Serum Opacity Factor (SOF) ofStreptococcus pyogenesEvokes 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 g 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.

Manuka honey inhibits the development of Streptococcus pyogenes biofilms and causes reduced expression of two fibronectin binding proteins

“…Sof is regarded as a major virulence factor that is known to contribute to pathogenesis of streptococcal infection in animal models (Courtney & Pownall, 2010). The sof gene was first sequenced over 15 years ago (Rakonjac et al, 1995) and its product was found to be a surface bound protein of over 100 kDa, with a C-terminal domain comprised of numerous repeating peptides that bound to both fibronectin and fibrinogen (Courtney et al, 2003;Courtney & Pownall, 2010). End point RT-PCR found that the genes encoding both of these proteins were differentially expressed in response to treatment with a sublethal dose of manuka honey.…”

Function of the Fibronectin-Binding Serum Opacity Factor ofStreptococcus pyogenesin Adherence to Epithelial Cells

“…However, conclusions were drawn without knowledge of the sfbX gene located downstream of sof, which was most likely also affected by the mutation strategy. An additional matrix-binding activity of fibrinogen was found to map to the repetitive domain at the C terminus of the SOF molecule (6), and SOF was shown to elicit antibodies with opsonizing activity toward heterologous SOF types (9). SOF and SfbX are both involved in adherence of GAS to immobilized fibronectin (20).…”

Vaccination equally enables both genetically susceptible and resistant mice to control infection with group A streptococci

“…That bacterial reduction was due to antibody-mediated opsonizing killing and not to bacterial aggregation by specific antibodies was demonstrated by performing a previously described assay [19]. Briefly, 5 10 3 CFU of GAS strain A20 was added to serum isolated from either GAS-vaccinated BALB/c or C3H/HeN mice or non-immune control mice and rotated for 3 h at 37°C.…”