PTPRC

PTPRC, also known as protein tyrosine phosphatase receptor type C or CD45, is a gene that encodes a receptor-type protein tyrosine phosphatase expressed primarily on leukocytes. It functions as a key regulator of signal transduction in lymphocytes, influencing activation and development of T and B cells. CD45 is widely used as a pan-leukocyte marker in immunology because its expression is found on most nucleated hematopoietic cells.

The CD45 protein has a typical receptor-type organization: an extracellular region composed of multiple fibronectin type III–like repeats, a single transmembrane segment, and a cytoplasmic region containing two intracellular phosphatase domains. The D1 domain is catalytically active, whereas the D2 domain is generally regulatory and often catalytically inactive in CD45. The extracellular portion undergoes extensive alternative splicing, generating a family of CD45 isoforms (such as CD45RA, CD45RB, CD45RC, and combinations like CD45RABC). Expression of these isoforms varies with cell type and activation state; naïve T cells typically express CD45RA, while memory T cells commonly express CD45RO, which lacks certain exons.

Functionally, CD45 modulates signaling by dephosphorylating specific substrates, including Src family kinases like Lck, thereby shaping TCR and BCR signaling thresholds. This regulation affects lymphocyte development, activation, differentiation, and immune responses. The gene is also studied in the context of immune-related disorders and cancer, where altered CD45 expression or function can influence immune cell behavior.

In research and clinical settings, PTPRC/CD45 remains an essential marker for identifying leukocytes and characterizing immune cell subsets, while its regulatory role in signaling continues to be a focus of immunology and hematology studies.