THP-1 monocytic leukemia cells express Fas ligand constitutively and kill Fas-positive Jurkat cells

Normal human monocytes express Fas and are susceptible to Fas ligand (FasL) -induced apoptosis. Because the myeloid leukemia cell lines HL-60 and THP-1 can be differentiated into functional monocytes and macrophages, we studie d their expression of Fas and Fas ligand (FasL) to determine whether there were differentiation-associated changes in these proteins. THP-1, HL-60 and HCW-2, both before and after treatment with PMA, expressed high levels of Fas ligand (FasL), but did not express Fas. The Fast expressed by THP-1 cel ls was functional as measured by their ability to kill Jurkat T-cells by ap optosis. The THP-1 Fas gene appears to be silent, because bacterial lipopol ysaccharide (LPS) induced Fas expression in fully differentiated THP-1 cell s. Our results suggest that Fast expression by leukemia cells may account i n part for the pathophysiology of myeloid leukemia, and that PMA-differenti ated THP-1 cells, while possessing many of the functional properties of nor mal macrophages, are abnormal with respect to a major apoptotic pathway. (C ) 1999 Elsevier Science Ltd. All rights reserved.