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. [ABSTRACT FROM AUTHOR]