Surface proteins of pathogenic streptococci

Thomas Areschoug

Research output: ThesisDoctoral Thesis (compilation)

Abstract

Streptococcus pyogenes (group A streptococcus) and the group B streptococcus (GBS) are two important human pathogens that cause different types of diseases and express different surface structures implicated in virulence. This thesis focuses on several surface proteins expressed by these pathogens, analyzing the biological function of these proteins and their ability to elicit protective immunity. R28 is a surface protein expressed by some strains of S. pyogenes isolated from cases of puerperal fever, suggesting that R28 may play a role in these infections. Molecular analysis of R28 showed that it is a novel member of a family of extremely repetitive surface proteins first identified through studies of the GBS proteins Rib and alfa. Like the Rib and alfa proteins, R28 was found to be a target for protective antibodies. Moreover, the R28 protein was found to act as an epithelial cell adhesin. Interestingly, the R28 and Rib proteins were shown to cross-react immunologically. This cross-reactivity was found to be surprisingly limited, but sufficient to confer cross-protective immunity between R28-expressing S. pyogenes strains and Rib-expressing GBS strains. Most GBS isolates express a polysaccharide capsule, which is the basis for serological typing of GBS. There are nine capsular serotypes of GBS, one of which, serotype V, has recently become increasingly important in GBS disease. Characterization of serotype V strains allowed identification of two novel GBS surface proteins, Fbs and “Rib-like”, which are targets for protective antibodies and therefore are interesting as possible components in a GBS vaccine. Interestingly, the “Rib-like” protein of type V strains was found to be closely related, if not identical, to the R28 protein of S. pyogenes. Both S. pyogenes and GBS express surface proteins that bind to the Fc part of human IgA. Little is known about the role of these interactions in pathogenesis. The IgA-binding proteins of S. pyogenes are M proteins, which are important virulence factors with antiphagocytic properties. The IgA-binding protein from GBS, the beta protein, is unrelated to the IgA-binding proteins from S. pyogenes. The binding site in IgA for the different streptococcal proteins was mapped to two hydrophobic loops in the Fc interdomain region. This region is also used by the human IgA-receptor CD89, an important mediator of IgA effector functions. In agreement with this result, the IgA-binding streptococcal proteins were found to inhibit binding of IgA to CD89. Thus, unrelated IgA-binding proteins from S. pyogenes and GBS bind the same region in IgA-Fc and may inhibit IgA effector function. The IgA-binding beta protein of GBS was found to contain a separate binding region for human factor H (FH), a plasma protein that regulates complement activation. Bacteria-bound FH retains its regulatory function, indicating that beta-expressing GBS may use FH to downregulate complement deposition and thereby inhibit phagocytosis.
Original languageEnglish
QualificationDoctor
Awarding Institution
  • Division of Medical Microbiology
Supervisors/Advisors
  • [unknown], [unknown], Supervisor, External person
Award date2002 Nov 23
Publisher
Print ISBNs91-628-5366-X
Publication statusPublished - 2002

Bibliographical note

Defence details

Date: 2002-11-23
Time: 10:00
Place: Segerfalksalen, Wallenberg Neurocenter, Sölvegatan 17, Lund

External reviewer(s)

Name: Hollingshead, Susan K.
Title: Prof
Affiliation: The University of Alabama at Birmingham, Birmingham, Alabama, USA

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Article: I. Stålhammar-Carlemalm, M.*, T. Areschoug*, C. Larsson, and G. Lindahl. 1999. The R28 protein of Streptococcus pyogenes is related to several group B streptococcal surface proteins, confers protective immunity and promotes binding to human epithelial cells. Mol Microbiol 33:208-19.* These authors made equal contributions.

Article: II. Stålhammar-Carlemalm, M., T. Areschoug, C. Larsson, and G. Lindahl. 2000. Cross-protection between group A and group B streptococci due to cross-reacting surface proteins. J Infect Dis 182:142-9.

Article: III. Areschoug, T., M. Stålhammar-Carlemalm, C. Larsson, and G. Lindahl. 1999. Group B streptococcal surface proteins as targets for protective antibodies: identification of two novel proteins in strains of serotype V. Infect Immun 67:6350-7.

Article: IV. Pleass, R. J.*, T. Areschoug*, G. Lindahl, and J. M. Woof. 2001. Streptococcal IgA-binding proteins bind in the Calfa2-Calfa3 interdomain region and inhibit binding of IgA to human CD89. J Biol Chem 276:8197-204.* These authors made equal contributions.

Article: V. Areschoug, T., M. Stålhammar-Carlemalm, I. Karlsson, and G. Lindahl. 2002. Streptococcal beta protein has separate binding sites for human factor H and IgA-Fc.J Biol Chem 277:12642-8.

Subject classification (UKÄ)

  • Microbiology in the medical area

Keywords

  • bacteriology
  • virology
  • mycology
  • Mikrobiologi
  • bakteriologi
  • virologi
  • mykologi
  • Microbiology
  • factor H
  • complement regulator
  • CD89
  • human IgA
  • protective immunity
  • surface protein
  • Streptococcus pyogenes
  • group B streptococcus

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