Prediagnostic Appearance of Thrombospondin Type-1 Domain 7A Autoantibodies in Membranous Nephropathy

Complement activation and effector pathways in membranous nephropathy

Complement activation has long been recognized as a central feature of membranous nephropathy (MN). Evidence for its role has been derived from the detection of complement products in biopsy tissue and urine from patients with MN and from mechanistic studies primarily based on the passive Heymann nephritis model. Only recently, more detailed insights into the exact mechanisms of complement activation and effector pathways have been gained from patient data, animal models, and in vitro models based on specific target antigens relevant to the human disease. These data are of clinical relevance, as they parallel the recent development of numerous specific complement therapeutics for clinical use. Despite efficient B-cell depletion, many patients with MN achieve only partial remission of proteinuria, which may be explained by the persistence of subepithelial immune complexes and ongoing complement-mediated podocyte injury. Targeting complement, therefore, represents an attractive adjunct treatment for MN, but it will need to be tailored to the specific complement pathways relevant to MN. This review summarizes the different lines of evidence for a central role of complement in MN and for the relevance of distinct complement activation and effector pathways, with a focus on recent developments.

THSD7A as a Promising Biomarker for Membranous Nephrosis

Membranous nephropathy (MN) is an autoimmune disease of the kidney glomerulus and one of the leading causes of nephrotic syndrome. The disease exhibits heterogeneous outcomes with approximately 30% of cases progressing to end-stage renal disease. Traditionally, the standard approach of diagnosing MN involves performing a kidney biopsy. Nevertheless, kidney biopsy is an invasive procedure that poses risks for the patient including bleeding and pain, and bears greater costs for the health system. The clinical management of MN has steadily advanced owing to the identification of autoantibodies to the phospholipase A2 receptor (PLA2R) in 2009 and thrombospondin domain-containing 7A (THSD7A) in 2014 on the podocyte surface. At present, serum anti-PLA2R antibody detection and glomerular PLA2R antigen staining have been used for clinical diagnosis and prognosis, but the related detection of THSD7A has not been widely used in clinical practice. Here, we summarized the emerging knowledge regarding the roles THSD7A plays in MN and its clinical implications as diagnostic, prognostic, and therapeutic response as well as Methods for detecting serum THSD7A antibodies.

The expanding spectrum and utility of antigens in membranous nephropathy

PURPOSE OF REVIEW

Multiple antigenic targets were discovered in membranous nephropathy, representing distinct autoimmune diseases with a similar morphologic pattern of injury. An overview of recent developments, including antigen types, clinical associations, serologic monitoring, and advancements in understanding disease pathogenesis are provided.

RECENT FINDINGS

Several new antigenic targets have defined subtypes of membranous nephropathy, including Neural epidermal growth factor-like 1, protocadherin 7, HTRA1, FAT1, SEMA3B, NTNG1, NCAM1, exostosin 1/2, transforming growth factor beta receptor 3, CNTN1, proprotein convertase subtilisin/kexin type 6, and neuron-derived neurotrophic factor. Autoantigens in membranous nephropathy may demonstrate unique clinical associations, assisting the nephrologist to identify potential disease etiologies and triggers, such as autoimmune disease, cancer, medications, and infections.

SUMMARY

We are entering an exciting era for which an antigen-based approach will further define subtypes of membranous nephropathy, allow for development of noninvasive diagnostics, and improve care for patients.