Protective Activity of Streptococcus pneumoniae Spr1875 Protein Fragments Identified Using a Phage Displayed Genomic Library

There is considerable interest in pneumococcal protein antigens capable of inducing serotype-independent immunoprotection and of improving, thereby, existing vaccines. We report here on the immunogenic properties of a novel surface antigen encoded by ORF spr1875 in the R6 strain genome. An antigenic fragment encoded by spr1875, designated R4, was identified using a Streptococcus pneumoniae phage displayed genomic library after selection with a human convalescent serum. Immunofluorescence analysis with anti-R4 antisera showed that Spr1875 was expressed on the surface of strains belonging to different serotypes. Moreover, the gene was present with little sequence variability in 27 different pneumococcal strains isolated worldwide. A mutant lacking Spr1875 was considerably less virulent than the wild type D39 strain in an intravenous mouse model of infection. Moreover, immunization with the R4 recombinant fragment, but not with the whole Spr1875 protein, induced significant protection against sepsis in mice. Lack of protection after immunization with the whole protein was related to the presence of immunodominant, non-protective epitopes located outside of the R4 fragment. In conclusion, our data indicate that Spr1875 has a role in pneumococcal virulence and is immunogenic. As the R4 fragment conferred immunoprotection from experimental sepsis, selected antigenic fragments of Spr1875 may be useful for the development of a pneumococcal protein-based vaccine

Induction of T Helper Type 1 Responses by a Polysaccharide Deacetylase from Cryptococcus neoformans

A 25-kDa cryptococcal deacetylase (d25) was found here to induce cell proliferation, as well as secretion of interleukin 2 and gamma interferon, but not interleukin 4, in spleen cells from d25-immunized or Cryptococcus neoformans-infected mice. The gamma interferon, but not the interleukin 2, response was required for the protective activities of d25 immunization in a murine cryptococcosis model

Lysine Residues in the MK-Rich Region Are Not Required for Binding of the PbsP Protein From Group B Streptococci to Plasminogen

Binding to plasminogen (Plg) enables bacteria to associate with and invade host tissues. The cell wall protein PbsP significantly contributes to the ability of group B streptococci, a frequent cause of invasive infection, to bind Plg. Here we sought to identify the molecular regions involved in the interactions between Plg and PbsP. The K4 Kringle domain of the Plg molecule was required for binding of Plg to whole PbsP and to a PbsP fragment encompassing a region rich in methionine and lysine (MK-rich domain). These interactions were inhibited by free L-lysine, indicating the involvement of lysine binding sites in the Plg molecule. However, mutation to alanine of all lysine residues in the MK-rich domain did not decrease its ability to bind Plg. Collectively, our data identify a novel bacterial sequence that can interact with lysine binding sites in the Plg molecule. Notably, such binding did not require the presence of lysine or other positively charged amino acids in the bacterial receptor. These data may be useful for developing alternative therapeutic strategies aimed at blocking interactions between group B streptococci and Plg

Protective activity of a protein fragment identified by screening of a phage display genomic library of Streptococcus pneumoniae

Objective: Streptococcus pneumoniae is a major cause of morbidity and mortality worldwide. The pathogenicity of pneumococci has been attributed to various virulence factors, most of which are located on its surface. The present study was undertaken to identify novel virulence factors and antigens with immunoprotective activity by using a phage display genomic library of Streptococcus pneumoniae. Methods. A lambda phage display library from the D39 S. pneumoniae strain was selected using sera from patients convalescing from invasive pneumococcal disease. For virulence studies, adult BALB/c mice (Charles River) were inoculated i.v. with the wild type D39 strain or with an equal number of CFUs from a mutant lacking spr1875 (Δspr1875). Results. Using one a convalescent serum, we selected from the phage display library an insert encoding for a fragment designated as R4, 161 amino acid in length, whose sequence matched ORF spr1875 D39 genome. This ORF encoded for a putative surface protein with a signal peptide and a LysM domain, which is found in a number of important virulence factors. To evaluate whether the spr1875 protein is involved in pneumococcal pathogenicity we constructed the Δspr1875. Using 7 x 106 CFUs for challenge, all mice inoculated with D39 died in six days, while 80% of the mice challenged with Δspr1875 survived. The R4 fragment was capable of inducing significant, albeit partial, protection in mice inoculated with a wide variety of virulent streptococcal strains. Conclusion. We have identified a novel virulence factor of S. pneumoniae that showed protective activity in a mouse model of systemic pneumococcal disease. Further studies are needed to characterize the biological activities of this antigen

IFN-alpha/beta signaling is required for polarization of cytokine responses toward a protective type 1 pattern during experimental cryptococcosis

The antiviral activities of type I IFNs have long been established. However, comparatively little is known of their role in defenses against nonviral pathogens. We examined here the effects of type I IFNs on host resistance against the model pathogenic yeast Cryptococcus neoformans. After intratracheal or i.v. challenge with this fungus, most mice lacking either the IFN-alpha/beta receptor (IFN-alpha/beta R) or IFN-beta died from unrestrained pneumonia and encephalitis, while all wild-type controls survived. The pulmonary immune response of IFN-beta/BR-/- mice was characterized by increased expression of IL-4, IL-13, and IL-10, decreased expression of TNF-alpha, IFN-gamma, inducible NO synthetase, and CXCL10, and similar levels of IL-12 mRNA, compared with wild-type controls. Histopathological analysis showed eosinophilic infiltrates in the lungs of IFN-alpha/beta(-/-) mice, although this change was less extensive than that observed in similarly infected IFN-gamma R-deficient animals. Type I IFN responses could not be detected in the lung after intratracheal challenge. However, small, but statistically significant, elevations in IFN-beta levels were measured in the supernatants of bone marrow-derived macrophages or dendritic cells infected with C neoformans. Our data demonstrate that type I IFN signaling is required for polarization of cytokine responses toward a protective type I pattern during cryptococcal infection

Type I IFN signaling is crucial for host resistance against different species of pathogenic bacteria

It is known that host cells can produce type I IFNs (IFN-alpha beta) after exposure to conserved bacterial products, but the functional consequences of such responses on the outcome of bacterial infections are incompletely understood. We show in this study that IFN-alpha beta signaling is crucial for host defenses against different bacteria, including group B streptococci (GBS), pneumococci, and Escherichia coli. In response to GBS challenge, most mice lacking either the IFN-alpha beta R or IFN-beta died from unrestrained bacteremia, whereas all wild-type controls survived. The effect of IFN-alpha beta R deficiency was marked, with mortality surpassing that seen in IFN-gamma R-deficient mice. Animals lacking both IFN-alpha beta R and IFN-gamma R displayed additive lethality, suggesting that the two IFN types have complementary and nonredundant roles in host defenses. Increased procluction of IFN-alpha beta was detected in macrophages after exposure to GBS. Moreover, in the absence of IFN-alpha beta signaling, a marked reduction in macrophage production of IFN-gamma, NO, and TNF-alpha was observed after stimulation with live bacteria or with purified LPS. Collectively, our data document a novel, fundamental function of IFN-alpha beta in boosting macrophage responses and host resistance against bacterial pathogens. These data may be useful to devise alternative strategies to treat bacterial infections

Analysis of the Streptococcus agalactiae exoproteome

International audienceThe two-component regulatory system CovRS is the main regulator of virulence gene expression in Group B Streptococcus (GBS), the leading cause of invasive infections in neonates. In this study we analyzed by mass spectrometry the GBS extracellular protein complex (i.e. the exoproteome) of NEM316 wild-type (WT) strain and its isogenic covRS deletion mutant (ΔcovRS). A total of 53 proteins, 49 of which had classical secretion signals, were identified: 12 were released by both strains while 21 and 20 were released exclusively by WT and ΔcovRS strains, respectively. In addition to known surface proteins, we detected here unstudied cell-wall associated proteins and/or orthologs of putative virulence factors present in other pathogenic streptococci. While the functional role of these proteins remains to be elucidated, our data suggest that the analysis of the exoproteome of bacterial pathogens under different gene expression conditions may be a powerful tool for the rapid identification of novel virulence factors and vaccine candidates

The plasminogen binding protein PbsP is required for brain invasion by hypervirulent CC17 Group B streptococci

Abstract Streptococcus agalactiae (Group B Streptococcus or GBS) is a frequent cause of serious disease in newborns and adults. Epidemiological evidence indicates a strong association between GBS strains belonging to the hypervirulent CC17 clonal complex and the occurrence of meningitis in neonates. We investigate here the role of PbsP, a cell wall plasminogen binding protein, in colonization of the central nervous system by CC17 GBS. Deletion of pbsP selectively impaired the ability of the CC17 strain BM110 to colonize the mouse brain after intravenous challenge, despite its unchanged capacity to persist at high levels in the blood and to invade the kidneys. Moreover, immunization with a recombinant form of PbsP considerably reduced brain infection and lethality. In vitro, pbsP deletion markedly decreased plasmin-dependent transmigration of BM110 through brain microvascular endothelial cells. Although PbsP was modestly expressed in bacteria grown under standard laboratory conditions, pbsP expression was markedly upregulated during in vivo infection or upon contact with cultured brain endothelial cells. Collectively, our studies indicate that PbsP is a highly conserved Plg binding adhesin, which is functionally important for invasion of the central nervous system by the hypervirulent CC17 GBS. Moreover, this antigen is a promising candidate for inclusion in a universal GBS vaccine