SIGLEC5 (sialic acid-binding immunoglobulin-type lectin 5) is a transmembrane protein belonging to the Siglec family of immune-regulatory receptors, primarily expressed on myeloid cells like macrophages, neutrophils, and dendritic cells. It recognizes sialic acid-containing glycans on cell surfaces, mediating cell-cell interactions and modulating immune responses. Structurally, SIGLEC5 contains an N-terminal V-set immunoglobulin domain responsible for ligand binding, followed by C2-set domains, a transmembrane region, and a cytoplasmic tail with immunoreceptor tyrosine-based inhibitory motifs (ITIMs). These motifs recruit phosphatases like SHP-1/2 to dampen signaling pathways, positioning SIGLEC5 as a checkpoint inhibitor in innate immunity.
SIGLEC5 antibodies are tools for studying its role in immune tolerance, inflammation, and disease. Dysregulation of SIGLEC5 is linked to cancers, autoimmune disorders, and infections, as tumor cells often exploit its immunosuppressive function to evade immune surveillance. Antibodies targeting SIGLEC5 can block its inhibitory signaling, potentially enhancing anti-tumor immunity. Conversely, agonist antibodies may suppress excessive inflammation in autoimmune contexts. Recent research also explores SIGLEC5's involvement in neurodegenerative diseases, where aberrant sialylation patterns are observed. Therapeutic antibodies, including bispecific formats or antibody-drug conjugates, are under investigation to modulate SIGLEC5 activity, highlighting its dual role as a biomarker and therapeutic target in diverse pathologies.