Protection against experimental pyelonephritis by antibodies to pili

Bacterial pili have been shown to be an important virulence factor for urinary tract infections. In this report we relate the results of studies which evaluated the influence of antipili antibody on the susceptibility of rats to ascending pyelonephritis and on several antibody-mediated antibacterial mechanisms. Rats immunized with E. coli type 1 pili, and animals infected with E. coli developed antipili antibodies in their serum. Active or passive immunization of rats with pili protected the animals from ascending pyelonephritis. Antipili antibody did not mediate complement-dependent bacteriolysis, opsonophagocytosis or promote more rapid intravascular clearance of injected E. coli. Humoral immunity to pili did, however, effectively inhibit bacterial adherence to epithelial cells. These studies indicate that type 1 E. coli pili are immunogenic and that antipili antibodies afford protection from ascending pyelonephritis. They suggest further that a mechanism of protection is inhibition of bacterial adherence.