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Original Article |
Correspondence to: Richard M. Pope, Division of Rheumatology, Department of Medicine, Northwestern University Medical School, 745 North Fairbanks Ct., Tarry 3-770, Chicago, IL 60611. Tel:312-503-8003 Fax:312-503-0994 E-mail:rmp158{at}nwu.edu.
Macrophages differentiated from circulating peripheral blood monocytes are essential for host immune responses and have been implicated in the pathogenesis of rheumatoid arthritis and atherosclerosis. In contrast to monocytes, macrophages are resistant to Fas-induced cell death by an unknown mechanism. FLICE (Fas-associated death domainlike interleukin 1ßconverting enzyme)inhibitory protein (Flip), a naturally occurring caspase-inhibitory protein that lacks the critical cysteine domain necessary for catalytic activity, is a negative regulator of Fas-induced apoptosis. Here, we show that monocyte differentiation into macrophages was associated with upregulation of Flip and a decrease in Fas-mediated apoptosis. Overexpression of Flip protected monocytes from Fas-mediated apoptosis, whereas acute Flip inhibition in macrophages induced apoptosis. Addition of an antagonistic Fas ligand antibody to Flip antisensetreated macrophages rescued cultures from apoptosis, demonstrating that endogenous Flip blocked Fas-induced cell death. Thus, the expression of Flip in macrophages conferred resistance to Fas-mediated apoptosis, which may contribute to the development of inflammatory disease.
Key Words: monocytes, macrophages, apoptosis, Flip, Fas
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