Early activation events differentiate the reactivity of two T-cell families to Staphylococcus enterotoxin A

Analysis of early activation events in two SEA responsive T-cell families demonstrated that low doses of SEA induced CD4+Vβ22 T-cells to down-regulate their TCR and express CD69, considerably earlier than CD4+Vβ5 T-cells. The rapid down-regulation of Vβ22 TCR led to its proliferation, whereas even a 10-fold higher dose of toxin induced only a partial down-regulation of Vβ5 TCR. Stimulation with SEA induced a significantly higher percentage of Vβ22 T-cells to produce IFN-γ compared to Vβ5 T-cells. SEAF47A, a mutant of SEA, known to have a lower binding affinity for the MHC class II molecule, failed to activate Vβ5 T-cells whereas Vβ22 T-cell activation was slightly decreased. Hence, early activation events highlighted the differential requirements of T-cell families to respond to SEA.