Nathalie Charland

Streptococcus suis serotype 2 interactions with human brain microvascular endothelial cells

ABSTRACT Streptococcus suis serotype 2 is a worldwide causative agent of many forms of swine infection and is also recognized as a zoonotic agent causing human disease, including meningitis. The pathogenesis of S. suis infections is poorly understood. Bacteria circulate in the bloodstream in the nonimmune host until they come in contact with brain microvascular endothelial cells (BMEC) forming the blood-brain barrier. The bacterial polysaccharide capsule confers antiphagocytic properties. It is known that group B streptococci (GBS) invade and damage BMEC, which may be a primary step in the pathogenesis of neonatal meningitis. Interactions betweenS. suis and human endothelial cells were studied to determine if they differ from those between GBS and endothelial cells. Invasion assays performed with BMEC and human umbilical vein endothelial cells demonstrated that unlike GBS, S. suisserotype 2 could not invade either type of cell. Adherence assays showed that S. suis adhered only to BMEC, whereas GBS adhered to both types of cell. These interactions were not affected by the presence of a capsule, since acapsular mutants from both bacterial species adhered similarly compared to the wild-type strains. Lactate dehydrogenase release measurements indicated that some S. suis strains were highly cytotoxic for BMEC, even more than GBS, whereas others were not toxic at all. Cell damage was related to suilysin (S. suis hemolysin) production, since only suilysin-producing strains were cytotoxic and cytotoxicity could be inhibited by cholesterol and antisuilysin antibodies. It is possible that hemolysin-positive S. suis strains use adherence and suilysin-induced BMEC injury, as opposed to direct cellular invasion, to proceed from the circulation to the central nervous system.

Prevention of Pneumococcal Disease in Mice Immunized with Conserved Surface-Accessible Proteins

ABSTRACT The development of a vaccine against Streptococcus pneumoniae has been complicated by the existence of at least 90 antigenically distinct capsular serotypes. Common protein-based vaccines could represent the best strategy to prevent pneumococcal infections, regardless of serotype. In the present study, the immunoscreening of an S. pneumoniae genomic library allowed the identification of a novel immune protein target, BVH-3. We demonstrate that immunization of mice with BVH-3 elicits protective immunity against experimental sepsis and pneumonia. Sequence analysis revealed that the bvh-3 gene is highly conserved within the species. Since the BVH-3 protein shows homology at its amino-terminal end with other pneumococcal proteins, it was of interest to determine if protection was due to the homologous or to the protein-specific regions. Immunoprotection studies using recombinant BVH-3 and BVH-3-related protein fragments as antigens allowed the localization of surface-exposed and protective epitopes at the protein-specific carboxyl termini, thus establishing that BVH-3 is distinct from other previously reported protective protein antigens. Immunization with a chimeric protein comprising the carboxyl-terminal regions of BVH-3 and of a BVH-3-related protein improved the protection by targeting two surface pneumococcal components. Thus, BVH-3 and the chimeric protein hold strong promise as vaccine components to control pneumococcal disease.

Protection from Group B Streptococcal Infection in Neonatal Mice by Maternal Immunization with Recombinant Sip Protein

ABSTRACT The protective potential of antibodies directed against group B streptococcus (GBS) Sip surface protein was determined by using the mouse neonatal infection model. Rabbit Sip-specific antibodies administered passively to pregnant mice protected their pups against a GBS lethal challenge. In addition, active immunization with purified recombinant Sip protein of female CD-1 mice induced the production of specific antibodies that also confer protection to the newborn pups against GBS strains of serotypes Ia/c, Ib, II, III, and V. These data confirm that Sip-specific antibodies can cross the placenta and conferred protective immunity against GBS infections.

Universal Proteins As an Alternative Bacterial Vaccine Strategy

In the last two decades, discoveries in biological sciences have allowed vaccine research to expand rapidly. Progress in the understanding of the regulatory mechanisms of the immune response to infection, molecular biology, genomics, proteomics and bioinformatics have revolutionized the way vaccines are designed. Vaccinology has established its own credibility, and it is no longer only a subject in microbiology and immunology classes but a true complex discipline. Vaccines are no longer just crude and complex preparations of killed or attenuated microorganisms but can be defined as proteins, polysaccharides (Ps), or nucleic acids that are delivered to the immune system as single entities, as part of complex particles, or by live attenuated agents or vectors, thereby inducing specific responses that inactivate, destroy, or suppress pathogens1.