Bovine herpesvirus 1 (BHV-1), an alphaherpesvirinae subfamily member, establishes latency in sensory neurons. Elevated corticosteroid levels, due to stress, reproducibly triggers reactivation from latency in the field. A single intravenous injection of the synthetic corticosteroid dexamethasone (DEX) to latently infected calves consistently induces reactivation from latency. Lytic cycle viral gene expression is detected in sensory neurons within 6 h after DEX treatment of latently infected calves. These observations suggested that DEX stimulated expression of cellular genes leads to lytic cycle viral gene expression and productive infection. In this study, a commercially available assay-Bovine Gene Chip-was used to compare cellular gene expression in the trigeminal ganglia (TG) of calves latently infected with BHV-1 versus DEX-treated animals. Relative to TG prepared from latently infected calves, 11 cellular genes were induced more than 10-fold 3 h after DEX treatment. Pentraxin three, a regulator of innate immunity and neurodegeneration, was stimulated 35-to 63-fold after 3 or 6 h of DEX treatment. Two transcription factors, promyelocytic leukemia zinc finger (PLZF) and Slug were induced more than 15-fold 3 h after DEX treatment. PLZF or Slug stimulated productive infection 20-or 5-fold, respectively, and Slug stimulated the late glycoprotein C promoter more than 10-fold. Additional DEX-induced transcription factors also stimulated productive infection and certain viral promoters. These studies suggest that DEX-inducible cellular transcription factors and/or signaling pathways stimulate lytic cycle viral gene expression, which subsequently leads to successful reactivation from latency in a small subset of latently infected neurons. Bovine herpesvirus 1 (BHV-1) is an alphaherpesvirinae subfamily member that causes significant economical losses to the cattle industry (86). The ability of BHV-1 to suppress the immune system can result in life-threatening pneumonia due to secondary bacterial infections. This multifactorial disorder is referred to as bovine respiratory disease complex (reviewed in references 35 and 39). Like different alphaherpesvirinae subfamily members, the primary site for BHV-1 latency is sensory neurons within trigeminal ganglia (TG). Viral gene expression (73) and infectious virus (29) are detected in TG from 1 to 6 days after acute infection. Lytic cycle viral gene expression is subsequently extinguished in sensory neurons, and latency is established. The BHV-1 genome is stably maintained in sensory neurons, but infectious virus is not detected by standard virus isolation procedures (reviewed in references 33 and 34). The only viral gene abundantly expressed in latently infected sensory neurons is the latency-related (LR) gene (reviewed in reference 38). Stress, due to confinement, transporting cattle, restricting food and water, weaning, or increased corticosteroid levels increases the incidence of reactivation from latency (35, 39). The latency reactivation cycle of BHV-1 is crucial for vi...

CD4 T cells that recognize peptide antigen in the context of class II MHC can differentiate into various subsets that are characterized by their helper functions. However, increasing evidence indicates that CD4 cells with direct cytolytic activity (CD4 CTL) play a role in chronic as well as acute infections, such as influenza A virus (IAV) infection. In the last couple of decades, techniques to measure the frequency and activity of these cytolytic cells has demonstrated their abundance in infections, such as human immunodeficiency virus, mouse pox, murine gamma herpes virus, cytomegalovirus, Epstein–Barr virus, and influenza among others. We now appreciate a greater role for CD4 CTL as direct effectors in viral infections and antitumor immunity through their ability to acquire perforin-mediated cytolytic activity and contribution to lysis of virally infected targets or tumors. As early as the 1980s, CD4 T cell clones with cytolytic potential were identified after influenza virus infection, yet much of this early work was dependent on in vitro culture and little was known about the physiological relevance of CD4 CTL. Here, we discuss the direct role CD4 CTL play in protection against lethal IAV infection and the factors that drive the generation of perforin-mediated lytic activity in CD4 cells in vivo during IAV infection. While focusing on CD4 CTL generated during IAV infection, we pull comparisons from the literature in other antiviral and antitumor systems. Further, we highlight what is currently known about CD4 CTL secondary and memory responses, as well as vaccination strategies to induce these potent killer cells that provide an extra layer of cell-mediated immune protection against heterosubtypic IAV infection.

Like other Alphaherpesvirinae subfamily members, bovine herpesvirus 1 (BHV-1) establishes latency in sensory neurons. The latency-related RNA (LR-RNA) is abundantly expressed in latently infected sensory neurons. An LR mutant virus with stop codons at the amino terminus of the first open reading frame (ORF) in the LR gene (ORF2) does not reactivate from latency, in part because it induces higher levels of apoptosis in infected neurons. ORF2 is not the only viral product expressed during latency, but it is important for the latency reactivation cycle because it inhibits apoptosis. In this study, a yeast 2-hybrid screen revealed that ORF2 interacted with two cellular transcription factors, Notch1 and Notch3. These interactions were confirmed in mouse neuroblastoma cells by confocal microscopy and in an in vitro "pulldown" assay. During reactivation from latency, Notch3 RNA levels in trigeminal ganglia were higher than those during latency, suggesting that Notch family members promote reactivation from latency or that reactivation promotes Notch expression. A plasmid expressing the Notch1 intercellular domain (ICD) stimulated productive infection and promoters that encode the viral transcription factor bICP0. The Notch3 ICD did not stimulate productive infection as efficiently as the Notch1 ICD and had no effect on bICP0 promoter activity. Plasmids expressing the Notch1 ICD or the Notch3 ICD trans-activated a late promoter encoding glycoprotein C. ORF2 reduced the trans-activation potential of Notch1 and Notch3, suggesting that ORF2 interfered with the trans-activation potential of Notch. These studies provide evidence that ORF2, in addition to inhibiting apoptosis, has the potential to promote establishment and maintenance of latency by sequestering cellular transcription factors.Bovine herpesvirus 1 (BHV-1) is an Alphaherpesvirinae subfamily member that causes significant economical losses to the cattle industry (60). The ability of BHV-1 to suppress the immune system can result in life-threatening pneumonia due to secondary bacterial infections, and this multifactorial disorder is known as bovine respiratory disease complex (reviewed in references 28, 31, and 32). As with other human Alphaherpesvirinae subfamily members, the primary site for BHV-1 latency is sensory neurons within trigeminal ganglia (TG). Viral gene expression (56) and infectious virus (21) are detected in TG from 1 to 6 days after infection, but latency is then established. Stress (due to confinement, transporting cattle, restricting food and water, or weaning) increases corticosteroid levels and can initiate reactivation from latency (31). Administration of a synthetic corticosteroid, dexamethasone (DEX), to calves or rabbits latently infected with BHV-1 reproducibly leads to reactivation from latency, as judged by virus shedding from ocular or nasal cavities and a secondary antibody response (21,26,27,29,30,52). Induction of lytic cycle viral gene expression is also consistently detected in TG neurons of calves latently infected with BHV-1 fo...

Bovine herpesvirus 1 (BoHV-1) is an important viral pathogen of cattle. Like other members of the subfamily Alphaherpesvirinae, BoHV-1 establishes latency in sensory neurons and has the potential to reactivate from latency. Dexamethasone (DEX) treatment of latently infected calves or rabbits consistently leads to reactivation from latency. The BoHV-1 transcript encoding the infected cell protein 0 (bICP0) is consistently detected during reactivation from latency, in part because the bICP0 early promoter is activated by DEX. During DEX-induced reactivation from latency, cyclin expression is stimulated in infected sensory neurons. Cyclindependent kinase activity phosphorylates Rb (retinoblastoma tumor suppressor gene product) family proteins and consequently releases the E2F family of transcription factors, suggesting that E2F family members stimulate productive infection and/or reactivation from latency. In this study, we provide evidence that repression of E2F1 by a specific small interfering RNA (siRNA) reduced productive infection approximately 5-fold. E2F1 or E2F2 stimulated bICP0 early promoter activity at least 100-fold in transient transfection assays. Two E2F-responsive regions (ERR) were identified within the early promoter, with one adjacent to the TATA box (ERR1) and one approximately 600 bp upstream from the TATA box (ERR2). Mobility shift assays suggested that E2F interacts with ERR1 and ERR2. E2F1 protein levels were increased at late times after infection, which correlated with enhanced binding to a consensus E2F binding site, ERR1, or ERR2. Collectively, these studies suggest that E2F1 stimulates productive infection and bICP0 early promoter activity, in part because E2F family members interact with ERR1 and ERR2.Bovine herpesvirus 1 (BoHV-1) is a significant viral pathogen of cattle that can cause conjunctivitis, rhinotracheitis, pneumonia, genital disorders, or abortions. BoHV-1 also initiates shipping fever, a potentially fatal polymicrobial disease (37). Like other members of the Alphaherpesvirinae subfamily, BoHV-1 establishes lifelong latency in trigeminal ganglionic neurons following acute replication in mucosal epithelium. Reactivation from latency occurs periodically, resulting in virus shedding and spread to susceptible cattle. Reactivation from latency can occur after stress or corticosteroid treatment, which mimics stress (30, 34). Dexamethasone (DEX), a synthetic corticosteroid, reproducibly induces expression of BoHV-1 lytic cycle genes and reactivation from latency in calves or rabbits (15,(17)(18)(19)(20)30).During productive infection of cultured cells, viral gene expression is temporally regulated in three distinct phases: the immediate-early (IE), early (E), and late (L) phases (reviewed in references 17 and 18). IE gene expression is stimulated by a virion component, bTIF, which interacts with a cellular transcription factor (Oct-1) to transactivate IE gene expression (22,23). Two IE transcription units exist, namely, IE transcription unit 1 (IEtu1) and IEtu2 (44-46). IEtu1 enc...

Cytolytic CD4 T cells (CD4 CTL) have been identified in vivo in response to viral infections; however, the factors necessary for driving the cytolytic phenotype have not been fully elucidated. Our previously published work suggests IL-2 may be the master regulator of perforin-mediated cytotoxicity in CD4 effectors. To further dissect the role of IL-2 in CD4 CTL generation, T cell receptor transgenic mice deficient in the ability to produce IL-2 or the high affinity IL-2 receptor (IL-2Rα, CD25) were used. Increasing concentrations of IL-2 were necessary to drive perforin (Prf) expression and maximal cytotoxicity. Granzyme B (GrB) expression and killing correlated with STAT5 activation and CD25 expression in vitro, suggesting that signaling through the high affinity IL-2R is critical for full cytotoxicity. IL-2 signaling was also necessary in vivo for inducing the Th1 phenotype and IFN-γ expression in CD4 T cells during influenza A (IAV) infection. In addition, GrB expression, as measured by mean fluorescent intensity, was decreased in CD25 deficient cells; however, the frequency of CD4 cells expressing GrB was unchanged. Similarly, analysis of cytolytic markers such as CD107a/b and Eomesodermin indicate high IL-2Rα expression is not necessary to drive the CD4 CTL phenotype during IAV infection. Thus, inflammatory signals induced by viral infection may overcome the need for strong IL-2 signals in driving cytotoxicity in CD4 cells.