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Malley, Richard

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Malley

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Richard

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Malley, Richard
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    Effect of Serotype on Pneumococcal Competition in a Mouse Colonization Model
    (American Society of Microbiology, 2015) Trzciński, Krzysztof; Li, Yuan; Weinberger, Daniel M.; Thompson, Claudette; Cordy, Derrick; Bessolo, Andrew; Malley, Richard; Lipsitch, Marc
    ABSTRACT Competitive interactions between Streptococcus pneumoniae strains during host colonization could influence the serotype distribution in nasopharyngeal carriage and pneumococcal disease. We evaluated the competitive fitness of strains of serotypes 6B, 14, 19A, 19F, 23F, and 35B in a mouse model of multiserotype carriage. Isogenic variants were constructed using clinical strains as the capsule gene donors. Animals were intranasally inoculated with a mixture of up to six pneumococcal strains of different serotypes, with separate experiments involving either clinical isolates or isogenic capsule-switch variants of clinical strain TIGR4. Upper-respiratory-tract samples were repeatedly collected from animals in order to monitor changes in the serotype ratios using quantitative PCR. A reproducible hierarchy of capsular types developed in the airways of mice inoculated with multiple strains. Serotype ranks in this hierarchy were similar among pneumococcal strains of different genetic backgrounds in different strains of mice and were not altered when tested under a range of host conditions. This rank correlated with the measure of the metabolic cost of capsule synthesis and in vitro measure of pneumococcal cell surface charge, both parameters considered to be predictors of serotype-specific fitness in carriage. This study demonstrates the presence of a robust competitive hierarchy of pneumococcal serotypes in vivo that is driven mainly, but not exclusively, by the capsule itself.
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    The immunological mechanisms that control pneumococcal carriage
    (Public Library of Science, 2017) Jochems, Simon P.; Weiser, Jeffrey N.; Malley, Richard; Ferreira, Daniela M.
    Colonization of the human nasopharynx by pneumococcus is extremely common and is both the primary reservoir for transmission and a prerequisite for disease. Current vaccines targeting the polysaccharide capsule effectively prevent colonization, conferring herd protection within vaccinated communities. However, these vaccines cover only a subset of all circulating pneumococcal strains, and serotype replacement has been observed. Given the success of pneumococcal conjugate vaccine (PCV) in preventing colonization in unvaccinated adults within vaccinated communities, reducing nasopharyngeal colonization has become an outcome of interest for novel vaccines. Here, we discuss the immunological mechanisms that control nasopharyngeal colonization, with an emphasis on findings from human studies. Increased understanding of these immunological mechanisms is required to identify correlates of protection against colonization that will facilitate the early testing and design of novel vaccines.
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    Protection against Nasopharyngeal Colonization by Streptococcus pneumoniae Is Mediated by Antigen-Specific CD4+ T Cells
    (American Society for Microbiology, 2008) Trzciński, Krzysztof; Thompson, Claudette; Srivastava, Amit; Basset, Alan; Malley, Richard; Lipsitch, Marc
    CD4(+) T-cell-dependent acquired immunity confers antibody-independent protection against pneumococcal colonization. Since this mechanism is poorly understood for extracellular bacteria, we assessed the antigen specificity of the induction and recall of this immune response by using BALB/c DO11.10Rag(-/-) mice, which lack mature B and T cells except for CD4(+) T cells specific for the OVA(323-339) peptide derived from ovalbumin. Serotype 6B Streptococcus pneumoniae strain 603S and unencapsulated strain Rx1Delta lytA were modified to express OVA(323-339) as a fusion protein with surface protein A (PspA) (strains 603OVA(1) and Rx1Delta lytAOVA(1)) or with PspA, neuraminidase A, and pneumolysin (Rx1Delta lytAOVA(3)). Whole-cell vaccines (WCV) were made of ethanol-killed cells of Rx1Delta lytA plus cholera toxin (CT) adjuvant, of Rx1Delta lytAOVA(1) + CT (WCV-OVA(1)), and of Rx1Delta lytAOVA(3) + CT (WCV-OVA(3)). Mice intranasally immunized with WCV-OVA(1), but not with WCV or CT alone, were protected against intranasal challenge with 603OVA(1). There was no protection against strain 603S in mice immunized with WCV-OVA(1). These results indicate antigen specificity of both immune induction and the recall response. Effector action was not restricted to antigen-bearing bacteria since colonization by 603S was reduced in animals immunized with vaccines made of OVA-expressing strains when ovalbumin or killed Rx1Delta lytAOVA(3) antigen was administered around the time of challenge. CD4(+) T-cell-mediated protection against pneumococcal colonization can be induced in an antigen-specific fashion and requires specific antigen for effective bacterial clearance, but this activity may extend beyond antigen-expressing bacteria. These results are consistent with the recruitment and/or activation of phagocytic or other nonspecific effectors by antigen-specific CD4(+) T cells.
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    Are Anticapsular Antibodies the Primary Mechanism of Protection against Invasive Pneumococcal Disease?
    (Public Library of Science (PLoS), 2005) Lipsitch, Marc; Whitney, Cynthia G; Zell, Elizabeth; Kaijalainen, Tarja; Dagan, Ron; Malley, Richard
    BACKGROUND: Antibody to capsular polysaccharide has been the basis of several vaccines that offer protection against invasive disease from Streptococcus pneumoniae. The success of such vaccines has led to the inference that natural protection against invasive pneumococcal disease is largely conferred by anticapsular antibody. If this is so, one would expect that the decline in disease from different serotypes would vary significantly, and that the appearance of substantial concentrations of anticapsular antibodies would coincide temporally with the decline in age-specific incidence. METHODS AND FINDINGS: Using incidence data from the United States, we show that, on the contrary, the decline in incidence with age is quite similar for the seven most important serogroups, despite large differences in exposure in the population. Moreover, only modest increases in antibody concentration occur over the second and third years of life, a period in which serotype-specific incidence declines to less than 25% of its peak. We also present detailed data on the distribution of antibody concentrations in Israeli toddlers, which are consistent with the United States findings. The same conclusion is supported by new data on age-specific incidence in Finland, which is compared with published data on antibody acquisition in Finnish toddlers. CONCLUSION: We suggest some additional studies of the mechanisms of protection that could distinguish among potential alternative mechanisms, including acquired immunity to noncapsular antigens, maturation of nonspecific immune responses, or changes in anatomy or exposure.
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    SpxB Is a Suicide Gene of Streptococcus pneumoniae and Confers a Selective Advantage in an In Vivo Competitive Colonization Model
    (American Society for Microbiology, 2007) Regev-Yochay, Gili; Trzcinski, K.; Thompson, Claudette; Lipsitch, Marc; Malley, Richard
    The human bacterial pathogen Streptococcus pneumoniae dies spontaneously upon reaching stationary phase. The extent of S. pneumoniae death at stationary phase is unusual in bacteria and has been conventionally attributed to autolysis by the LytA amidase. In this study, we show that spontaneous pneumococcal death is due to hydrogen peroxide (H(2)O(2)), not LytA, and that the gene responsible for H(2)O(2) production (spxB) also confers a survival advantage in colonization. Survival of S. pneumoniae in stationary phase was significantly prolonged by eliminating H(2)O(2) in any of three ways: chemically by supplementing the media with catalase, metabolically by growing the bacteria under anaerobic conditions, or genetically by constructing DeltaspxB mutants that do not produce H(2)O(2). Likewise, addition of H(2)O(2) to exponentially growing S. pneumoniae resulted in a death rate similar to that of cells in stationary phase. While DeltalytA mutants did not lyse at stationary phase, they died at a rate similar to that of the wild-type strain. Furthermore, we show that the death process induced by H(2)O(2) has features of apoptosis, as evidenced by increased annexin V staining, decreased DNA content, and appearance as assessed by transmission electron microscopy. Finally, in an in vivo rat model of competitive colonization, the presence of spxB conferred a selective advantage over the DeltaspxB mutant, suggesting an explanation for the persistence of this gene. We conclude that a suicide gene of pneumococcus is spxB, which induces an apoptosis-like death in pneumococci and confers a selective advantage in nasopharyngeal cocolonization.
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    Antibodies to Conserved Pneumococcal Antigens Correlate with, but Are Not Required for, Protection against Pneumococcal Colonization Induced by Prior Exposure in a Mouse Model
    (American Society for Microbiology, 2005) Trzcinski, K.; Thompson, Claudette; Malley, Richard; Lipsitch, Marc
    In mice following intranasal exposure to Streptococcus pneumoniae, protection against pneumococcal colonization was independent of antibody but dependent on CD4+ T cells. Nonetheless, concentrations of antibodies to three conserved pneumococcal antigens correlated with protection against colonization. Concentrations of antibodies to conserved pneumococcal antigens may be correlates of protection without being effectors of protection.
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    Antibody-Independent, Interleukin-17A-Mediated, Cross-Serotype Immunity to Pneumococci in Mice Immunized Intranasally with the Cell Wall Polysaccharide
    (American Society for Microbiology, 2006) Malley, Richard; Srivastava, Amit; Lipsitch, Marc; Thompson, Claudette; Watkins, C.; Tzianabos, A.; Anderson, Porter
    Serotype-specific immunity to Streptococcus pneumoniae is conferred by antibodies to the capsular polysaccharides, which define the 90 known serotypes. Whether antibody to the species-common cell wall polysaccharide (C-Ps) is protective has been a matter of controversy. Here we show that C-Ps given intranasally with mucosal adjuvant increased the resistance of mice to experimental nasopharyngeal colonization by capsulated S. pneumoniae of serotype 6B. This immunity could be induced in mice congenitally lacking immunoglobulin but was dependent upon CD4+ T cells. Elimination of the charged amino group on the polymer backbone by N acetylation of C-Ps reduced the immunity, as did treatment of the mice with antibody to the cytokine interleukin-17A at the time of challenge, both consistent with the hypothesis of T-cell activation due to the zwitterionic motif of the polymer. C-Ps also protected in a model of fatal aspiration pneumonia by heavily capsulated serotype 3. These findings suggest a novel immunization strategy against S. pneumoniae.
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    CD4+ T cells mediate antibody-independent acquired immunity to pneumococcal colonization
    (Proceedings of the National Academy of Sciences, 2005) Malley, Richard; Trzcinski, K.; Srivastava, Amit; Thompson, Claudette; Anderson, Porter; Lipsitch, Marc
    Acquired immunity to Streptococcus pneumoniae (pneumococcus) has long been assumed to depend on the presence of anticapsular antibodies. We found, however, that colonization with live pneumococci of serotypes 6B, 7F, or 14 protected mice against recolonization by any of the serotypes and that protection from acquisition of a heterologous or homologous strain did not depend on anticapsular antibody. Further, intranasal immunization by live pneumococcal colonization or by a killed, nonencapsulated whole-cell vaccine protected antibody-deficient mice against colonization, suggesting independence of antibodies to any pneumococcal antigens. Protection by intranasal immunization with whole-cell vaccine was completely abrogated in T cell-deficient mice, and in mice that were congenitally deficient in CD4+ T cells or depleted of these cells at the time of challenge. In contrast, mice congenitally deficient in, or depleted of, CD8+ T cells were fully protected. Protection in this model was observed beyond 2 months after immunization, arguing against innate or nonspecific immune mechanisms. Thus, we find that immunity to pneumococcal colonization can be induced in the absence of antibody, independent of the capsular type, and this protection requires the presence of CD4+ T cells at the time of challenge.
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    In Vitro Bactericidal Activity of Streptococcus pneumoniae and Bactericidal Susceptibility of Staphylococcus aureus Strains Isolated from Cocolonized versus Noncocolonized Children
    (American Society for Microbiology, 2007) Regev-Yochay, Gili; Malley, Richard; Rubinstein, E.; Raz, M.; Dagan, R.; Lipsitch, Marc
    Streptococcus pneumoniae is bactericidal to Staphylococcus aureus in vitro. To determine whether this in vitro effect accounts for the inverse relation between S. pneumoniae and S. aureus colonization reported in previous epidemiologic studies, we compared S. pneumoniae and S. aureus strains from cocolonized children to those from noncocolonized children. Cocolonizing pneumococci were less bactericidal and cocolonizing staphylococci less susceptible to this effect; however, the magnitude of the effect was small. Thus, in vitro killing is not the major determinant of the pattern of cocolonization.
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    Interference between Streptococcus pneumoniae and Staphylococcus aureus: In Vitro Hydrogen Peroxide-Mediated Killing by Streptococcus pneumoniae
    (American Society for Microbiology, 2006) Regev-Yochay, Gili; Trzcinski, K.; Thompson, Claudette; Malley, Richard; Lipsitch, Marc
    The bactericidal activity of Streptococcus pneumoniae toward Staphylococcus aureus is mediated by hydrogen peroxide. Catalase eliminated this activity. Pneumococci grown anaerobically or genetically lacking pyruvate oxidase (SpxB) were not bactericidal, nor were nonpneumococcal streptococci. These results provide a possible mechanistic explanation for the interspecies interference observed in epidemiologic studies.