A macrophage marker, Siglec-1, is increased on circulating monocytes in patients with systemic sclerosis and induced by type I interferons and toll-like receptor agonists.
OBJECTIVE
Microarray analyses of peripheral blood leukocytes have shown that patients with systemic lupus erythematosus express increased levels of type I interferon (IFN)-regulated genes. In this study we examined gene expression by peripheral blood mononuclear cells (PBMCs) from patients with systemic sclerosis (SSc) to better understand the dysregulation of the immune system in this disease.


METHODS
PBMC gene expression was analyzed by microarray and confirmed by real-time polymerase chain reaction (PCR). Surface protein expression of Siglec-1 was analyzed by flow cytometry in PBMCs from healthy control subjects and patients with SSc, and in control PBMCs that were cultured in vitro with Toll-like receptor (TLR) agonists.


RESULTS
SSc patients showed increased expression of a cluster of IFN-regulated genes, including Siglec-1 (CD169, sialoadhesin). This result was verified and extended by real-time PCR, showing that a subset of the SSc patients expressed strikingly increased levels of Siglec-1 messenger RNA (mRNA). Flow cytometry of PBMCs from SSc patients and healthy controls showed increased Siglec-1 surface protein expression, which was restricted to CD14+ monocytes. In vitro studies showed that type I IFN and certain TLR agonists, including TLR-7 and TLR-9, induced Siglec-1 mRNA and protein expression. Moreover, TLR induction of surface Siglec-1 was shown to be type I IFN-dependent. Increased numbers of Siglec-1+ cells were observed by immunohistochemistry in the skin of SSc patients compared with healthy controls.


CONCLUSIONS
Increased expression of Siglec-1 in circulating SSc monocytes and tissue macrophages suggests that type I IFN-mediated activation of monocytes occurs in SSc, possibly through TLR activation of IFN secretion. These observations indicate a potential role for type I IFN-activated monocyte/macrophages in the pathogenesis of SSc.
York
Michael R
MR
Boston University Medical Center, Boston, Massachusetts 02118, USA.
Nagai
Taro
T
Mangini
Alyson J
AJ
Lemaire
Raphaël
R
van Seventer
Jean Maguire
JM
Lafyatis
Robert
R
D000293:Adolescent; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D002478:Cells, Cultured; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007370:Interferon Type I / Q000819:agonists* / Q000502:physiology; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins / Q000097:blood* / Q000235:genetics; D046228:Microarray Analysis; D008875:Middle Aged; D009000:Monocytes / Q000276:immunology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011971:Receptors, Immunologic / Q000097:blood* / Q000235:genetics; D012595:Scleroderma, Systemic / Q000097:blood* / Q000378:metabolism; D063267:Sialic Acid Binding Ig-like Lectin 1; D051193:Toll-Like Receptors / Q000819:agonists* / Q000502:physiology
D015415:Biomarkers; D007370:Interferon Type I; D018950:Lipopolysaccharide Receptors; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011971:Receptors, Immunologic; C571166:SIGLEC1 protein, human; D063267:Sialic Acid Binding Ig-like Lectin 1; D051193:Toll-Like Receptors