In vivo administration of intravenous immunoglobulin (IVIg) can lead to enhanced erythrocyte sequestration

Enhanced erythrocyte sequestration is one of the very few major adverse effects of intravenous immunoglobulin (IVIg). Mg contains high molecular weight IgG complexes (similar to 300 kDa) which, in the presence of serum, mimic immune complexes by activating complement, binding to CR1 of red blood cells (RBC) (CD35) and mediating erythrophagocytosis. Four of seven patients undergoing Mg therapy showed significant drops in haematocrit and haemoglobin that were not due to isoantibodies in the Mg. Prior to treatment, patients' RBC carried IgG and complement (C') 3d that were not bound as immune complexes via CR1 (CD35). The patients whose RBC bound immune complex-like moieties and showed drops in haematocrit and haemoglobin subsequent to Mg were young adults (22-35 years); older patients (50-69 years) showed no ill effects. In the presence of complement, RBC of young patients bound Mg complexes in vitro while those of older patients did not. It is not the absolute levels of erythrocyte-associated IgG or C'3 fragments, neither pre- nor post-therapy, which are predictive of Mg associated decreases in haematocrit and haemoglobin levels. Patient age and RBC inability to bind the Mg immune complex-like moieties in vitro both appear to be predictors of resistance to sequestration after in vivo treatment with Mg. (C) 1999 Academic Press.