CD45

CD45, also known as leukocyte common antigen (LCA), is a protein tyrosine phosphatase expressed on the surface of most leukocytes, including T cells, B cells, and macrophages. This molecule plays a critical role in the activation and function of the immune system. CD45 is encoded by the PTPRC (protein tyrosine phosphatase, receptor type C) gene in humans.

Function

CD45 is essential for efficient antigen-induced T cell and B cell receptor signaling. It acts by dephosphorylating specific phosphotyrosines on various enzymes involved in signal transduction pathways, thereby modulating their activity. This regulation is crucial for the development, activation, and survival of lymphocytes. Moreover, CD45 has been implicated in the control of cell growth and differentiation.

Isoforms

The CD45 molecule exists in multiple isoforms due to alternative splicing of the exons that encode the extracellular domain. These isoforms, which include CD45RA, CD45RB, CD45RC, and CD45RO, are differentially expressed on various cell types and at different stages of T cell and B cell maturation. The expression of specific CD45 isoforms serves as a marker for distinguishing among subsets of lymphocytes and their state of activation.

Clinical Significance

Alterations in CD45 expression or function have been associated with several diseases. For example, reduced or abnormal expression of CD45 has been observed in certain leukemias and lymphomas, making it a target for diagnostic and therapeutic strategies. Additionally, because of its pivotal role in immune regulation, CD45 is being explored as a potential target for immunotherapy in various autoimmune diseases and cancers.

Research

Research on CD45 continues to uncover its complex role in the immune system. Studies are focused on understanding how CD45 regulates lymphocyte activation and the signaling pathways involved. There is also interest in developing therapeutic agents that can modulate CD45 activity to treat immune-related conditions.

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