Diminished Innate Antiviral Response to Adenovirus Vectors in cGAS/STING-Deficient Mice Minimally Impacts Adaptive Immunity.

UNLABELLED: Infection by adenovirus, a nonenveloped DNA virus, induces antiviral innate and adaptive immune responses. Studies of transformed human and murine cell lines using short hairpin RNA (shRNA) knockdown strategies identified cyclic guanine adenine synthase (cGAS) as a pattern recognition receptor (PRR) that contributes to the antiadenovirus response. Here we demonstrate how the cGAS/STING cascade influences the antiviral innate and adaptive immune responses in a murine knockout model. Using knockout bone marrow-derived dendritic cells (BMDCs) and bone marrow-derived macrophages (BMMOs), we determined that cGAS and STING are essential to the induction of the antiadenovirus response in these antigen-presenting cells (APCs) in vitro We next determined how the cGAS/STING cascade impacts the antiviral response following systemic administration of a recombinant adenovirus type 5 vector (rAd5V). Infection of cGAS(-/-) and STING(-/-) mice results in a compromised early antiviral innate response compared to that in wild-type (WT) controls: significantly lower levels of beta interferon (IFN-ß) secretion, low levels of proinflammatory chemokine induction, and reduced levels of antiviral transcript induction in hepatic tissue. At 24 h postinfection, levels of viral DNA and reporter gene expression in the liver were similar in all strains. At 28 days postinfection, clearance of infected hepatocytes in cGAS or STING knockout mice was comparable to that in WT C57BL/6 mice. Levels of neutralizing anti-Ad5V antibody were modestly reduced in infected cGAS mice. These data support a dominant role for the cGAS/STING cascade in the early innate antiviral inflammatory response to adenovirus vectors. However, loss of the cGAS/STING pathway did not affect viral clearance, and cGAS deficiency had a modest influence on the magnitude of the antiviral humoral immune response to adenovirus infections. IMPORTANCE: The detection of viral infection by host sentinel immune cells contributes to the activation of a complex and varied antiviral innate and adaptive immune response, which limits virus replication, spread, and susceptibility to infection. In this study, we have characterized how the cGAS/STING DNA-sensing cascade contributes to early detection of adenovirus infections. cGAS influences APC activation and early innate antiviral inflammatory immune responses, but adaptive immune pathways associated with virus clearance and anti-Ad antibody production were minimally influenced by the loss of the cGAS PRR signaling cascade.

Relative contribution of free-virus and synaptic transmission to the spread of HIV-1 through target cell populations.

Human immunodeficiency virus can spread through target cells by transmission of cell-free virus or directly from cell-to-cell via formation of virological synapses. Although cell-to-cell transmission has been described as much more efficient than cell-free infection, the relative contribution of the two transmission pathways to virus growth during multiple rounds of replication remains poorly defined. Here, we fit a mathematical model to previously published and newly generated in vitro data, and determine that free-virus and synaptic transmission contribute approximately equally to the growth of the virus population.

Regulatory T cells inhibit T cell proliferation and decrease demyelination in mice chronically infected with a coronavirus.

Mice infected with the neurotropic JHM strain of mouse hepatitis virus (JHMV) develop acute and chronic demyelinating diseases with histopathological similarities to multiple sclerosis. The process of demyelination is largely immune-mediated, as immunodeficient mice (RAG1(-/-) mice) do not develop demyelination upon infection; however, demyelination develops if these mice are reconstituted with either JHMV-immune CD4 or CD8 T cells. Because myelin destruction is a consequence of the inflammatory response associated with virus clearance, we reasoned that decreasing the amount of inflammation would diminish clinical disease and demyelination. Given that regulatory T cells (Tregs) have potent anti-inflammatory effects, we adoptively transferred Tregs into infected C57BL/6 and RAG1(-/-) mice. In both instances, transfer of Tregs decreased weight loss, clinical scores, and demyelination. Transferred Tregs were not detected in the CNS of infected RAG1(-/-) mice, but rather appeared to mediate their effects in the draining cervical lymph nodes. We show that Tregs dampen the inflammatory response mediated by transferred JHMV-immune splenocytes in infected RAG1(-/-) mice by decreasing T cell proliferation, dendritic cell activation, and proinflammatory cytokine/chemokine production, without inducing apoptosis. By extension, decreasing inflammation, whether by Treg transfer or by otherwise enhancing the anti-inflammatory milieu, could contribute to improved clinical outcomes in patients with virus-induced demyelination.

Atrial Fibrillation Ablation in a Patient with Cor Triatriatum Sinister and Left Common Pulmonary Vein: Impact of Left Atrium Anatomy on Ablation Approach.

Atrial fibrillation is the most common presentation in adult patients with cor triatriatum sinister. The key to successful and safe catheter ablation in these patients is an accurate exploration and thorough understanding of the left atrial anatomy, both before and during the procedure. Catheter manipulation is highly dependable on left atrial anatomy, including the interatrial septum, insertion of pulmonary veins and cor triatriatum membrane. Anatomical variants such as the left common pulmonary trunk may influence the ablation approach and outcome. We report the case of a 52-year-old patient with cor triatriatum sinister and the left common pulmonary vein variant who underwent successful high-power, short-duration catheter ablation for paroxysmal atrial fibrillation.

Role of regulatory T cells in coronavirus-induced acute encephalitis.

C57BL/6 mice infected with mouse hepatitis virus, strain JHM (JHMV) develop a rapidly fatal acute encephalitis. Previously, we showed that this disease is partially CD4 T cell-mediated since infection with a recombinant JHMV (rJ) mutated in only a single immunodominant CD4 T cell epitope (epitope M133, rJ.M(Y135Q)) results in a nonlethal disease. Increased mortality correlated with a greater number of JHMV-specific CD4 T cells in the brains of rJ compared to rJ.M(Y135Q)-infected mice. Here, we extend these results to show that the diminished number of virus-specific T cells correlates with a reduced cytokine/chemokine response in the infected brain. We also show that regulatory CD4 T cells (Tregs) are critical for mild disease in rJ.M(Y135Q)-infected mice because their depletion results in increased mortality. Further, a relative paucity of Tregs characterizes lethal infection because adoptive transfer of Tregs into rJ-infected mice increases survival from 0% to 50%. These results support the notion that clinical disease in coronavirus-induced acute encephalitis results from a balance between factors critical for virus clearance, such as virus-specific effector T cells and anti-inflammatory elements, such as Tregs. These findings also show that unlike chronic infections, in which an excessive number of Tregs contributes to pathogen persistence, Tregs in the setting of acute encephalitis may help to limit immunopathological disease without delaying virus clearance.

Pathogenic role for virus-specific CD4 T cells in mice with coronavirus-induced acute encephalitis.

Acute viral encephalitis is believed to result from direct virus destruction of infected cells and from virus-induced host immune response, but the relative contribution of each remains largely unknown. For example, C57BL/6 (B6) mice infected with mouse hepatitis virus (JHM strain, JHMV) develop severe encephalitis, with death occurring within 7 days. Here, we show that the host response to a single JHMV-specific immunodominant CD4 T-cell epitope is critical for severe disease. We engineered a recombinant JHMV with mutations in the immunodominant CD4 T-cell epitope (rJ.M(Y135Q)). Infection of naïve B6 mice with this virus resulted in mild disease with no mortality. However, introduction of a CD4 T-cell epitope from Listeria monocytogenes into rJ.M(Y135Q) generated a highly virulent virus. The decrease in disease severity was not due to a switch from Th1 to Th2 predominance in rJ.M(Y135Q)-infected mice, an effect on CD8 T-cell function, or differential expression of tumor necrosis factor-alpha by JHMV-specific CD4 T cells. These results show that the response to a single virus-specific CD4 T-cell epitope may contribute to a pathogenic host response in the setting of acute viral disease and that abrogation of this response ameliorates clinical disease without diminishing virus clearance.

Bystander CD8 T-cell-mediated demyelination is interferon-gamma-dependent in a coronavirus model of multiple sclerosis.

Mice infected with the coronavirus mouse hepatitis virus, strain JHM (JHM) develop a disease that shares many histological characteristics with multiple sclerosis. We previously demonstrated that JHM-infected mice that only have CD8 T cells specific for an epitope not in the virus develop demyelination on specific activation of these cells. Herein we show that this process of bystander T-cell-mediated demyelination is interferon-gamma (IFN-gamma)-dependent. The absence of IFN-gamma abrogated demyelination but did not change T-cell infiltration or expression levels of inflammatory cytokines or chemokines in the spinal cord. These results are consistent with models in which IFN-gamma contributes to CD8 T-cell-mediated demyelination by activation of macrophages/microglia, the final effector cells in the disease process.