Effect of IgG anti-Rho(D) in adult patients with chronic autoimmune thrombocytopenia.

Seventeen adult patients with chronic (15 cases) or acute (two cases) autoimmune thrombocytopenia (ITP) were given intravenous and/or intramuscular injections of 0.75-4.5 mg of IgG anti-Rho(D) over a period of 1-5 days. Significant elevations of the platelet count (increments greater than 50 X 10(9)/liter) resulted in 13 of 15 Rh-positive patients but not in either of two Rh-negative patients. Heat-aggregated human albumin given to one of the Rh-negative patients also did not lead to a significant increase of the platelet count. The elevation of the platelet counts in Rh-positive patients after IgG anti-Rho(D) administration was often transient (less than 4 weeks), but long-term benefit (greater than 5 months) was achieved in five cases. The IgG concentration on RBC from five Rh-positive patients studied increased from a usually undetectable value before to approximately 700-1,700 IgG molecules/per RBC after anti-Rho(D) administration resulting in a strongly positive direct antiglobulin test. Nevertheless, an overt clinical hemolysis was seen in only one patient. The clearance of autologous 51Cr-labeled RBC was determined in four patients and was slightly enhanced in three and normal in one splenectomized patient. We conclude that the Fc receptor blockade involved in platelet sequestration was not associated with the induction of significant RBC clearance and that a reversible interaction of sensitized RBC with phagocytic cells and/or a low-grade destruction of these cells might be sufficient for the elevation of circulating platelets in the majority of patients with ITP.