Serum level of proximal renal tubular epithelial cell-binding immunoglobulin G in patients with lupus nephritis

In vitro data showed that immunoglobulin G (IgG) from lupus nephritis (LN) patients could bind to proximal renal tubular epithelial cells (PTEC), but the clinical relevance of such binding remained unclear. Binding of IgG and subclasses to PTEC was measured by cellular ELISA (expressed as OD index) in 189 serial serum samples from 23 Class III/IV ± V LN patients who had repeated renal flares (48 during renal flares, 141 during low level disease activity (LLDA)), and compared with 64 patients with non-lupus glomerular diseases (NLGD) and 23 healthy individuals. Total IgG PTEC-binding index was 0.34 ± 0.16, 0.29 ± 0.16, 0.62 ± 0.27 and 0.83 ± 0.38 in healthy controls, NLGD, LN patients during LLDA, and LN patients during nephritic flare, respectively (p < 0.001, LLDA vs. renal flare; p < 0.001, healthy controls or NLGD vs. LN during LLDA or renal flare). PTEC-binding index for IgG1 was 0.09 ± 0.05, 0.16 ± 0.12, 0.44 ± 0.34 and 0.71 ± 0.46 for the corresponding groups (p < 0.001, LLDA vs. renal flare; p < 0....