The immunofluorescence microscopy analysis revealed autofluorescence of the observed granules. Furthermore, when stained with Jones silver staining, the granules, predominantly present in the proximal tubular cells from segment S1 to S3, showed notable argyrophilia. Other observed features on proximal tubular cells included conserved height, but noticeable atrophy, apical blebbing, thickening of the basement membrane, interstitial expansion, fibrosis and defective proliferation. All these alterations suggested a remarkable deterioration of regenerative capacity (2).
Further investigation addressed the origin of the CINAC granules. They exhibited positive staining for Cathepsin B and lysosome-associated membrane protein 1 (LAMP-1). Electron microscopy analysis demonstrated dysmorphic intracellular granules containing dispersed electron dense aggregates in the proximal tubular epithelial cells (Figure 2). The observations were comparable with light microscopy, but there was still insufficient data to confirm these were lysosomes. The final confirmation came from a specific technique, called the Transmission Electron Microscopy Energy-Dispersive X-ray spectroscopy (TEM-EDX), which was applied on the Jones stained tissue section, verifying that observed granules in fact originated from lysosomes.
The connection between lesions in CINAC patients and patients treated with calcineurin-inhibitors
Analysis of biopsy samples from patients with suspected CINAC from different parts of the world showed remarkable similarity, suggesting an epidemic of very large proportion (Figure 2).