In addition, C57BL/6 mice were immunized by intramuscular and subcutaneous routes with STAg, for comparative purposes. Primary immunization was performed with 25 mg of STAg in 50 mL of PBS and equal volume of Freund's complete adjuvant (Sigma). Two boosters were performed at 15 day intervals, with 25 mg of STAg with Freund's incomplete adjuvant. Serum samples were collected weekly and stored at 220uC until use.