Serum flow cytometric C1q binding antibody analysis of renal recipients with low levels of sensitization.

Aim: Patients displaying flow cytometric crossmatch results within the grey zone of positivity are hard to evaluate, especially if they are undergoing their first transplantation. For these patients assays of donor-specific anti-HLA (human leukocyte antigen) antibodies with complement-fixing properties to cause cell lysis are important for antibody-mediated rejection and graft failure. The aim of this study was to detect the relevance of serum C1q-binding antibodies detected in renal recipients with grey zone crossmatch reactivity who were considered to show low levels of sensitization against their potential donors.

Method: This study includes 114 patients who were admitted for their first renal transplantation between September 2009 and August 2011, including 33 subjects considered by flow cytometric cross-match to be the sensitized group, whereas the remaining 81 recipients had negative results. We analyzed the accumulation of serum the immunoglobulin (Ig)G bound C1q on HLA-coated flow cytometric panel reactive antibody (FlowPRA) beads. The serum samples were retrospectively analyzed with [C1q]FlowPRA (HLA class I and II), which were collected during the pretransplantation period every 6 months and every week posttransplantation within the first month and every 3 months thereafter. All serum samples were analyzed for the presence of anti-FlowPRA IgG alloantibody. We compared the C1q FlowPRA-positive and-negative groups for the number of posttransplantation days that the serum creatinine level was below <2 mg/dL as a metric of graft function.

Results: With a mean follow-up of 492 ± 84 days, there was a significant difference between flow cytometric crossmatch results and creatinine decrease rate (P = .02). The serum creatinine decrease rates of the 9 C1q-positive versus the 15 C1q-negative subjects showed significant difference (P < .05).

Conclusion: C1q-binding antibody analysis shows the presence of serum antibodies capable of complement binding and antibody-mediated rejection, which could be useful to assess rejection risk among the "grey zone" of renal recipients with low levels of sensitization against their donors.