Our laboratory has focused on Porin B (PorB), an outer membrane protein from Neisseria meningitidis and TLR2 ligand-based adjuvant, to characterize specific molecular and cellular pathways involved in improved immune responses induced by vaccine adjuvants. PorB's ability to form micellar nanoparticular multi-molecular organized structures and its interaction with Toll-like receptor 2/1 complexes likely accounts for its potent adjuvant activity. Downstream from this stimulation, we have observed enhanced antigen uptake in antigen presenting cells (APC), greater antigen deposition in secondary lymphoid organs, and promotion of germinal center reactions. In mice, antigen-specific IgGs were increased after PorB adjuvanted vaccination using the model antigen ovalbumin (OVA). Likewise, this formulation resulted in more IL-4 and IFN-γ positive T cells. Mice that received PorB adjuvanted vaccinations benefitted from lower bacterial burdens when challenged with recombinant Listeria monocytogenes expressing OVA. Mouse models lacking MyD88 signaling in various APC types helped identify macrophages as an essential cell type for the adjuvant activity of PorB. We believe the work presented here provides examples of the mechanistic studies required to understand how vaccine adjuvants are contributing to the establishment of protective immunity.
Keywords: Adjuvant; MyD88; Neisseria meningitidis; PorB; TLR; germinal center.