A Novel Biomarker for Post-Transplant Recurrent IgA Nephropathy.

BACKGROUND: The serum levels of galactose-deficient immunoglobulin (Ig)A1 (Gd-IgA1) represent the most promising candidate biomarker for IgA nephropathy (IgAN). The aim of this study was to evaluate the serum levels of Gd-IgA1 as a novel noninvasive biomarker for post-transplant IgAN recurrence.

METHODS: Serum Gd-IgA1 levels of 18 patients with recurrent IgAN were compared with control renal transplant recipients (n = 23) with non-recurrent IgAN and control non-transplant IgAN patients (n = 44) and healthy relatives (n = 11). Serum Gd-IgA1 levels of patients were measured with the use of KM55 enzyme-linked immunosorbent assay (ELISA). The effects of serum Gd-IgA1 concentrations on IgAN recurrence, post-transplant events, and graft survival were evaluated.

RESULTS: All recurrent IgAN patients presented with renal dysfunction (mean serum creatinine, 1.62 ± 0.39 mg/dL) and detectable proteinuria at the time of diagnosis. Serum Gd-IgA1 levels of recurrent IgAN patients (8735 ± 10854 ng/mL [log10: 3.71 ± 0.45]) were significantly higher than those of non-recurrent IgAN patients (4790 ± 6089 ng/μL [log10: 3.31 ± 0.64]) (P = .027). Serum Gd-IgA1 levels of non-transplant IgAN patients were significantly higher (8791 ± 8700 ng/μL [log10: 3.79 ± 0.36]) than those of non-recurrent IgAN patients (4790 ± 6089 ng/μL [log10: 3.31 ± 0.64]) and healthy relatives (2615 ± 1611 ng/μL [log10: 3.34 ± 0.27]) (P < .001 and P = .021, respectively). Receiver-operating characteristic curve analysis revealed that the area under the curve for recurrence of IgAN was 0.69 (0.53-0.85) for serum Gd-IgA1 (P = .038). Biopsy-confirmed allograft rejection rates were similar in the recurrent IgAN group [3 (17%)] compared with the non-recurrent IgAN [6 (26%)] group (P = .47). Graft failure rate was not also significantly different in the recurrent IgAN group [4 (22.2%)] compared with the non-recurrent IgAN group [2 (8.7%)] (P = .224).

CONCLUSIONS: This novel lectin-independent Gd-IgA1 ELISA that can detect serum Gd-IgA1 in patients with recurrent IgAN can be used as a biomarker for diagnosis and activity assessment of post-transplant recurrent IgAN.