Semaphorin 4D (SEMA4D)

CD100 was first identified as a cell surface protein of resting T cells; previous studies had shown that it was involved in lymphocyte activation. Hall et al. (1996) cloned CD100 from a cDNA library of phytohemagglutinin-activated human T cells. Sequence analysis showed that CD100 encodes an 863-amino acid polypeptide containing a secretory signal sequence, a single transmembrane domain, an immunoglobulin (Ig)-like domain, and a conserved 500-amino acid sema domain. Thus, Hall et al. (1996) stated that CD100 is a member of the semaphorin family and the first semaphorin believed to be involved in the immune system. See SEMA3F and SEMA3B. Northern blot analysis revealed that CD100 is expressed primarily as a 4.5-kb message in a variety of tissues, both hematopoietic and nonhematopoietic.