O-glycoforms of polymeric IgA1 in the plasma of patients with IgA nephropathy are associated with pathological phenotypes

BACKGROUND

IgA1 O-glycosylation plays an important role in the pathogenesis of IgA nephropathy (IgAN). However, variations in IgA1 O-glycoforms have not been explored. We aimed to investigate the IgA1 O-glycoforms in the hinge region (HR) of polymeric IgA1 and then evaluate the association between IgA1 O-glycoforms and crescent formation in IgAN.

METHODS

The discovery cohort (cohort 1) comprised 11 crescentic IgAN patients, 10 noncrescentic IgAN patients and 10 healthy controls, and the validation cohort (cohort 2) comprised 11 crescentic IgAN patients, 9 noncrescentic IgAN patients, and 9 healthy controls. A total of 143 IgAN patients with different crescent percentages (cohort 3) were also included. Polymeric IgA1 was purified from the plasma of the participants. The variation in O-glycoforms was evaluated by estimating the molecular weights of IgA1 hinge glycopeptides using reversed-phase liquid chromatography (LC) and tandem mass spectrometry under electron-transfer/higher-energy collision dissociation (EThcD) fragmentation mode.

RESULTS

In discovery cohort (cohort 1), the numbers of GalNAc bound to one HR were lower in IgAN patients. The proportions of GalNAc3 (defined as O-glycans bound to one HR at 3 sites) and GalNAc4 were highest in crescentic IgAN patients followed by noncrescentic IgAN patients and were lowest in healthy controls (GalNAc 3: 9.92%±3.37% vs 6.65%±1.53% vs 4.05%±1.24%; P < 0.001; GalNAc4: 45.91%±4.75% vs 41.13%±2.95% vs 40.98%±2.95%; P = 0.004). The proportions of GalNAc5 and GalNAc6 were lowest in crescentic IgAN patients followed by noncrescentic IgAN patients and were highest in healthy controls (GalNAc5: 50.15%±4.27% vs 47.92%±4.09% vs 45.87%±3.79%, P = 0.028; GalNAc6: 6.58%±2.53% vs 6.04%±1.35% vs 4.65%±2.27%; P = 0.034). These results were consistent in the validation cohort (cohort 2); In another cohort with 143 patients with different crescents percentage (cohort 3), the numbers of GalNAc in polymeric IgA1 decreased with increasing percentage of crescents.

CONCLUSIONS

The numbers of GalNAc in IgA1 HRs were lower in IgAN patients, especially in crescentic IgAN patients, and may be associated with a severe IgAN phenotype.

Crescentic IgA nephropathy along with simultaneous cellular and antibody-mediated rejection in a kidney transplant leading to rapid allograft failure

Crescentic IgA Nephropathy in a renal transplant can lead to rapid loss of graft function despite treatment. Concurrent treatment-resistant acute cellular and antibody-mediated rejection make the prognosis even worse.

Coexistence of atypical hemolytic uremic syndrome and crescentic IgA nephropathy treated with eculizumab: a case report

Rapid progression to end-stage renal disease has been reported in a minority of patients with immunoglobulin A (IgA) nephropathy. In particular, crescentic IgA nephropathy has a poor prognosis in patients with a higher initial serum creatinine level. The complement system plays an important role in the pathogenesis of crescentic IgA nephropathy. Atypical hemolytic uremic syndrome (aHUS), which is characterized by thrombotic microangiopathy, is distinct from Shigatoxin-induced HUS and thrombotic thrombocytopenic purpura. aHUS is associated with dysregulation of the alternative complement system. Eculizumab, an anti-C5 antibody, is effective in limiting complement activation in patients with paroxysmal nocturnal hemoglobinuria, aHUS, or refractory IgA nephropathy in some case reports. We herein report the case of a 42-year-old man with acute kidney injury (AKI) clinically and histologically diagnosed with the coexistence of aHUS and crescentic IgA nephropathy. The patient was treated with steroids, plasmapheresis, and hemodialysis; however, eculizumab treatment was initiated on hospital day 21 due to resistance to and dependence on the conventional aggressive therapy. Clinical remission of aHUS was achieved on day 70, but the renal function failed to recover from dialysis dependence. To the best of our knowledge, this is the first report showing the clinical course of a refractory patient with the coexistence of aHUS and crescentic IgA nephropathy treated with eculizumab. This case highlights the clinical importance of early diagnosis and appropriate initiation of eculizumab for the treatment of this type of AKI.