Siglec-1, an easy and contributory inflammation marker in rheumatology

Objectives: Inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are poorly informative about interferon (IFN)-related disorders. In these conditions, the measure of the interferon score (IS), obtained by measuring the expression of IFN-stimulated genes, has been proposed. Flow cytometry-based assays measuring sialic-acid-binding Ig-like lectin 1 (Siglec-1) expression could be a more practical tool for evaluating IFN-inflammation. The study compared Siglec-1 measures with IS and other inflammatory indexes. We compared Siglec-1 measures with IS and other inflammatory indexes in real-world paediatric rheumatology experience. Methods: We recruited patients with immuno-rheumatological conditions, acute infectious illness and patients undergoing orthopaedic surgery as controls. Siglec-1 expression was measured in all samples, and IS, ESR and CRP were also recorded if available. Results: Overall, 98 subjects were enrolled in the study, with a total of 104 measures of Siglec-1. Compared with IS, Siglec-1 expression showed good accuracy (86.0%), specificity (72.7%) and sensitivity (85.7%). The measure of the percentage of Siglec-1-positive cells performed best at low levels of IFN-inflammation, while the measure of mean fluorescence intensity performed best at higher levels. Ex vivo studies on IFN-stimulated monocytes confirmed this behaviour. There was no link between Siglec-1 expression and either ESR or CRP, and positive Siglec-1 results were found even when ESR and CRP were normal. A high Siglec-1 expression was also recorded in subjects with acute infections. Conclusion: Siglec-1 measurement by flow cytometry is an easy tool to detect IFN-related inflammation, even in subjects with normal results of common inflammation indexes.