Antiphagocytic Function of an IgG Glycosyl Hydrolase from Streptococcus equi subsp. equi and Its Use as a Vaccine Component

EndoSe from Streptococcus equi subsp. equi is an enzyme hydrolyzing glycosyl groups on IgG, analogous to EndoS from Strepto-coccus pyogenes. We here show that the activity of EndoSe leads to an antiphagocytic function and may thus be a contributory factor to immune evasion of S. equi. Despite the damaging effect that EndoSe has on IgG, antibodies against EndoSe can neutral-ize its function. Antibodies against EndoSe restored the opsonic activity of specific opsonizing antibodies. Mice infected with either S. equi subsp. equi or subsp. zooepidemicus or S. pyogenes could be protected by vaccination with EndoSe. It is speculated that EndoSe could be a suitable vaccine candidate against streptococcal infections. EndoS is a glycosyl hydrolase from Streptococcus pyogenes,which can hydrolyze the glycan on the IgG Fc region (4, 5, 7). For IgG, there is a conserved asparagine residue (position 297 in human IgG), which is known to be linked to glucans in different species. The N-linked sugars that are attached to IgG have a com-mon biantenna core structure, consisting of two N-acetylglucos-amines (GlcNAc) and three mannoses. The Fc region is recog-nized by Fc receptors on phagocytic cells and is also required for complement activation. The intactness of the Fc region is required for recognition (16), and the hydrolysis by EndoS of the glyca