What is the role of CD45 in T cell activation?

CD45, which is also known as leukocyte common antigen (LCA) and protein tyrosine phosphatase receptor type C (PTPRC), plays a major role in the immune system and regulates T-cell receptor signaling. CD45 activates Lck, a tyrosine kinase. Lck in turn phosphorylates the T-cell antigen receptor (TCR), which allows T-cells to respond to antigens.