High-dose intravenous gamma globulin reduces macrophage colony-stimulating factor levels in idiopathic thrombocytopenic purpura.

We investigated the effect of high-dose intravenous gamma globulin therapy on the plasma level of macrophage-colony stimulating factor (M-CSF) level in 13 patients with chronic idiopathic thrombocytopenic purpura. M-CSF and interleukin-6 levels were determined by enzyme-linked immunosorbent assay. The mean +/- S.D. level of M-CSF in the patients was 1235 +/- 439 U/ml, and the level in 8 patients was higher than the mean + S.D. (903.6 U/ml) in normal controls. All 8 patients had steroid-refractory disease. M-CSF levels were significantly correlated with the serum levels of interleukin-6 (r = 0.66, P < 0.05). Interleukin-6 levels were also significantly raised in the high M-CSF group compared with the normal M-CSF group (P < 0.05). In the whole patient population, M-CSF levels decreased, but not significantly, after intravenous gamma globulin, while interleukin-6 decreased significantly. However, in the patients with high pretreatment M-CSF levels, both M-CSF and interleukin-6 decreased significantly after treatment (M-CSF, 4 weeks, P < 0.05; IL-6, 1 week, P < 0.05, 4 weeks, P < 0.01). These findings suggest that high-dose intravenous gamma globulin causes thrombocytosis by the decrease of M-CSF levels in idiopathic thrombocytopenic purpura.