The emerging roles of semaphorin4D/CD100 in immunological diseases.

In vertebrates, the semaphorin family of proteins is composed of 21 members that are divided into five subfamilies, i.e. classes 3 to 7. Semaphorins play crucial roles in regulating multiple biological processes, such as neural remodeling, tissue regeneration, cancer progression, and, especially, in immunological regulation. Semaphorin 4D (SEMA4D), also known as CD100, is an important member of the semaphorin family and was first characterized as a lymphocyte-specific marker. SEMA4D has diverse effects on immunologic processes, including immune cell proliferation, differentiation, activation, and migration, through binding to its specific membrane receptors CD72, PLXNB1, and PLXNB2. Furthermore, SEMA4D and its underlying signaling have been increasingly linked with several immunological diseases. This review focuses on the significant immunoregulatory role of SEMA4D and the associated underlying mechanisms, as well as the potential application of SEMA4D as a diagnostic marker and therapeutic target for the treatment of immunological diseases.