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The Sema domain, a protein interacting module, of semaphorin 4A (Sema4A) Sema4A is expressed in immune cells and is thus termed an "immune semaphorin". It plays critical roles in T cell-DC interactions in the immune response. It has been reported to enhance activation and differentiation of T cells in vitro and generation of antigen-specific T cells in vivo. The function of Sema4A in the immune response implicates its role in infectious and noninfectious diseases. Sema4A exerts its function through three receptors, namely Plexin B, Plexin D1, and Tim-2. Sema4A belongs to the class 4 transmembrane semaphorin family of proteins. Semaphorins are regulatory molecules in the development of the nervous system and in axonal guidance. They also play important roles in other biological processes, such as angiogenesis, immune regulation, respiration systems and cancer. TThe Sema domain is located at the N-terminus and contains four disulfide bonds formed by eight conserved cysteine residues. It serves as a receptor-recognition and -binding module.
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