Group B streptococci escape host immunity by deletion of tandem repeat elements of the alpha C protein - PubMed (original) (raw)

Group B streptococci escape host immunity by deletion of tandem repeat elements of the alpha C protein

L C Madoff et al. Proc Natl Acad Sci U S A. 1996.

Abstract

Group B streptococci (GBS) are the most common cause of neonatal sepsis, pneumonia, and meningitis. The alpha C protein is a surface-associated antigen; the gene (bca) for this protein contains a series of tandem repeats (each encoding 82 aa) that are identical at the nucleotide level and express a protective epitope. We previously reported that GBS isolates from two of 14 human maternal and neonatal pairs differed in the number of repeats contained in their alpha C protein; in both pairs, the alpha C protein of the neonatal isolate was smaller in molecular size. We now demonstrate by PCR that the neonatal isolates contain fewer tandem repeats. Maternal isolates were susceptible to opsonophagocytic killing in the presence of alpha C protein-specific antiserum, whereas the discrepant neonatal isolates proliferated. An animal model was developed to further study this phenomenon. Adult mice passively immunized with antiserum to the alpha C protein were challenged with an alpha C protein-expressing strain of GBS. Splenic isolates of GBS from these mice showed a high frequency of mutation in bca--most commonly a decrease in repeat number. Isolates from non-immune mice were not altered. Spontaneous deletions in the repeat region were observed at a much lower frequency (6 x 10(-4)); thus, deletions in that region are selected for under specific antibody pressure and appear to lower the organism's susceptibility to killing by antibody specific to the alpha C protein. This mechanism of antigenic variation may provide a means whereby GBS evade host immunity.

PubMed Disclaimer

Similar articles

Cited by

References

    1. Cell. 1991 Jun 28;65(7):1127-41 - PubMed
    1. Infect Immun. 1995 Mar;63(3):891-8 - PubMed
    1. Proc Natl Acad Sci U S A. 1988 Nov;85(21):8271-5 - PubMed
    1. Infect Immun. 1990 Sep;58(9):2760-9 - PubMed
    1. Infect Immun. 1991 Jan;59(1):204-10 - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources