The predominant proteins in the outer membranes of N. gonorrhoeae are trimeric porin proteins (PI). They are considered good vaccine candidates because porin protein is expressed by all strains, they are surface exposed, and, although antigenic variation exists between different strains, there is no phase variation during an infection as there is for both pilin and lipooligosaccharide (LOS). A model of these neisserial porin proteins predicts eight surface exposed loops. Regions of variability between serotypes in the genes coding for these proteins have been mapped and it is predicted that these variable region (VR) loops form the epitopes for both serotyping and bactericidal antibodies. A genotyping method to differentiate VRs of PIB strains of N. gonorrhoeae has been developed. Five collections of gonococcal isolates have been typed using this method: (1) 24 endemic Korean strains from experimental vaccinees, (2) a panel of 17 temporally and geographically diverse strains, (3) a group of partner strains from a Baltimore STD clinic, (4) additional partner strains, (5) strains with published sequences for reference (Dr, M. Hobbs, North Carolina). The results suggest that in a group of temporally and geographically related strains there is a limited degree of variation in regions of the PI protein that are of suspected immunologic importance. Differences between strains of the same serovar and similarities between strains of different serovar were found illustrating that a variable region specific typing system is preferable in studies designed to address questions about the antigenicity and protective potential of the PI gonococcal protein. Sexual contact pairs from Baltimore and the U.K. showed identical hybridizations for each variable region typed except for one discordant (PIA _ PIB)pair. Comparison of hybridization results with PIB sequence data showed the variable region sequence was identical to the hybridizing probe in > 50% of cases, and the greatest difference seen between actual sequence and probe sequence was 2 base pairs. This work was presented at the 1999 ASM General meeting and at a workshop at the ISSTDR meeting, July 1999, in Denver, CO., and has been published. A similar typing system has been developed for gonococcal PIA strains. Both PIA and PIB probes have been adapted for use in checkerboard hybridization experiments which allows for typing of up to 35 strains with up to 40 probes per hybridization. We are currently examining the molecular epidemiology of gonococcal PI protein VRs in strains collected over the past 10 years in the STD clinics of Baltimore City using our PI VR typing method. This project is supported by an FDA Office of Women's Health Grant.
