Cross-Reactivity of Antipneumococcal Surface Protein C (PspC) Antibodies with Different Strains and Evaluation of Inhibition of Human Complement Factor H and Secretory IgA Binding via PspC

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Pneumococcal surface protein C (PspC) is an important candidate for a cost-effective vaccine with broad coverage against pneumococcal diseases. Previous studies have shown that<jats:named-content content-type="genus-species">Streptococcus pneumoniae</jats:named-content>is able to bind to both human factor H (FH), an inhibitor of complement alternative pathway, and human secretory IgA (sIgA) via PspC. PspC was classified into 11 groups based on variations of the gene. In this work, we used three PspC fragments from different groups (PspC3, PspC5, and PspC8) to immunize mice for the production of antibodies. Immunization with PspC3 induced antibodies that recognized the majority of the clinical isolates as analyzed by Western blotting of whole-cell extracts and flow cytometry of intact bacteria, while anti-PspC5 antibodies showed cross-reactivity with the paralogue pneumococcal surface protein A (PspA), and anti-PspC8 antibodies reacted only with the PspC8-expressing strain. Most of the isolates tested showed strong binding to FH and weaker interaction with sIgA. Preincubation with anti-PspC3 and anti-PspC5 IgG led to some inhibition of binding of FH, and preincubation with anti-PspC3 partially inhibited sIgA binding in Western blotting. The analysis of intact bacteria through flow cytometry showed only a small decrease in FH binding after incubation of strain D39 with anti-PspC3 IgG, and one clinical isolate showed inhibition of sIgA binding by anti-PspC3 IgG. We conclude that although anti-PspC3 antibodies were able to recognize PspC variants from the majority of the strains tested, partial inhibition of FH and sIgA binding through anti-PspC3 antibodies<jats:italic>in vitro</jats:italic>could be observed for only a restricted number of isolates.</jats:p>

Mapping of Epitopes Recognized by Antibodies Induced by Immunization of Mice with PspA and PspC

“…Antibodies to a PspC from group 11 (PspC11) were shown in flow cytometry experiments to block the binding of FH to the homologous serotype 3 strain expressing PspC11 (50). Results published by our group also showed that preincubation with IgG anti-PspC3 led to partial inhibition of FH and sIgA binding to strains expressing different PspC variants in Western blot analyses and flow cytometry experiments (33). In summary, we mapped immunogenic linear epitopes at the initial N-terminal region of PspA, but the induction of antibodies against these epitopes did not confer protection to mice against a lethal pneumococcal challenge.…”

“…Thus, the choice of PspA and PspC molecules capable of inducing antibodies with broad cross-reactivities is essential. We previously showed that PspA from clade 4 (PspA4), PspA from clade 5 (PspA5), and PspC from group 3 (PspC3) induced antibodies that recognized the majority of the pneumococcal clinical isolates tested (31)(32)(33). Alternatively, cross-reactive immunogenic epitopes present in PspA and PspC can be selected to compose a multiepitope protein vaccine.…”

Expression of Streptococcus pneumoniae Virulence-Related Genes in the Nasopharynx of Healthy Children

“…These factors include the capsular polysaccharide, pneumococcal pneumolysin (Ply), adhesins, several proteins implicated in fratricide and regulators. Some of the best characterized candidates as proteinaceous components of new vaccine formulations are Ply [22], [23], pneumococcal surface protein A (PspA) [24], [25], pneumococcal surface protein C (PspC) [26] and pneumococcal surface antigen A (PsaA). There is a lack of information, however, to evaluate expression of these vaccine candidates or other pneumococcal proteins in the human nasopharynx during carriage, or in any other anatomic site during disease.…”

Streptococcus pneumoniae PspC Subgroup Prevalence in Invasive Disease and Differences in Contribution to Complement Evasion

“…Analysis of strain collections including carriage and invasive isolates from the same region and period may help to further dissect the contribution of PspC subgroups and types to invasive disease potential. Additionally, more insight into epidemiological differences in PspC type prevalence and their contributions to invasive disease may have implications for vaccine design, because PspC is an important vaccine candidate (46)(47)(48). Our study demonstrates PspC subgroup and type distributions in invasive disease analogous to serotype distribution in invasive disease.…”