Molecular cloning and characterization of mouse CD97

The EGF-TM7 family (CD97 and EMR1) is a group of class II seven-span transm embrane receptors predominantly expressed by cells of the immune system. Re cently, we have identified CD55, a regulatory molecule of the complement ca scade, as a cellular ligand of human CD97 (hCD97), In this study, the molec ular properties of mouse CD97 (mCD97) are described. Like hCD97, mCD97 has an extended extracellular region with several epidermal growth factor-like (EGF) domains. Due to alternative RNA splicing, isoforms with three and fou r EGF domains exist, designated mCD97(EGF1,2,4) and mCD97(EGF1,2,3,4) respe ctively. All EGF domains, except for the N-terminal one, possess a calcium- binding site. In a third isoform mCD97(EGF1,2,X,3,4), a sequence of 45 amin o acids was found between the second and third EGF domain that does not cor respond to any known protein module. Using newly generated mCD97 mAb, we sh ow that analogous to the blood expression pattern of hCD97, mCD97 can be fo und on lymphoid and myeloid cells. Adhesion of mouse erythrocytes and splen ocytes to COS cells expressing mCD97(EGF1,2,4) or mCD97(EGF1,2,3,4) could b e blocked by mouse CD55 (mCD55) antibody, identifying mCD55 as a cellular l igand for mCD97, Consistent with the necessity of directly linked EGF domai ns for the integrity of the CD55-binding site on hCD97, no adhesion was det ected to the largest mouse isoform mCD97(EGF1,2,X,3,4), Remarkably, we foun d that the interaction between CD97 and CD55 is phylogenetically restricted , as indicated by the selective adhesion of primate erythrocytes to hCD97 t ransfectants, and of mouse and rat erythrocytes to mCD97 transfectants resp ectively.