Abstract
Autoantibodies to the angiotensin II type 1 receptor (AT1R) are thought to be important in antibody-mediated rejection (AMR), especially in the absence of anti-HLA antibodies. We used a variety of methods to examine the specificity of a commercially available kit designed to quantitate anti-AT1R antibodies. We found that fibrin formation in serum samples from patients awaiting cardiac transplantation with ventricular assist devices (VADs) can produce falsely elevated anti-AT1R values. In addition, absorption studies with a variety of cell lines with or without expression of human AT1R, and those that express xenoantigens, suggest that many of the antibodies detected in the AT1R test system are heterophilic and have reactivity to xenoantigens. Furthermore, we provide data that show that reactivity to the sialic acid Neu5Gc is a common finding among samples that are highest in anti-AT1R levels. We conclude that a common laboratory method for quantitation of anti-AT1R antibodies is nonspecific and overestimates the frequency of true positives. A reevaluation of the role that anti-AT1R antibodies play in allograft function and patient outcomes is warranted.