PMC7738783_01
All the glomeruli displayed membranoproliferative features, with increased cellularity and a lobular pattern (a) (H-E, 400x). A single arteriole showed a luminal thrombus, composed of fibrin and platelets, together with blood extravasation and karyorrhectic debris (b) (H-E, 400x). CD61 immunostaining was performed (400x), which demonstrated platelet content (c).
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fig1
There were mild tubular atrophy and interstitial fibrosis as estimated at 15-20% (as shown in Figure 1).
Direct immunofluorescence on fresh frozen tissue was performed; no evidence of deposits was observed (a) (IgG, 400x). Direct immunofluorescence on paraffin-embedded, pronase-digested sections was carried out; in contrast to routine IF, there were deposits of IgG and kappa light chains in the capillary walls (b) (kappa, 400x).
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fig2
On the other hand, the IF on pronase-digested paraffin-embedded (IF-P) sections showed subendothelial deposits of IgG and kappa light chain (++/+++) with negative staining for C3 and lambda light chain (as shown in Figure 2).
Electron microscopy showed subendothelial and mesangial deposits (a) (10000x); for the most part, these were nonorganized; however, there were some fibrillary deposits with parallel arrangement measuring approximately 10-15 nm (b) (30000x).
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fig3
The immunohistochemistry technique for DNAJB9 was negative, which ruled out FG (as shown in Figure 3).