CD45RA is an isoform of CD45 (leukocyte common antigen), with a molecular weight of approximately 220kDa or 180kDa (the specific value may vary depending on different studies or measurement methods). This protein is primarily expressed on B cells, monocytes, and a small subset of T cells. In T cells, CD45RA plays a crucial role in regulating immune receptor signaling pathways, modulating T cell activation and suppression. In NK cells, CD45RA is essential for the exertion of cytotoxicity. In the thymus, the expression of CD45RA increases as T cells mature, regulating the transition from naive T cells to mature T cells. Additionally, the protein encoded by the CD45RA gene possesses dephosphorylating activity, which can affect the proliferation, differentiation, and activation of immune cells. In medical applications, CD45RA is used in combination with other B-cell antibodies for the study of B-cell lymphomas. It also plays a key role in the diagnosis of diseases such as acute lymphocytic leukemia and aplastic anemia.