Ultrasensitive Immunoassay Using a Novel Galactose-Deficient IgA1 Antibody and Its Clinical Application in the Diagnosis of IgAN.

INTRODUCTION

IgA nephropathy (IgAN) diagnosis remains dependent on invasive renal biopsy because currently available serologic biomarkers, including galactose-deficient IgA1 (Gd-IgA1), have limited diagnostic performance. This study aimed to develop and evaluate a high-sensitivity time-resolved fluorescence immunoassay (TRFIA) based on a novel anti-Gd-IgA1 monoclonal antibody (i.e., MH33) for Gd-IgA1 detection in IgAN.

METHODS

MH33 glycoepitope specificity was characterized using surface plasmon resonance (SPR). An MH33-based TRFIA was developed and evaluated for analytical and diagnostic performance in healthy controls (HCs), non-IgAN renal disease controls, and patients with IgAN, with comparison to a KM55-based assay.

RESULTS

SPR analysis showed that MH33 recognized a GalNAc-modified IgA1 hinge-region glycopeptide distinct from the KM55 epitope. The MH33-based TRFIA achieved a detection limit of 0.20 response units (RU)/ml, a quantification range of 0.20 to 600 RU/ml, and acceptable analytical performance (intra-/inter-assay coefficients of variation: 2.32%-5.49% and 3.97%-5.23%; recoveries: 89.80%-103.76%). Correlation with KM55 was moderate (IgAN, r = 0.23, P = 0.09). For distinguishing IgAN from combined controls (HCs and non-IgAN renal diseases), the MH33-based TRFIA yielded an area under the curve (AUC) of 0.90 (95% confidence interval [CI]: 0.86-0.93), compared with 0.78 (95% CI: 0.71-0.86) for KM55. At the optimal cutoff value (22.0 RU/ml), the assay achieved a specificity of 93.82% and sensitivity of 64.44%.

CONCLUSION

MH33-based TRFIA provides a sensitive approach for Gd-IgA1 detection and demonstrates favorable diagnostic performance for IgAN.