Significance of cytokines and CD68‐positive microparticles in immune thrombocytopenic purpura

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Abstract
We investigated the significance of cytokines (soluble interleukin‐2 receptor, granulocyte‐macrophage colony‐stimulating factor, interleukin‐6, and interferon‐gamma) and CD68‐positive microparticles in immune thrombocytopenic purpura. Cytokines were measured by enzyme‐linked immunosorbent assay and microparticles were detected by flow cytometry. CD68 expression by histiocytic U937 cells incubated with lipopolysaccharide or cytokines was also assessed in a control study. The level of CD68‐positive microparticles was significantly higher in the patients with thrombocytopenia than in normal controls (p<0.01). The soluble interleukin‐2 receptor level was also significantly higher in patients than in controls (p20000/μl) had significantly higher levels of granulocyte‐macrophage colony‐stimulating factor and interleukin‐6 than the controls (p<0.05). When opsonized platelets were incubated with activated U937 cells, lipopolysaccharide and granulocyte‐macrophage colony‐stimulating factor caused an increase of CD68‐positive microparticles in the supernatant. These results suggest that granulocyte‐macrophage colony‐stimulating factor is released by activated T cells in immune thrombocytopenic purpura and activates monocyte/macrophage phagocytosis, resulting in an increase of circulating CD68‐positive microparticles and enhanced platelet destruction.