No abstract

Background Influenza is a highly contagious, acute, febrile respiratory infection caused by a negative-sense, single-stranded RNA virus, which belongs in the Orthomyxoviridae family. Cigarette smoke (CS) exposure worsens influenza infection in terms of frequency and severity in both human and animal models. Methods C57BL/6 mice with or without CS exposure for 6 weeks were inoculated intranasally with a single, non-lethal dose of the influenza A virus (IAV) A/Puerto Rico/8/1934 (PR8) strain. At 7 and 10 days after infection, lung and mediastinal lymph nodes (MLN) cells were collected to determine the numbers of dendritic cells (DC), neutrophils, total CD4+ and CD8+ T cells, and IAV-specific CD4+ and CD8+ T cells using flow cytometry. Results CS exposure reduced numbers of CD103+ DCs in the lung and MLN of mice at day10, but not day7 post-infection. CS increased eosinophil number in mice with IAV infection at day10. CS exposure alone increased neutrophil numbers in mock-infected mice. IAV infection induced neutrophil in the lung, but CS exposure did not affect the number of neutrophil induced by IAV. Remarkably, CS increased total CD4+ and CD8+ T cell numbers in MLN in mice with IAV infection at day 7 and 10 compared to air-exposed mice. IAV-specific CD4+ and CD8+ T cells were increased by CS at day10. CS exposure also led to increased numbers of IAV-specific IFNγ -bearing CD8+ T cells in the lung and MLN. Conclusions Our results demonstrated that CS exposure alone induced neutrophil infiltration and inflammation in the lung. CS increased numbers of IAV antigen-specific CD4+ and CD8+ T cells, which produced more IFN-γ from day 7 after infection. CS-mediated induction of IFN-γ + CD4+ and CD8+ T cells may play a role in the increased mortality of the CS-exposed IAV-infected mice.

Retinoic acid-inducible gene I (RIG-I) is an important regulator of virus-induced antiviral interferons (IFNs) and proinflammatory cytokines. It requires interaction with an adaptor molecule, mitochondrial antiviral-signaling protein (MAVS), to activate downstream signaling pathways. To elucidate the mechanism(s) by which RIG-I-dependent recognition of IAV infection in vivo triggers innate immune responses, we infected mutant mice lacking RIG-I or MAVS with influenza A virus (IAV) and measured their innate immune responses. As has previously been demonstrated with isolated deletion of the virus recognition receptors TLR3, TLR7, and NOD2, RIG-I or MAVS knockout (KO) did not result in higher mortality and did not reduce IAV-induced cytokine responses in mice. Infected RIG-I KO animals displayed similar lung inflammation profiles as did WT mice, in terms of the protein concentration, total cell count, and inflammatory cell composition in the bronchoalveolar lavage fluid. RNA-Seq results demonstrated that all types of mice exhibited equivalent antiviral and inflammatory gene responses following IAV infection. Together, the results indicated that although RIG-I is important in innate cytokine responses in vitro, individual deletion of the genes encoding RIG-I or MAVS did not change survival or innate responses in vivo after IAV infection in mice.

No abstract