Description
CD99 is an integral membrane protein of 185 amino acids that is expressed highly on cells of the hematopoietic system and on Ewing tumor cells. CD99 is supposed to be involved in cell adhesion and cell death and may participate through these processes in the differentiation of T- cell precursors at a critical stage of thymocyte differentiation when positive selection is known to occur. Engagement of the CD99 molecule by CD99 monoclonal antibodies has been shown to induce homotypic aggregation of various cell types. CD99 is expressed constitutively on all peripheral blood T-cells and becomes further up-regulated upon cell activation. CD99 mediates TCR/CD3-dependent activation of resting peripheral blood T-cells and specifically induces the production of the Th1 cytokines TNF-alpha and IFN-gamma