PBDX is the XG blood group gene

We have identified the Xg a antigen, encoded by the XG blood group gene, by employing rabbit polyclonal and mouse monoclonal antibodies raised against a peptide derived from the N-terminal domain of a candidate gene, referred to earlier as PBDX . In indirect haemagglutination assays, these anti-peptide antibodies react with Xg(a+) but not Xg(a−) erythrocytes. In antibody-specific immobilization of antigen (ASIA) and immunoblot assays, the anti-peptide antibodies react with the same molecule as does human anti-Xg a . Therefore, by its identity with PBDX, Xg a is identified as a cell-surface protein that is 48% homologous to CD99 (previously designated the 12E7 antigen), the product of MIC2 which is tightly linked to XG . PBDX is renamed here XG .