SIGNIFICANCE OF CYTOKINES AND CD68-POSITIVE MICROPARTICLES IN IMMUNE THROMBOCYTOPENIC PURPURA

We investigated the significance of cytokines (soluble interleukin-2 r eceptor, granulocyte-macrophage colony-stimulating factor, interleukin -6, and interferon-gamma) and CD68-positive microparticles in immune t hrombocytopenic purpura. Cytokines were measured by enzyme-linked immu nosorbent assay and microparticles were detected by flow cytometry. CD 68 expression by histiocytic U937 cells incubated with lipopolysacchar ide or cytokines was also assessed in a control study. The level of CD 68-positive microparticles was significantly higher in the patients wi th thrombocytopenia than in normal controls (p<0.01). The soluble inte rleukin-2 receptor level was also significantly higher in patients tha n in controls (p<0.01), but the other cytokines did not show a signifi cant difference. However, patients with severe thrombocytopenia (plate let count > 20 000/mu l) had significantly higher levels of granulocyt e-macrophage colony-stimulating factor and interleukin-6 than the cont rols (p<0.05). When opsonized platelets were incubated with activated U937 cells, lipopolysaccharide and granulocyte-macrophage colony-stimu lating factor caused an increase of CD68-positive microparticles in th e supernatant. These results suggest that granulocyte-macrophage colon y-stimulating factor is released by activated T cells in immune thromb ocytopenic purpura and activates monocyte/macrophage phagocytosis, res ulting in an increase of circulating CD68-positive microparticles and enhanced platelet destruction.