Clinicopathological study of patients with mesangial isolated C3d deposition in various glomerular diseases

C1q nephropathy in association with Gitelman syndrome: a case report

There have been rare reports of glomerulopathies developing in patients with Bartter syndrome (BS) and its milder variant, Gitelman syndrome (GS). We present the first case of C1q nephropathy (C1qN) in an African American child with GS. This child was diagnosed with GS at 9 years of age and subsequently developed nephrotic range proteinuria 3 years later. Renal biopsy revealed mesangial hypercellularity and focal segmental glomerulosclerosis (FSGS). The segmental lesions were generally located at the vascular pole. Dominant C1q (2+) staining along with IgG (1-2+) was demonstrated in the mesangium, which correlated with scattered electron dense mesangial deposits demonstrated by electron microscopy. Treatment with an angiotensin-converting enzyme inhibitor led to an improvement in proteinuria to near-normal values (urine protein/creatinine ratio down to 0.5), but the creatinine clearance declined to approximately 58 ml/min/1.73 m(2). This case highlights the possible association between the milder hypokalemic tubulopathy, GS, and glomerular disease, including C1qN. Prompt evaluation of proteinuria with renal biopsy in these patients is recommended to detect significant glomerular pathology. Further research is needed to define risk factors for this complication.

Clinicopathologic features, outcome, and therapeutic interventions in four children with isolated C3 mesangial proliferative glomerulonephritis

Since isolated C3 mesangial proliferative glomerulonephritis in the absence of systemic disease (i-C3-GN) is an uncommon chronic glomerular disease, long-term prognosis and optimal therapeutic intervention for it are not yet fully defined, especially in children. We report clinical features, outcome, and interventions in 4 patients, ranging from 6 to 18 years old, with i-C3-GN. Microscopic or macroscopic hematuria with or without proteinuria was first noted between 3 and 8 years. When present, proteinuria ranged from 0.2 to 1.0 g/24 h. Persistent hypocomplementemia and circulating immune complexes were found in 1 patient. None of the patients had nephrotic syndrome or hypertension. Percutaneous renal biopsy specimens showed varying degrees of mesangial proliferative glomerulonephritis; 2 patients showed mild mesangial proliferation, while others exhibited moderate histologic severity. In 1 patient with a mild mesangial increase, tubulointerstitial changes were associated. Both patients exhibiting mild mesangial changes followed a benign clinical course with normal renal function over 10 years of follow-up. Patients with moderately severe mesangial alteration manifested slight renal function loss and moderate proteinuria at the time of biopsy, but these largely resolved after a six-month course of prednisolone combined with cyclophosphamide, warfarin, and an angiotensin-converting enzyme inhibitor. Thus, clinical manifestations and the need for aggressive treatment appear to vary among pediatric patients with i-C3-GN. Therapy combining prednisolone with immunosuppression seemed to reduce proteinuria and improve glomerular function in patients with moderately severe mesangial proliferation.

Incidental healed postinfectious glomerulonephritis: a study of 1012 renal biopsy specimens examined by electron microscopy

Glomerulonephritis (GN) characterized by immune complex deposits typical of postinfectious GN but with a paucity or absence of overt clinical symptoms and/or urinary abnormalities may occur after a group A streptococcus infection. The overall incidence of this type of subclinical GN is not known. To address this question, electron microscopy findings in 1012 consecutive renal biopsy specimens (952 native kidney, 60 transplant) examined by a single renal pathologist from August 1999 to April 2002 were retrospectively reviewed for the presence of distinct subepithelial and intramembranous deposits indicative of postinfectious GN. Such deposits were noted in 83 biopsy specimens, including 26 with a primary diagnosis of postinfectious GN (acute, persistent, or latent) and 57 in which these deposits were an incidental finding. In each of the latter 57 cases, some or all of the deposits showed partial or extensive loss of electron density typical of partially or largely resorbed deposits. A diagnosis of incidental postinfectious GN was not made in any biopsy specimen exhibiting another immune complex-related glomerular disease that could possibly account for the deposits, composing 443 of the 1012 biopsy specimens examined. Thirty of the 57 biopsy specimens with incidental postinfectious GN showed mesangial hypercellularity, although this was focal and segmental in all but 3 cases and was not accompanied by the endocapillary hypercellularity typical of acute postinfectious lesions. Immunofluorescence microscopy revealed glomerular deposits of C3 in >90% of these biopsy specimens and IgM deposits in 66%, but only rare IgG, IgA, and Cq deposits. Twenty-three (40%) of these 57 biopsy specimens exhibited diabetic nephropathy, either alone or in combination with another lesion; for perspective, only 128 (13%) of the 1012 biopsy specimens examined showed evidence of diabetic nephropathy. In summary, incidental evidence of resolving or largely healed postinfectious GN was noted in up to 10.5% of renal biopsy specimens (57 of 543, not including specimens with a primary diagnosis of an immune complex-related glomerular disease). The recognition of such lesions is potentially important in the interpretation of certain renal biopsy specimens.

Biosynthesis of C3 by human mesangial cells. Modulation by proinflammatory cytokines

Deposits of complement (C) components are found in the glomeruli of patients with various glomerulonephritides without detectable immunoglobulins, thus suggesting a pathogenetic role of the locally produced proteins of this system. In the present study, we have examined human mesangial cells (HMC) for their ability to secrete C3. Three different cell lines were examined and all showed a basal production of C3, which was up-regulated following stimulation with IL-1 beta. IL-6 had no direct stimulatory effect on its own, but synergized with IL-1 to induce an increased production of C3 in the culture supernatant and its relative amount was confirmed by SDS-PAGE and immunoblot. Another agonist such as lipopolysaccharide was not able to induce any significant C3 synthesis. Analysis of C3 HMC gene expression, performed by both reverse transcription-polymerase chain reaction of isolated RNA and Northern blot, confirmed the parallel increase of the specific transcript under IL-1 beta and IL-1 beta + IL-6 stimulation. From these data we conclude that production of C3 in the mesangium could have a pathophysiologic relevance.

Classical pathway of complement activation in normal and diseased human glomeruli

Monoclonal antibodies (mAb) reactive against complement components involved in the classical activation pathway were applied in an indirect immunoperoxidase technique for the histological study of normal and diseased human renal tissues. Prominent staining with antibodies against the C4d fragment was seen in all glomeruli and some renal arteriolar walls. The C4d staining was mesangial with light microscopy, whereas the subendothelial site of the glomerular basement membrane (GBM) also appeared to be positive in immunoelectron microscopy. In similar localization, albeit with distinctly weaker intensity, IgM and C4 binding protein (C4bp) were detected. In kidney biopsies from patients with various types of glomerulonephritis, C4d reactive antibodies stained the glomerular structures in a strong, diffuse or granular pattern in contrast to the more segmental distribution and weaker staining intensity in normal kidney specimens. Increased amounts of C4d, occasionally also of C4b, were paralleled in diseased kidney tissues by distinct deposits of IgM and/or IgG in the presence of C4bp. This study suggests that the C4d fragment in normal human glomeruli is indicative of a continuous, local complement activation via the classical pathway induced by the physiological deposition of IgM-containing immune complexes.

Processing of colloidal gold particles in the glomerular mesangium and macula densa of the duck kidney

Bovine-serum-albumin coated colloidal gold particles were injected intravenously into healthy, adult domestic ducks. The fate of these tracer particles was followed in a time-sequence up to 4.5 days in the renal glomerular mesangium--distal tubule macula densa junction with transmission electron microscopy. The bulk of particle aggregates is 'trapped' in the mesangial channel system, phagocyted by mesangial cells, exocyted back into the mesangial channels, transported extracellularily towards the vascular hilus, rephagocyted by macula densa cells and expelled into the tubular lumen. This process requires about nineteen hours in the experimental model chosen, although it continues to take place to a much lower extent even 4.5 days after administration of the tracer. This mode of macromolecular excretion may be of interest in connection with the pathogenesis of several forms of glomerulonephritis.