Bone marrow stromal antigen 2, also known as CD317, is a lipid raft associated protein that is encoded by the BST2 gene. This protein is constitutively expressed in mature B cells, plasma cells and plasmacytoid dendritic cells, and in many other cells, it is only expressed as a response to stimuli from IFN pathway. BST2 is a cellular protein which inhibits retrovirus infection by preventing the diffusion of virus particles after budding from infected cells. BST2 has been shown as a Type-I-IFN biomarker using flow cytometry, B cell BST2 was used as a Cell-Specific Assay for Response to Type I Interferon Predicts Clinical Features and Flares in Systemic Lupus Erythematosus. BST2 has also been predicted to be involved in cell adhesion and cell migration. It has also been identified as the protein that help stabilize lipid rafts by joining nearby lipid rafts to form a cluster.