The outcome of immune responses critically depends on the pattern of lymphokines secreted by CD4 + T cells. CD4 + T cells may differentiate into interleuldn 2 (IL-2) and interferon 3' secreting T helper 1 (Thl)-like cells or IL-4/IL-5/IL-IO secreting Th2-1ike cells. However, the mechanisms that regulate production of IL-4 or other T cell lymphokines in vivo remain unknown. We use the superantig...