Cluster Of Differentiation 99 (CD99)

CD99 is a cell surface glycoprotein involved in leukocyte migration, T-cell adhesion, ganglioside GM1 and transmembrane protein transport, and T-cell death by a caspase-independent pathway. In addition, the encoded protein may have the ability to rearrange the actin cytoskeleton and may also act as an oncosuppressor in osteosarcoma.

Cyclophilin A binds to CD99 and may act as a signaling regulator of CD99. This gene is found in the pseudoautosomal region of chromosomes X and Y and escapes X-chromosome inactivation. Two transcript variants encoding different isoforms have been found for this gene.It is expressed on all leukocytes but highest on thymocytes and is believed to augment T-cell adhesion,apoptosis of double positive t cells,and participates in migration and activation.