[A case of immunotactoid glomerulopathy with IgA2, kappa deposition ameliorated by steroid therapy].

We report a case of idiopathic immunotactoid glomerulopathy with IgA2, kappa light chain deposition, ameliorated by steroid therapy. A 28-year-old male patient was admitted to our hospital due to exacerbation of nephrotic syndrome. The onset of his renal disease was at 24 years of age and the renal biopsy revealed membranoproliferative glomerulonephritis with moderate-degree deposition of IgA, IgG, IgM, C3 and C1q. Prednisolone therapy was started at the dose of 50 mg/day and effective for nephrotic syndrome and renal dysfunction. Two years later, the proteinuria and microscopic hematuria gradually exacerbated during reduction of prednisolone. The second renal biopsy showed mesangioproliferative glomerulonephritis with predominant deposition of IgA and C3. The glomerular proliferative changes were successfully suppressed by steroid treatment. On electron microscopy, a microtubular deposit with an average width of 40 nm and double-tracked appearance was observed in the mesangial and subendothelial areas. Immunohistochemical examination revealed that the deposit was predominantly composed of IgA2 subclass and kappa light chain. Selective deposition of IgA2 subclass and kappa light chain indicated that the glomerular lesion should be induced by monoclonal immunoglobulin, although it could not be detected in the serum and urine clinically. Immunoglobulin subclass staining of renal biopsy specimens provides an important clue for understanding the pathogenesis of immunotactoid glomerulopathy or fibrillary glomerulonephritis.