Type I IFN induction in monocytes by DNA-LL37 complexes requires dsDNA but is independent of DNA sequence and methylation. (A) IFN-α produced by pDCs (5 × 104 cells/condition) and monocytes (2 × 105 cells/condition) after overnight stimulation with 10 μg/mL of ssCpG DNA, or dsCpG DNA sequences of phosphodiester backbone alone or in complex with LL37 (10μM), with or without pretreatment with bafilomycin (50nM). In contrast to pDCs, in monocytes ssDNA sequences in complex with LL37 failed to induce IFN-α production. Data are representative of at least 4 independent experiments; error bars represent the SD of triplicate wells. (B) IFN-α produced by pDCs and monocytes after overnight stimulation with 10 μg/mL of a CpG-containing plasmid or a CpG-free plasmid, alone or with LL37 (10μM), with or without pretreatment with 50nM bafilomycin. Each symbol represents an independent experiment, and horizontal bars represent the mean. (C) IFN-α produced by pDCs (5 × 104 cells/condition) and monocytes (2 × 105 cells/condition) after overnight stimulation with 10 μg/mL of unmethylated or methylated dsCpG DNA, either alone or in complex with LL37 (10μM). Data are presented as mean ± SEM of 3 independent experiments. *P < .0001 (paired Student t test).
