SIGLEC1 (CD169) is a sialic acid-binding immunoglobulin-like lectin primarily expressed on macrophages that serves critical roles in immune regulation and pathogen recognition. The protein functions as a cell surface receptor that binds to sialylated gangliosides, facilitating various cellular interactions 1. In the context of viral infections, SIGLEC1 mediates viral capture and can influence both protective immunity and viral dissemination - it enables HIV-1 capture by dendritic cells in a CD169-dependent manner, potentially facilitating viral transmission 2, while also supporting antiviral responses through type I interferon signaling in respiratory infections 3. SIGLEC1 expression serves as a biomarker for interferon pathway activation, particularly in autoimmune conditions like juvenile dermatomyositis where it appears on monocyte surfaces as an interferon-related marker 4. The protein is expressed on distinct macrophage populations including subcapsular sinus macrophages that regulate B cell memory responses to vaccination 5 and splenic marginal metallophilic macrophages essential for post-myocardial infarction wound healing 6. Additionally, SIGLEC1 expression helps distinguish different macrophage subsets in tissues, with CD169+ macrophages typically representing alveolar macrophages in lung tissue 7.