Immunological and biochemical characterization of streptococcal pyrogenic exotoxins I and J (SPE-I and SPE-J) from Streptococcus pyogenes

Recently, we described the identification of novel streptococcal superantig ens (SAgs) by mining the Streptococcus pyogenes M1 genome database at Oklah oma University. Here, we report the cloning, expression, and functional ana lysis of streptococcal pyrogenic exotoxin (SPE)-J and another novel SAg (SP E-I). SPE-1 is most closely related to SPE-H and staphylococcal enterotoxin I, whereas SPE-J is most closely related to SPE-C. Recombinant forms of SP E-I and SPE-J were mitogenic for PBL, both reaching half maximum responses at 0.1 pg/ml. Evidence from binding studies and cell aggregation assays usi ng a human B -lymphoblastoid cell line (LG-2) suggests that both toxins exc lusively bind to the polymorphic MHC class Alpha-chain in a zinc-dependent mode but not to the generic MHC class II a-chain. The results from analysis by light scattering indicate that SPE-J exists as a dimer in solution abov e concentrations of 4.0 mg/ml. Moreover, SPE-J induced a rapid homotypic ag gregation of LG-2 cells, suggesting that this toxin might cross-link MHC cl ass II molecules on the cell surface by building tetramers of the type HLA- DRG-SPE-J-SPE J-HLA-DR beta. SPE-I preferably stimulates T cells bearing th e V beta 18.1 TCR, which is not targeted by any other known SAg. SPE-J almo st exclusively stimulates V beta2.1 T cells, a V beta that is targeted by s everal other streptococcal SAgs, suggesting a specific role for this T cell subpopulation in immune defense. Despite a primary sequence diversity of 5 1%, SPE-J is functionally indistinguisabable from SPE-C and might play a ro le in streptococcal disease, which has previously been addressed to SPE-C. The Journal of immunology, 2001,