PROPERTIES OF IGG-BINDING PROTEINS EXPRESSED BY STREPTOCOCCUS-PYOGENES ISOLATES ARE PREDICTIVE OF INVASIVE POTENTIAL

Recent clinical Streptococcus pyogenes isolates of the M1 serotype can be grouped according to the IgG-binding properties of their M protein s, One group expressed an IgG-binding M1 protein reactive with human I gG1, IgG2, IgG3, and IgG4 (type IIo); the other expressed a protein wi th predominant reactivity with human IgG3 alone (type IIb). Both IgG-b inding protein phenotypes were equally resistant to phagocytosis in hu man blood; however, when they were injected into a skin air sac on out bred CD1 mice, all mice injected with Mi isolates of the type IIo phen otype were dead within 70 h, while only 40% of those injected with Mi isolates of the type IIb phenotype died within the same period. Bacter ia recovered from the spleens of animals that died after injection wit h type IIb phenotype isolates demonstrated a change in their IgG-bindi ng profile and were indistinguishable, in vitro or in vivo, from isola tes displaying the type IIo phenotype.