Fig. 2.

TLR signaling pathway for IFN-α production in plasmacytoid dendritic cells (pDCs). TLR7 and TLR8 respond to RNA viruses by recognizing ssRNA in endosomes. In contrast, TLR9 responds to DNA viruses by recognizing CpG-rich sequences. The receptors transmit their signals through an associated multiprotein complex containing the adaptor protein MyD88 and the transcription factor IRF-7. In contrast to most other cells, pDCs constitutively express IRF-7 (Kerkmann et al., 2003, Prakash et al., 2005). Some pathogenic viruses interfere with this pathway. See text for details.