Type b Capsule Inhibits Ingestion of Haemophilus influenzae by Murine Macrophages: Studies with Isogenic Encapsulated and Unencapsulated Strains

• Published in: The Journal of infectious diseases 1992-07, Vol.166 (1), p.178-182
• Main Authors: Noel, Gary J., Hoiseth, Susan K., Edelson, Paul J.
• Format: Article
• Language: English
• Subjects: Agglutination Tests; Animals; Bacteremia; Bacteremia - immunology; Bacteria; Bacterial Capsules - immunology; Bacterial Outer Membrane Proteins - analysis; Blood; Blotting, Southern; Cells, Cultured; Concise Comunications; DNA, Bacterial - analysis; Haemophilus Infections - immunology; Haemophilus influenzae; Haemophilus influenzae - chemistry; Haemophilus influenzae - genetics; Haemophilus influenzae - immunology; Humans; Ingestion; Inoculation; Macrophages; Macrophages - immunology; Male; Mice; Nucleic Acid Hybridization; Phagocytosis; Virulence
• ISSN: 0022-1899; 1537-6613
• DOI: 10.1093/infdis/166.1.178

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 maybe an important virulence determinant of type b organisms.