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Published on: December 15, 2011
Punctate IgG staining particles localize in the budding ballooning clusters of reactive foot processes in minimal
Ping L Zhang1, Vasudevan D Mahalingam1, Brandon D Metcalf1
1Department of Pathology, Corewell Health East, Royal Oak, MI, USA.
Abstract:
The etiology of minimal change disease (MCD) remains a mystery as the only characteristic findings are the diffuse effacement of foot processes seen on electron microscopy (EM). Punctate IgG staining found floating outside glomerular capillary loops in MCD cases was recently identified as autoimmune antibodies against nephrin of podocytes. We hypothesized that the punctate IgG staining is located on budding ballooning clusters (BBC) of reactive foot processes in Bowman's space found on EM. We identified seven patients with MCD cases showing IgG staining that were subsequently evaluated for BBC on EM. We concurrently examined 12 negative controls, either unremarkable cases or tubulointerstitial diseases, by EM. Immunogold labeling was performed to confirm the presence of IgG and determine localization. In seven MCD cases, there were positive punctate IgG staining particles outside of the glomerular basement membranes (GBM) along with concurrent punctate staining for C3, kappa, and lambda. By EM, all seven (100%) MCD cases revealed BBC that was characterized by ballooning foot processes ranging from 1 to 6 µm and was either budding or detached from the GBM in 3-7 clusters; no electron-dense materials were seen in BBC. BBC was also seen in only 1 of 12 (8%) negative controls. Immunogold labeling identified IgG particles within BBC of MCD by EM, but not in the negative control. Our data suggest that BBC are EM structures of reactive foot processes that are most likely correlated with punctate IgG staining seen in cases of MCD, supported by immunogold labeling for IgG.
Insights
Minimal change disease (MCD) involves mysterious foot process effacement. New research links punctate IgG staining in MCD to budding ballooning clusters (BBC) of reactive podocytes, suggesting a potential autoimmune link.
Area of Science:
- Nephrology
- Immunology
- Pathology
Background:
- The cause of minimal change disease (MCD) is unknown, with only foot process effacement visible on electron microscopy (EM).
- Punctate IgG staining outside glomerular capillaries in MCD suggests antibodies against podocyte nephrin.
Purpose of the Study:
- To investigate the hypothesis that punctate IgG staining in MCD is located on budding ballooning clusters (BBC) of reactive foot processes in Bowman's space.
- To correlate the presence of BBC with IgG staining in MCD cases.
Main Methods:
- Seven MCD patients with IgG staining were evaluated for BBC using EM.
- Twelve control cases (unremarkable or tubulointerstitial diseases) were examined by EM.
- Immunogold labeling was used to confirm IgG presence and localization within BBC.
Main Results:
- All seven MCD cases (100%) showed BBC, characterized by ballooning foot processes budding or detached from the glomerular basement membrane (GBM).
- Punctate IgG, C3, kappa, and lambda staining were found outside the GBM in MCD cases.
- BBC were present in only 8% of control cases.
- Immunogold labeling confirmed IgG particles within BBC in MCD cases but not controls.
Conclusions:
- Budding ballooning clusters (BBC) are EM structures of reactive foot processes in MCD.
- BBC are strongly correlated with punctate IgG staining in MCD.
- These findings suggest BBC may be the site of autoimmune attack in minimal change disease.
