Patients with a severe autoimmune disease that attacks the blood vessels lack the membrane form of a protein (SEMA4D) found in white blood cells, research reveals. The absence of membrane-bound SEMA4D prevents inflammation from being restrained in these patients, while increased soluble SEMA4D upregulates inflammatory signaling. The findings suggest SEMA4D could not only be used as a marker of disease but could also be targeted as a novel form of therapy.