A Human Origin Anti-GdIgA1 Antibody and Its Implications in IgA Nephropathy

Background: IgA nephropathy (IgAN) is a common kidney disease where IgA deposits in the mesangial region, leading to mesangial cell proliferation. The underlying mechanism of IgAN remains unclear. The 'four-hit' hypothesis proposes that immune complexes formed by Galactose-deficient IgA1 (GdIgA1) and anti-GdIgA1 are crucial in the disease. However, the reasons for the deposition of these immunoglobulins in the mesangial region and their role in the disease process are not yet understood. Methods: The study collected GdIgA1 binding B cells from peripheral blood and sequenced through scBCR-Seq. A set of candidate antibodies was then synthesized and screened. Among these candidates, P4 showed high affinity for GdIgA1. The study investigated the binding affinity between mature and naïve P4 by reverting sequences to germline. Furthermore, P4, HAA, and KM55 were used to compare the GdIgA1 levels in IgAN patients and healthy controls. Finally, preliminary in vitro experiments were conducted to explore the role of P4 in the pathogenesis of IgAN. Results: High-affinity anti-GdIgA1 antibody (P4) was obtained in peripheral blood B cells (PBMCs), encoded by IGHV3-64D|IGHJ4, IGKV1-39|IGKJ2 and IGHA2, with a KD value of 1.508×10-8(M) to GdIgA1. Heavy chain dictated the binding to GdIgA1, while the light chain affected the affinity slightly. Most importantly, P4 in naïve state did not bind to GdIgA1 which indicate it was elicited by antigens other than GdIgA1. P4 exhibited comparable ability in measuring serum GdIgA1 levels with KM55 and HAA. A larger validation set conducted by third-party laboratory confirmed the potential of P4 in clinical usage. In vitro experiments revealed that co-stimulation of mesangial cells with P4 and GdIgA1 upregulates the Wnt pathway and potentially cause the proliferation of the mesangial cell while neither P4 nor GdIgA1 alone had this effect. Conclusion: In summary, the discovery of a high-affinity anti-GdIgA1 antibody, P4, holds promise for effectively measuring GdIgA1 levels. The study's findings suggest that high-affinity anti-GdIgA1 auto-antibodies may be induced by antigens mimicking the hinge region of GdIgA1. Moreover, the upregulation of the Wnt pathway by co-stimulation of P4 and GdIgA1 highlights the critical role of P4. Further exploration of the molecular and cellular mechanisms of IgAN may offer valuable insights. Funding: Government Support – Non-U.S.