Semaphorin-4A (SEMA4A) is also known as Semaphorin-B (SEMAB), which belongs to the semaphorin family. SEMA4A contains one Ig-like C2-type (immunoglobulin-like) domain, one PSI domain and one sema domain. SEMA4A is cell surface receptor for PLXNB1, PLXNB2, PLXNB3 and PLXND1 that plays an important role in cell-cell signaling. SEMA4A plays a role in priming antigen-specific T-cells, promotes differentiation of Th1 T-helper cells, and thereby contributes to adaptive immunity. SEMA4A also promotes phosphorylation of TIMD2 and inhibits angiogenesis. SEMA4A promotes axon growth cone collapse and inhibits axonal extension by providing local signals to specify territories inaccessible for growing axons.