Summary:
Our study focused on the identification of immunodominant B cell epitopes
within surface pneumococcal virulence proteins in pediatric patients with
invasive pneumococcal disease (IPD). The identification of immunodominant B
cell epitopes within surface pneumococcal virulence proteins is a valuable
approach to define novel vaccine candidates.
To this aim, we evaluated sera from children with IPD against 141
20-mer synthetic peptides covering the entire sequence of major, previously
identified, antigenic fragments within pneumococcal virulence proteins; namely
the choline-binding protein D (CbpD), the pneumococcal histidine triad proteins
(PhtD and PhtE), th pneumococcal surface protein A (PspA), the plasminogen and
fibronectin binding protein B (PfbB) and the zinc metalloproteinase B (ZmpB).
Ten immunodominant B cell epitopes were identified: CbpD-pep4 (amino
acids (aa) 291-310), PhtD-pep11 (aa 88-107), PhtD-pep17 (aa 172-191),
PhtD-pep19 (aa 200-219), PhtE-pep32 (aa 300-319), PhtE-pep40 (aa 79-98),
PfbB-pep76 (aa 180-199), PfbB-pep79 (aa 222-241), PfbB-pep90 (aa 484-503) and
ZmpB-pep125 (aa 431-450). All epitopes were highly conserved among different
pneumococcal serotypes, while four of them were located within the functional
zinc-binding domain of the histidine triad proteins PhtD and PhtE. Peptides
CbpD-pep4, PhtD-pep19 and PhtE-pep40 were broadly recognized by IPD patients’
sera with prevalence of 96.4%, 92.9%, and 71.4% respectively, whereas controls’
sera exhibited only minor reactivities (<10.7%). Peptides’ specificities for
IPD were 93.3%, 95%, and 96.7%, their sensitivities were 96.4%, 92.9% and 71.4%
and their positivity likelihood ratios for IPD were 14.5, 18.6 and 21.4
respectively. Furthermore, purified antibodies against CbpD-pep4, PhtD-pep19,
and PhtE-pep40 readily bound on the surface of different pneumococcal
serotypes, as assessed by FACS and immunofluorescence analysis.
