Serum and urogenital antibody responses to Escherichia coli pili in cystitis.

Antipili antibody (APA) was quantitated by enzyme-linked immunosorbent assay in the serum, urine, and vaginal secretions of 12 women with cystitis due to Escherichia coli. Pili were purified from the strain infecting each patient. The geometric mean titers of APA in serum taken at the initial visit were: immunoglobulin G (IgG), 23.7 +/- 3.9; IgA, 4.1 +/- 4.0; and IgM, 4.4 +/- 5.7. No consistent change was observed between samples obtained at 3 and 6 weeks. APA in serum from 10 control patients was assayed against a pool of pili assembled from the 12 infecting isolates. The geometric mean titers of the control sera were: IgG, 8.4 +/- 3.2; IgA, 9.6 +/- 2.4; and IgM, 0. Antipili IgG and IgM were significantly greater in the infected than in the control sera (P less than 0.05). APA was not detected in the urine or vaginal secretions from any infected or control patient. Antigenic relationships between the 12 infecting strains were investigated by indirect immune electron microscopy. All but 1 of 12 infecting strains shared antigenic determinants. Two patients had a second E. coli infection during the study. The pili of the reinfecting isolates showed partial antigenic cross-reactivity with the pili of the initial infecting bacteria. These observations indicate that although cystitis stimulates the development of serum APAs, it fails to stimulate local APA and thus may not engender any immunological barrier to subsequent recolonization.