Stabilized Prefusion F-Protein as Vaccine Antigen
The vaccine delivers a locked prefusion shape of the RSV fusion protein.
- Arexvy/Abrysvo: Vaccines (approved 2023)
- Prefusion F: Antigen form (engineered stable)
- Recombinant: Platform (protein subunit)
- F-protein: Target (fusion machinery)
Why prefusion shape matters
Locking F-protein pre-fusion exposes better neutralizing epitopes.
Antigen-Presenting Cells Detect the Antigen
Dendritic cells capture antigen and present it to helper T cells.
- Dendritic: Cell type (antigen-presenting)
- MHC-II: Signal (presentation pathway)
- T-helper: Response (activation)
- Days 1-3: Timeframe (post-injection)
From antigen to activation
Recognition triggers downstream B-cell help signals.
B Cells Differentiate into Antibody-Secreting Plasma Cells
Activated B cells expand and mature into plasma cells over weeks.
- ~Week 4: Peak titer (post-vaccination)
- IgG: Antibody type (neutralizing)
- Plasma cells: Cell source (bone marrow, lymph)
- B cells: Memory (long-term)
Titer rise over time
Antibody levels climb quickly then plateau and slowly decline.
Circulating Antibodies Bind RSV F-Protein Spikes
Neutralizing antibodies attach directly to F-protein on virions.
- Site Ø/V: Binding site (prefusion epitopes)
- Neutralization: Effect (blocks infectivity)
- Microneutralization: Assay (titer measured)
- RSV-A/B: Coverage (both subtypes)
Antibody-virion binding
Bound antibodies coat spikes, tagging virions as neutralized.
Fusion Blockade Prevents Host Cell Entry
Antibody-coated F-protein cannot trigger membrane fusion into cells.
- ~82%: Efficacy older adults (severe disease)
- ~82%: Efficacy maternal (infant protection)
- Fusion block: Mechanism (entry prevented)
- Reduced LRTD: Outcome (lower respiratory disease)
End result of protection
Virus is neutralized before it can fuse and infect cells.
Placeholder: durability declines gradually after peak response.