A 26-year-old man develops dysuria and purulent urethral discharge following unprotected sex with a new partner. Nucleic acid amplification testing is positive for Neisseria gonorrhoeae infection. The patient develops antibody against the bacterial pili that enhance attachment to host cells. His symptoms resolve with adequate treatment. His partner does not receive treatment. Several weeks later, the patient develops N gonorrhoeae reinfection after repeat exposure to the same partner. Which of the following is the most likely reason for the lack of long-lasting immunity against the bacteria despite antibody formation in this patient?

Question

A 26-year-old man develops dysuria and purulent urethral discharge following unprotected sex with a new partner.  Nucleic acid amplification testing is positive for Neisseria gonorrhoeae infection.  The patient develops antibody against the bacterial pili that enhance attachment to host cells.  His symptoms resolve with adequate treatment.  His partner does not receive treatment.  Several weeks later, the patient develops N gonorrhoeae reinfection after repeat exposure to the same partner.  Which of the following is the most likely reason for the lack of long-lasting immunity against the bacteria despite antibody formation in this patient?

Quizplus · Accepted Answer

Many strains of Neisseria gonorrhoeae have pili, hair-like protein polymers projecting from the bacterial surface that are involved in organism attachment to mucosal surfaces. When the host produces antibodies against gonococcal pili, mucosal adherence is inhibited. At a given time, only 1 pilus gene is functional, so only 1 pilus type is expressed. However, the structural genes for pilus proteins undergo antigenic variation at a high frequency; they undergo recombination with each other to produce new antigenic types of pili. The number of possible antigenic pilus types is theoretically quite large. This diversity is a reason that vaccine development against N gonorrhoeae pili has been challenging. (Choice A) Antigenic mimicry is the sharing of antigenic sequences between the microorganism and the host cell, facilitating immune evasion. The gonococcal lipooligosaccharide is similar in structure to human cell membrane glycosphingolipids. However, this is not related to antibody formation against the pilus. Antigenic mimicry can lead to autoimmune disease if the host mounts an immune response against the infectious epitope and that epitope has sufficient sequence homology with a host antigen. (Choice C) Plasmid conjugation plays an important role in gonococcal antibiotic resistance. (Choice D) Pilin proteins do not represent a low molecular weight structure that would be poorly immunogenic. (Choice E) Gonococcal pili are protein polymers. In addition, vaccines have been developed against non-protein structures (eg, meningococcal vaccine, pneumococcal vaccine). Educational objective: Gonococci use their pili to mediate adherence to the mucosal epithelium. Through antigenic variation, each gonococcus can modify the pilus protein expressed, thereby avoiding host defenses (to some degree) and making vaccination directed against the pilus protein difficult.

A 26-Year-Old Man Develops Dysuria and Purulent Urethral Discharge Following