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 A2 receptor (PLA2 R) is a major target antigen in idiopathic adult membranous nephropathy (MN). Histological PLA2 R staining in the renal tissue has proven to be useful for the detection of idiopathic MN. However, glomerular PLA2 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 PLA2 R epitopes, with the resulting production of PLA2 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 PLA2 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 PLA2 R, leading to the development of MN-lesions.