CD99 antigen, a 32 kD T-Cell surface
glycoprotein, is also known as MIC2, E2, 12E7, HuLy-m6 or FMC29. This antigen is
expressed on the cell membrane of some lymphocytes, cortical thymocytes, and
granulosa cells of the ovary. CD99 is also expressed by most pancreatic islet
cells, Sertoli cells of the testis and some endothelial cells. Mature
granulocytes express limited or no CD99. Engagement of distinct epitopes on CD99
rapidly induces T-cell death by a novel caspase-independent pathway. CD99 is a
highly restricted cell surface antigen of Ewing’s sarcoma and primitive
peripheral neuroectodermal tumors; therefore, CD99 is a sensitive marker for
Ewing’s sarcoma and peripheral neuroectodermal tumors and is useful in the
differential diagnosis of small blue cell
tumors.