The effect of antithymocyte globulin on anti-human leukocyte antigen antibody detection assays

Background. We evaluated the effect of antithymocyte globulin (ATG) on anti-human leukocyte antigen (HLA) antibody assays. Methods. We tested sera from six in vivo ATG-treated kidney transplant patients after measuring serum concentrations, as well as six nonsensitized sera with ATG added in vitro. T- and B-cell complement-dependent cytotoxicity (CDC), flow cytometric (FXM), and solid-phase HLA class I and II assays based on antigen-coated microspheres and enzyme-linked immunosorbent assay (ELISA) were studied. Sera were then retested after treatment to remove ATG. Results. We found that ATG affects test results differently depending on whether sera is obtained from in vivo treated patients or added in vitro. In vitro treated sera produced ATG concentration-dependent positive results for T/B CDC, FXM, and flow bead testing for HLA I/II, while the ELISA-based assay was unaffected. In vivo treated sera from ATG-treated patients produced positive test results for T CDC and T/B FXM, while the B-cell CDC crossmatch remained negative. Solid phase assays were minimally affected using in vivo treated sera. After ATG extraction, all tests became negative. Conclusion. We conclude that ATG produces positive results in anti-HLA antibody testing, and treatment to remove ATG abolishes this effect. This treatment allows ATG-treated patients to be monitored for anti-HLA antibodies.