ABSTRACT
The consequences of the decision to differentiate into TH1 or TH2 cells are profound, as selective production of TH1 cells enables the immune response to activate macrophages and cell-mediated immunity, whereas selective production of TH2 biases the response towards antibody production only. The decision as to which pathway a naive T cell will follow is made during its first encounter with antigen. An antigen that interacts strongly with the T-cell receptor causes the cell to mature into a TH1 cell, whereas a weak interaction leads to TH2 development. Differentiation is also dependent on cytokines. TH1 differentiation is dependent on IL-12 and IFN-g, whereas TH2 differentiation is dependent on IL-4 (see Fig. 30.2). These cytokines trigger pathways of signal transduction; for example, mice deficient in the intracellular signaling molecule STAT6, which is induced by IL-4, fail to develop TH2 cells.
