Activation of ERK-2 by S-Ag peptide 1. Western blotting was used to show that in a time-dependent manner the chemoattractant 1-20 aa S-Ag peptide, labeled S-Ag pep1, induced increased ERK phosphorylation, with a maximum response observed at 20 minutes (A). Further, a non-chemoattractant S-Ag peptide corresponding to aa 171-190 did not induce ERK phosphorylation (B), even when 5μg/mL of peptide were used for a 20-minute stimulation. Finally, ERK activation by S-Ag pep 1 was dose dependent, with increased phosphorylation observed from 100 ng/mL and to 5 μg/mL (C).