An Indirect Immunofluorescence Method Facilitates Detection of Thrombospondin Type 1 Domain–Containing 7A–Specific Antibodies in Membranous Nephropathy

Abstract

Thrombospondin type 1 domain–containing 7A (THSD7A) is a target antigen identified in adult membranous nephropathy (MN) along with the major antigen phospholipase A₂ receptor 1 (PLA₂R1). The prevalence of THSD7A-Ab–positive patients is unknown, and it is unclear whether the clinical presentation differs between patients positive for PLA₂R1-Ab or THSD7A-Ab. We screened serum samples of 1276 patients with MN from three different cohorts for the presence of THSD7A-Ab by Western blot analysis and a newly developed indirect immunofluorescence test (IFT). Compared with Western blot analysis, the IFT had a 92% sensitivity and a 100% specificity. The prevalence of THSD7A-associated MN in a prospective cohort of 345 patients with MN was 2.6%, and most were women. In this cohort, the percentage of patients with THSD7A-associated MN and malignant disease significantly exceeded that of patients with PLA₂R1-associated MN and malignant disease. In all cohorts, we identified 40 patients with THSD7A-associated MN, eight of whom developed a malignancy within a median time of 3 months from diagnosis of MN. In one patient with THSD7A-associated MN and metastases of an endometrial carcinoma, immunohistochemistry showed THSD7A expression on the metastatic cells and within follicular dendritic cells of the metastasis–infiltrated lymph node. We conclude that the IFT allows sensitive and specific measurement of circulating THSD7A-Ab in patients with MN. Patients with THSD7A-associated MN differ in their clinical characteristics from patients with PLA₂R1-associated MN, and more intensive screening for the presence of malignancies may be warranted in those with THSD7A-associated MN.