CD45RA is a splice variant of the CD45 protein, encoded by the PTPRC gene, and is a transmembrane glycoprotein with receptor-type protein tyrosine phosphatase activity. It contains the exon 4 in its structure, which distinguishes it from other CD45 isoforms like CD45RO. CD45RA is predominantly expressed on na?ve T cells, indicating their potential for activation and differentiation into effector and memory T cells. Its unique extracellular domain, composed of fibronectin type III repeats, is crucial for modulating intracellular signaling pathways, particularly the T-cell receptor （TCR） signaling cascade. The presence of CD45RA on proliferating cells also serves as a marker for tracking clonal expansions in immune responses.