New approaches for detecting complement-fixing antibodies

Purpose of review Complement-fixing human leukocyte antigen (HLA) antibodies are a contraindication to solid organ transplant. Newer solid phase assays for HLA antibody definition have created treatment quandaries because many more antibodies are detected by these methods. It is unclear which of the antibodies identified are clinically relevant as all IgG-binding antibodies are detected whether they can fix complement or not. Recent findings Two methods have been developed to assess complement-fixing capability in the solid phase assays: C4d and C1q. These assays, especially the sensitive C1q method, have been reported to more closely correlate with renal and cardiac graft dysfunction, rejection, and graft failure than antibodies detected only by the traditional IgG method. Additionally, the C1q method can be used to predict and monitor desensitization status pre and posttransplant in patients being treated with intravenous immunoglobulin. Summary The availability of these complement-fixing assays provides new tools for making treatment decisions by discriminating antibodies with known clinical relevance and to assess the clinical relevance of binding antibodies that cannot fix complement. The assays also provide a means of assessing when to transplant a patient undergoing desensitization or when to discontinue augmented immunosuppression for resolving antibody-mediated rejection.