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T-cell transcriptome analysis points up a thymic disorder in idiopathic nephrotic syndrome. Background Idiopathic nephrotic syndrome is a proteinuric disease secondary to the release of a nonidentified circulating glomerular permeability factor by T cells. Because specificities of T-cell activation in idiopathic nephrotic syndrome remain unknown, we evaluated transcriptional activation of T cells in nephrotic patients during proteinuria. Methods Transcriptomes of CD2+ cells were analyzed by serial analyis of gene expression (SAGE) in a nephrotic child during proteinuria relapse and after remission, away from any immunosuppressive treatment. Expression of specific transcripts overexpressed during proteinuria relapse was compared by reverse transcription-polymerase chain reaction (RT-PCR) in CD2+ cells from 11 nephrotic patients during relapse and remission and 11 nonnephrotic patients during infection and after recovery. Results Differential analysis of CD2+ cell transcriptome identified >200 mRNA tags overexpressed during proteinuria relapse, including many T-cell markers. RT-PCR analysis of expression of specific transcripts indicated that ( 1 ) under remission conditions, nephrotic children displayed induction of four transcripts, including IKBKB , and repression of NFKBIA as compared to nonnephrotic children after recovery, and ( 2 ) proteinuria relapse was associated with induction of L-selectin and T-lymphocyte maturation–associated protein, two markers of T-cell differentiation and recent emigrant/naive T cells. Conclusion Results indicate that circulating T cells from relapsing nephrotic patients include a significant population of low-mature cells while those from nephrotic patients in remission are characterized by constitutive activation of nuclear factor-κB (NF-κB), altogether suggesting a thymic dysregulation of apoptosis in nephrotic patients.

Protease resistance and binding of Ig light chains in myeloma-associated tubulopathies. Kidney tubule dysfunction and lesions are frequent complications of myeloma, related to unknown properties of the monoclonal light chain. We have analyzed protease sensitivity and binding properties of urinary light chains from four patients with Fanconi's syndrome, 12 with cast nephropathy, and four control patients without myeloma-associated tubulopathy. All light chains were normal-sized, monomeric and/or dimeric, and none was N-glycosylated. Kinetic studies of light chain digestion by pepsin and the lysosomal enzyme cathepsin B showed the generation of a protease-resistant 12 kDa fragment, corresponding to the V domain of the κ chain in the four Fanconi's syndrome patients; in two out of four the V domain was also completely resistant to trypsin. Western and dot blots revealed similar patterns of reactivity of light chains from patients with the Fanconi's syndrome towards other light chains. Properties of cast-nephropathy light chains were more heterogeneous but clearly differed from those of Fanconi's syndrome: (i) 9 out of 12 were of the λ-type; (ii) only four yielded a transient 12 kDa fragment after cathepsin B digestion, but all showed some resistance to proteolysis of the entire molecule or a fragment thereof to at least one protease, at variance with control light chains; (iii) they displayed various patterns of reactivity with other light chains; (iv) 7 out of 12 reacted specifically with Tamm-Horsfall protein (THP) by ELISA, in contrast with those of Fanconi's syndrome. In one patient who presented with cast nephropathy and the Fanconi's syndrome, the light chain exhibited both partial resistance of the Vκ domain to cathepsin B and the highest reactivity with THP. These results suggest that light chain toxicity in Fanconi's syndrome is related to the resistance of the V domain to degradation in lysosomes of proximal tubule epithelial cells. In contrast, cast nephropathy is an heterogeneous entity whose pathogenesis may involve multiple factors such as protease resistance, in addition to light chain reactivity with THP.