title: Defense of zebrafish embryos against Streptococcus pneumoniae infection is dependent on the phagocytic activity of leukocytes.
abstract: Severe community acquired pneumonia caused by Streptococcus pneumoniae is the most common cause of death from infection in developing countries. Serotype specific conjugate vaccines have decreased the incidence of invasive infections, but at the same time, disease due to non-vaccine serotypes have increased. New insights into host immune mechanisms against pneumococcus may provide better treatment and prevention strategies. Zebrafish is an attractive vertebrate model for studying host immune responses and infection biology. Here we show that an intravenous challenge with pneumococcus infects zebrafish embryos leading to death in a dose dependent manner. Survival rates correlate with the bacterial burden in the embryos. The production of proinflammatory cytokines is induced in zebrafish after pneumococcal exposure. Importantly, morpholino treated embryos lacking either myeloid cells or the ability to phagocytose bacteria have lowered survival rates compared to wild type embryos after pneumococcal challenge. These data suggest that the survival of zebrafish embryos upon intravenous infection with S. pneumoniae is dependent on the clearance of the bacteria by phagocytosing cells. Additionally, we demonstrate that mutant pneumococci lacking known virulence factors are attenuated in the zebrafish model. Our data demonstrate that zebrafish embryos can be used for study innate immune responses as well as virulence determinants in pneumococcal infections.
authors.affiliation: Institute of Biomedical Technology, University of Tampere, Tampere, Finland. samuli.rounioja@uta.fi
authors.forename: Samuli
authors.initials: S
authors.lastname: Rounioja
authors.forename: Anni
authors.initials: A
authors.lastname: Saralahti
authors.forename: Lilli
authors.initials: L
authors.lastname: Rantala
authors.forename: Mataleena
authors.initials: M
authors.lastname: Parikka
authors.forename: Birgitta
authors.initials: B
authors.lastname: Henriques-Normark
authors.forename: Olli
authors.initials: O
authors.lastname: Silvennoinen
authors.forename: Mika
authors.initials: M
authors.lastname: Rämet
mesh_terms: D000818:Animals; D004625:Embryo, Nonmammalian; D054884:Host-Pathogen Interactions / Q000276:immunology*; D008856:Microscopy, Fluorescence; D016254:Mutagenesis, Insertional / Q000379:methods; D010587:Phagocytosis / Q000276:immunology*; D011008:Pneumococcal Infections / Q000276:immunology* / Q000382:microbiology; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013296:Streptococcus pneumoniae / Q000276:immunology*; D037521:Virulence Factors / Q000235:genetics / Q000276:immunology; D015027:Zebrafish
chemical_list: D012333:RNA, Messenger; D037521:Virulence Factors