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Infection and Immunity, February 2001, p. 695-705, Vol. 69, No. 2
Department of Molecular Microbiology and
Immunology, University of Missouri-Columbia, Columbia, Missouri 65212
Received 2 August 2000/Returned for modification 7 September
2000/Accepted 8 November 2000
A common feature of many different organisms causing bacteremia is
the ability to avoid the bactericidal effects of normal human serum. In
Haemophilus influenzae encapsulated strains are particularly serum resistant; however, we found that a nonencapsulated strain (R2866) isolated from the blood of an immunocompetent child with
meningitis who had been successfully immunized with H. influenzae type b conjugate vaccine was serum resistant. Since
serum resistance usually involves circumventing the action of the
complement system, we defined the deposition of various complement
components on the surfaces of this H. influenzae strain
(R2866), a nonencapsulated avirulent laboratory strain (Rd), and a
virulent type b encapsulated strain (Eagan). Membrane attack complex
(MAC) accumulation correlated with the loss of bacterial viability;
correspondingly, the rates of MAC deposition on the serum-sensitive
strain Rd and the serum-resistant strains differed. Analysis of
cell-associated immunoglobulin G (IgG), C1q, C3b, and C5b indicated
that serum-resistant H. influenzae prevents MAC
accumulation by delaying the synthesis of C3b through the classical
pathway. Among the initiators of the classical pathway, IgG deposition
contributes most of the C3 convertase activity necessary to start the
cascade ending with MAC deposition. Despite similar IgG binding, strain
R2866 delays C3 convertase activity compared to strain Rd. We conclude
that strain R2866 can persist in the bloodstream, in part by inhibiting
or delaying C3 deposition on the cell surface, escaping complement
mediated killing.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.2.695-705.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Serum Resistance in an Invasive, Nontypeable
Haemophilus influenzae Strain
*
Corresponding author. Mailing address: M616 DCO44.00,
Medical Sciences Building, University of Missouri, Columbia, MO 65212. Phone: (573) 882-8989. Fax: (573) 882-4287. E-mail
smithal{at}health.missouri.edu.
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