Evidence for renal tubular resorption of collagen fragments from immunostaining of rat kidney with antibodies specific for denatured type I collagen.

Antibodies to rat collagens I and III were raised in sheep. The antisera to collagen I were separated by affinity chromatography into components specific for either native or denatured forms. Immunolabelling of rat kidney sections with antibodies to native collagen I showed staining only of the interstitial matrix. By contrast, antibodies to denatured collagen I revealed the presence of immunoreactive material primarily in the upper part of the proximal tubules, detected in both fixed and cryostat sections. In fixed material, the granular appearance of staining in the region of the brush border was shown to be distinct from the protein droplets counterstained by toluidine blue. Collagen III antibodies stained the interstitial matrix in a similar pattern to that for native collagen I, but no proximal tubule staining was observed despite the fact that antibodies to denatured collagen III were shown to be present. No material reactive with denatured collagen I antibodies was detected in urine or serum by an inhibition ELISA technique. The results are discussed in terms of renal tubular resorption of collagen degradation products.