Cluster of differentiation 97 is a protein also known as BL-Ac[F2] encoded by the ADGRE5 gene. CD97 is a member of the adhesion G protein-coupled receptor (GPCR) family. Adhesion GPCRs are characterized by an extended extracellular region often possessing N-terminal protein modules that is linked to a TM7 region via a domain known as the GPCR-Autoproteolysis INducing (GAIN) domain. CD97 is widely expressed on, among others, hematopoietic stem and progenitor cells, immune cells, epithelial cells, muscle cells as well as their malignant counterparts. In the case of CD97 the N-terminal domains consist of alternatively spliced epidermal growth factor (EGF)-like domains. Alternative splicing has been observed for this gene and three variants have been found. The N-terminal fragment of CD97 contains 3-5 EGF-like domains in human and 3-4 EGF-like domains in mice.