MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis: In the present study, we investigated the expression of claudin-1 and its colocalization with ZO-1 in various human glomerular diseases including IgA nephropathy, purpura nephritis, ANCA associated vasculitis (MPO-ANCA and PR-3 ANCA), anti-GBM-RPGN, and lupus nephritis.