Inhibition of B Cell Death Causes the Development of an IgA Nephropathy in (New Zealand White × C57BL/6)F1-bcl-2 Transgenic Mice

Abstract

Little is known about the pathogenic mechanisms of IgA nephropathy, despite being the most prevalent form of glomerulonephritis in humans. We report in this study that in (New Zealand White (NZW) × C57BL/6)F1 mice predisposed to autoimmune diseases, the expression of a human bcl-2 (hbcl-2) transgene in B cells promotes a CD4-dependent lupus-like syndrome characterized by IgG and IgA hypergammaglobulinemia, autoantibody production, and the development of a fatal glomerulonephritis. Histopathological analysis of glomerular lesions reveals that the glomerulonephritis observed in these animals resembles that of human IgA nephropathy. The overexpression of Bcl-2 in B cells selectively enhances systemic IgA immune responses to T-dependent Ags. Significantly, serum IgA purified from (NZW × C57BL/6)F1-hbcl-2 transgenic mice, but not from nontransgenic littermates, shows reduced levels of galactosylation and sialylation and an increased ability to deposit in the glomeruli, as observed in human patients with IgA nephropathy. Our results indicate that defects in the regulation of B lymphocyte survival associated with aberrant IgA glycosylation may be critically involved in the pathogenesis of IgA nephropathy, and that (NZW × C57BL/6)F1-hbcl-2 Tg mice provide a new experimental model for this form of glomerulonephritis.

O-Glycosylated IgA Rheumatoid Factor Induces IgA Deposits and Glomerulonephritis

“…These data indicate that Gal deficiency in N-glycans of IgA is not essential for the development of the 6-19 model of GN, although Gal deficiency of serum IgA has previously been reported to be associated with the development of glomerular lesions in other murine models of IgAN. [14][15][16] The possibility of a critical pathogenic role of O-glycans present in the 6-19 IgA hinge region for the development of glomerular lesions remains to be tested. It should be stressed that 6-19 IgA O-glycans were highly galactosylated, in contrast to the hypogalactosylated O-glycans of IgA1 in patients with IgAN.…”

“…The peptide fraction containing the 62-amino acid hinge peptide of each IgA mAb obtained by treatment with trypsin and lysylendopeptidase ( Figure 4) was collected by HPLC and subjected to matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS). The analysis of [6][7][8][9][10][11][12][13][14][15][16][17][18][19] IgA RF mAb identified, in addition to a peak containing the nonglycosylated hinge peptide at m/z 6627, four additional peaks of O-glycosylated hinge peptides, which contained GalNAc monosaccharide, GalNAc-Gal disaccharide, and its monoand disialylated forms ( Figure 5). The prevailing form of the carbohydrate composition of O-glycans was GalNAc-Gal disaccharide at m/z 6992, and the abundance of the glycosylated peptide ions at this peak was similar to that of the nonglycosylated ones.…”

“…12 In contrast, murine IgA carries at least two N-linked oligosaccharide side chains in CH1 and CH3 domains, 8,9,13 and Gal deficiency of N-linked glycans (N-glycans) has been reported to be associated with the development of glomerular lesions in murine models of IgAN. [14][15][16] In the present study, we explored the nephritogenic potential of two different monoclonal IgA anti-IgG2a rheumatoid factors (RFs) bearing the Igh-2 a allotype (6-19 and 46-42) in relation to the possible presence of O-glycans in their hinge regions and to the structural abnormality of N-glycans in their CH1 and CH3 domains. We observed that only 6-19 IgA RF mAb carrying O-glycans in the hinge region is able to induce severe glomerular lesions characterized by mesangial IgA deposits, although its O-glycans are highly galactosylated, and that the structure of N-glycans present in the CH1 domain of 6-19 IgA RF is also markedly different from that of non-nephritogenic 46-42 IgA RF.…”

CD4+CD25+ T Cell-Dependent Inhibition of Autoimmunity in Transgenic Mice Overexpressing Human Bcl-2 in T Lymphocytes

“…For kidney, the organs were processed, stained, and scored as described previously (11). For the study of CIA, all mice were killed 10 -12 wk after immunization and the hind legs were fixed in 10% phosphate-buffered formaldehyde solution, decalcified in Parengy's decalcification solution overnight.…”

“…The F 1 female hybrids used in this study were obtained in our animal facilities. The presence of the hbcl-2 Tg in F 1 mice was assessed in PBMC by flow cytometry using a specific mAb against hBcl-2 (clone 6C8; BD Pharmingen), as described previously (11). The in vivo depletion of CD8 ϩ T cells was performed from birth up to 12 mo of age in the experiments with the SLE model, or from day 3 before immunization with bovine collagen type II (col-II) emulsified in CFA until the 12th week after immunization in the experiments with the CIA model, using an anti-CD8 mAb (H35-17.2: rat IgG2b) as described previously (32).…”