Immune response in urinary tract infection determined by radioimmunoassay and immunofluorescence: serum antibody levels against infecting bacterium and Enterobacteriaceae common antigen

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Abstract
A solid-phase radioimmunoassay (RIA) procedure was compared with the indirect fluorescent antibody (IFA) test in a serological study of 76 female adults with urinary tract infections. Relative serum antibody activity was determined against patients'' homologous infecting enterobacteria by RIA and IFA and against heterologous enterobacterial common antigen (Escherichia coli O14) by RIA. There was marked correlation between results of the IFA and RIA methods using the homologous system; 22 of 51 patients (43%) with pyelonephritis had significantly elevated serum antibody activity by both IFA (titers .gtoreq. 512) and RIA (binding ratio .gtoreq. 2.0) when compared with normal serum controls; 3 had significant antibody activity detectable by RIA only. Eighteen (72%) of 25 patients with pyelonephritis had RIA binding ratios of .gtoreq. 2.0 against their homologous bacterial isolates and the enterobacterial common antigen; an additional 6 patients had binding ratios of .gtoreq. 2.0 against the antigen only. All 25 patients with cystitis had low serum antibody levels by IFA and RIA when tested against their own isolate as well as enterobacterial common antigen. The RIA procedure was objective, quantitative, and less tedious to perform than IFA.