GBP1 and HIV-1 infection: We confirmed the HIV-1 infection efficiency of these cells by quantifying levels of GP120 mRNA (see below) as well as mRNAs representative of the host antiviral immune response (interferon-induced guanylate-binding protein 1 [GBP1] and interferon-induced protein with tetratricopeptide repeats 1 [IFIT1]) (data not shown).