title: L-ficolin and capsular polysaccharide-specific IgG in cord serum contribute synergistically to opsonophagocytic killing of serotype III and V group B streptococci.
abstract: Group B streptococci (GBS; Streptococcus agalactiae) are the most common cause of neonatal sepsis and meningitis. Serotype-specific IgG antibody is known to protect neonates against GBS infections by promoting opsonophagocytosis. The L-ficolin-mediated lectin pathway of the complement is also a potential mechanism for opsonization of GBS, because L-ficolin activates the complement after binding to serotype Ib, III, V, VI, and VIII GBS. In the present study, we investigated how L-ficolin and serotype-specific IgG in cord sera contribute to opsonophagocytic killing of GBS. Neither L-ficolin nor serotype-specific IgG concentrations correlated with C3b deposition on serotype Ib and VI GBS, suggesting L-ficolin- and serotype-specific IgG-independent mechanisms of complement activation. The percentage of serotype VIII GBS killed was high regardless of the concentration of L-ficolin and IgG. In contrast, L-ficolin and serotype-specific IgG can each initiate C3b deposition on serotype III and V GBS and promote phagocytosis by polymorphonuclear leukocytes, but L-ficolin and serotype-specific IgG together promote opsonophagocytic killing to a greater extent than does either alone in vitro. This synergy was observed when serotype III-specific IgG concentrations were between 1 and 6 μg/ml and when serotype V-specific IgG concentrations were between 2 and 5 μg/ml. Concentrations of serotype III-specific IgG in cord blood above 7 μg/ml are considered protective for neonates colonized with GBS, but most neonates with IgG levels of less than 7 μg/ml do not develop GBS infections. The data presented here suggest that L-ficolin enhances opsonophagocytosis of serotype III and V GBS when serotype-specific IgG alone is suboptimal for protection.
authors.affiliation: Division of Microbiology, University, Sakado, Japan.
authors.forename: Mioko
authors.initials: M
authors.lastname: Fujieda
authors.forename: Youko
authors.initials: Y
authors.lastname: Aoyagi
authors.forename: Kousaku
authors.initials: K
authors.lastname: Matsubara
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Takeuchi
authors.forename: Wakae
authors.initials: W
authors.lastname: Fujimaki
authors.forename: Misao
authors.initials: M
authors.lastname: Matsushita
authors.forename: John F
authors.initials: JF
authors.lastname: Bohnsack
authors.forename: Shinji
authors.initials: S
authors.lastname: Takahashi
mesh_terms: D000918:Antibody Specificity; D016667:Bacterial Capsules / Q000276:immunology*; D036022:Capsid Proteins; D005312:Fetal Blood / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D007231:Infant, Newborn; D037102:Lectins / Q000235:genetics / Q000378:metabolism*; D009504:Neutrophils / Q000502:physiology; D009895:Opsonin Proteins; D010587:Phagocytosis / Q000502:physiology; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D012703:Serotyping; D013292:Streptococcus agalactiae / Q000276:immunology* / Q000502:physiology; D000097604:Ficolins
chemical_list: D036022:Capsid Proteins; D007074:Immunoglobulin G; D037102:Lectins; D009895:Opsonin Proteins; D011135:Polysaccharides, Bacterial; D000097604:Ficolins; C018315:hexon capsid protein, Adenovirus