Receptor potentially involved in both adhesion and signaling processes early after leukocyte activation. Plays an essential role in leukocyte migration. Forms a heterodimer, consisting of a large extracellular region (alpha subunit) non-covalently linked to a seven-transmembrane moiety (beta subunit). Interacts with complement decay-accelerating factor (DAF). The largest isoform (isoform 1) interacts with chondroitin sulfate. Broadly expressed, found on most hematopoietic cells, including activated lymphocytes, monocytes, macrophages, dendritic cells, and granulocytes. Expressed also abundantly by smooth muscle cells. Expressed in thyroid, colorectal, gastric, esophageal and pancreatic carcinomas too. Expression are increased under inflammatory conditions in the CNS of multiple sclerosis and in synovial tissue of patients with rheumatoid arthritis. Increased expression of CD97 in the synovium is accompanied by detectable levels of soluble CD97 in the synovial fluid. Rapid up-regulation during lymphocyte activation. The first two EGF domains mediate the interaction with DAF. A third tandemly arranged EGF domain is necessary for the structural integrity of the binding region. Binding to chondroitin sulfate is mediated by the fourth EGF domain. Proteolytically cleaved into 2 subunits, an extracellular alpha subunit and a seven-transmembrane subunit. Belongs to the G-protein coupled receptor 2 family. LN-TM7 subfamily.