Test Details: CD8 is a transmembrane glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). Along with the TCR, the CD8 co-receptor plays a role in T cell signalling and aiding with cytotoxic T cell-antigen interactions. CD8 is widely used as a marker of cytotoxic T lymphocytes. CD8+ cells are called T cell suppressor cells, cytotoxic T cells and OKT8. The CD8 molecule is a marker for cytotoxic T cell population. It is expressed in T cell lymphoblastic lymphoma.