OR52 AT1R antibody in pediatric heart transplant patients: What are we really detecting

Aim The frequency and impact of AT1R antibodies in pediatric heart transplantation has not been well studied. Our aim was to measure AT1R antibodies (AT1R-Ab) in this patient population and pediatric controls and to assess for non-specific reactivity in this assay. Methods We included 42 patients ( n  = 154 samples) for whom pre- and post-transplant sera and HLA Ab data were available. AT1R-Ab were measured by ELISA (One Lambda Inc.). Samples were tested/interpreted as per product insert. Age-matched, sex-balanced, non-transplant patient controls ( n  = 27) were collected from cardiac–catheterization laboratory. A subset with positive results ( n  = 52 sera from 20 patients) was re-tested following Adsorb Out (One Lambda Inc.). Analysis was performed using GraphPad. Results No significant difference was observed between patient and control AT1R antibody levels (Fig. 1). Values over 40 U/ml were detected in 38% of patient sera. Adsorbed sera had significantly decreased AT1R values vs non-adsorbed sera (Fig. 2A). There was no significant change in AT1R-Ab from pre- to post-transplant overall in either group but a higher proportion of patients changed from positive to negative using adsorbed vs non-adsorbed sera (20% vs 12.5%) (Fig. 2B and C). Conclusions A high proportion of patients and controls were positive for AT1R-Ab, however, many sera appear to be false positive, possibly due to BSA reactivity or incomplete blocking in the assay. As more assays for non-HLA Ab are added into our clinical algorithms, appropriate controls must be included. A ‘blank’ well would be useful in this assay for accurate interpretation of results. Association of the adsorbed and non-adsorbed AT1R-Ab to transplant outcomes is currently being assessed.