Anti-neutrophil cytoplasmic antibody-associated glomerulonephritis with detection of myeloperoxidase and phospholipase A₂ receptor in membranous nephropathy-lesions: report of two patients with microscopic polyangiitis

Podocyte phospholipase A₂ receptor (PLA₂R) is a major target antigen in idiopathic adult membranous nephropathy (MN). Histological PLA₂R staining in the renal tissue has proven to be useful for the detection of idiopathic MN. However, glomerular PLA₂R deposits have also been recently observed in several patients with secondary MN, such as hepatitis B virus-associated, hepatitis C virus-associated, and neoplasm-associated MN. Certain inflammatory environments have been suggested to lead to abnormal expression of PLA₂R epitopes, with the resulting production of PLA₂R autoantibodies.

We report two patients diagnosed with anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis with MN-lesions, in whom ANCA titers for myeloperoxidase (MPO) were persistently positive. The first patient was a 52-years-old man who presented with interstitial pneumonitis. Microscopic hematuria and proteinuria were found when the interstitial pneumonitis became more severe. Renal biopsy findings yielded a diagnosis of ANCA-associated glomerulonephritis (mixed class) with MN-lesions. The second patient was a 63-years-old woman who had been treated for relapsing polychondritis. Her renal tissue showed evidence of focal ANCA-associated glomerulonephritis with MN-lesions. Interestingly, both MPO and PLA₂R were detected in the glomerular subepithelial deposits of both patients. Immunoglobulin G (IgG) 1 and IgG2 were positive in the glomeruli of patient 2, and all subclasses of IgGs were positive in patient 1.

The present cases suggest that ANCA-associated glomerulonephritis could expose PLA₂R, leading to the development of MN-lesions.