What is the mechanism of action of extracorporeal photopheresis (ECP)?

Updated: Nov 21, 2016
  • Author: Vikas Shrivastava, MD; Chief Editor: William D James, MD  Dirk M Elston, MD  more...
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There has been much speculation and research performed on the mechanism of action of extracorporeal photopheresis (ECP). It is known that the combination of 8-MOP and UVA radiation causes apoptosis of treated leukocytes and may cause preferential apoptosis of activated or abnormal T cells. [1] However, given that only a small percentage of the body's lymphocytes are treated, this is not likely the only mechanism of action. [1]

It has also been shown that upon reinfusion, ECP-treated apoptotic cells are taken up by antigen-presenting dendritic cells and macrophages. Through their interaction with these antigen-presenting cells and subsequently T and B lymphocytes, it is thought that the apoptotic cells promote immune tolerance, production of antigen-specific regulatory lymphocytes (CD4/8 T, B), and rebalance of an otherwise skewed immune system. [1, 9, 10] Supporting this is the down-regulation of inflammatory cytokines evident after ECP, with the subsequent increase in anti-inflammatory cytokine production. [6, 10, 11]

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