Ontology of Biological Attributes identifier OBA_2055331 (F2R/SEMA4D protein level ratio in blood) can be described as follows. A compound attribute that is the ratio of amount of proteinase-activated receptor 1 (human) in blood to amount of semaphorin-4D (human) in blood. Also known as: the ratio of amount of proteinase-activated receptor 1 (human) in blood to amount of semaphorin-4D (human) in blood.