Anti-neutrophil cytoplasmic antibody-associated glomerulonephritis with detection of myeloperoxidase and phospholipase A(2) receptor in membranous nephropathy-lesions: report of two patients with microscopic polyangiitis

BACKGROUND: Podocyte phospholipase A(2) receptor (PLA(2)R) is a major target antigen in idiopathic adult membranous nephropathy (MN). Histological PLA(2)R staining in the renal tissue has proven to be useful for the detection of idiopathic MN. However, glomerular PLA(2)R 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 PLA(2)R epitopes, with the resulting production of PLA(2)R autoantibodies. CASE PRESENTATION: 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 PLA(2)R 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. CONCLUSION: The present cases suggest that ANCA-associated glomerulonephritis could expose PLA(2)R, leading to the development of MN-lesions.