Significance of antibody-coated bacteria in urinary sediment in experimental pyelonephritis

The sequential appearance of antibody-coated bacteria in urinary sediment was followed in experimental pyelonephritis produced with Escherichia coli O6:K13:H1. It was possible to determine against which antigen of the organism this antibody was directed. Antibody-coated bacteria appeared by day 11 of infection, a time which coincided with the synthesis of local (intrarenal) antibody. Bacteria coated with antibody more than three days after serum antibody but four days before urinary antibody appeared. Antibody eluted from coated bacteria was directed against the O-antigen of the infecting organism but not the K-antigen. Newly synthesized intrarenal antibody and urinary antibody were directed only against O-antigen, but not against K-antigen; this finding would explain why the antibody that coated the bacteria was antibody to lipopolysaccharide. Thus, a positive test for antibody-coated bacteria indicates that a local immune response to O-antigen has occurred. It is postulated that this immune response could relate to the clinical symptomatology of acute symptomatic pyelonephritis since most patients presenting with acute pyelonephritis have bacteria coated with antibody.