P06127

CD5 also known as LEU1 is a crucial transmembrane glycoprotein predominantly expressed on approximately 70% of normal peripheral blood lymphocytes and nearly all T lymphocytes in the thymus and peripheral blood. CD5′s primary function involves modulating T cell activation; when T cells are activated through the T cell receptor (TCR), CD5 undergoes tyrosine phosphorylation, which is essential for regulating T cell responses. Notably, absence of CD5 leads to hyper-responsiveness of T cells to TCR-mediated activation, highlighting CD5′s role in maintaining immune homeostasis. CD5 interacts with the TCR/CD3-ζ chain and the Src family kinase Lck p56, significantly enhancing Lck′s kinase activity by 10- to 15-fold when bound to CD5.