Fas/APO-1 (CD95) expression in myelodysplastic syndromes. 
Increased apoptosis of myeloid precursors appears to contribute to the pathophysiology of cytopenias in myelodysplastic syndromes (MDS).  Fas /APO-1(CD95) is a cell surface protein inducing an apoptotic signal after its binding to Fas ligand or to a functional anti-Fas antibody.  Here we studied Fas expression by immunocytochemistry on marrow slides from 30 cases of MDS.  Increased Fas expression in erythroblasts and/or immature granulocytes, compared to controls, was seen in 12 (40%) of the cases.  In addition, in 16 of the 18 cases with > or = 5% marrow blasts, a variable proportion of blasts expressed Fas.  Increased apoptosis was found by morphological analysis and/or TUNEL technique in marrow cells from 8 of the 26 cases analyzed (31%) The ability of Fas antigen to trigger apoptosis was studied after addition of a functional anti Fas antibody in 5 of the patients with Fas overexpression.  Addition of this antibody, however, only lead to mild increase of apoptosis in immature granulocytes (but not other myeloid cells) in 2 of the 5 cases.  Thus, increased Fas expression is seen in myeloid and/or blast cells in the majority of MDS cases.  However, the relationship between this finding and increased apoptosis in MDS still remains to be established.