New protective antigen of group A streptococci

J Clin Invest. 1999 May;103(9):1261-8. doi: 10.1172/JCI5118.


It is widely believed that the surface M protein of group A streptococci is the predominant surface protein of these organisms containing opsonic epitopes. In the present study, we identified a new surface protein, distinct from M protein, that evokes protective antibodies. A type 18 M-negative mutant was found to be both resistant to phagocytosis in human blood and virulent in mice. The wild-type strain, but not the M-negative mutant, was opsonized by antisera against purified recombinant M18 protein or a synthetic peptide copying the NH2-terminus of M18. However, antisera raised against a crude pepsin extract of the M-negative mutant opsonized both strains, indicating the presence of a protective antigen in addition to type 18 M protein. This antiserum was used to identify and purify a 24-kDa protein fragment (Spa, streptococcal protective antigen) that evoked antibodies that opsonized the M18 parent and the M-negative mutant. The results of passive mouse protection tests confirmed the presence of protective epitopes within Spa. The deduced amino acid sequence of a 636-bp 5' fragment of the spa18 gene showed no homology with sequences in GenBank. These studies reveal the presence of a new protective antigen of certain strains of group A streptococci that may prove to be an important component of vaccines to prevent streptococcal infections.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antibodies, Bacterial / biosynthesis
  • Antibodies, Bacterial / immunology
  • Antibodies, Bacterial / isolation & purification
  • Antigens, Bacterial / genetics
  • Antigens, Bacterial / immunology
  • Antigens, Bacterial / isolation & purification*
  • Bacterial Vaccines
  • Base Sequence
  • Cloning, Molecular
  • Cross Reactions
  • DNA, Bacterial
  • Immune Sera
  • Mice
  • Molecular Sequence Data
  • Streptococcus pyogenes / immunology*


  • Antibodies, Bacterial
  • Antigens, Bacterial
  • Bacterial Vaccines
  • DNA, Bacterial
  • Immune Sera
  • streptococcal protective antigen

Associated data

  • GENBANK/AF086813