| PilE is the primary subunit of type IV pili from Neisseria gonorrhoeae , and contains a surface-exposed hypervariable region that has prevented development of a pilin-based vaccine. We have created a 3-D structure-based antigen by replacing the hypervariable region of PilE with an aspartate-glutamine linker chosen from the sequence of Pseudomonas aeruginosa PilA. We then characterized murine immune responses to this novel protein to determine if HE conserved regions could serve as a vaccine candidate. The control PilE protein elicited strong T cell-dependent B cell responses that are specific to epitopes in both the hypervariable deletion and control proteins. In contrast, the hypervariable deletion protein was unable to elicit an immune response in mice, suggesting that in the absence of the hypervariable region, the conserved regions of PilE alone are not sufficient for antibody production. Further analysis of these PilE proteins with suppressor cell assays showed that neither suppresses T or B cell responses, and flow cytometry experiments suggested they do not exert suppressor effects by activating T regulatory cells. Our results definitively show that the hypervariable region of PilE is required to activate immune responses to pilin, whereas the conserved regions are unusually nonimmunogenic. In addition, we show that both hypervariable and conserved regions of pilin are not suppressive, suggesting that PilE does not cause the decrease in T cell populations observed during gonococcal cervicitis. This work describes the creation of a novel PilE protein using the conserved regions of PilE. In this dissertation I have not only demonstrated that the HE conserved region would not be an appropriate vaccine component, but have also shown that regions of a bacterial protein can be immuno-silent without homology to mammalian proteins. |
