Serum anti-β2 spectrin IgA antibodies are produced in a CD4 T cell-independent manner in IgA nephropathy model mouse.

INTRODUCTION

IgA nephropathy (IgAN) is characterized by deposition of IgA antibodies (Abs) in the glomerular mesangium. In IgAN, the mechanism by which IgA Abs are selectively deposited in the glomerular mesangial region remain unclear. Current study reported the presence of autoantibodies-IgA against β2 spectrin of mesangial cells in sera of IgAN model mice (gddY) and patients with IgAN, and identified β2-spectrin as the target antigen. And it found that IgA+ plasmablasts (PBs) secreting anti-β2-spectrin IgA Abs accumulated in the kidneys of gddY mice. These PBs exhibited a substantial accumulation of somatic hypermutations in both their heavy- and light-chain variable region genes.

METHODS

Lymphocytes from kidneys, renal lymph node, spleen, bone marrow and nasopharyngeal associated lymphoid tissue of 3-week-old ddY mice were analyzed by flow cytometry. To deplete CD4+ T cells in gddY mice, anti-CD4 monoclonal Abs (mAbs) were administered from 3 weeks of age. Renal phenotype (blood urea nitrogen (BUN), urinary albumin and renal pathology), the cell numbers of IgA+ PBs in the kidney and serum anti-β2 spectrin Abs were evaluated by Fuji-DRY-CHEM 7000V, enzyme-linked immunosorbent assay, microscopy, flow cytometry and western blotting, respectively.

RESULTS

Depletion of CD4+ cells in gddY mice caused significant reduction of the number of IgA+ PBs spontaneously accumulating in the kidneys in the anti-CD4 treatment (29.0 ± 12.1/105 cells) than the control (154.0 ± 55.0/105 cells). However, The results showed the level of urinary albumin and BUN were no difference in in the anti-CD4 treatment (5627.0 ± 1316.2 μg/dL, 40.3 ± 4.5 mg/dL, respectively) compared to the control (4766.5 ± 809.2 μg/dL, 69.9 ± 33.2, respectively). And also the treatment did not affect the production of anti-β2-spectrin IgA Abs in sera, glomerular IgA deposition nor pathology.

DISCUSSION: Our data suggest that the serum anti-β2-spectrin IgA Abs are produced in a CD4+ T cell-independent manner and the PBs infiltrating in the kidney are not the major source of serum anti-β2-spectrin IgA Abs at least in animal model. The present study will help to elucidate the mechanism of production of anti-β2-spectrin IgA Abs.