Experimental gonococcal urethritis and reinfection with homologous gonococci in male volunteers

Background: Reinfection, a common occurrence with gonorrhea, may result fro m a lack of protective immune response, or from the tremendous gonococcal s train variation. Goal: A two-phase study in human volunteers tested whether experimental inf ection with Neisseria gonorrhoeae MS11mkC would protect against reinfection with the same organisms. Study Design: In phase 1, an intraurethral inoculum of 57,000 piliated, tra nsparent (opacity protein-negative [Opa(-)]) MS11mkC N gonorrhoeae infected 14 of 15 (93%) volunteers. The volunteers were encouraged to delay treatme nt for at least 5 days. In phase 2, which began 2 weeks after treatment for the initial infection, volunteers were inoculated with 7,100 piliated, Opa (-) MS11mkC. Results: The phase 2 challenge infected 6 of 14 (43%) previously infected v olunteers and 5 of 10 (50%) naive control subjects. Phase I volunteers who resisted reinfection were significantly more likely to have had a fourfold or greater increase in lipooligosaccharide immunoglobulin G during phase I than those who did not resist reinfection (P = 0.026). Conclusions: Although infection did not provide protection from reinfection under the conditions used, the results suggest that immunity to reinfectio n is more complex than anticipated by the experimental design.