Urinary IgG antibody against mixed heat-killed coliform antigen and lipopolysaccharide core antigen.

AIMS To determine whether antibody to lipopolysaccharide-core (LPS-core) antigen is an important component of the antibody, detected by mixed heat-killed coliform antigen, in urine from patients with suspected urinary tract infection. METHODS LPS-core antigen and mixed heat-killed coliform antigen were used in an enzyme linked immunosorbent assay (ELISA) to measure IgG antibody in midstream urine samples. Seventy two samples from students attending their general practitioner with symptoms suggestive of urinary tract infection, six samples from which a Gram positive organism was isolated, and 16 asymptomatic controls were tested. Plates coated with LPS-core antigen were also used to absorb out the antibody detected by the mixed heat-killed coliform antigen. RESULTS Antibody to either antigen was associated with a positive culture, but neither was a useful predictor of a positive culture. There was a significant correlation between the results of the two assays (r = 0.7633; p less than 0.001), and absorption with LPS-core antigen did reduce the level of antibody to the mixed heat-killed coliform antigen. Antibody to both preparations was found in patients with Gram positive urinary tract infection. CONCLUSION Antibody to LPS-core antigen forms a substantial part of the antibody detected by mixed heat-killed coliform ELISA. The antibodies detected by these assays are probably the result of non-specific leakage of antibody into the urine, rather than a specific immune response.