Modulatory effects of 1,25-dihydroxyvitamin D3 on human B cell differentiation

1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) can modulate immune responses, but whether it directly affects B cell function is unknown. Patients with systemic lupus erythematosus, especially those with antinuclear Abs and increased disease activity, had decreased 1,25(OH)(2)D(3) levels, suggesting that vitamin D might play a role in regulating autoantibody production. To address this, we examined the effects of 1,25(OH)(2)D(3) on B cell responses and found that it inhibited the ongoing proliferation of activated B cells and induced their apoptosis, whereas initial cell division was unimpeded. The generation of plasma cells and postswitch memory B cells was significantly inhibited by 1,25(OH)(2)D(3), although the up-regulation of genetic programs involved in B cell differentiation was only modestly affected. B cells expressed mRNAs for proteins involved in vitamin D activity, including 1 alpha-hydroxylase, 24-hydroxylase, and the vitamin D receptor, each of which was regulated by 1,25(OH)(2)D(3) and/or activation. Importantly, 1,25(OH)(2)D(3) up-regulated the expression of p27, but not of p18 and p21, which may be important in regulating the proliferation of activated B cells and their subsequent differentiation. These results indicate that 1,25(OH)(2)D(3) may play an important role in the maintenance of B cell homeostasis and that the correction of vitamin D deficiency may be useful in the treatment of B cell-mediated autoimmune disorders.

[Diagnostic pathway of an unusual case of nephrotic syndrome: immunotactoid glomerulopathy]

Immunotactoid glomerulopathy is a clinicopathological entity characterized by extracellular deposition of microtubular substructures, which are negative for the usual staining that identifies amyloid within the mesangium and capillary walls of renal glomeruli. Despite ongoing debate in the nephrological community, it is kept distinct from fibrillary glomerulonephritis on the basis of the size and arrangement of the microtubules and microfibrils. It is clinically characterized by the presence of glomerular proteinuria in the nephrotic range, microscopic hematuria and hypertension, and is often associated with hypocomplementemia, monoclonal gammopathy, and lymphoprolipherative disorders. A 47-year-old woman was referred to our unit for evaluation of proteinuria associated with nephrotic syndrome. Laboratory findings revealed a serum M component and hypocomplementemia. Renal biopsy yielded three fragments for optical microscopy, immunofluorescence, and electron microscopy; Congo red staining was used. Renal histology showed a morphological pattern of membranoproliferative glomerulonephritis. Immunofluorescence showed IgG deposits with monoclonal kappa light chain restriction as well as C3 and C1q deposits. Electron microscopy revealed the presence within the mesangium of microtubules measuring >35 nm that were focally parallel oriented. The final diagnosis was nephrotic syndrome caused by immunotactoid glomerulopathy. The clinical diagnosis of immunotactoid glomerulopathy is based on pathological, clinical and hematological features and requires the exclusion of other diseases that are associated with organized glomerular deposits. We discuss the diagnostic options offered by the clinical and morphological elements of this case; the use of electron microscopy is emphasized, especially when a renal syndrome is associated with paraproteinemia.