We therefore investigated IFN-ß and IL-6 production in response to dsRNA in WT, GADD34 DC/DC and CReP 2/2 MEFs. CReP 2/2 MEFs were used as a control, since CReP (Ppp1r15b) is a non-inducible co-factor of PP1 and displays some functional redundancy with GADD34 [57] . Although basal levels of eIF2a phosphorylation were higher in CReP 2/2 , PKR expression and translation inhibition upon poly I:C delivery were equivalent in WT and CReP 2/2 MEFs ( Fig. S7A and S7B ). Quantification of IFN-ß and IL-6 levels in culture supernatants indicated that, although abundant and comparable amounts of these cytokines were secreted by WT and CReP 2/2 cells, they were both absent in poly I:C-treated GADD34 DC/DC MEFS ( Fig. 4C and S7C) .