Since the initial descriptions of CD4+ T cell subsets with distinct functions and cytokine production profiles, the question of how these cells originate during an immune response has been asked. Both Th1 and Th2 cells can develop from naive, peripheral CD4+ T cell (Thp) populations, and individual Thp cells appear capable of differentiating into either Th subset (reviewed in reference 1). The differentiation process is initiated by ligation of the TCR, but additional signals are required for maturation into cells capable of producing high levels of cytokines upon restimulation. The most clearly defined differentiation inducers are themselves cytokines: IFN-γ and IL-12 for Th1, and IL-4 for Th2 induction. Thus, understanding the cellular origin and control of production of these cytokines during a primary immune response is central to understanding the genesis of Th1 and Th2 responses.
The principal early events that lead to Th1 differentiation in...
