Endogenous dsRNA from cells lacking Trp53 induces an innate immune response in transfected cells. (A) Schematic representation of the experiment. Endogenous dsRNA was isolated from purified total RNA of wild-type, Trp53 mutant and Adar1;Trp53 double mutant MEFs by immunoprecipitation with J2 antibody and transfected back into reporter cells of the same lines. (B) Immunoblot showing the expression of MDA5 and RIG-I receptors after wild-type, Trp53 and Adar1;Trp53 reporter MEFs were transfected with dsRNA. Data are representative of two independent experiments. Black lines indicate where the image was cut to make the same alignment for all three immunoblot images; the original images are in Supplemental Figure S2. (C) ELISA showing mean levels of IL-6 in cell culture supernatants of Trp53 MEFs transfected with dsRNA. Results are normalized to cytokine expression in nontransfected cells. Data are mean ± SD of n = 3. (D) RT-qPCR analysis of transcripts encoding IFN-α, two dsRNA receptors, and three other ISG mRNAs in Trp53 MEFs transfected with dsRNA. Results are normalized to mRNA expression in nontransfected cells. Data are mean ± SD of three independent experiments. (*) P ≤ 0.05, (**) P ≤ 0.01, (***) P ≤ 0.001.