Gonococcal salpingitis is less likely to recur with Neisseria gonorrhoeae of the same principal outer membrane protein antigenic type.

If protective immunity were to develop following an episode of gonococcal pelvic inflammatory disease (salpingitis), PID should recur with organisms bearing antigens that do not react with these immune mechanisms. To test this hypothesis, gonococci from 15 women with gonococcal PID, who experienced 19 subsequent episodes of gonococcal infection, were serotyped for their principal outer membrane protein (Protein I) antigens. Of nine cases in which the initial and subsequent infections involved the same Protein I serotype, none was associated with recurrence of PID. Of 10 cases in which the initial and subsequent infections involved different Protein I types, five were associated with recurrent PID (p = 0.02). These data suggest that an episode of gonococcal PID produces some immunity to repeated episodes of salpingitis with the same Protein I serotype, while not preventing reinfection with the same Protein I serotype. The immune response to Protein I antigen may thus provide serotype-specific protection against gonococcal salpingitis.