Kristen Ogden, Vanderbilt University Medical Center

Kristen M. Ogden (Vanderbilt University Medical Center, Nashville, TN, USA) John T. Tossberg (Vanderbilt University Medical Center, Nashville, TN, USA) Philip S. Crooke 3rd (Vanderbilt University, Nashville, TN, USA) Timothy W. Thoner Jr. ((Vanderbilt University Medical Center, Nashville, TN, USA) Thomas M. Aune (Vanderbilt University Medical Center, Nashville, TN, USA)

Pathogenesis and Immunity

To defend against viral infection, host cells recognize pathogen-associated molecular patterns (PAMPs), which can induce interferon regulatory factor (IRF)- and nuclear factor-kappa B (NF-kB)-regulated genes that activate the immune system. Alu elements are primate-specific, short interspersed elements that comprise ~10% of the human genome, form dsRNAs recognized by host sensors, and potently induce IRF and NF-kB transcriptional responses. To prevent this induction, Alu RNA adenosines are deaminated to inosine by ADAR enzymes, referred to as A-to-I editing. We previously found that IRF- and NF-kB-regulated genes, levels of Alu dsRNAs, and loss of A-to-I editing are elevated during multiple sclerosis relapse and that RNA from individuals with multiple sclerosis relapse or from reovirus-infected HeLa cells induces IRF- and NF-kB-regulated genes when transfected into recipient cells. We sought to identify conditions for induction of these RNAs in HeLa cells after reovirus infection and to determine their origin. Our data suggest that RNA from reovirus-infected HeLa cells stimulates innate immune responses, and the source of the immunostimulatory activity is endogenous RNA, including Alu dsRNA, rather than viral RNA. Reovirus particles lacking the genome induce RNA immunostimulatory activity, suggesting viral capsids may be PAMPs. Reovirus infection reduces A-to-I editing, and infection or reduced ADAR expression increases IRF- and NF-kB-regulated gene expression. Collectively, these findings support a model in which viral infection induces an ‘early warning system’ in human cells that involves rapid inhibition of A-to-I editing to allow accumulation of Alu dsRNAs, activating innate immune responses, which may prevent virus accumulation.