Primary IgA nephropathy: current challenges and future prospects

Abstract

IgA nephropathy (IgAN) is the most common form of primary glomerulonephritis worldwide, exhibiting a variable clinical and pathological course and significantly contributing to the global burden of chronic kidney disease and end-stage renal disease. Current standards of care focus on optimization of antihypertensive and antiproteinuric therapies (typically renin- angiotensin system blockade) to reduce disease progression. Much recent attention has focused on whether additional immunosuppression confers better outcomes than supportive management alone, and indeed, several trials have demonstrated renoprotective effects following the use of oral corticosteroids. However, results have been inconsistent, and perceived benefits must be balanced against risks and adverse effects associated with generalized immunosuppression, as highlighted by the high-profile STOP-IgAN and TESTING clinical trials. Recent translational research in vitro and animal models of IgAN have generated greater insight into potential therapeutic targets for this complex autoimmune disease. Deeper understanding of the roles of the mucosal immune barrier, complement activation and deposition, T-cell dependent and independent mechanisms of B cell activation, and of the deposition and downstream inflammatory signaling pathways of nephritogenic polymeric IgA1 complexes (e.g., signaling of immune receptors via spleen tyrosine kinase) has formed the rationale for the development of novel agents and clinical trials of more targeted therapies. However, translating findings into clinical practice is challenging, with many immunopathological features of IgAN specific to humans. Recent comprehensive reviews outline current understanding of mechanisms of IgAN as well as ongoing and future clinical trials; it is not our aim to replicate this here. Instead, we take a mechanistic approach to current treatment strategies, outlining advantages and limitations of each before exploring ongoing research with potential translation into future targeted therapies for this complex disease.

Keywords: IgA nephropathy; Syk; chronic kidney disease; complement; glomerulonephritis; immunosuppression.

Figure 1

Histopathology of IgA nephropathy. Notes: (A) Light microscopy demonstrating a segmental area of endocapillary proliferation within the glomerular tuft (hematoxylin and eosin, original magnification: ×200). (B) Immunofluorescence staining for IgA, showing predominantly mesangial IgA deposits. (C) Electron microscopy, demonstrating electron dense immune deposits in the glomerular mesangium.

Figure 2

Pathogenesis and potential therapeutic targets in IgA nephropathy. Notes: (A) Development of IgG and/or IgA autoantibodies against polymeric galactose-deficient IgA1. (B) B-cell depletion of autoantibody-producing plasma cells using rituximab. (C) Targeting BAFF or APRIL. These may be involved in promoting B-cell class switch to IgA1-producing plasma cells. (D) Using budesonide to target dysregulation of the mucosal immune system. (E) Targeting mesangial cell activation and production of inflammatory mediators such as via Syk or NF-kB. (F) Targeting elements of the complement cascade such as properdin or C3. Abbreviations: APRIL, a proliferation-inducing ligand; BAFF, B-cell activation factor of the TNF family; MAC, membrane attack complex; NF-kB, nuclear factor-kappa B; Syk, spleen tyrosine kinase.