Interaction of bladder glycoprotein GP51 with uropathogenic bacteria

Purpose: A major component of bladder surface mucin is a glycoprotein GP51 (molecular weight 51 kD.). GP51, which has previously been isolated from ra bbit mucosa, appears to function as part of the defense mechanism in an in vivo infection model. GP51 coats the epithelium and is secreted into the ur ine, as detected by immunohistochemical testing and enzyme-linked immunosor bent assay (ELISA). Increased urinary GP51 occurs during urinary tract infe ction. To elucidate the role of GP51 as a component of the primary defense mechanism we studied interactions with uropathogenic bacterial isolates and urine from symptomatic patients with urinary tract infection. Materials and Methods: ELISA was performed to demonstrate the binding of GP 51 and various uropathogens. Immunochemical studies were done using monoclo nal antibodies to GP51 to determine the interaction of GP51 with certain ur opathogenic isolates, including Escherichia coli, Enterobacter cloacae, Kle bsiella pneumoniae, Proteus vulgaris, Pseudomonas aeruginosa, Serratia marc escens, Staphylococcus aureus, S. epidermidis and Streptococcus faecalis. I nfected urinary sediments and uropathogenic bacterial cultures were examine d by immunocytochemical testing to localize GP51. Antigen inhibition ELISA was done to quantitate urinary GP51 in the urine of 17 normal controls and 19 patients with urinary tract infection. Results: ELISA revealed that GP51 binds to a wide spectrum of gram-positive and gramnegative uropathogens in semiquantitative fashion. Immunochemical methods confirmed that purified GP51 binds to bacteria, encapsulating and a ggregating the bacteria. Clinical specimens showed GP51 localized to bacter ia and uroepithelial cells. We observed a significant increase in urinary G P51 in urinary tract infection compared to uninfected urine (p = 0.0003). Conclusions: These studies suggest that GP51, a component of bladder mucin, may be a strategic factor in the primary defense mechanism of the bladder.