The genetic background of Streptococcus pneumoniae affects protection in mice immunized with PspA

Polyamine transporter in Streptococcus pneumoniae is essential for evading early innate immune responses in pneumococcal pneumonia

Streptococcus pneumoniae is the most common bacterial etiology of pneumococcal pneumonia in adults worldwide. Genomic plasticity, antibiotic resistance and extreme capsular antigenic variation complicates the design of effective therapeutic strategies. Polyamines are ubiquitous small cationic molecules necessary for full expression of pneumococcal virulence. Polyamine transport system is an attractive therapeutic target as it is highly conserved across pneumococcal serotypes. In this study, we compared an isogenic deletion strain of S. pneumoniae TIGR4 in polyamine transport operon (ΔpotABCD) with the wild type in a mouse model of pneumococcal pneumonia. Our results show that the wild type persists in mouse lung 24 h post infection while the mutant strain is cleared by host defense mechanisms. We show that intact potABCD is required for survival in the host by providing resistance to neutrophil killing. Comparative proteomics analysis of murine lungs infected with wild type and ΔpotABCD pneumococci identified expression of proteins that could confer protection to wild type strain and help establish infection. We identified ERM complex, PGLYRP1, PTPRC/CD45 and POSTN as new players in the pathogenesis of pneumococcal pneumonia. Additionally, we found that deficiency of polyamine transport leads to up regulation of the polyamine synthesis genes speE and cad in vitro.

Immunization with Pneumococcal Surface Protein K of Nonencapsulated Streptococcus pneumoniae Provides Protection in a Mouse Model of Colonization

Current vaccinations are effective against encapsulated strains of Streptococcus pneumoniae, but they do not protect against nonencapsulated Streptococcus pneumoniae (NESp), which is increasing in colonization and incidence of pneumococcal disease. Vaccination with pneumococcal proteins has been assessed for its ability to protect against pneumococcal disease, but several of these proteins are not expressed by NESp. Pneumococcal surface protein K (PspK), an NESp virulence factor, has not been assessed for immunogenic potential or host modulatory effects. Mammalian cytokine expression was determined in an in vivo mouse model and in an in vitro cell culture system. Systemic and mucosal mouse immunization studies were performed to determine the immunogenic potential of PspK. Murine serum and saliva were collected to quantitate specific antibody isotype responses and the ability of antibody and various proteins to inhibit epithelial cell adhesion. Host cytokine response was not reduced by PspK. NESp was able to colonize the mouse nasopharynx as effectively as encapsulated pneumococci. Systemic and mucosal immunization provided protection from colonization by PspK-positive (PspK(+)) NESp. Anti-PspK antibodies were recovered from immunized mice and significantly reduced the ability of NESp to adhere to human epithelial cells. A protein-based pneumococcal vaccine is needed to provide broad protection against encapsulated and nonencapsulated pneumococci in an era of increasing antibiotic resistance and vaccine escape mutants. We demonstrate that PspK may serve as an NESp target for next-generation pneumococcal vaccines. Immunization with PspK protected against pneumococcal colonization, which is requisite for pneumococcal disease.

Immunization with pneumolysin protects against both retinal and global damage caused by Streptococcus pneumoniae endophthalmitis

PURPOSE

To determine whether immunization with pneumolysin (PLY) protects against pneumococcal endophthalmitis.

METHODS

New Zealand white rabbits were immunized with a mutant form of PLY that retains only 1% of its cytolytic activity until serum IgG titers were ≥51,200. For a negative control, rabbits were immunized with phosphate-buffered saline (mock). Each vitreous was injected with 10(2) colony-forming units of a clinical endophthalmitis isolate of Streptococcus pneumoniae. Severity of endophthalmitis was graded by slit lamp examination at 24 and 48 h postinfection (PI). Serial dilutions of vitreous were plated for bacterial colony-forming units quantitation, eyes were extracted for histology, and a whole blood survival assay was performed.

RESULTS

Immunized rabbits had a significantly lower mean slit lamp examination score at 24 and 48 h PI when compared to mock immunized rabbits (P ≤ 0.002). There was not a significant difference in bacterial load in the vitreous at 24 or 48 h PI. Histological sections showed that retinas of mock immunized rabbits appeared to be destroyed, whereas those of PLY immunized rabbits remained largely intact. Damage spread to the aqueous humor, stroma, and conjunctiva of mock immunized rabbits by 48 h PI. Minimal damage was observed in the vitreous of PLY immunized rabbits and did not spread to other parts of the eye. Whole blood from immunized rabbits inhibited the growth of bacteria better than whole blood from mock immunized rabbits.

CONCLUSION

Immunization with PLY helps protect the eye from damage caused by pneumococcal endophthalmitis.

Interaction of pneumococcal histidine triad proteins with human complement

The pneumococcal histidine triad (Pht) proteins PhtA, PhtB, PhtD, and PhtE form a group of conserved pneumococcal surface proteins. Humans produce antibodies to Pht proteins upon exposure to pneumococcus, and immunization of mice has provided protective immunity against sepsis and pneumonia and reduced nasopharyngeal colonization. Pht proteins are candidates for inclusion in multicomponent pneumococcal protein vaccines. Their biological function in pneumococcal infections is not clear, but a role in complement inhibition has been suggested. We measured complement deposition on wild-type and Pht mutant strains in four genetic backgrounds: Streptococcus pneumoniae D39 (serotype 2) and R36A (unencapsulated derivative of D39) and strains of serotypes 3, 4, and 19F. PspA and PspC single and double mutants were compared to the wild-type and Pht-deficient D39 strains. Factor H binding was measured to bacterial cells, lysates, and protein antigens. Deletion of all four Pht proteins (Pht(-)) resulted in increased C3 deposition on the serotype 4 strain but not on the other strains. Pht antigens did not bind factor H, and deletion of Pht proteins did not affect factor H binding by bacterial lysates. The Pht(-) mutant serotype 4 strain bound slightly less factor H than the wild-type strain when binding was measured by flow cytometry. Pht proteins may play a role in immune evasion, but the mechanism of function is unlikely to be mediated by factor H binding. The relative contribution of Pht proteins to the inhibition of complement deposition is likely to be affected by the presence of other pneumococcal proteins and to depend on the genetic background.

Pneumococcal virulence gene expression and host cytokine profiles during pathogenesis of invasive disease

Pneumococcal disease continues to account for significant morbidity and mortality worldwide. For the development of novel prophylactic and therapeutic strategies against the disease spectrum, a complete understanding of pneumococcal behavior in vivo is necessary. We evaluated the expression patterns of the proven and putative virulence factor genes adcR, cbpA, cbpD, cbpG, cpsA, nanA, pcpA, piaA, ply, psaA, pspA, and spxB after intranasal infection of CD1 mice with serotype 2, 4, and 6A pneumococci by real-time reverse transcription-PCR. Simultaneous gene expression patterns of selected host immunomodulatory molecules, CCL2, CCL5, CD54, CXCL2, interleukin-6, and tomor necrosis factor alpha, were also investigated. We show that pneumococcal virulence genes are differentially expressed in vivo, with some genes demonstrating niche- and serotype-specific differential expression. The in vivo expression patterns could not be attributed to in vitro differences in expression of the genes in transparent and opaque variants of the three strains. The host molecules were significantly upregulated, especially in the lungs, blood, and brains of mice. The pneumococcal-gene expression patterns support their ascribed roles in pathogenesis, providing insight into which protein combinations might be more appropriate as vaccine antigens against invasive disease. This is the first simultaneous comparison of bacterial- and host gene expression in the same animal during pathogenesis. The strategy provides a platform for prospective evaluation of interaction kinetics between invading pneumococci and human patients in culture-positive cases and should be feasible in other infection models.

Immunization with PspA incorporated into a poly(ethylene oxide) matrix elicits protective immunity against Streptococcus pneumoniae

CBA/N mice were immunized with PspA in a poly(ethylene oxide) matrix to examine its ability to deliver the antigen and modulate the immune response. All mice receiving PspA in the matrix survived a lethal pneumococcal challenge and had serum anti-PspA antibody levels statistically higher than mice receiving PspA alone (P < 0.009).