title: Group B streptococcal beta-hemolysin/cytolysin activates neutrophil signaling pathways in brain endothelium and contributes to development of meningitis.
abstract: Meningitis occurs when blood-borne pathogens cross the blood-brain barrier (BBB) in a complex interplay between endothelial cells and microbial gene products. We sought to understand the initial response of the BBB to the human meningeal pathogen group B Streptococcus (GBS) and the organism's major virulence factors, the exopolysaccharide capsule and the beta-hemolysin/cytolysin toxin (beta-h/c). Using oligonucleotide microarrays, we found that GBS infection of human brain microvascular endothelial cells (HBMEC) induced a highly specific and coordinate set of genes including IL-8, Groalpha, Grobeta, IL-6, GM-CSF, myeloid cell leukemia sequence-1 (Mcl-1), and ICAM-1, which act to orchestrate neutrophil recruitment, activation, and enhanced survival. Most strikingly, infection with a GBS strain lacking beta-h/c resulted in a marked reduction in expression of genes involved in the immune response, while the unencapsulated strain generally induced similar or greater expression levels for the same subset of genes. Cell-free bacterial supernatants containing beta-h/c activity induced IL-8 release, identifying this toxin as a principal provocative factor for BBB activation. These findings were further substantiated in vitro and in vivo. Neutrophil migration across polar HBMEC monolayers was stimulated by GBS and its beta-h/c through a process involving IL-8 and ICAM-1. In a murine model of hematogenous meningitis, mice infected with beta-h/c mutants exhibited lower mortality and decreased brain bacterial counts compared with mice infected with the corresponding WT GBS strains.
authors.affiliation: Department of Pediatrics, University of California, San Diego, School of Medicine, La Jolla, California 92093-0672, USA. kdoran@ucsd.edu
authors.forename: Kelly S
authors.initials: KS
authors.lastname: Doran
authors.forename: George Y
authors.initials: GY
authors.lastname: Liu
authors.forename: Victor
authors.initials: V
authors.lastname: Nizet
mesh_terms: D001426:Bacterial Proteins; D001812:Blood-Brain Barrier; D001921:Brain / Q000098:blood supply / Q000187:drug effects* / Q000378:metabolism; D002465:Cell Movement; D004195:Disease Models, Animal; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D020869:Gene Expression Profiling; D006460:Hemolysin Proteins / Q000633:toxicity*; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis; D016920:Meningitis, Bacterial / Q000209:etiology*; D009504:Neutrophils / Q000187:drug effects* / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*; D013292:Streptococcus agalactiae / Q000472:pathogenicity*
chemical_list: D001426:Bacterial Proteins; D006460:Hemolysin Proteins; D016209:Interleukin-8; C071495:streptococcal group B hemolysin