Sialoadhesin deficiency does not influence the severity of lupus nephritis in New Zealand black x New Zealand white F1 mice.

INTRODUCTION: Systemic lupus erythematosus (SLE) is a chronic inflammatory condition with multisystem involvement. One of the key features of the disease is the upregulation of type I interferons, resulting in the so-called "interferon signature". Recent flow cytometric and transcriptomic studies identified Sialoadhesin (Sn, CD169) as an important interferon-induced blood monocyte biomarker in diseased patients. To investigate a potential causative role of Sn in SLE, we generated NZBWF1 (New Zealand Black x New Zealand White F1) mice lacking Sn and compared onset and progression of disease with NZBWF1 expressing normal levels of Sn. METHODS: Sn expression in renal tissues of pre-diseased and diseased NZBWF1 mice was evaluated by Quantitative real time PCR (QPCR) and immunohistochemistry. Sn-/- NZBWF1 mice were generated by speed congenics. Disease severity of Sn+/+ and Sn-/- NZBWF1 mice was assessed by serum immunoassays, flow cytometry, light microscopy and immunohistochemistry. RESULTS: Renal tissues from proteinuric NZBWF1 mice exhibited a significant upregulation of Sn mRNA and protein expression following disease onset. Further immunohistochemical analysis showed that Sn+ macrophages assumed a distinct periglomerular distribution and, unlike CD68+ macrophages, were not present within the glomeruli. Analysis of disease severity in Sn-/- and Sn+/+ NZBWF1 mice revealed no significant differences in the disease progression between the two groups although Sn-deficient mice showed a more rapid onset of proteinuria. CONCLUSIONS: These data confirm a positive correlation of Sn with disease activity. However, Sn deficiency does not have a significant effect on the severity and progression of lupus nephritis in the NZBWF1 mouse model.

An intact sialoadhesin (Sn/SIGLEC1/CD169) is not required for attachment/internalization of the porcine reproductive and respiratory syndrome virus.

Surface expression of SIGLEC1, also known as sialoadhesin or CD169, is considered a primary determinant of the permissiveness of porcine alveolar macrophages for infection by porcine reproductive and respiratory syndrome virus (PRRSV). In vitro, the attachment and internalization of PRRSV are dependent on the interaction between sialic acid on the virion surface and the sialic acid binding domain of the SIGLEC1 gene. To test the role of SIGLEC1 in PRRSV infection, a SIGLEC1 gene knockout pig was created by removing part of exon 1 and all of exons 2 and 3 of the SIGLEC1 gene. The resulting knockout ablated SIGLEC1 expression on the surface of alveolar macrophages but had no effect on the expression of CD163, a coreceptor for PRRSV. After infection, PRRSV viremia in SIGLEC1(-/-) pigs followed the same course as in SIGLEC1(-/+) and SIGLEC1(+/+) littermates. The absence of SIGLEC1 had no measurable effect on other aspects of PRRSV infection, including clinical disease course and histopathology. The results demonstrate that the expression of the SIGLEC1 gene is not required for infection of pigs with PRRSV and that the absence of SIGLEC1 does not contribute to the pathogenesis of acute disease.

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.