Tissue-binding affinity of Proteus mirabilis fimbriae in the human urinary tract

Abstract

Binding characteristics of the two major fimbrial hemagglutinin types of uropathogenic Proteus mirabilis were determined in frozen sections of human kidney and in exfoliated uroepithelial cells. P. mirabilis 3087, which expresses the MR/P fimbriae, adhered avidly to the tubular epithelial cells of the kidney and also to the epithelial cells of urinary sediment. No adhesion to glomerular or peritubular elements of the kidney was detected. Indirect immunogold silver staining also showed that the purified MR/P fimbriae recognized the same kidney domains. Adhesion of strain 3087 to uroepithelial cells was completely inhibited by Fab fragments of antibodies against the purified MR/P fimbriae. A completely different tissue-binding pattern was exhibited by the MR/K fimbriae of P. mirabilis 2456. In the kidney, the MR/K fimbriae bound strongly to the Bowman's capsule of the glomeruli and to the tubular basement membranes. A weak binding to glomerular mesangium and tubular epithelial cells was also seen. Strain 2456 did not adhere to epithelial cells of urinary sediment. Analysis of normal human urine showed that it contains low-molecular-weight molecules capable of inhibiting the binding of the MR/P fimbriae; no urinary inhibitors could be detected for the MR/K fimbriae. Poor in vivo binding capacity to intact human uroepithelial cells may be an important factor in explaining the relatively low pathogenicity of P. mirabilis in healthy hosts.