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Expression of an inaccessible P1.7 subtype epitope on meningococcal class 1 proteins
E Wedege1, R Dalseg, D A Caugant
1National Institute of Public Health, Oslo, Norway.
Abstract:
Dot-blot analysis of whole-cell suspensions of meningococci showed that 81% of B:15:P1.16 strains from patients reacted with a monoclonal antibody (MAb) against subtype P1.7. The remaining strains, which did not react on dot-blots or in ELISA, demonstrated the P1.7 subtype epitope on immunoblots after denaturation of the cells with sodium dodecyl sulphate. The monomeric class 1 proteins of the two P1.16 subtype variants had slightly different mol. wts, but bound the P1.7 antibody equally well. These results were explained by a deletion of three codons in the gene encoding the first variable region of the P1.16 class 1 protein. The deletion accounted for the non-exposure of the P1.7 epitope on native cells. Other patient strains, with subtypes P1.3, P1.9 or without any known subtype, also showed a binding site for the P1.7 MAb, which became available only after denaturation. Demonstration of inaccessible epitopes may have consequences for subtype designations and vaccine development.
Insights
Meningococcal P1.16 subtype strains often hide their P1.7 epitope. Denaturation revealed this epitope, impacting meningococcal (Neisseria meningitidis) strain typing and vaccine development.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Neisseria meningitidis (meningococcus) is classified by serogroup and serotype, with outer membrane proteins (OMPs) like PorA being key targets.
- Subtyping of PorA based on variable regions is crucial for epidemiological tracking and vaccine design.
- Previous studies identified distinct PorA subtypes, but the accessibility of epitopes can vary.
Purpose of the Study:
- To investigate the reactivity of meningococcal B:15:P1.16 strains with a monoclonal antibody (MAb) against the P1.7 subtype epitope.
- To determine if the P1.7 epitope is expressed on the surface of native meningococcal cells or becomes accessible after cell treatment.
- To understand the molecular basis for epitope inaccessibility and its implications for meningococcal subtyping and vaccine development.
Main Methods:
- Dot-blot and Enzyme-Linked Immunosorbent Assay (ELISA) were used to assess antibody binding to whole-cell suspensions.
- Immunoblotting after denaturation with sodium dodecyl sulphate (SDS) was performed to expose hidden epitopes.
- Analysis of the molecular weight (mol. wt) of monomeric class 1 proteins and sequencing to identify genetic variations.
Main Results:
- 81% of B:15:P1.16 meningococcal strains reacted with the P1.7 MAb on dot-blots.
- The remaining strains, non-reactive in dot-blots/ELISA, showed P1.7 epitope binding after SDS denaturation.
- A three-codon deletion in the gene for the P1.16 class 1 protein explained the inaccessibility of the P1.7 epitope on native cells.
- Other meningococcal subtypes (P1.3, P1.9) also exhibited P1.7 MAb binding sites only after denaturation.
Conclusions:
- The P1.7 epitope is often masked on native B:15:P1.16 meningococcal cells due to a specific genetic deletion.
- Demonstrating inaccessible epitopes is critical for accurate meningococcal subtyping.
- These findings have significant implications for the development of effective meningococcal vaccines that target conserved or accessible epitopes.