Abstract
Vaccines play a vital role in modern medicine. The development of novel vaccines for emerging and resistant pathogens has been aided in recent years by the use of novel adjuvants in subunit vaccines. A deeper understanding of the molecular pathways behind adjuvanticity is required to better select immunostimulatory molecules for use in individual vaccines. To this end, we have undertaken a study of the essential signaling pathways involved in the innate and adaptive immune responses to the Neisseria meningitidis outer membrane protein Porin B (PorB). We have previously demonstrated that PorB is an agonist of Toll-Like Receptor 2 (TLR2) and acts as an adjuvant in vaccines for protein, carbohydrate and lipopolysaccharide antigens using murine models. Here we demonstrate NFκB translocation following stimulation with PorB only occurs in the presence of TLR2. IL-6 and TNF-α secretion was shown to be MAPK dependent. Surface expression of activation markers on macrophages, including CD40, CD69, and CD86, was increased following PorB stimulation in vitro. Interestingly, some upregulation of CD54 and CD69 was still observed in macrophages obtained from TLR2 KO mice, indicating a possible non-TLR2 mediated activation pathway induced by PorB. In a murine vaccination model, using ovalbumin as the antigen and PorB as the adjuvant, a decreased antigen-specific IgG production was observed in TLR2 KO mice; adjuvant-dependent increased IgG production was entirely ablated in MyD88 KO mice. These observations demonstrate the importance of the above pathways to the adjuvant activity of PorB. The potential TLR2 independent effect is currently being explored.
Highlights
Vaccines against infectious diseases have been one of modern medicines greatest tools in the last century [1]
We confirm the Toll-Like Receptor 2 (TLR2)-dependent ability of Porin B (PorB) to induce secretion of inflammatory mediators in vitro and show evidence of Mitogen Activated Protein Kinase (MAPK) signaling pathway induction We report that PorB requires TLR2 to induce expression of multiple co-stimulatory molecules on Antigen Presenting Cells (APCs), and maximal antigen-specific IgG production when used as a vaccine adjuvant in the murine model
To demonstrate that PorB stimulated the release of pro-inflammatory cytokines, we measured the release of IL-6 and TNFα by C57BL/6 bone marrow derived macrophages (BMDM) in response to PorB
Summary
Vaccines against infectious diseases have been one of modern medicines greatest tools in the last century [1] Many of those pathogens that remain a risk in the 21st century, have been stubbornly resistant to classical strategies of vaccine design [2,3,4]. From a rational vaccine design standpoint, it should be possible to pick and choose among the vast array of available PAMPs for specific vaccine adjuvants each tailored to a desired outcome [7,23] For this to be possible, a more detailed knowledge of the molecular mechanisms behind each ligand, and the skewing of the immune response generated by the presence of those ligands, is required. We set out to characterize, in more detail, the pathways activated by one particular TLR2 ligand, the outer membrane protein (OMP) Porin B (PorB) from Neisseria meningitidis [24]
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