The successful treatment of idiopathic thrombocytopenic purpura with the low dose non specific IgG component of anti D immunoglobulin.

Five patients with ITP were treated with 2 gram intravenous infusions of intramuscular human non specific immunoglobulin (IMIg). Increased platelet counts similar to those achieved with intravenous Rhesus anti D immunoglobulin were observed in four patients. 5000 iu anti D immunoglobulin contain up to 2 g of IMIg, and the clinical responses seen in ITP patients treated with anti D may therefore be attributed to this non specific fraction. This was supported by the in vitro finding that adsorption of the rhesus specific IgG from anti D immunoglobulin did not reduce its inhibitory effect on monocyte Fc receptor function. The dose of intravenous IMIg which produced a response in ITP was less than 2% of the recommended standard dose of intravenous immunoglobulin. This correlated with the higher concentration of IgG polymers in IMIg, and we suggest therefore that the mechanism of action of this material is due to the inhibitory effect of its polymeric IgG fraction on low affinity monocyte/phagocyte Fc receptors.