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Uromodulin, also known as Tamm–Horsfall protein, is the most abundant protein in urine. It has recently been reported that uromodulin exists in a small amount in blood and that its concentration correlates with the estimated glomerular filtration rate (eGFR). First, we generated anti-human uromodulin mouse monoclonal antibodies (mAb(s)) and established a specific enzyme-linked immunosorbent assay (ELISA) for uromodulin. We then performed an observational clinical study to determine if there was a correlation between serum uromodulin concentration and estimates of kidney function and whether the serum uromodulin value could be a biomarker in clinical nephrology. The clinical study included 308 patients with and without chronic kidney disease and healthy volunteers. Serum concentrations of creatinine, cystatin C, and uromodulin were measured and correlations were sought between the eGFR calculated from the creatinine and cystatin C levels and the serum uromodulin concentration. There was a good correlation between the serum uromodulin concentration and the eGFR value calculated from the creatinine (r = 0.76) and cystatin C (r = 0.79) levels. The mean serum uromodulin level in the group with an eGFR > 90 mL/min/1.73 m2 calculated using cystatin C was significantly higher than that in the group with an eGFR of 80–89 mL/min/1.73 m2. The serum uromodulin measurement could be a useful biomarker for identification of patients with early deterioration of kidney function.

Antineutrophil cytoplasmic antibody (ANCA) has been known to cause pauci-immune crescentic glomerulonephritis. In addition, several reports described membranous glomerulonephritis (MN) concurrent with ANCA-associated glomerulonephritis. Because the two glomerular diseases simultaneously appear in an ANCA-positive patient, the mechanisms whereby ANCA causes the two different glomerular diseases remain ambiguous. Herein, we report a case of 19-year-old man who presented with hematuria, pre-nephrotic proteinuria, and high titer of myeloperoxidase (MPO)-ANCA. The first renal biopsy revealed MN with chronic glomerular scar lesions of unknown etiology. Predominant immunoglobulin (Ig) G1 subclass and negative phospholipase-A2 receptor staining, together with granular-positive glomerular capillary co-localization of MPO and IgG staining, suggested secondary MN due to MPO-MPO-ANCA immune-complex. Five years later, the patient presented with fever, severe renal dysfunction, and alveolar hemorrhage with high titer of MPO-ANCA that indicated pulmonary renal syndrome due to ANCA-associated vasculitis. The second renal biopsy revealed pauci-immune crescentic glomerulonephritis without either apparent MN-lesion or glomerular IgG staining. This is the first reported case showing that MPO-ANCA caused two different glomerular diseases, MN and pauci-immune crescentic glomerulonephritis, in the same patient at the different time points. Our case indicated that common MPO-ANCA might cause different glomerular diseases by different immune mechanisms.

AH amyloidosis is a rare type of amyloidosis caused by deposition of monoclonal immunoglobulin heavy chain. The key diagnostic feature is positive immunostaining for a single class of immunoglobulin heavy chain. We report a case of AH amyloidosis with immunoglobulin G (IgG) λ monoclonal gammopathy that was diagnosed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) after immunostaining of renal tissue for immunoglobulin heavy chain gave negative results. The molecular weight of the purified renal amyloid protein was ∼11kDa, which was determined by LC-MS/MS analysis to correspond to an amino acid sequence comprising the variable region and a truncated portion of the constant region of IgG heavy chain. The exact same truncated heavy chain was detected by LC-MS/MS of a protein isolated from the patient's serum, suggesting that the truncated serum protein was the precursor of the amyloid protein. Because antibodies to immunoglobulin heavy chain recognize the Fc portion, the large deletion in the constant region could explain the negative results upon immunostaining. Direct protein detection by LC-MS/MS is a powerful aid to diagnose renal AH amyloidosis, particularly when the findings of immunoglobulin staining are inconsistent with the background monoclonal gammopathy.

Background Immunoglobulin heavy-and-light-chain amyloidosis (AHL amyloidosis) is a newly established disease entity where both the immunoglobulin heavy-chain and light-chain compose amyloid fibrils. The immunoglobulins responsible for the amyloid fibrils are generally identified by immunostaining and/or laser microdissection-liquid chromatography-tandem mass spectrometry (LMD-LC-MS/MS). However, both techniques do not biochemically differentiate immunoglobulins that formed amyloid fibrils from non-responsible immunoglobulins. Case presentation We herein report a case of 67-year-old female patient with renal amyloidosis due to lymphoplasmacytic lymphoma secreting monoclonal immunoglobulin M (IgM)-kappa. Renal immunostaining monotypically positive for IgM-kappa and LMD-LC-MS/MS identification of mu heavy-chain and kappa light-chain were consistent with the diagnosis of AHL amyloidosis. In order to confirm that both the immunoglobulin heavy-chain and light-chain were forming amyloid fibrils, we performed LC-MS/MS of renal amyloid fibrils isolated by the traditional amyloid purification method. The additional LC-MS/MS identified kappa light-chain only without any heavy-chain component. These results were suggestive that amyloid fibrils were composed by kappa light-chain only and that the mu heavy-chain identified by immunostaining and LMD-LC-MS/MS was derived from the non-specific co-deposition of monoclonal IgM-kappa. Conclusion The case was AL amyloidosis with non-amyloid forming monoclonal immunoglobulin deposition. While immunostaining and LMD-LC-MS/MS are irreplaceable techniques to classify amyloidosis, confident exclusion of the present condition should be required to diagnose AHL amyloidosis.

We report a middle-aged Japanese man who had a past history of malignant lymphoma with tubulointerstitial nephritis (TIN) presenting a high serum immunoglobulin G4 (IgG4) concentration and bilateral kidney enlargement and swelling of many lymph nodes. Although lymph node biopsy was not evident of a recurrence of lymphoma, kidney biopsy showed prominent infiltration of IgG4-positive plasma cells in a tubulointerstitial lesion but not in glomeruli. We made a diagnosis of IgG4-related TIN and lymphadenopathy; administration of oral prednisolone improved his physical and laboratory parameters. This is the first report of a case of IgG4-related TIN and lymphadenopathy after therapy for malignant lymphoma.