title: Serum opacity factor (SOF) of Streptococcus pyogenes evokes antibodies that opsonize homologous and heterologous SOF-positive serotypes of group A streptococci.
abstract: Serum opacity factor (SOF) is a protein expressed by Streptococcus pyogenes that opacifies mammalian serum. SOF is also a virulence factor of S. pyogenes, but it has not been previously shown to elicit a protective immune response. Herein, we report that SOF evokes bactericidal antibodies against S. pyogenes in humans, rabbits, and mice. Rabbit antiserum against purified recombinant SOF2 opsonized SOF-positive M type 2, 4, and 28 S. pyogenes in human blood but had no effect on SOF-negative M type 5 S. pyogenes. Furthermore, affinity-purified human antibodies against SOF2 also opsonized SOF-positive streptococci. A combination of antisera against M2 and SOF2 proteins was dramatically more effective in killing streptococci than either antiserum alone, indicating that antibodies against SOF2 enhance the opsonic efficiency of M protein antibodies. Mice tolerated an intravenous injection of 100 microg of SOF without overt signs of toxicity, and immunization with SOF protected mice against challenge infections with M type 2 S. pyogenes. These data indicate that SOF evokes opsonic antibodies that may protect against infections by SOF-positive serotypes of group A streptococci and suggest that different serotypes of SOF have common epitopes that may be useful vaccine candidates to protect against group A streptococcal infections.
authors.affiliation: Veterans Affairs Medical Center and Department of Medicine, University of Tennessee, Memphis, Tennessee 38104, USA. hcourtney@utmem.edu
authors.forename: Harry S
authors.initials: HS
authors.lastname: Courtney
authors.forename: David L
authors.initials: DL
authors.lastname: Hasty
authors.forename: James B
authors.initials: JB
authors.lastname: Dale
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000096:biosynthesis*; D003429:Cross Reactions; D005798:Genes, Bacterial; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008969:Molecular Sequence Data; D009895:Opsonin Proteins / Q000096:biosynthesis; D010447:Peptide Hydrolases / Q000235:genetics / Q000276:immunology* / Q000633:toxicity; D011817:Rabbits; D012703:Serotyping; D013297:Streptococcus pyogenes / Q000145:classification / Q000235:genetics / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D009895:Opsonin Proteins; C021908:opacity factor; D010447:Peptide Hydrolases