Abstract Body: A major cause of cardiovascular disease is atherosclerosis, a condition in which imbalances in lipid metabolism and maladaptive immune responses drive chronic inflammation in the artery wall resulting in plaque formation. Investigating the molecular mechanisms underlying persistent atherosclerotic inflammation may identify novel pathways that can be harnessed for the treatment of cardiovascular disease. The last decade has seen extraordinary growth in our understanding of the human genome and revealed powerful roles for long noncoding RNAs (lncRNA) in genome organization and the orchestration of gene expression. Using unbiased sequencing data from human and mouse atherosclerotic plaques, we identified an antisense lncRNA, IRF1-AS1 and its mouse ortholog Gm12216, that are highly expressed in plaque macrophages and correlate with the expression of interferon-stimulated genes that promote atherosclerotic inflammation. Molecular interrogation of IRF1-AS1 function revealed that it is co-induced in primary human macrophages with its proximal gene IRF1 upon treatment with oxidized LDL or interferon (IFN)b. Knockdown of IRF1-AS1 using antisense oligonucleotide GapmeRs decreased expression of IRF1, a key transcriptional regulator of type I IFNs and inflammatory as well as metabolic genes implicated in atherogenesis. Notably, IRF1-AS1 depletion in macrophages diminished lipid droplet accumulation and reduced levels of secreted type I and type II IFNs. Using synteny analysis, we identified Gm12216 as the mouse ortholog of IRF1-AS1 and showed that its regulation and function in mouse macrophages is conserved, including co-expression of Irf1 and regulation of both IFN and IFN-stimulated genes. To test its function in vivo, we generated a Gm12216 knock-out mouse line and show that Gm12216-mediated regulation of IFN signaling drives the progression of diet-induced atherosclerosis. Our data demonstrate that IRF1-AS1/Gm12216 is a critical regulator of atherosclerosis at the crossroads of the IFN-driven immune response and lipid metabolism, and that targeting IRF1-AS1 has the potential to dampen atherosclerotic inflammation and reverse plaque progression. Further study of conserved lncRNAs, such as IRF1-AS1, and their molecular regulation of processes that contribute to atherogenesis may lead to the identification of novel diagnostic and/or therapeutic approaches in cardiovascular disease.