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Blood, 15 August 2008, Vol. 112, No. 4, pp. 1240-1248.
Prepublished online as a Blood First Edition Paper on May 29, 2008; DOI 10.1182/blood-2008-02-138131.
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IMMUNOBIOLOGY
The cytoplasmic tail of CD45 is released from activated phagocytes and can act as an inhibitory messenger for T cells
Stefanie Kirchberger1,
Otto Majdic1,
Stefan Blüml1,
Catharina Schrauf1,
Judith Leitner1,
Christopher Gerner2,
Wolfgang Paster3,
Nina Gundacker2,
Maria Sibilia2, and
Johannes Stöckl1
1 Institute of Immunology,
2 Institute of Cancer Research, and
3 Department of Molecular Immunology, Medical University of Vienna, Vienna, Austria
CD45 is the prototypic transmembrane protein tyrosine phosphatase (PTP), which is expressed on all nucleated hematopoietic cells and plays a central role in the integration of environmental signals into immune cell responses. Here we report an alternative function for the intracellular domain of CD45. We dis-covered that CD45 is sequentially cleaved by serine/metalloproteinases and -secretases during activation of human monocytes and granulocytes by fungal stimuli or phorbol 12-myristate 13-acetate but not by other microbial stimuli. Proteolytic processing of CD45 occurred upon activation of monocytes or granulocytes but not of T cells, B cells, or dendritic cells and resulted in a 95-kDa fragment of the cytoplasmic tail of CD45 (ct-CD45). ct-CD45 was released from monocytes and granulocytes upon activation-induced cell death. Binding studies with ct-CD45 revealed a counter-receptor on preactivated T cells. Moreover, T-cell proliferation induced by dendritic cells or CD3 antibodies was inhibited in the presence of ct-CD45. Taken together, the results of our study demonstrate that fragments of the intracellular domain of CD45 from human phagocytes can function as intercellular regulators of T-cell activation.

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