Podocyte bridges between the tuft and Bowman's capsule: an early event in experimental crescentic glomerulonephritis

Although experimental crescentic glomerulonephritis starts with an endocapillary inflammation, the crescents themselves seem to originate from the proliferation of parietal epithelial cells (PEC). In this study, an attempt was made to disclose a link between the two processes by a morphologic analysis of early stages of the disease. Mice were immunized with rabbit IgG in complete Freund's adjuvant on day -6. At day 0, they received an intravenous injection of a rabbit antiglomerular basement membrane serum. On days 3, 6, and 10, the kidneys were fixed by vascular perfusion for examination by light and electron microscopy. On day 3, morphologic alterations affected mainly the endocapillary compartment; most podocytes appeared to be intact. On day 6, alterations of podocytes were widespread, including foot process effacement and prominent microvillous transformation, and some crescents were found. On day 10, crescents were found in 40% of glomeruli. The most surprising finding was podocytes that adhered to both the glomerular basement membrane and the parietal basement membrane, thus forming bridges between the tuft and Bowman's capsule. Those podocyte bridges were sparse on day 3 but were regularly encountered on days 6 and 10 in glomeruli without crescents and also as a component of crescents. They were interposed between PEC and later between the cells of a crescent without formation of junctional connection with these cells. It is proposed that the spreading of podocytes on the parietal basement membrane represents a lesion of the parietal epithelium and that this process initiates the proliferation of PEC to form a crescent.