Figure 4.

Increased urinary excretion and decreased tubular reabsorption of albumin in affected dogs. (a) Dogs with a functional defect in cubilin expression (n = 6) reveals a significant, approximately sevenfold increase (P = 0.00003) in urinary albumin/creatinine excretion compared with normal control dogs (n = 6). (b and c) Immunohistochemistry using an anti-dog albumin antibody (1:100,000) to identify albumin in the kidney cortex of normal (b) and affected (c) dogs. In normal dogs (b), evidence of reabsorbed and endocytosed albumin in proximal tubules is clear (arrows), whereas no albumin can be identified inside the proximal tubules of affected dogs (c). In all dogs, a faint labeling was observed in basement membranes due to a basal deposition of albumin. ×600. Three affected and three normal dogs were examined using two different anti-albumin antibodies, all showing the same labeling pattern. (d) Electron microscopic immunocytochemistry using anti-dog albumin antibody (1:5,000) on a section of normal dog proximal tubule cells. Intense labeling of four lysosomes and part of a fifth is observed corresponding to the vesicular labeling observed with light microscopic immunohistochemistry. ×33,000.