TLR7 and HIV infectious disease: In line with this, it is notable that HIV infection of macrophages fails to induce type 1 IFN production [51] (thought to be due to lack of high-level expression of TLR7 or other pattern recognition receptors capable of recognising HIV and triggering type 1 IFN production [52]); and that HIV infection of CD4+ T cells is associated with depletion of interferon-regulatory factor-3 (IRF-3), which impairs IFN induction through the retinoic acid-inducible gene I (RIG-I) pathway [53].