Figure 1. Inhibition of mitogenic activity in sera 96/2 and 99/1 with anti-superantigen (SAg) antisera. A) Peripheral blood lymphocytes (PBLs) were stimulated with 5% patient serum in the presence of 5% anti-SAg antiserum or 5% fetal calf serum (FCS) only. After 3 days, 3[H]-thymidine was added, and PBLs were incubated for another 24 h, before being washed and counted. The results were blotted as percentage of inhibition with specific anti-SAg serum compared to FCS. Antistreptococcal pyrogenic exotoxin (SPE)-J antiserum inhibited the mitogenic activity of serum 96/2 by 51%, while antistreptococcal mitogenic exotoxin (SME) Z antiserum inhibited the activity in 96/2 by 59% and the serum in 99/1 by 68%. B) The specificities of the anti–SPE-J and anti–SMEZ sera were demonstrated by stimulating PBLs with recombinant SAgs in the presence of 5% antiserum. SSA, streptococcal superantigen.