Introduction. Donor specific antibodies (DSA) are associated with an increased risk of chronic antibody mediated rejection (CAMR). DSA characterization by single antigen bead (SAB) assays has enhanced donor selection. Importantly, complement-binding DSA has a strong association with CAMR. The novel complement-fixing SAB binding assays (C1q/C3d) may add more information to the “traditional” IgG SAB assay (measures total IgG) as far as prediction of CAMR, however data regarding this is lacking. The aim of this study was to compare the sensitivities (s) of the IgG, C1q and C3d SAB assays in detecting complement-binding antibodies.

Methods. Sera (n=20) from sensitized patients, previously used for serologic Class I HLA typing by complement-dependent cytotoxicity (CDC) method were tested with 3 different SAB assays (IgG[undiluted and 1:8 dilution], C1q, C3d). Serological anti-HLA specificities were compared with those obtained by IgG, C1q and C3d SAB assays and sensitivities were established.

Results. 24 complement-fixing specificities were defined by CDC. IgG SAB identified 24 specificities (s 24/24 = 1, OR Infinity), C1q recognized 21 (s 21/24 = 0.875, OR 89.63) and 12 were obtained by C3d assay (s 12/24 = 0.500, OR 48.23).Pearson correlation showed the association between: 1) C1q and IgG SAB assays (cut off C1q SAB 1000 MFI, cut off IgG SAB 5000 MFI: r=0.347 p<0.0001; and 2) C3d and IgG SAB assays (cut off 500 MFI C3d SAB, 5000 MFI for IgG SAB: r= -0.173, p=0.279). Conclusions. For Class I anti-HLA antibodies, IgG SAB was more sensitive in detecting complement-binding antibodies when compared to C1q/C3d SAB assays.

CITATION INFORMATION: Moreno Gonzales M, Mitema D, Smith B, Schinstock C, Stegall M, Gandhi M. Comparison Between IgG, C1q and C3d Single Antigen Bead Assays in Detecting Class I Complement-Binding Anti-HLA Antibodies. Am J Transplant. 2017;17 (suppl 3).

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