Deletion of repeats in the alpha C protein enhances the pathogenicity of group B streptococci in immune mice

Claudia Gravekamp, Bernard Rosner, L. C. Madoff

Research output: Contribution to journalArticle

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Abstract

The alpha C protein is a protective surface-associated antigen of group B streptococci (GBS). The prototype alpha C protein of GBS (strain A909) contains nine identical tandem repeats, each comprising 82 amino acids, flanked by N- and C-terminal domains. Clinical isolates of GBS show variable numbers of repeats with a normal distribution and a median of 9 to 10 repeats. Here, we show that escape mutants of GBS expressing one-repeat alpha C protein were 100-fold more pathogenic than GBS expressing wild-type nine- repeat alpha C protein in neonatal mice whose dams were immunized with antiserum elicited to nine-repeat alpha C protein (50% lethal doses of 1.6 x 103 and 1.8 x 105, respectively; P = 0.0073). There was no difference in pathogenicity in nonimmune mice. Enzyme-linked immunosorbent assay inhibition showed that nine-repeat but not one-repeat alpha C protein is readily available for antibody binding on the surface of intact GBS. Immune electron microscopy studies with antibodies to the capsular polysaccharide (CPS) and to the alpha C protein demonstrated localization of the nine-repeat alpha C protein and the CPS at similar distances from the cell wall. The one-repeat alpha C protein was visualized poorly and only in close proximity to the cell wall, thus suggesting that antibody binding to the protein was hindered by CPS or other cell surface components. We concluded that deletion in the repeat region of the alpha C protein enhanced the pathogenicity of GBS in immune mice by (i) loss of a protective (conformational) epitope(s) and (ii) loss of antibody binding to the alpha C protein due to a decrease in antigen size relative to cell wall components and/or CPS.

Original languageEnglish (US)
Pages (from-to)4347-4354
Number of pages8
JournalInfection and Immunity
Volume66
Issue number9
StatePublished - 1998
Externally publishedYes

Fingerprint

Streptococcus agalactiae
Protein C
Virulence
Polysaccharides
Cell Wall
Antibodies
Cellular Structures
Tandem Repeat Sequences
Normal Distribution
Lethal Dose 50
Surface Antigens
Immune Sera
Epitopes
Electron Microscopy
Carrier Proteins
Enzyme-Linked Immunosorbent Assay
Antigens
Amino Acids

ASJC Scopus subject areas

  • Immunology

Cite this

Deletion of repeats in the alpha C protein enhances the pathogenicity of group B streptococci in immune mice. / Gravekamp, Claudia; Rosner, Bernard; Madoff, L. C.

In: Infection and Immunity, Vol. 66, No. 9, 1998, p. 4347-4354.

Research output: Contribution to journalArticle

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