The Gram-positive bacterium Streptococcus pneumoniae is a major cause of pneumonia, sepsis and meningitis. Although the invasive disease is severe, some 40% of individuals harbour the pneumococcus in the nasopharynx asymptomatically. Here we investigate the molecular elements of the encounter between host and pathogen that distinguish these different outcomes. We show that inflammatory activation of human cells shifts the targeting of the pneumococcus to a new receptor, that for the G-protein-coupled platelet-activating factor (PAF). Only virulent pneumococci engage the PAF receptor. Attachment of the bacterial phosphorylcholine to the PAF receptor enhanced adherence, which was coupled to invasion of endothelial, epithelial and PAF-receptor-transfected cells. This progression could be arrested in vitro and in vivo by PAF-receptor-specific antagonists, suggesting a possible approach to therapy.

Pneumococcus has been shown to bind to epithelial cells of the nasopharynx and lung, and to endothelial cells of the peripheral vasculature. To characterize bacterial elements required for attachment to these cell types, a library of genetically altered pneumococci with defects in exported proteins was screened for the loss of attachment to glycoconjugates representative of the nasopharyngeal cell receptor, type II lung cells (LC) and human endothelial cells (EC). A mutant was identified which showed a greater than 70% loss in the ability to attach to all cell types. This mutant also showed decreased adherence to the glycoconjugates containing the terminal sugar residues GalNAcbeta1-3Gal, GalNAcbeta1-4Gal and the carbohydrate GlcNAc, which are proposed components of the pneumococcal receptors specific to the surfaces of LC and EC. Analysis of the locus altered in this mutant revealed a gene, spxB, that encodes a member of the family of bacterial pyruvate oxidases which decarboxylates pyruvate to acetyl phosphate plus H2O2 and CO2. This mutant produced decreased concentrations of H2O2 and failed to grow aerobically in a chemically defined medium, unless supplemented with acetate which presumably restores acetyl phosphate levels by the action of acetate kinase, further suggesting that spxB encodes a pyruvate oxidase. The addition of acetate to the growth medium restored the adherence properties of the mutant indicating a link between the enzyme and the expression of bacterial adhesins. A defect in spxB corresponded to impaired virulence of the mutant in vivo. Compared to the parent strain, an spxB mutant showed reduced virulence in animal models for nasopharyngeal colonization, pneumonia, and sepsis. We propose that a mutation in spxB leads to down-regulation of the multiple adhesive properties of pneumococcus which, in turn, may correlate to diminished virulence in vivo.

SummaryPhosphorylcholine is an important bioactive adduct to the teichoic acid (TA) and lipoteichoic acid (LTA) of the surface of Streptococcus pneumoniae. We have identi®ed and characterized a genetic locus lic that is required for phosphorylcholine metabolism in S. pneumoniae.

Oligosaccharides that block the adherence of bacteria to epithelial cells in vitro--lacto-N-neotetraose (LNnT) and its alpha2-3- and alpha2-6-sialylated derivatives--were tested for their abilities to attenuate the course of pneumococcal pneumonia and to prevent colonization of the nasopharynx in animal models. Intratracheal administration of these agents concurrently with bacteria dramatically decreased pneumococcal load in the lungs of rabbits and conferred protection from bacteremia. The oligosaccharides ameliorated pneumonia and bacteremia when given therapeutically 24 h after infection was established. When administered intranasally, neoglycoconjugates of the active oligosaccharides prevented colonization of the nasopharynx of infant rats. In addition to in vitro anti-adherence properties, LNnT acted directly on cultured lung epithelial cell lines to induce changes such that pneumococcal adherence was prevented for prolonged periods. These activities encourage continued development of oligosaccharides as a class of potentially preventive and therapeutic agents for infectious diseases.

We evaluated a study setting for assessment of the long-term vaccine efficacy (VE) of human papillomavirus (HPV) virus-like-particle (VLP) vaccine against cervical carcinoma. A total of 22,412 16- to 17-year old adolescent women from seven cities in Finland were invited by letter to participate in a phase III study of a quadrivalent HPV (types 6, 11, 16, 18) VLP vaccine, between September 2002 and March 2003. A total of 30,947 18-year old women were invited to participate as unvaccinated controls. These women were asked about their willingness to participate in an HPV vaccination trial and to fill a health questionnaire. These three population-based cohorts of adolescent women, including women vaccinated with HPV vaccine or placebo vaccine and unvaccinated control women, are systematically followed over time. The study cohort database will be linked with the Finnish Cancer Registry using cervical carcinoma in situ (CIS) and invasive cervical carcinoma (ICC) as endpoints. Assuming that the cumulative incidence of CIS and ICC over 15 years is 0.45%, and that there is no loss to follow-up, and power of 80%, the determination of 70% total VE will require 3357 HPV vaccine recipients, 3357 placebo vaccine recipients, and 6714 unvaccinated controls. At the baseline, 2632 (12%) of the invited adolescents volunteered to the phase III vaccination trial, and 6790 (22%) responded to the questionnaire study. During a recruitment period of 10 months, 874 HPV vaccine recipients, 875 placebo recipients and 1919 unvaccinated controls were enrolled. Population-based enrollment of large cohorts of vaccinated and unvaccinated adolescents for passive registry-based follow-up with cervical carcinoma as the end-point is feasible and currently going on in Finland.