Stephania tetrandra and other related species of Menispermaceae are the major sources of the bis-benzylisoquinoline alkaloids tetrandrine (TET), fangchinoline (FAN), and cepharanthine (CEP). Although the pharmacological properties of these compounds include anticancer and anti-inflammatory activities, the antiviral effects of these compounds against human coronavirus (HCoV) remain unclear. Hence, the aims of the current study were to assess the antiviral activities of TET, FAN, and CEP and to elucidate the underlying mechanisms in HCoV-OC43-infected MRC-5 human lung cells. These compounds significantly inhibited virus-induced cell death at the early stage of virus infection. TET, FAN, and CEP treatment dramatically suppressed the replication of HCoV-OC43 as well as inhibited viral S and N protein expression. The virus-induced host response was reduced by compound treatment as compared with the vehicle control. Taken together, these findings demonstrate that TET, FAN, and CEP are potential natural antiviral agents for the prevention and treatment of HCoV-OC43 infection. Biomolecules 2019, 9, 696 2 of 16anticancer, anti-inflammatory, and anti-oxidative activities [6]. TET exhibits broad pharmacological actions that include anti-inflammatory effects as well as immunosuppressant and anticancer activities [5]. Several studies have reported the effects of TET against the infection of different types of viruses such as herpes simplex virus, dengue virus, and Ebola virus [7][8][9]; others have shown that FAN inhibits the replication of human immunodeficiency virus type 1 (HIV-1) [10] and that CEP possesses antiviral activities against HIV-1 [11] and herpes simplex virus type 1 [12]. Coronaviruses (CoVs) are enveloped, positive-sense, single-stranded RNA viruses that infect a broad range of animal species and cause multiple respiratory outcomes of varying severity, including the common cold, bronchiolitis, and pneumonia [13]. CoVs are subdivided into four genera (Alpha-, Beta-, Gamma-, and Delta-) [14]. Among the six CoVs isolated from humans [15], the World Health Organization declared that accelerated research and the development of antivirals for the treatment of emerging zoonotic viruses, including β-CoVs, Middle East respiratory syndrome-related coronavirus (MERS-CoV), and severe acute respiratory syndrome-related coronavirus (SARS-CoV), are urgently needed [16]. Since the mid-1960s, human coronavirus strains OC43 (HCoV-OC43; β-CoV) and 229E (α-CoV) have been considered as mostly responsible for the common cold [17,18]. Notably, HCoV-OC43, which is the most prevalent subtype of HCoV [19], is responsible for up to 30% of respiratory infections and can cause repeated reinfections throughout life [20,21]. Moreover, HCoV-OC43 is most closely related to SARS-CoV and MERS-CoV, and shares several functional properties with both [22,23]. Due to the similarities with SARS-CoV and MERS-CoV, HCoV-OC43 has been used as an alternative model for research of these emerging viral strains to avoid the limitation of the requirement fo...

Interleukin-6 (IL-6) plays an important role in the development and progression of inflammatory responses, autoimmune diseases, and cancers. Many viral infections, including Theiler's murine encephalomyelitis virus (TMEV), result in the vigorous production of IL-6. However, the role of IL-6 in the development of virus-induced inflammatory responses is unclear. The infection of susceptible mice with TMEV induces the development of chronic demyelinating disease, which is considered a relevant infectious model for multiple sclerosis. In this study, we demonstrate that resistant C57BL/6 mice carrying an IL-6 transgene (IL-6 Tg) develop a TMEV-induced demyelinating disease accompanied by an increase in viral persistence and an elevated Th17 cell response in the central nervous system. Either IL-6 or IL-17 induced the expression of Bcl-2 and Bcl-xL at a high concentration. The upregulated expression of prosurvival molecules in turn inhibited target cell destruction by virus-specific CD8 ؉ T cells. More interestingly, IL-6 and IL-17 synergistically promoted the expression of these prosurvival molecules, preventing cellular apoptosis at a much lower (<5-fold) concentration. The signals involved in the synergy appear to include the activation of both STAT3 and NF-B via distinct cytokine-dependent pathways. Thus, the excessive IL-6 promotes the generation of Th17 cells, and the resulting IL-6 and IL-17 synergistically promote viral persistence by protecting virus-infected cells from apoptosis and CD8؉ T cell-mediated target destruction. These results suggest that blocking both IL-6 and IL-17 functions are important considerations for therapies of chronic viral diseases, autoimmune diseases, and cancers. IMPORTANCEThis study indicates that an excessive level of IL-6 cytokine produced following viral infection promotes the development of IL-17-producing pathogenic helper T cells. We demonstrate here for the first time that IL-6 together with IL-17 synergistically enhances the expression of survival molecules to hinder critical host defense mechanisms removing virus-infected cells. This finding has an important implication in controlling not only chronic viral infections but also autoimmune diseases and cancers, which are associated with prolonged cell survival.

Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) serves as virus-induced model of chronic progressive multiple sclerosis. Infection of susceptible SJL/J mice leads to life-long CNS virus persistence and a progressive autoimmune demyelinating disease mediated by myelin-specific T cells activated via epitope spreading. In contrast, virus is rapidly cleared by a robust CTL response in TMEV-IDD-resistant C57BL/6 mice. We investigated whether differential induction of regulatory T cells (Tregs) controls susceptibility to TMEV-IDD. Infection of disease-susceptible SJL/J, but not B6 mice, leads to rapid activation and expansion of Tregs resulting in an unfavorable CNS ratio of Treg:Teffector cells. In addition, anti-CD25-induced inactivation of Tregs in susceptible SJL/J, but not resistant B6, mice results in significantly decreased clinical disease concomitant with enhanced anti-viral CD4 + , CD8 + and antibody responses resulting in decreased CNS viral titers. This is the first demonstration that virus-induced Treg activation regulates susceptibility to autoimmune disease differentially in susceptible and resistant strains of mice and provides a new mechanistic explanation for the etiology of infection-induced autoimmunity.

Infection with Theiler's murine encephalomyelitis virus (TMEV) in the central nervous system (CNS) causes an immune system-mediated demyelinating disease similar to human multiple sclerosis in susceptible but not resistant strains of mice. To understand the underlying mechanisms of differential susceptibility, we analyzed viral replication, cytokine production, and costimulatory molecule expression levels in microglia and macrophages in the CNS of virus-infected resistant C57BL/6 (B6) and susceptible SJL/J (SJL) mice. Our results indicated that message levels of TMEV, tumor necrosis factor alpha, beta interferon, and interleukin-6 were consistently higher in microglia from virus-infected SJL mice than in those from B6 mice. However, the levels of costimulatory molecule expression, as well as the ability to stimulate allogeneic T cells, were significantly lower in TMEV-infected SJL mice than in B6 mice. In addition, microglia from uninfected naïve mice displayed differential viral replication, T-cell stimulation, and cytokine production, similar to those of microglia from infected mice. These results strongly suggest that different levels of intrinsic susceptibility to TMEV infection, cytokine production, and T-cell activation ability by microglia contribute to the levels of viral persistence and antiviral T-cell responses in the CNS, which are critical for the differential susceptibility to TMEV-induced demyelinating disease between SJL and B6 mice.BeAn and DA are members of Theiler's original subgroup of Theiler's murine encephalitis virus (TMEV) (52). Intracerebral inoculation of susceptible mice, such as SJL/J (SJL) mice, with either of these viruses results in a biphasic disease characterized by early encephalitis and late chronic demyelination (24). Infection of susceptible mice with these viruses results in a chronic, white matter-demyelinating disease similar to human multiple sclerosis (24). In susceptible strains, infection of the central nervous system (CNS) with TMEV leads to a chronic immune response to viral antigens, which eventually leads to autoimmune responses against myelin autoantigens (29). In contrast, resistant mouse strains, such as C57BL/6 (B6), rapidly clear virus from the CNS and do not develop demyelinating disease, suggesting that viral persistence in these mice corresponds to susceptibility to disease (26,42,45). Demyelination in susceptible mice is considered to be immunity mediated, as removal of immune components reduces the clinical onset and severity of demyelinating disease (9,25,44,47).In particular, infiltration of proinflammatory CD4 ϩ Th1-type cells has been associated with tissue destruction and demyelination (41, 56). A number of CD4 ϩ T cells specific for TMEV during the course of disease in SJL mice recognize four predominant viral capsid epitopes (VP1 233-250 , VP2 74-86 , VP3 24-37 , and VP4 51-70 ), with one each on the external and internal capsid proteins (10,19,55,56). The external capsid epitopes appear to account for the majority (ϳ80%) of major histocompatibili...