title: Type b capsule inhibits ingestion of Haemophilus influenzae by murine macrophages: studies with isogenic encapsulated and unencapsulated strains.
abstract: Phagocytosis may be important in clearing Haemophilus influenzae from the bloodstream. To define the effect of type b capsule on phagocytosis, binding and ingestion by macrophages was measured for 5 isogenic sets of capsule-sufficient strains (clinical isolates and type b transformants of capsule-deficient mutants) and capsule-deficient mutants (strains lacking a 9-kb EcoRI fragment of chromosomal DNA associated with type b capsule expression). Capsule-sufficient strains were not bound in the absence of serum, whereas capsule-deficient strains were bound and ingested (1.8-5.1 organisms/macrophage; 59%-97% ingested). In the presence of nonimmune serum, capsule-sufficient strains were largely bound but not ingested (4.7-7.2 organisms/macrophage; 7%-21% ingested), whereas capsule-deficient strains were nearly all ingested (6.2-10.5 organisms/macrophage; 93%-97% ingested). Strains resisting ingestion caused persistent bacteremia 24 h after intravenous challenge in mice and were more likely than readily ingested strains to cause persistent bacteremia or death in infant rats. Thus, type b capsule inhibits ingestion by macrophages; resistance to ingestion may be an important virulence determinant of type b organisms.
authors.affiliation: Department of Pediatrics, New York Hospital-Cornell University Medical Center, NY 10021.
authors.forename: G J
authors.initials: GJ
authors.lastname: Noel
authors.forename: S K
authors.initials: SK
authors.lastname: Hoiseth
authors.forename: P J
authors.initials: PJ
authors.lastname: Edelson
mesh_terms: D000372:Agglutination Tests; D000818:Animals; D016470:Bacteremia / Q000276:immunology*; D016667:Bacterial Capsules / Q000276:immunology*; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis; D015139:Blotting, Southern; D002478:Cells, Cultured; D004269:DNA, Bacterial / Q000032:analysis; D006192:Haemophilus Infections / Q000276:immunology*; D006193:Haemophilus influenzae / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D006801:Humans; D008264:Macrophages / Q000276:immunology*; D008297:Male; D051379:Mice; D009693:Nucleic Acid Hybridization
chemical_list: D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial