Neutropenia and anaemia due to carbimazole-dependent antibodies

Carbimazole-dependent antibodies to erythrocytes were detected in the sera of three anaemic patients who had been treated with carbimazole for hyperth yroidism. By the use of Rh-null-typed erythrocytes, we could show that some of these were directed against the proteins of the Rh complex. Carbimazole -dependent antibodies eluted from erythrocytes showed no binding to other b lood cells. One patient also presented with neutropenia and mild thrombocyt openia. Additional carbimazole-dependent antibodies against the neutrophil- specific Fc gamma receptor IIIb (Fc gamma RIIIb, CD16b) and the broadly exp ressed platelet endothelial cell adhesion molecule 1 (PECAM-1; CD31) were d etected in this patient's serum. Surprisingly, the PECAM-1-reactive drug-de pendent antibodies were also detectable in the sera of the other two patien ts with normal leucocyte and platelet counts. We assume that carbimazole ca n induce cell lineage-specific drug-dependent antibodies that cause cytopen ia and also drug-dependent antibodies against the broadly expressed PECAM-1 molecule that may cause mild but not severe cytopenia.