA 2509 and si-RNA 3618 in a concentration of 40 pmol/L had an inhibition rate of 0. 54 ±0. 11 or 0. 52 ±0. 16 vs 1. 00 ±0. 24 (control group) , t =5. 227 and 4. 992, respectively, all P < 0.01, while M-CSF 10 ng/ml could increase Siglec-1 mRNA expression approximately 4-fold (4. 16 ± 1. 25 vs 1.00 ±0. 24, t =7. 448, P<0. 01). The secretion of MCP-1, MIP-1 alpha, and MIP-2 in si-RNA3618-Siglec-1 group [(359. 28±47. 80) pg/ml, (33. 76 ± 14. 28) ng/ml and (7.87±1.55) ng/ml for MCP-1,MIP-1 alpha, and MIP-2, respectively] was significantly reduced in compare with ox-LDL 100 μg/ml group [ (577. 89 ± 35. 95 ) pg/ml, (69. 17 ± 11. 82) ng/ml and (12.28 ± 1.19) ng/ml for MCP-1, MIP-1 alpha, and MIP-2, respectively], with P value of 0.01, 0.05 and 0.01. In contrary, ox-LDL 100 μg/ml plus M-CSF 10 ng/ml group could significantly promote macrophage chemokine secretion [ (672. 89 ± 43.80) pg/ml, (101.31 ±24.17) ng/ml and (14.81 ±0.54) ng/ml for MCP-1, MIP-1 alpha, and MIP-2, respectively], with P < 0.05 compared with ox-LDL 100 μg/ml group. Meanwhile, lipid intemalization and foam cell formation was inhibited in si-RNA3618-Siglec-l group while ox-LDL 100 μg/ml plus M-CSF 10 ng/ml group could enhance the phagocytosis of ox-LDL by macrophage. Conclusions Siglec-1 may served as a potential phagocytic receptor for ox-LDL involving in macrophage uptake of lipid and turn into foam cells. Furthermore, it can active macrophages and enhance the secretion of MIP-1 alpha, MCP-1 and IL-8, attracting more macrophages and lymphocytes to the site of inflammatory plaque. Targeted inhibition of Siglec-1 reduces macrophage uptake of lipid and secretion of chemokines. Siglec-1 may possibly serve as a potential target of treatment or delay the development of atherosclerosis. Key words: Atherosclerosis; Oxidized low-density lipoprotein; Siglec-1; Macrophage; Phagocytosis; Chemokine

Increased Siglec-1 Expression in Monocytes of Patients with Primary Biliary Cirrhosis

Objectives: To evaluate Siglec-1 protein (CD169) and mRNA levels in peripheral blood monocytes of patients with primary biliary cirrhosis (PBC) and investigate its role in PBC pathogenesis by looking for correlations between Siglec-1 expression and key PBC associated biochemical indices. Methods: FACS analysis was used to identify the percentage of peripheral blood monocytes positive for both CD14 and Siglec-1 in (a) 45 PBC patients, (b) 40 patients with liver cirrhosis after hepatitis B infection and (c) 36 healthy controls. Siglec-1 mRNA was measured by real-time RT-PCR and serum biomarkers by routine biochemistry. Results: The percentage of CD14-Siglec-1 double positive cells was significantly higher (p< 0.01) in PBC patients than in healthy controls or cirrhosis post-hepatitis patients (13.68 ± 2.44%, 1.0 ± 0.2 %, and 4.1 ± 0.5 %, respectively). Siglec-1 mRNA expression in the PBC group was 3.42 times higher than in healthy controls (p < 0.01). Conclusion: We investigated the role of Siglec-1 in PBC by assessing its expression in mononuclear cells of PBC patients and levels of secreted cytokines in cell supernatants after Siglec-1 RNA interference. It is possible that elevated Siglec-1 expression in peripheral blood monocytes of PBC patients is correlated with monocyte-mediated inflammatory responses during the development of PBC.