Molecular Characterization of Endothelial Monocyte Antigens

Previous reports have demonstrated the existence of an alloantigenic system not detectable on resting T and B lymphocytes, which is expressed on renal capillary endothelium and monocytes (1,2). In contrast to resting B lymphocytes, EBV-transformed B cells appeared to express EM antigens as shown by absorption studies. These endothelium monocyte (EM) antigens appear to be important in transplantation immunology since EM antibodies are present in the circulation during acute graft rejection and can be eluted from biopsies taken from a graft that is being rejected (2–6). Although the genetics is not completely clear, EM antigens have shown to be polymorphic (7). However, the molecular localization of these antigens has been a question of debate. Therefore, this was studied by analyzing immunoprecipitates obtained of EBV-transformed B cells using EM alloantisera. Gel electrophoretic techniques showed that EM alloantigenic determinants are located on a subset of HLA-DR molecules.