RESUMO
Streptococcus pneumoniae is a problematic infectious agent, whose seriousness to human health has been underscored by the recent rise in the frequency of isolation of multidrug-resistant strains. Pneumococcal pneumonia in the elderly is common and often fatal. Young children in the developing world are at significant risk for fatal pneumococcal respiratory disease, while in the developed world otitis media in children results in substantial economic costs. Immunocompromised patients are extremely susceptible to pneumococcal infection. With 90 different capsular types thus far described, the diversity of pneumococci contributes to the challenges of preventing and treating S. pneumoniae infections. The current capsular polysaccharide vaccine is not recommended for use in children younger than 2 years and is not fully effective in the elderly. Therefore, innovative vaccine strategies to protect against this agent are needed. Given the immunogenic nature of S. pneumoniae proteins, these molecules are being investigated as potential vaccine candidates. Pneumococcal surface protein A (PspA) has been evaluated for its ability to elicit protection against S. pneumoniae infection in mouse models of systemic and local disease. This review focuses on immune system responsiveness to PspA and the ability of PspA to elicit cross-protection against heterologous strains. These parameters will be critical to the design of broadly protective pneumococcal vaccines.
Assuntos
Proteínas de Bactérias/imunologia , Vacinas Bacterianas/imunologia , Pneumonia Pneumocócica/prevenção & controle , Streptococcus pneumoniae/imunologia , Animais , Humanos , CamundongosRESUMO
A live oral recombinant Salmonella vaccine strain expressing pneumococcal surface protein A (PspA) was developed. The strain was attenuated with Deltacya Deltacrp mutations. Stable expression of PspA was achieved by the use of the balanced-lethal vector-host system, which employs an asd deletion in the host chromosome to impose an obligate requirement for diaminopimelic acid. The chromosomal Deltaasd mutation was complemented by a plasmid vector possessing the asd+ gene. A portion of the pspA gene from Streptococcus pneumoniae Rx1 was cloned onto a multicopy Asd+ vector. After oral immunization, the recombinant Salmonella-PspA vaccine strain colonized the Peyer's patches, spleens, and livers of BALB/cByJ and CBA/N mice and stimulated humoral and mucosal antibody responses. Oral immunization of outbred New Zealand White rabbits with the recombinant Salmonella strain induced significant anti-PspA immunoglobulin G titers in serum and vaginal secretions. Polyclonal sera from orally immunized mice detected PspA on the S. pneumoniae cell surface as revealed by immunofluorescence. Oral immunization of BALB/cJ mice with the PspA-producing Salmonella strain elicited antibody to PspA and resistance to challenge by the mouse-virulent human clinical isolate S. pneumoniae WU2. Immune sera from orally immunized mice conferred passive protection against otherwise lethal intraperitoneal or intravascular challenge with strain WU2.
Assuntos
Antígenos de Bactérias/imunologia , Proteínas de Bactérias/imunologia , Vacinas Bacterianas/imunologia , Vetores Genéticos , Infecções Pneumocócicas/prevenção & controle , Salmonella typhimurium , Streptococcus pneumoniae/imunologia , Vacinas Sintéticas/imunologia , Administração Oral , Animais , Anticorpos Antibacterianos/imunologia , Antígenos de Bactérias/genética , Proteínas de Bactérias/genética , Vacinas Bacterianas/genética , Avaliação de Medicamentos , Feminino , Fluorescência , Expressão Gênica , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos CBA , Coelhos , Distribuição Tecidual , Vacinas Atenuadas/imunologia , Vacinas Sintéticas/genéticaRESUMO
To date our studies demonstrate that PspA is a highly immunogenic molecule in mice and that it can elicit immunity to otherwise fatal infections following iv, ip, in, and it challenge. Although the molecule is serologically variable, it is sufficiently cross-reactive so that immunization with a single PspA can protect against strains of highly diverse serotypes. It is anticipated that a vaccine composed of a mixture of carefully chosen PspA molecules will be able to elicit protective immunity to virtually all pneumococci. If this vaccine proved efficacious in man, it would provide a more simple and less costly means of immunizing against pneumococcal infection than using recombinant vaccines. This could be especially important in the developing world where the cost of successful vaccines must be no more than pennies per dose. If PspA is found to be less efficacious than capsular polysaccharides, it may be valuable as a protein component of a PS-protein conjugate vaccine. In this capacity, PspA might expand the breath of protection elicited by a vaccine composed of only a few polysaccharide-protein conjugates representing capsule types most commonly associated with infectious pneumococci.
Assuntos
Antígenos de Superfície/imunologia , Proteínas de Bactérias/imunologia , Imunização , Infecções Pneumocócicas/imunologia , Streptococcus pneumoniae/imunologia , Animais , Antígenos de Superfície/química , Proteínas de Bactérias/química , Vacinas Bacterianas/imunologia , Portador Sadio/prevenção & controle , Reações Cruzadas , Humanos , Imunidade nas Mucosas , Camundongos , Nasofaringe/microbiologia , Infecções Pneumocócicas/prevenção & controle , Streptococcus pneumoniae/crescimento & desenvolvimento , Streptococcus pneumoniae/patogenicidade , VirulênciaRESUMO
Immunization with pneumococcal surface protein A (PspA) from Streptococcus pneumoniae strain Rx1 cross-protects mice against challenge with diverse pneumococci. Truncated Rx1 PspA, consisting of amino acids 192-588, elicits protection against the mouse-virulent strain WU2. The possibility that homologous regions of other PspAs could also elicit cross-protection was investigated. Oligonucleotide primers designed according to the Rx1 pspA gene sequence were used to amplify chromosomal DNA from 15 diverse pneumococci. Three recombinant PspAs were evaluated for their ability to elicit protection in mice against challenge with 7 strains representing capsular types 3, 4, 5, 6A, and 6B. Two of the three truncated PspAs each elicited cross-protection against 71%-100% of the S. pneumoniae challenge strains examined. These data suggest that this technique may be useful for the generation of diverse PspAs for inclusion in a broadly protective pneumococcal vaccine.
Assuntos
Proteínas de Bactérias/imunologia , Infecções Pneumocócicas/prevenção & controle , Streptococcus pneumoniae/imunologia , Animais , Anticorpos Monoclonais , Antígenos de Superfície/genética , Antígenos de Superfície/imunologia , Proteínas de Bactérias/genética , Vacinas Bacterianas/administração & dosagem , Sequência de Bases , Reações Cruzadas , Primers do DNA/química , DNA Bacteriano/análise , Eletroforese em Gel de Poliacrilamida , Ensaio de Imunoadsorção Enzimática , Imunidade , Imunização , Camundongos , Camundongos Endogâmicos CBA , Dados de Sequência Molecular , Streptococcus pneumoniae/genética , Vacinas Sintéticas/administração & dosagemRESUMO
Bacterial attachment to host tissue is considered to be a crucial primary step in pathogen infection. Previous studies have shown that Streptococcus defectivus adheres specifically to cell-secreted extracellular matrix (ECM). Though generally not exposed in vivo, this host tissue is exposed at endothelial cell junctions and sites of tissue injury. In this report, we identify a ca. 200-kDa surface protein of S. defectivus involved in ECM adherence. Nitrous acid-derived mutant strains that were unable to bind ECM and which failed to adsorb adhesin-specific antibody from polyclonal inhibitory sera were isolated. A surface protein (ca. 200 kDa) was absent from ECM-nonadherent mutants, indicating its involvement in ECM attachment. Additionally, affinity-purified antibody to the ca. 200-kDa protein inhibited whole-cell S. defectivus ECM attachment, whereas antibody to the same region of the nonadherent mutant cell wall-associated protein profile did not. Furthermore, solubilized cell wall-associated protein extracts of parent but not mutant strains bound ECM, confirming the significance of this protein in ECM adherence. Therefore, we propose that the ca. 200-kDa protein is the major S. defectivus surface component that mediates the ECM attachment of these organisms.
Assuntos
Adesinas Bacterianas , Aderência Bacteriana/fisiologia , Proteínas de Bactérias/fisiologia , Matriz Extracelular/fisiologia , Streptococcus/fisiologia , Animais , Antígenos de Bactérias/química , Antígenos de Bactérias/genética , Antígenos de Bactérias/fisiologia , Aderência Bacteriana/genética , Proteínas de Bactérias/química , Proteínas de Bactérias/imunologia , Células Cultivadas , Cricetinae , Técnicas In Vitro , Peso Molecular , Mutação , Streptococcus/genética , Streptococcus/patogenicidadeRESUMO
Pathogenesis of nutritionally variant streptococcal (NVS) endocarditis initiates with bacterial attachment to and colonization of the damaged heart valve surface. Underlying extracellular matrix (ECM) exposed to the environment during damage to cardiac endothelium provides additional receptors that could be involved in bacterial adherence. The ability of NVS and endocarditis-associated streptococci to bind ECM was investigated by using an enzyme-linked immunosorbent assay system that incorporated ECM secreted by baby hamster kidney and human umbilical vein endothelial cells in culture. Streptococcus defectivus, the major species isolated from NVS endocarditis cases, bound ECM of fibroblasts and endothelial cells, indicating that the ECM molecule involved in the binding was a common constituent of diverse matrices. The specific binding of S. defectivus to ECM was demonstrated by saturation binding and specific antibody inhibition studies. Of the 15 S. defectivus strains analyzed, 13 bound ECM, whereas Streptococcus adjacens and NVS serotype III strains were unable to bind the matrix. This selective binding suggested that S. defectivus binds to heart valves through a mechanism different from those of other NVS in subacute bacterial endocarditis. A survey of non-NVS streptococcal endocarditis isolates demonstrated that S. mutans, S. mitis, S. sanguis, and S. faecalis also bound ECM, whereas other viridans species were unable to bind the matrix.