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A small number of reports have described cases of heparin-induced thrombocytopenia complicating hematological disorders with impaired platelet production. We describe the case of a 66-year-old woman with acute myeloid leukemia who exhibited unexplained refractoriness to platelet transfusion, while receiving heparin flushes, and was found to have anti-platelet factor 4 (PF4)/heparin antibodies with high optical density (OD) values (>2 units) detected by an enzyme-linked immunosorbent assay. After cessation of heparin flushes, her refractoriness to platelet transfusion resolved. We retrospectively confirmed that the OD values for anti-PF4/heparin antibodies declined gradually; refractoriness to platelet transfusion resolved when the OD values fell below 1.0 units. Given the absence of any other evident explanation for this phenomenon, and the correlation between the OD values for anti-PF4/heparin antibodies and the efficacy of platelet transfusions, we conclude that the patient's refractoriness to platelet transfusion was most likely caused by anti-PF4/heparin antibodies that had platelet-activating properties.

Spontaneous neutrophil apoptosis during culture was delayed by granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage CSF (GM-CSF), or dibutyryl-cyclic adenosine monophosphate (cAMP), whereas apoptosis was accelerated by cycloheximide or actinomycin D. G-CSF-mediated antiapoptosis was completely abolished by cycloheximide or actinomycin D, whereas GM-CSF-mediated antiapoptosis was not completely abolished by these inhibitors. Antiapoptosis induced by dibutyryl-cAMP was highly resistant to cycloheximide, and that induced by benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone was unaffected by cycloheximide. G-CSF- and GM-CSF-mediated antiapoptosis and phosphorylation of signal transducer and activator of transcription 3 (STAT3) and STAT5 were inhibited by AG490, an inhibitor of Janus kinase. The level of Mcl-1 protein was not associated with neutrophil apoptosis. The results suggest that (a) neutrophil survival in the resting state is primarily regulated by the constitutive synthesis of antiapoptotic proteins; (b) the prevention of spontaneous apoptosis is mediated through the protein synthesis-dependent and/or protein synthesis-independent mechanisms according to the stimuli used; and (c) the Janus kinase-STAT pathway is involved in G-CSF- and GM-CSF-mediated antiapoptosis.