CD172b, also known as SIRPβ (Signal Regulatory Protein β), is a transmembrane glycoprotein belonging to the SIRP family, which includes CD172a (SIRPα) and CD172g (SIRPγ). Expressed primarily on myeloid cells such as dendritic cells, macrophages, and neutrophils, CD172b features extracellular immunoglobulin (Ig)-like domains but lacks intracellular signaling motifs, distinguishing it from CD172a. Instead, it associates with adaptor proteins like DAP12 or FcRγ to mediate signal transduction. CD172b interacts with CD47. a widely expressed ligand, though with lower affinity compared to CD172a. This interaction modulates immune cell functions, including phagocytosis inhibition, inflammatory cytokine production, and cell adhesion.
Research highlights its role in regulating innate immune responses and inflammation. Unlike CD172a, which delivers inhibitory signals, CD172b often activates pro-inflammatory pathways, influencing autoimmune diseases, infections, and cancer. In cancer, CD172b-CD47 axis dysregulation may contribute to immune evasion, making it a potential therapeutic target. Antibodies targeting CD172b are valuable tools for studying its function, with applications in flow cytometry, immunohistochemistry, and functional blocking experiments. Recent studies explore its therapeutic potential in modulating immune checkpoints or enhancing anti-tumor immunity. However, its exact signaling mechanisms and context-dependent roles remain under investigation, necessitating further research to clarify its physiological and pathological contributions.