62-OR

Abstract

Aim The presence of C1q antibodies may be important for assessing the risk of antibody mediated rejection (AMR) in solid organ transplants. We studied the correlation between the C1q-single antigen bead assay (C1q-SAB) with the long-incubation complement-dependent lymphocytotoxicity assay (CDC) and the IgG-single antigen bead assay (IgG-SAB). Methods 60 reference sera (38 Class I and 22 Class II) from the UCLA serum exchange program were characterized using the CDC, Luminex PRA (Gen-probe Inc.) and IgG-SAB (One Lambda Inc.) assays. We also tested pre- and post-transplant sera from 16 renal allograft recipients. All patients had persistent posttransplant DSA as demonstrated by the IgG-SAB assay. Results The C1q-SAB assay showed 85% concordance with the CDC assay as 15% of the CDC positive antibodies were negative in the C1q test. Correlation between the SAB MFI and C1q positivity showed that 90% of sera with the MFI of >18,000 in the IgG-SAB assay were C1q binding. A retrospective study of 16 renal transplant recipients developing post-transplant donor specific antibodies (DSA) showed 5 of 9 patients diagnosed as C4d+ AMR displayed C1q positive DSA (P = 0.145). One out of 7 patients without AMR displayed C1q binding DSA. Conclusions Our data indicate that antibody strength correlates with the capacity to bind C1q (Fig. 1). However we identified a subset of antibodies that displayed high MFI values and CDC positivity, that failed to bind C1q. The development of C1q positive DSA was not significantly associated with positive C4d staining on the graft. Additional studies are required using a larger cohort of patients to verify these findings [Fig. 1]. Download : Download full-size image