We verified that GADD34 inactivation, and no other deficiency, was truly responsible for the loss of cytokine production by complementing GADD34 DC/DC MEFs with GADD34 cDNA prior poly I:C delivery. IFN-ß secretion was partially restored in transfected GADD34 DC/DC cells while eIF2a was efficiently dephosphorylated in both WT and GADD34 DC/DC transfected MEFs (Fig. 4E) . To further demonstrate that the phosphatase activity of GADD34 controls cytokine production upon dsRNA detection, we treated WT MEFs with guanabenz, a small molecule, which selectively impairs GADD34-dependent eIF2a dephosphorylation [58] . Upon treatment with this compound, a dose dependent inhibition of IFN-ß secretion was observed in poly I:C-treated MEFs, confirming the importance of GADD34 in this process (Fig. S10) .