Heterogeneity of group A streptococcal pyrogenic exotoxin type B

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Abstract
Streptococcal pyrogenic exotoxin type B purified from culture filtrates of the NY-5 or T-19 strain of group A streptococcus was heterogeneous in charge. Three protein fractions with isoelectric points of 8.0, 8.4 and 9.0 were isolated by differential solubility in ethanol and acetate-buffered saline followed by isoelectric focusing and shown to be antigenically identical to streptococcal pyrogenic exotoxin type B. The MW of all 3 fractions were approximately 17,500, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with aggregates forming in the presence of hyaluronic acid. Only the pI [isoelectric point] 8.4 fraction showed the characteristic activities of streptococcal pyrogenic exotoxin in rabbits: pyrogenicity and ability to enhance susceptibility to lethal endotoxin shock. The pI 8.0 and pI 9.0 fractions were not pyrogenic, but could be used to immunize against pyrogenicity. These 2 fractions failed either to enhance lethal endotoxin shock or to immunize against enhancement activity. When the isolated fractions were electrofocused again they appeared heterogeneous, suggesting an instability of the B toxin molecular forms.