Deconvolution of intergenic polymorphisms determining high expression of Factor H binding protein in meningococcus
Marco Spinsanti1, Tarcisio Brignoli1,2, Margherita Bodini1
1GSK, Siena, Italy.
Abstract:
Neisseria meningitidis is a strictly human pathogen and is the major cause of septicemia and meningitis worldwide. Factor H binding protein (fHbp) is a meningococcal surface-exposed lipoprotein that binds the human Complement factor H allowing the bacterium to evade the host innate immune response. FHbp is also a key antigen in two vaccines against N. meningitidis serogroup B. Although the fHbp gene is present in most circulating meningococcal strains, level of fHbp expression varies among isolates and has been correlated to differences in promoter sequences upstream of the gene. Here we elucidated the sequence determinants that control fHbp expression in globally circulating strains. We analyzed the upstream fHbp intergenic region (fIR) of more than 5800 strains representative of the UK circulating isolates and we identified eleven fIR sequence alleles which represent 88% of meningococcal strains. By engineering isogenic recombinant strains where fHbp expression was under the control of each of the eleven fIR alleles, we confirmed that the fIR sequence determines a specific and distinct level of expression. Moreover, we identified the molecular basis for variation in expression through polymorphisms within key regulatory regions that are known to affect fHbp expression. We experimentally established three expression groups, high-medium-low, that correlated directly with the susceptibility to killing mediated by anti-fHbp antibodies and the ability of the meningococcal strain to survive within human serum. By using this sequence classification and information about the variant, we predicted fHbp expression in the panel of UK strains and we observed that strains with higher expressing fIR alleles are more likely associated with invasive disease. Overall, our findings can contribute to understand and predict vaccine coverage mediated by fHbp as well as to shed light on the role of this virulence factor in determining an invasive phenotype.
Insights
Sequence variations in the Factor H binding protein (fHbp) intergenic region (fIR) of Neisseria meningitidis influence fHbp expression levels. These variations impact bacterial survival and association with invasive disease, informing vaccine strategies.
Area of Science:
- Microbiology
- Immunology
- Genetics
Background:
- Neisseria meningitidis causes severe invasive diseases like meningitis and septicemia globally.
- Factor H binding protein (fHbp) is a key meningococcal virulence factor and vaccine antigen, crucial for evading host immunity.
- fHbp expression levels vary significantly between strains, impacting disease potential and vaccine efficacy.
Purpose of the Study:
- To identify sequence determinants controlling fHbp expression in Neisseria meningitidis.
- To correlate fHbp expression levels with bacterial virulence and susceptibility to host immune responses.
- To inform the development of more effective vaccines against serogroup B meningococcal disease.
Main Methods:
- Analysis of over 5800 Neisseria meningitidis isolates from the UK to identify fHbp intergenic region (fIR) alleles.
- Engineering of isogenic strains to assess the impact of different fIR alleles on fHbp expression.
- Experimental determination of bacterial susceptibility to complement-mediated killing and serum survival.
Main Results:
- Eleven fIR sequence alleles were identified, accounting for 88% of UK meningococcal strains, each conferring distinct fHbp expression levels.
- Polymorphisms in regulatory regions of the fIR were identified as the molecular basis for expression variation.
- High fHbp expression correlated with increased resistance to anti-fHbp antibodies and serum survival, and was associated with invasive disease phenotypes.
Conclusions:
- The fHbp intergenic region sequence is a critical determinant of fHbp expression in Neisseria meningitidis.
- fHbp expression levels significantly influence bacterial virulence and immune evasion.
- Understanding these sequence-expression-virulence relationships is vital for predicting vaccine effectiveness and disease risk.
