IFN-γ production by antigen-presenting cells: mechanisms emerge

The suggestion that antigen-presenting cells (APCs) produce interferon γ (IFN-γ) is controversial because it conflicts with the initial paradigm in which the production of IFN-γ was restricted to lymphoid cells. However, some answers to this skepticism have been provided by recent findings of high-level production and intracellular expression of IFN-γ by interleukin-12 (IL-12)-stimulated macrophages and dendritic cells. New data are now emerging to explain the mechanism of production of IFN-γ vby APCs. As in lymphoid cells, IL-12-induced IFN-γ production in APCs requires signal transducer and activator of transcription 4 (STAT4), although the precise molecular events that govern the transcription of the gene encoding IFN-γ are enigmatic still. Understanding these processes in lymphoid, and now nonlymphoid, cells remains an important challenge.