Herpes Simplex Virus Type-1-Induced Activation of Myeloid Dendritic Cells: The Roles of Virus Cell Interaction and Paracrine Type I IFN Secretion

Herpes simplex virus interference with immunity: Focus on dendritic cells

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are highly prevalent in the human population. These viruses cause lifelong infections by establishing latency in neurons and undergo sporadic reactivations that promote recurrent disease and new infections. The success of HSVs in persisting in infected individuals is likely due to their multiple molecular determinants involved in escaping the host antiviral and immune responses. Importantly, HSVs infect and negatively modulate the function of dendritic cells (DCs), key immune cells that are involved in establishing effective and balanced immunity against viruses. Here, we review and discuss several molecular and cellular processes modulated by HSVs in DCs, such as autophagy, apoptosis, and the unfolded protein response. Given the central role of DCs in establishing optimal antiviral immunity, particular emphasis should be given to the outcome of the interactions occurring between HSVs and DCs.

Sendai Virus, a Strong Inducer of Anti-Lentiviral State in Ovine Cells

Small ruminant lentiviruses (SRLVs) are widely spread in the ovine and caprine populations, causing an incurable disease affecting animal health and production. Vaccine development is hindered owing to the high genetic heterogeneity of lentiviruses and the selection of T-cell and antibody escape mutants, requiring antigen delivery optimization. Sendai virus (SeV) is a respiratory paramyxovirus in mice that has been recognized as a potent inducer of innate immune responses in several species, including mouse and human. The aim of this study was to stimulate an innate antiviral response in ovine cells and evaluate the potential inhibitory effect upon small ruminant lentivirus (SRLV) infections. Ovine alveolar macrophages (AMs), blood-derived macrophages (BDMs), and skin fibroblasts (OSFs) were stimulated through infection with SeV encoding green fluorescent protein (GFP). SeV efficiently infected ovine cells, inducing an antiviral state in AM from SRLV naturally-infected animals, as well as in in vitro SRLV-infected BDM and OSF from non-infected animals. Supernatants from SeV-infected AM induced an antiviral state when transferred to fresh cells challenged with SRLV. Similar to SRLV, infectivity of an HIV-1-GFP lentiviral vector was also restricted in ovine cells infected with SeV. In myeloid cells, an M1-like proinflammatory polarization was observed together with an APOBEC3Z1 induction, among other lentiviral restriction factors. Our observations may boost new approximations in ameliorating the SRLV burden by stimulation of the innate immune response using SeV-based vaccine vectors.

mRNA expression of IFN-λs in the gingival tissue of patients with chronic or aggressive periodontitis: A polymerase chain reaction study

BACKGROUND

Several studies have proven the existence of herpesviruses in periodontal pockets of patients with chronic or aggressive periodontitis. Recently discovered interferon lambda (IFN-λ) has antiviral properties and is induced by herpesviruses. The present study was a quantitative analysis of messenger RNA (mRNA) expression of IFN-λs (IFN-λ1, IFN-λ2, IFN-λ3) in the gingival tissues of patients with chronic or aggressive periodontitis.

METHODS

A total of 90 participants (50 men and 40 women; age range 19-50 years, mean age 31.50 ± 7.8) were categorized into three groups: healthy participants, patients with chronic periodontitis, and patients with aggressive periodontitis. mRNA expression of IFN-λs in gingival tissues was estimated using reverse transcriptase polymerase chain reaction and was correlated with clinical parameters such as gingival index (GI), probing pocket depth (PPD), and clinical attachment level (CAL).

RESULTS

mRNA of IFN-λ1, IFN-λ2, and IFN-λ3 was expressed in gingival tissues of healthy participants and in patients with chronic or aggressive periodontitis. The highest level of IFN-λ1 was observed in patients with aggressive periodontitis (3.049 ± 9.793), whereas IFN-λ2 (4.322 ± 11.310) and IFN-λ3 (11.932 ± 27.479) were highest in patients with chronic periodontitis. The difference in mRNA expression of IFN-λ1 (P = 0.008) and IFN-λ3 (P = 0.043) among three groups was statistically significant CONCLUSION: Increased quantity of IFN-λs in patients with chronic and patients with aggressive periodontitis suggests a role in periodontitis. Variation in the expression of IFN-λ1 and IFN-λ3 in patients with periodontitis needs to be further evaluated. The mRNA expression of antiviral IFN-λs in gingival tissues might enhance our understanding related to viral pathogenesis of periodontal diseases.

Myeloid Cells during Viral Infections and Inflammation

Myeloid cells represent a diverse range of innate leukocytes that are crucial for mounting successful immune responses against viruses. These cells are responsible for detecting pathogen-associated molecular patterns, thereby initiating a signaling cascade that results in the production of cytokines such as interferons to mitigate infections. The aim of this review is to outline recent advances in our knowledge of the roles that neutrophils and inflammatory monocytes play in initiating and coordinating host responses against viral infections. A focus is placed on myeloid cell development, trafficking and antiviral mechanisms. Although known for promoting inflammation, there is a growing body of literature which demonstrates that myeloid cells can also play critical regulatory or immunosuppressive roles, especially following the elimination of viruses. Additionally, the ability of myeloid cells to control other innate and adaptive leukocytes during viral infections situates these cells as key, yet under-appreciated mediators of pathogenic inflammation that can sometimes trigger cytokine storms. The information presented here should assist researchers in integrating myeloid cell biology into the design of novel and more effective virus-targeted therapies.

Autophagic degradation of lamins facilitates the nuclear egress of herpes simplex virus type 1

Turan and Grosche et al. show that herpes simplex virus type 1 (HSV-1) infection leads to autophagic degradation of nuclear lamins in immature dendritic cells, facilitating HSV-1 nuclear egress and the formation of infectious progeny virus. In mature dendritic cells, autophagy is inhibited due to elevated KIF1B and KIF2A protein levels.

Dendritic cells (DCs) are crucial for the induction of potent antiviral immune responses. In contrast to immature DCs (iDCs), mature DCs (mDCs) are not permissive for infection with herpes simplex virus type 1 (HSV-1). Here, we demonstrate that HSV-1 infection of iDCs and mDCs induces autophagy, which promotes the degradation of lamin A/C, B1, and B2 in iDCs only. This in turn facilitates the nuclear egress of progeny viral capsids and thus the formation of new infectious particles. In contrast, lamin protein levels remain stable in HSV-1–infected mDCs due to an inefficient autophagic flux. Elevated protein levels of KIF1B and KIF2A in mDCs inhibited lamin degradation, likely by hampering autophagosome–lysosome fusion. Therefore, in mDCs, fewer progeny capsids were released from the nuclei into the cytosol, and fewer infectious virions were assembled. We hypothesize that inhibition of autophagic lamin degradation in mDCs represents a very powerful cellular counterstrike to inhibit the production of progeny virus and thus viral spread.

Therapeutic DNA Vaccines for Human Papillomavirus and Associated Diseases

Human papillomavirus (HPV) has long been recognized as the causative agent of cervical cancer. High-risk HPV types 16 and 18 alone are responsible for over 70% of all cases of cervical cancers. More recently, HPV has been identified as an etiological factor for several other forms of cancers, including oropharyngeal, anogenital, and skin. Thus, the association of HPV with these malignancies creates an opportunity to control these HPV lesions and HPV-associated malignancies through immunization. Strategies to prevent or to therapeutically treat HPV infections have been developed and are still pushing innovative boundaries. Currently, commercial prophylactic HPV vaccines are widely available, but they are not able to control established infections or lesions. As a result, there is an urgent need for the development of therapeutic HPV vaccines, to treat existing infections, and to prevent the development of HPV-associated cancers. In particular, DNA vaccination has emerged as a promising form of therapeutic HPV vaccine. DNA vaccines have great potential for the treatment of HPV infections and HPV-associated cancers due to their safety, stability, simplicity of manufacturability, and ability to induce antigen-specific immunity. This review focuses on the current state of therapeutic HPV DNA vaccines, including results from recent and ongoing clinical trials, and outlines different strategies that have been employed to improve their potencies. The continued progress and improvements made in therapeutic HPV DNA vaccine development holds great potential for innovative ways to effectively treat HPV infections and HPV-associated diseases.

Correlation of the interleukin-29 levels in crevicular fluid and plasma with the genetic polymorphism in chronic and aggressive periodontitis patients

OBJECTIVE

To assess the effect of single nucleotide polymorphism (SNP) on the Interleukin (IL-29) quantity in gingival crevicular fluid (GCF) and plasma of chronic and aggressive periodontitis patients.

DESIGN

Patients with periodontal health (n=30), chronic generalized periodontitis (n=30) and generalized aggressive periodontitis (n=30) were subjected to IL-29 quantity estimation in GCF and plasma using enzyme linked immunosorbent assay and was correlated with IL-29 SNP (rs30461) using polymerase chain reaction.

RESULTS

IL-29 concentration in GCF and plasma was highest in aggressive periodontitis patients (114.17 ± 95.07pg/ml and 149.69 ± 109.90pg/ml respectively). The least concentration was found in subjects with healthy periodontium (47.50 ± 37.75pg/ml and 54.52 ± 37.53pg/ml) and in chronic periodontitis it was found to be 65.01 ± 41.26pg/ml and 81.17 ± 46.23pg/ml. The difference in the quantity of IL-29 in GCF and plasma among different groups was statistically significant (p<0.001 and p<0.001 respectively). rs30461 polymorphism of IL-29 analysis revealed that difference in the prevalence of A/A, A/G and G/G genotype among three groups was not statistically significant (p=0.097).

CONCLUSION

Increased quantity of IL-29 in GCF and plasma of subjects with periodontitis suggests a role in pathogenesis of periodontitis and the SNP (rs30461) is not related to susceptibility to periodontitis in this population of Indian individuals.

In vitro antiviral and immunomodulatory activity of arbidol and structurally related derivatives in herpes simplex virus type 1-infected human keratinocytes (HaCat)

Arbidol (ARB) is an antiviral drug that has broad-spectrum activity against a number of viral infections. To date, there are no specific data regarding its effects against a herpesvirus. Here, the in vitro antiviral effect of ARB and structurally related derivatives were evaluated in HaCat cells on different steps of herpes simplex virus type 1 replication: adsorption, entry and post-entry. The simplified pyrrolidine analogue, 9a2, showed the best antiviral activity in vitro by reducing the plaque numbers by about 50% instead of 42% obtained with ARB at the same concentration. Furthermore, we have reported that all tested compounds evaluated for their immunomodulatory activity showed the ability to reduce the viral proteins VP16 and ICP27 and to modify the virus-induced cytokine expression, allowing the host cell a more efficient antiviral response.

Immunological control of herpes simplex virus infections

Herpes simplex virus type 1 (HSV-1) is capable of causing a latent infection in sensory neurons that lasts for the lifetime of the host. The primary infection is resolved following the induction of the innate immune response that controls replication of the virus until the adaptive immune response can clear the active infection. HSV-1-specific CD8⁺ T cells survey the ganglionic regions containing latently infected neurons and participate in preventing reactivation of HSV from latency. The long-term residence and migration dynamics of the T cells in the trigeminal ganglia appear to distinguish them from the traditional memory T cell subsets. Recently described tissue resident memory (T_RM) T cells establish residence and survive for long periods in peripheral tissue compartments following antigen exposure. This review focuses on the immune system response to HSV-1 infection. Particular emphasis is placed on the evidence pointing to the HSV-1-specific CD8⁺ T cells in the trigeminal belonging to the T_RM class of memory T cells and the role of T_RM cells in virus infection, pathogenesis, latency, and disease.

Herpes simplex virus 2 (HSV-2) prevents dendritic cell maturation, induces apoptosis, and triggers release of proinflammatory cytokines: potential links to HSV-HIV synergy

Herpes simplex virus 2 (HSV-2) may cause frequent recurrences, highlighting its ability to evade host defense. This study tested the hypothesis that HSV-2 interferes with dendritic cell (DC) function as an escape mechanism, which may contribute to enhanced HIV replication in coinfected populations. Immature monocyte-derived human DCs were exposed to live or UV-inactivated HSV-2 or lipopolysaccharide. Little or no increase in the maturation marker CD83 was observed in response to HSV-2 and HSV-2 exposed DCs were impaired in their ability to present antigen (influenza) to T cells. Exposure to UV-inactivated virus stimulated a modest, but significant increase in CD83, suggesting that viral gene expression contributes to the block in DC maturation. The functional impairment of HSV-2-exposed DCs could be partially attributed to the induction of apoptosis. Live and inactivated HSV-2 triggered an increase in the number of early and late apoptotic cells in both the infected and bystander cell populations; apoptosis was associated with a decrease in cellular FLICE-inhibitory protein (c-FLIP). Paradoxically, HSV-2 induced Akt phosphorylation, which typically promotes DC maturation and survival. Despite these aberrant responses, live and inactivated HSV-2 induced the release of cytokines into culture supernatants, which were sufficient to activate HIV-1 replication in latently infected U1 cells. Together, these findings suggest that in the presence of overt or subclinical HSV-2, the function of mucosal DCs would be impaired. These responses may allow HSV to escape immune surveillance but may also promote HIV infection and contribute to the epidemiological link between HIV and HSV.

Immunobiology of dendritic cells and the influence of HIV infection

Recent progress in phenotyping of human dendritic cells (DCs) has allowed a closer alignment of the classification and functions of murine and human dendritic cell subsets. Marked differences in the functions of these human DC subsets and their response to HIV infection have become apparent, relevant to HIV pathogenesis and vaccine and microbicide development. Systems biology approaches to studying HIV uptake and infection of dendritic cells has revealed how markedly HIV subverts their functions, especially in relation to the trafficking pathways and viral transfer to T cells. Furthermore the interactions between DCs and other innate immune cells, NK cells, NKT cells and gamma delta T cells are now known to influence DC and T cell function and are also disturbed by HIV infection in vitro and in vivo. Such cellular interactions are potential targets for vaccine adjuvants and immunotherapy.

Induction of IFNα or IL-12 depends on differentiation of THP-1 cells in dengue infections without and with antibody enhancement

Background

Appropriate induction of the early Th1 cytokine IL-12 is a critical defense directed against viral infection. We have previously shown that different viruses elicited either IL-12 or IFNα dependent Th1 reactions. Using dengue-2 virus, we sought to explore how dengue-2 induced IL-12 or IFNα expression by monocytic and its derived dendritic cells.

Methods

We employed human monocytic cell line, THP-1, to investigate whether differentiation of monocytic cells is involved in the switch between IFNα and IL-12 induction. Flow cytometry, RT-PCR and ELISA were respectively used to determine cell differentiation, IL-12 and IFNα mRNA expression and protein production.

Results

THP-1, expressing CD123, which is a plasmacytoid dendritic cell marker, but not CD14, CD11b or CD11c revealed IFNα mRNA expression while stimulated by dengue-2. In contrast, PMA-induced THP-1 differentiation toward monocytic cells expressed CD11b⁺, and CD14⁺, but not CD123, and revealed exclusively IL-12 expression while stimulated by dengue-2. Further studies showed that CD123⁺ expressing THP-1 cells elicited higher IFNα expression in dose and time dependent induction after infection, and PMA-induced monocytic differentiation of THP-1 cells revealed IL-12 expression. Antibody-dependent enhancement of DEN-2 infection significantly suppressed the DEN-2 induced IL-12 p40 expression in monocytic differentiated THP-1 cells.

Conclusions

Clarification and modulation of the early Th1 reaction in different monocytic cells may change or prevent complication from dengue infection.

Herpes keratitis

Herpes simplex virus-1 (HSV-1) infects the majority of the world's population. These infections are often asymptomatic, but ocular HSV-1 infections cause multiple pathologies with perhaps the most destructive being herpes stromal keratitis (HSK). HSK lesions, which are immunoinflammatory in nature, can recur throughout life and often cause progressive corneal scaring resulting in visual impairment. Current treatment involves broad local immunosuppression with topical steroids along with antiviral coverage. Unfortunately, the immunopathologic mechanisms defined in animal models of HSK have not yet translated into improved therapy. Herein, we review the clinical epidemiology and pathology of the disease and summarize the large amount of basic research regarding the immunopathology of HSK. We examine the role of the innate and adaptive immune system in the clearance of virus and the destruction of the normal corneal architecture that is typical of HSK. Our goal is to define current knowledge of the pathogenic mechanisms and recurrent nature of HSK and identify areas that require further study.

Host genetic factors in susceptibility to herpes simplex type 1 virus infection: contribution of polymorphic genes at the interface of innate and adaptive immunity

HSV-1 establishes life-long latency that can result in clinical relapses or in asymptomatic virus shedding. Although virtually all adults have been exposed to HSV-1, the clinical course varies remarkably. Genetic host variability could be related to this clinical diversity. In this study, we analyzed the contribution of gene families in chromosomes 1, 6, 12, and 19, which encode key regulators of the innate and adaptive immunity, in a cohort of 302 individuals. Class I and class II alleles of the HLA system, the copy-number variation of NK cell receptor genes (KIR and NKG2C), the combinations of killer cell Ig-like receptor and their HLA ligands, and CD16A and CD32A allotypes of variable affinity for IgG subclasses were all studied. Although no major susceptibility locus for HSV-1 was identified, our results show that the risk of suffering clinical HSV-1 infection is modified by MHC class I allotypes (B*18, C*15, and the group of alleles encoding A19), the high-affinity receptor/ligand pair KIR2DL2/HLA-C1, and the CD16A-158V/F dimorphism. Conversely, HLA class II and CD32A polymorphisms and NKG2C deletion did not seem to influence the clinical course of herpetic infection. Collectively, these findings support an important role in host defense against herpetic infection for several polymorphic genes implicated in adaptive immunity and in surveillance of its subversion. They confirm the crucial role of cytotoxic cells (CTL and NK) and the contribution of genetic diversity to the clinical course of HSV-1 infection.

Natural killer cell activation by dendritic cells: balancing inhibitory and activating signals

Natural killer (NK) cells have originally been identified by their spontaneous cytolytic potential against tumor cells, which, however, might result from pre-activation due to prior pathogen exposure. Resting NK cells, on the contrary, require activation by bystander antigen-presenting cells to reach their full functional competence. In this review, we will summarize studies on how dendritic cells (DCs), the most potent type of antigen-presenting cell, communicate with human NK cells to activate them in secondary lymphoid organs and to integrate signals from activated NK cells at sites of inflammation for their own maturation. Furthermore, we will review aspects of the immunological synapse, which mediates this cross-talk. These studies provide the mechanistic understanding of how mature DCs can activate NK cells and survive to go on for the activation of adaptive immunity. This feature of DCs, to activate different waves of immune responses, could be harnessed for immunotherapies, including vaccinations.

Sensing herpes: more than toll

To launch an effective antiviral immune response, cells must recognize the virus, activate a cytokine response, and initiate inflammatory processes. Herpes simplex virus 1 (HSV-1) and HSV-2 are nuclear-replicating viruses composed of a double-stranded DNA genome plus glycoproteins that are incorporated into a lipid bilayer envelope that surrounds an icosahedral capsid. Several novel receptors that mediate innate recognition of HSV and that activate the innate immune response have been identified in recent years. The host-virus interactions that lead to type I interferon (IFN), type III IFN, and cytokine production include cellular recognition of viral envelope and structural proteins, recognition of viral genomic DNA and recognition of virus-derived double-stranded RNAs. Such RNAs can interact with cellular pattern-recognition receptors, including Toll-like receptors and a number of cytoplasmic and nuclear receptors for virus DNA and virus-derived RNAs. In this review, I present a systematic overview of innate cellular recognition of HSV infection that leads to immune activation, and I discuss the implications of the known cell-host interactions. In addition, I discuss the use of innate stimulation to improve anti-HSV treatment and vaccine response and I discuss future research aims.

Interferon-lambda serum levels in hepatitis C

BACKGROUND & AIMS

Dendritic cells (DCs) trigger adaptive immune responses and are an important source of antiviral cytokines. In hepatitis C virus (HCV) infection DC function is markedly impaired. Thus far, studies have focused on types I and II interferon (IFN). We studied IFN-lambda1 (IL-29) and IFN-lambda2/3 (IL-28A/B) serum levels in patients with different outcomes of HCV infection.

METHODS

IFN-lambdas were measured by ELISAs detecting IL-29 or IL-28A and IL-28B, respectively. Results were stratified with respect to the recently discovered rs12979860 T/C polymorphism upstream of the IL-28B gene.

RESULTS

In general IL-29 serum levels exceeded IL-28A/B at least twofold, with IL-29 and IL-28A/B levels being significantly higher in carriers of the rs12979860 C allele than in TT homozygous individuals (p<0.02). IL-29 levels were substantially lower in patients with chronic hepatitis C than in healthy controls (p=0.005) and patients with spontaneously resolved hepatitis (p=0.001). Patients with acute hepatitis C showed IL-29 levels intermediate between chronic hepatitis C and normal controls; and IL-29 serum levels were higher in patients who spontaneously resolved hepatitis C than in those who became chronic. In vitro HCV proteins NS3 and E2 directly inhibited IL-29 production in poly I:C-stimulated purified DCs.

CONCLUSIONS

Our data suggest that HCV proteins modify IFN-lambda production in DCs. Carriers of the rs12979860 C allele associated with resolution of HCV infection exhibited increased IFN-lambda levels. Moreover, high IFN-lambda levels predisposed to spontaneous resolution of HCV infection. Thus, IFN-lambdas seem to play an important role in the control of hepatitis C.

The Role of Plasmacytoid Dendritic Cells in Innate and Adaptive Immune Responses against Alpha Herpes Virus Infections

In 1999, two independent groups identified plasmacytoid dendritic cells (PDC) as major type I interferon- (IFN-) producing cells in the blood. Since then, evidence is accumulating that PDC are a multifunctional cell population effectively coordinating innate and adaptive immune responses. This paper focuses on the role of different immune cells and their interactions in the surveillance of alpha herpes virus infections, summarizes current knowledge on PDC surface receptors and their role in direct cell-cell contacts, and develops a risk factor model for the clinical implications of herpes simplex and varicella zoster virus reactivation. Data from studies involving knockout mice and cell-depletion experiments as well as human studies converge into a "spider web", in which the direct and indirect crosstalk between many cell populations tightly controls acute, latent, and recurrent alpha herpes virus infections. Notably, cells involved in innate immune regulations appear to shape adaptive immune responses more extensively than previously thought.

Interplay between modified vaccinia virus Ankara and dendritic cells: phenotypic and functional maturation of bystander dendritic cells

Modified vaccinia virus Ankara (MVA) is an attenuated poxvirus strain, currently under evaluation as a vaccine vector in various clinical settings. It has been reported that human dendritic cells (DCs) mature after infection with MVA, but reports on the functionality of DCs have so far been controversial. In this work, we studied the phenotype and functionality of MVA-infected DCs. As previously reported, we found that human monocyte-derived DCs upregulated CD86 and HLA-DR in response to MVA infection. Moreover, infected DCs produced a broad array of chemokines and cytokines and were able to activate and induce gamma interferon (IFN-γ) production both in CD4(+) and in CD8(+) allogeneic T cells and in specific autologous peripheral blood lymphocytes (PBLs). Analysis of DC maturation following infection with a recombinant green fluorescent protein (GFP)-expressing MVA revealed that upregulation of CD86 expression was mainly observed in GFP(neg) (bystander) cells. While GFP(pos) (infected) DCs produced tumor necrosis factor alpha (TNF-α), they were unable to produce CXCL10 and were less efficient at inducing IFN-γ production in CEF-specific autologous PBLs. Maturation of bystander DCs could be achieved by incubation with supernatant from infected cultures or with apoptotic infected cells. Type I IFNs were partially responsible for the induction of CXCL10 on bystander DCs. Our findings demonstrate for the first time that, in MVA-infected DC cultures, the leading role with respect to functionality and maturation characteristics is achieved by the bystander DCs.

HIV infection of dendritic cells subverts the IFN induction pathway via IRF-1 and inhibits type 1 IFN production

Many viruses have developed mechanisms to evade the IFN response. Here, HIV-1 was shown to induce a distinct subset of IFN-stimulated genes (ISGs) in monocyte-derived dendritic cells (DCs), without detectable type I or II IFN. These ISGs all contained an IFN regulatory factor 1 (IRF-1) binding site in their promoters, and their expression was shown to be driven by IRF-1, indicating this subset was induced directly by viral infection by IRF-1. IRF-1 and -7 protein expression was enriched in HIV p24 antigen-positive DCs. A HIV deletion mutant with the IRF-1 binding site deleted from the long terminal repeat showed reduced growth kinetics. Early and persistent induction of IRF-1 was coupled with sequential transient up-regulation of its 2 inhibitors, IRF-8, followed by IRF-2, suggesting a mechanism for IFN inhibition. HIV-1 mutants with Vpr deleted induced IFN, showing that Vpr is inhibitory. However, HIV IFN inhibition was mediated by failure of IRF-3 activation rather than by its degradation, as in T cells. In contrast, herpes simplex virus type 2 markedly induced IFNβ and a broader range of ISGs to higher levels, supporting the hypothesis that HIV-1 specifically manipulates the induction of IFN and ISGs to enhance its noncytopathic replication in DCs.

Circulating myeloid dendritic cells are increased in individuals with severe aplastic anemia

The objectives of the study were to investigate the number of myeloid dendritic cells (mDC) and plasmacytoid dendritic cells (pDC) present in peripheral blood mononuclear cells (PBMC) from severe aplastic anemia (SAA) patients before and after intensive immunosuppressive therapy (IST) and to assess the expression of co-stimulatory molecules (CD80, CD86, and CD40) expressed by dendritic cells (DC) from SAA patients. The quantities of mDC and pDC and ratios of mDC to pDC in PBMC were measured in 38 SAA patients at active phase, 19 patients at recovery phase, and 17 normal controls. The surface expression of CD80, CD86, and CD40 on DCs and B lymphocytes was analyzed in 16 SAA patients and 15 normal controls. The percentages of mDC and the ratio of mDC:pDC of SAA patients at active phase increased compared to that of healthy controls [0.65% (range 0.10-2.19%) vs. 0.40% (range 0.11-1.54%), 2.64% (range 1.07-4.33%) vs. 1.56% (range 0.89-2.27), respectively (P < 0.05)]. The percentages of mDCs in recovered SAA patients decreased to 0.43% (range 0.06-0.80), and the ratio of mDC:pDC decreased to 1.78% (range 0.49-3.07). The percentages of mDC and pDC in 10 SAA patients were 0.87% (range 0.10-1.85) and 0.35% (range 0.05-0.65) before IST, which decreased to 0.24% (range 0.06-0.52) and 0.14% (range 0.01-0.28) after IST (P < 0.05). The percentages of CD86 expression on DC of SAA patients increased compared to that of healthy controls [29.84% (range 20.28-39.40) vs. 11.97% (range 0.02-24.15), respectively (P < 0.05)]. The number of mDCs increased in SAA patients, which was associated with stage of disease. The increased number of mDCs and the high expression of costimulatory molecules (CD86) on these DCs may contribute to abnormal activation of T lymphocytes in these patients and subsequent immune system-mediated bone marrow failure.

Adjuvant effects of formalin-inactivated HSV through activation of dendritic cells and inactivation of myeloid-derived suppressor cells in cancer immunotherapy

Use of adequate adjuvant is necessary for induction of effective antitumor immune responses. To develop an effective adjuvant for cancer immunotherapy, we selected formalin-inactivated (f)-HSV as an adjuvant component, and analyzed the mechanisms underlying its adjuvant effects. First, we found that f-HSV can induce the tumor antigen-specific CTLs by enhancing antigen cross-presentation by dendritic cells (DCs), mainly through TLR2, but not TLR9. Next, f-HSV was also found to prevent the accumulation of myeloid-derived suppressor cells (MDSCs). We demonstrated that the expansion of MDSCs in the blood and spleen during tumor progression required B cells producing the inflammatory angiogenesis factors, vascular endothelial growth factor (VEGF)-A and neuropilin-1 (NRP-1), a co-receptor for VEGF receptor-2 (VEGFR-2). Interestingly, the transmembrane-type NRP-1 on B cells changed to soluble-type NRP-1 (sNRP-1) by f-HSV treatment. We further showed that the sNRP-1 and VEGF-A secreted from B cells by f-HSV treatment could abrogate the immunosuppressive ability of MDSCs. These results suggest that f-HSV can enhance antitumor immune responses as an adjuvant, not only through activation of DCs, but also inactivation of MDSCs via B cells.

Immune response modeling of interferon beta-pretreated influenza virus-infected human dendritic cells

The pretreatment of human dendritic cells with interferon-beta enhances their immune response to influenza virus infection. We measured the expression levels of several key players in that response over a period of 13 h both during pretreatment and after viral infection. Their activation profiles reflect the presence of both negative and positive feedback loops in interferon induction and interferon signaling pathway. Based on these measurements, we have developed a comprehensive computational model of cellular immune response that elucidates its mechanism and its dynamics in interferon-pretreated dendritic cells, and provides insights into the effects of duration and strength of pretreatment.

Type I interferons mediate the innate cytokine response to recombinant fowlpox virus but not the induction of plasmacytoid dendritic cell-dependent adaptive immunity

Type I interferons (IFNs) are considered to be important mediators of innate immunity due to their inherent antiviral activity, ability to drive the transcription of a number of genes involved in viral clearance, and their role in the initiation of innate and adaptive immune responses. Due to the central role of type I IFNs, we sought to determine their importance in the generation of immunity to a recombinant vaccine vector fowlpox virus (FPV). In analyzing the role of type I IFNs in immunity to FPV, we show that they are critical to the secretion of a number of innate and proinflammatory cytokines, including type I IFNs themselves as well as interleukin-12 (IL-12), tumor necrosis factor-alpha (TNF-alpha), IL-6, and IL-1beta, and that deficiency leads to enhanced virus-mediated antigen expression. Interestingly, however, type I IFNs were not required for adaptive immune responses to recombinant FPV even though plasmacytoid dendritic cells (pDCs), the primary producers of type I IFNs, have been shown to be requisite for this to occur. Furthermore, we provide evidence that the importance of pDCs may lie in their ability to capture and present virally derived antigen to T cells rather than in their capacity as professional type I IFN-producing cells.

The virion host shut-off (vhs) protein blocks a TLR-independent pathway of herpes simplex virus type 1 recognition in human and mouse dendritic cells

Molecular pathways underlying the activation of dendritic cells (DCs) in response to Herpes Simplex Virus type 1 (HSV-1) are poorly understood. Removal of the HSV virion host shut-off (vhs) protein relieves a block to DC activation observed during wild-type infection. In this study, we utilized a potent DC stimulatory HSV-1 recombinant virus lacking vhs as a tool to investigate the mechanisms involved in the activation of DCs by HSV-1. We report that the release of pro-inflammatory cytokines by conventional DC (cDC) during HSV-1 infection is triggered by both virus replication-dependent and replication-independent pathways. Interestingly, while vhs is capable of inhibiting the release of cytokines during infection of human and mouse cDCs, the secretion of cytokines by plasmacytoid DC (pDC) is not affected by vhs. These data prompted us to postulate that infection of cDCs by HSV triggers a TLR independent pathway for cDC activation that is susceptible to blockage by the vhs protein. Using cDCs isolated from mice deficient in both the TLR adaptor protein MyD88 and TLR3, we show that HSV-1 and the vhs-deleted virus can activate cDCs independently of TLR signaling. In addition, virion-associated vhs fails to block cDC activation in response to treatment with TLR agonists, but it efficiently blocked cDC activation triggered by the paramyxoviruses Sendai Virus (SeV) and Newcastle Disease Virus (NDV). This block to SeV- and NDV-induced activation of cDC resulted in elevated SeV and NDV viral gene expression indicating that infection with HSV-1 enhances the cell's susceptibility to other pathogens through the action of vhs. Our results demonstrate for the first time that a viral protein contained in the tegument of HSV-1 can block the induction of DC activation by TLR-independent pathways of viral recognition.

The role of dendritic cells in alphaherpesvirus infections: archetypes and paradigms

Dendritic cells (DCs) play a critical role in orchestrating both innate and adaptive components of the immune system and are therefore of pivotal importance in the initiation of immune responses to control and eliminate viral infections. A major focus of this review is to give an overview on the recent findings that point out the importance of DCs in controlling alphaherpesvirus infections, but also indicate that these viruses have evolved several strategies to inhibit and/or exploit DC functions to delay or escape elimination by the immune system. In addition, we point out the common features and interspecies differences between DCs from man and animal, and discuss the potential use of animal alphaherpesvirus homologues to gain further insights into the interaction between alphaherpesviruses and DCs in their natural virus-host environment. Finally, recent knowledge on the potential of alphaherpesviruses as vectors for DC stimulation and their use for immunotherapy is presented.

Evasion of the mucosal innate immune system by herpes simplex virus type 2

Understanding the mechanisms by which herpes simplex virus (HSV) evades host immune defenses is critical to defining new approaches for therapy and prevention. We performed transcriptional analyses and immunocytochemistry on sequential biopsy specimens of lesional tissue from the acute through the posthealing phases of recurrent mucocutaneous HSV-2 infection. Histological analysis of these biopsy specimens during the acute stage revealed a massive infiltration of T cells, as well as monocytes/macrophages, a large amount of myeloid, and a small number of plasmacytoid dendritic cells, in the dermis of these lesional biopsy specimens. Type I interferon (IFN-beta and IFN-alpha) was poorly expressed and gamma IFN (IFN-gamma) potently induced during time periods in which we detected abundant amounts of HSV-2 antigens and HSV-2 RNA. IFN-stimulated genes were also markedly upregulated, with expression patterns that more closely matched those in primary human fibroblasts treated by IFN-gamma than those in fibroblasts treated by IFN-beta. Transcriptional arrays of the same lesional biopsy sites during healing and at 2 and 4 weeks posthealing revealed no HSV nucleic acids or antigen; however, there was persistent expression of IFN-gamma, with very low levels of IFN-beta and IFN-alpha. The findings of extremely low levels of IFN-alpha and IFN-beta, despite the presence of a large number of cells capable of synthesizing these substances, suggest a potent alteration in host defense during HSV-2 infection in vivo. HSV-2's blockade of the innate immune system's production of type I IFN may be a major factor in allowing the virus to break through host mucosal defenses.

The gamma 1 34.5 protein of herpes simplex virus 1 is required to interfere with dendritic cell maturation during productive infection

The gamma(1)34.5 protein of herpes simplex virus 1 is an essential factor for viral virulence. In infected cells, this viral protein prevents the translation arrest mediated by double-stranded RNA-dependent protein kinase R. Additionally, it associates with and inhibits TANK-binding kinase 1, an essential component of Toll-like receptor-dependent and -independent pathways that activate interferon regulatory factor 3 and cytokine expression. Here, we show that gamma(1)34.5 is required to block the maturation of conventional dendritic cells (DCs) that initiate adaptive immune responses. Unlike wild-type virus, the gamma(1)34.5 null mutant stimulates the expression of CD86, major histocompatibility complex class II (MHC-II), and cytokines such as alpha/beta interferon in immature DCs. Viral replication in DCs inversely correlates with interferon production. These phenotypes are also mirrored in a mouse ocular infection model. Further, DCs infected with the gamma(1)34.5 null mutant effectively activate naive T cells whereas DCs infected with wild-type virus fail to do so. Type I interferon-neutralizing antibodies partially reverse virus-induced upregulation of CD86 and MHC-II, suggesting that gamma(1)34.5 acts through interferon-dependent and -independent mechanisms. These data indicate that gamma(1)34.5 is involved in the impairment of innate immunity by inhibiting both type I interferon production and DC maturation, leading to defective T-cell activation.

Antiviral-activated dendritic cells: a paracrine-induced response state

Infection of immature dendritic cells (DCs) by virus stimulates their maturation into APC. Infected DCs can also expose uninfected DCs to a panoply of cytokines/chemokines via paracrine signaling. Mathematical modeling suggests that a high rate of paracrine signaling is likely to occur among DCs located in three-dimensional space. Relatively little is known about how secreted factors modify the early response to virus infection. We used a transwell experimental system that allows passage of secreted factors, but not direct contact, between virus-infected DCs and uninfected DCs to investigate paracrine signaling responses. Paracrine signaling from infected DCs induced an antiviral-primed DC state distinct from that of mature virus-infected DCs that we refer to as antiviral-activated DCs (AVDCs). AVDCs had increased surface MHC class II and CD86 levels, but in contrast to virus-infected DCs, their MHC class I levels were unchanged. Imaging flow cytometry showed that AVDCs had an increased rate of phagocytosis compared with naive DCs. Experiments with IFN-beta cytokine indicated that it may be responsible for CD86, but not MHC class II regulation in AVDCs. Both IFN-inducible and IFN-independent genes are up-regulated in AVDCs. Notably, AVDCs are relatively resistant to virus infection in comparison to naive DCs and achieve accelerated and augmented levels of costimulatory molecule expression with virus infection. AVDCs show a distinct antiviral-primed state of DC maturation mediated by DC paracrine signaling. Although further in vivo study is needed, the characteristics of the AVDC suggest that it is well suited to play a role in the early innate-adaptive transition of the immune system.

Modulations of phenotype and cytokine expression of porcine bone marrow-derived dendritic cells by porcine reproductive and respiratory syndrome virus

Phenotypic and functional property changes of bone marrow-derived immature dendritic cells (BM-imDCs) after porcine reproductive and respiratory syndrome virus (PRRSV) infection have been detailed in a previous report. A down-regulated expression of MHC I molecules along with an up-regulated expression of CD80/86 were observed in BM-imDCs after the exposure to PRRSV. In this study, we further investigate the expression of surface phenotypes of BM-imDCs in relation to their infection status. Exposure of PRRSV to BM-imDCs resulted in a down-regulated expression of MHC I and an up-regulated expression of CD80/86 in infected cells, as demonstrated by significant alterations in both percentage of expressing cells and mean fluorescence intensity (MFI) in PRRSV-positive cells. A significant suppression in MFI of MHC I and an increase in percentage of cells expressing CD80/86 were observed in noninfected bystander cells. We also demonstrated that exposure of BM-imDCs to PRRSV resulted in a significantly increased secretion of IL-1, IL-6, IL-8, IL-10 and IFN-gamma but not IL-12 or TNF-alpha. In addition, the PRRSV infection modulates cytokine expressions of BM-imDCs through their response to microbial pathogen-associated molecular patterns. These results will prove helpful in clarification of the factors that mediate host defense against PRRSV, as well as the possible interaction mechanisms between PRRSV and other microbes in the pathogenesis of PRRSV infection in pigs.

Functional characterization of ex vivo blood myeloid and plasmacytoid dendritic cells after infection with dengue virus

Myeloid and plasmacytoid dendritic cells (mDC and pDC) are naturally distinctive subsets. We exposed both subsets to dengue virus (DV) in vitro and investigated their functional characteristics. High levels of DV replication in mDC were found to correlate with DC-SIGN expression. Production of inflammatory cytokines by mDC increased gradually after DV-infection, which was dependent on DV replication. Co-stimulatory markers were upregulated on mDC upon DV-infection. On the contrary, lower levels of DV-replication were observed in pDC, but the cytokine production in pDC was quicker and stronger. This cytokine response was not dependent on viral replication, but dependent on cell endosomal activity and TLR7, and could be also induced by purified DV genome RNA. These results clearly suggested functional differences between mDC and pDC in response to DV infection. Additionally, the TLR7-mediated recognition of DV RNA may be involved in pDC functional activation.

Interferon-beta pretreatment of conventional and plasmacytoid human dendritic cells enhances their activation by influenza virus

Influenza virus produces a protein, NS1, that inhibits infected cells from releasing type I interferon (IFN) and blocks maturation of conventional dendritic cells (DCs). As a result, influenza virus is a poor activator of both mouse and human DCs in vitro. However, in vivo a strong immune response to virus infection is generated in both species, suggesting that other factors may contribute to the maturation of DCs in vivo. It is likely that the environment in which a DC encounters a virus would contain multiple pro-inflammatory molecules, including type I IFN. Type I IFN is a critical component of the viral immune response that initiates an antiviral state in cells, primarily by triggering a broad transcriptional program that interferes with the ability of virus to establish infection in the cell. In this study, we have examined the activation profiles of both conventional and plasmacytoid dendritic cells (cDCs and pDCs) in response to an influenza virus infection in the context of a type I IFN-containing environment. We found that both cDCs and pDCs demonstrate a greater activation response to influenza virus when pre-exposed to IFN-β (IFN priming); although, the priming kinetics are different in these two cell types. This strongly suggests that type I IFN functions not only to reduce viral replication in these immune cells, but also to promote greater DC activation during influenza virus infections.

Influenza infection leads to a serious respiratory infection of the lung epithelium. Lying directly below the epithelial cells are immune system sentinels known as dendritic cells. These cells interact with the virus and carry parts of the virus to draining lymph nodes to activate killer T cells. In order to effectively carry out this function, DCs must perceive the presence of a virus using receptors specially adapted for this function. However, when DCs are mixed with influenza virus in the laboratory, no activation occurs because the virus produces a protein called NS1 that blocks the receptors. Yet, patients infected with influenza virus develop a strong adaptive response that leads to recovery from infection. This observation suggests that additional factors must be present that contribute to the activation of the DCs. The most likely contributor is type I interferon, a ubiquitous protein released from many cells upon exposure to virus. In this study, we mixed influenza virus with DCs in the presence of type I interferon and found that this greatly enhanced their activation. Treatment with interferon allowed the DC to bypass the block in activation mediated by the influenza NS1 protein. Our data suggest that the production of type I interferon within an infected patient may endow the DCs with the ability to fully respond to influenza virus.

Interferon-beta expressed by a rabies virus-based HIV-1 vaccine vector serves as a molecular adjuvant and decreases pathogenicity

Type I interferon is important in anti-viral responses and in coordinating the innate immune response. Here we explore the use of interferon-beta to adjuvant the response to a rabies virus (RV) vaccine vector expressing both HIV-1 Gag and IFN-beta. Viral load and immune responses of immunized mice were analyzed over time. Our results indicate that the RV expressing IFN-beta (IFN+) is highly attenuated when compared to control RV and demonstrate that the expression of IFN-beta reduces viral replication approximately 100-fold. Despite the decrease in replication, those mice immunized with the IFN+ RV had a significantly greater number of activated CD8+ T cells. The increased activation of CD8+ T cells was dependent on IFN-beta signaling, as we saw no difference following infection of IFNAR-/- mice. Although mice immunized with IFN+ have a greater primary immune response than controls, immunized mice that were challenged with vaccinia-expressing Gag had no significant difference in the number or functionality of CD8+ T cells. The increased CD8+ T cell activation in the presence of IFN-beta, even with greatly reduced viral replication, indicates the beneficial effect of IFN-beta for the host.

Involvement of HVEM receptor in activation of nuclear factor kappaB by herpes simplex virus 1 glycoprotein D

The UV-inactivated herpes simplex virus 1 (HSV-1) and glycoprotein D (gD) of HSV-1 have been shown to activate nuclear factor kappaB (NF-kappaB) in U937 cells, but mechanisms involved in this activation have not been elucidated. Here we report that: (i) UV-inactivated HSV-1 induced an increased NF-kappaB activation in cells expressing human HVEM (for herpesvirus entry mediator) at surface level, naturally or following stable transfection, but not in cells in which this receptor was not detected by flow cytometry analysis, (ii) treatment with soluble gD induced a dose-dependent NF-kappaB activation in THP-1 cells naturally expressing HVEM, and a monoclonal antibody that prevents binding of gD to HVEM significantly reduced NF-kappaB activation by soluble gD in the same cells, (iii) coculture with transfectants expressing wild-type gD on their surface induced an approximately twofold increase in NF-kappaB activation in cells naturally expressing HVEM, while coculture with transfectants expressing a mutated form of gD, lacking its capability to bind HVEM, did not induce a similar effect and (iv) treatment with soluble gD induced a dose-dependent NF-kappaB activation in CHO transfectants expressing HVEM, but not in control CHO transfectants lacking any functional gD receptor. Overall, these results establish that HVEM is involved in NF-kappaB activation by HSV-1 gD.

Glycoprotein-dependent and TLR2-independent innate immune recognition of herpes simplex virus-1 by dendritic cells

Innate immune recognition is an important early event in the host response to herpes simplex virus-1 (HSV-1) infection. Dendritic cells (DC) play an important sentinel role in this recognition. Previous studies have shown that monocyte-derived DC (MDDC) respond to HSV-1 by up-regulation of costimulatory molecules and type I IFN release, but the molecular targets on the virus recognized by the DC have not been defined. In this study we show that MDDC recognize and respond to the four essential viral glycoproteins, gB, gD, and gHgL, independent of other viral proteins or nucleic acids. DC recognition of these four glycoproteins leads to the up-regulation of CD40, CD83, CD86, and HLA-DR and to the production of IFN-alpha and IL-10, but not IL-12p70. Glutaraldehyde-fixation and nonfunctional gH mutants were used to show that recognition of glycoproteins does not require membrane fusion. The nature of the recognition event was probed further by transfecting glycoproteins individually or in combination, by blocking individual proteins with Abs, or by using mutant gD constructs unable to bind to their known cognate receptors. Unexpectedly, MDDC responses were found to require expression of all four glycoproteins. Furthermore, gD mutants that cannot bind nectin-1 and/or herpesvirus entry mediator can still induce DC maturation. Finally, although HSV-1 can signal via the TLR2 receptor, this receptor does not mediate recognition of glycoproteins. Thus, the complex of the four essential HSV-1 entry glycoproteins on the cell surface can provide a target for innate immune recognition of this virus.

Viral danger signals control CD1d de novo synthesis and NKT cell activation

The nonpolymorphic CD1 molecules present lipid antigens to T cells. In myeloid DC humans express five different CD1 proteins (CD1a-e; the corresponding CD1 genes are designated CD1A-E). A role for CD1d-restricted NKT cells in the control of virus infections has been delineated from clinical observations, mouse models and viral evasion mechanisms targeting CD1d. How NKT cells are activated by virus infections is unclear. We found that human myeloid DC differentially regulate CD1 antigen presentation in response to viral danger signals. Stimulation with type I IFN, viral TLR ligands or viruses strongly enhanced the number of CD1D transcripts in human myeloid DC but diminished the abundance of CD1A, CD1B and CD1E mRNA. These changes on the transcriptional level were mirrored by altered cellular distribution and increased surface expression of CD1d. As a consequence NKT cells were activated and showed a Th1-like response. Moreover, NKT cell activation in PBMC exposed to viral danger signals was dependent on human plasmacytoid DC which produce large amounts of IFN-alpha. In conclusion, our data indicate that viral danger signals trigger NKT cell activation by enhancing CD1d de novo synthesis through increasing the abundance of CD1D mRNA in human myeloid DC.

MyD88 and IFN-alphabeta differentially control maturation of bystander but not Salmonella-associated dendritic cells or CD11cintCD11b+ cells during infection

The interface between dendritic cells (DCs) and T cells is critical to elicit effective immunity against pathogens. The maturation state of DCs determines the quality of the interaction and governs the type of response. DCs can be matured directly through activating Toll-like receptors (TLRs) or indirectly by cytokines. We explore the role of the TLR adaptor MyD88 on DC maturation during Salmonella infection. Using Salmonella expressing GFP, we also examine the phenotype and function of bacteria-associated DCs matured in the absence of bacteria-mediated TLR signalling. MyD88 was required for upregulation of CD80 on DCs during infection, whereas CD86 and CD40 were upregulated independently of MyD88, although requiring a higher bacterial burden in the MLN. MyD88-independent upregulation was mediated by IFN-alphabeta produced during infection. In infected MyD88(-/-)IFN-alphabetaR(-/-) mice, which lack most bacteria-driven TLR signalling, indirect DC maturation was abolished. In contrast, DCs containing Salmonella upregulated co-stimulatory molecules independently of MyD88 and IFN-alphabeta, revealing a pathway of phenotypic maturation active in infected DCs. However, despite high co-stimulatory molecule expression, Salmonella-containing DCs from MyD88(-/-) or MyD88(-/-)IFN-alphabetaR(-/-) mice had a compromised capacity to activate T cells. Thus, bacterial stimulation of TLRs influences DC function at multiple levels that modulates their capacity to direct antibacterial immunity.

Streptococcus pyogenes activates human plasmacytoid and myeloid dendritic cells

Human peripheral blood contains two major dendritic cell (DC) populations, namely CD11c(-)CD123+ plasmacytoid DCs (PDCs) and CD11c+CD123(-) myeloid DCs (MDCs). Although the activation of these DC types by various TLR ligands has been relatively well-characterized, less is known about the ability of whole live bacteria to induce PDC and MDC activation. In the present report, we have compared the activation of human PDCs and MDCs in response to major human bacterial pathogen Streptococcus pyogenes (group A streptococci) and influenza A virus. S. pyogenes stimulation resulted in the maturation of both DC types, as evidenced by enhanced expression of costimulatory molecules and production of proinflammatory cytokines and chemokines. Furthermore, S. pyogenes-stimulated PDCs and MDCs activated naïve CD4+ T cells and enhanced their Th1 cytokine production. Influenza A virus infection induced rapid PDC activation, whereas MDCs were extremely sensitive to influenza A virus-induced cell death. The most significant differences between DC types were seen in the production of IL-10 and IL-12, which were only produced by S. pyogenes-stimulated MDCs. Although S. pyogenes was able to induce PDC activation, only influenza A virus infection resulted in detectable IFN-alpha production. Our results show that depending on the infecting microbe, the functions of PDCs and MDCs may be partially overlapping, suggesting a considerable flexibility of the human DC system.

An oncolytic mutant of herpes simplex virus type-1 in which replication is governed by a promoter/enhancer of human papillomavirus type-16

Although herpes simplex virus type-1 (HSV-1) can be used as an oncolytic virus it has the undesirable side effect of neurotoxicity. To create a virus with improved specificity for oral cancer we used a fragment of human papillomavirus type-16, which is frequently found in oral and cervical cancers, but not elsewhere. The upstream regulatory region, URR16, was shown to have a high level of transcriptional activity in three of four oral cancer cell lines but low activity in three cell lines derived from brain cancers. URR16 was therefore placed in HSV-1, replacing the promoter of the essential gene ICP4, and the resulting virus was named HSPV-1. When cells were infected with HSPV-1, ICP4 was expressed at levels that were not associated with the level of activity of URR16. The virus replicated in each type of cell to a final titer that showed a correlation with the level of expression of ICP4, but with no correlation to either the tumor of origin or the presence of HPV sequences in the cells. To find if some function of HSV-1 was affecting the activity of URR16, oral cancer cells were transfected with a URR-reporter construct and were then infected with virus. This induced transcription, which was attributed to immediate-early viral genes other than ICP4. A promoter/enhancer from a papillomavirus therefore has the potential to regulate the functions of an oncolytic strain of HSV-1, and is affected by functions of both the host cell and of HSV-1 itself.

Understanding HSV-1 entry glycoproteins

Herpes Simplex Virus‐1 is a common infectious agent, but the precise detail of entry and infection of cells has only now begun to be clarified. Four viral surface glycoproteins (gB, gD, gH and gL) are required. This review summarises the known structure and function of each of these essential viral envelope glycoproteins, and explores what is known about their close cooperation with each other in mediating cellular membrane fusion. It is suggested that, following gD binding to one of its entry receptors, membrane fusion is mediated by gB and the heterodimer gH/gL. Significantly, these four entry glycoproteins also play a key role in the interaction between HSV and the host immune system. The glycoproteins serve an important role as targets of adaptive immunity. However, recent studies have demonstrated that the same proteins also play a key role in initiating the early innate immune response to HSV. Understanding the complex functions of these HSV proteins may be essential for successful development of vaccines for HSV. Copyright © 2007 John Wiley & Sons, Ltd.

Whatever turns you on: accessory-cell-dependent activation of NK cells by pathogens

Natural killer (NK) cells have a crucial role in combating infections and cancers and their surface receptors can directly recognize and respond to damaged, transformed or non-self cells. Whereas some virus-infected cells are recognized by this same route, NK-cell responses to many pathogens are triggered by a different mechanism. Activation of NK cells by these pathogens requires the presence of accessory cells such as monocytes, macrophages and dendritic cells. Recent studies have identified numerous pathogen-recognition receptors that enable accessory cells to recognize different pathogens and subsequently transmit signals--both soluble and contact-dependent--to NK cells, which respond by upregulating their cytotoxic potential and the production of inflammatory cytokines.

The role of type I interferon production by dendritic cells in host defense

Type I interferons (IFN) and dendritic cells (DC) share an overlapping history, with rapidly accumulating evidence for vital roles for both production of type 1 IFN by DC and the interaction of this IFN both with DC and components of the innate and adaptive immune responses. Within the innate immune response, the plasmacytoid DC (pDC) are the "professional" IFN producing cells, expressing specialized toll-like receptors (TLR7 and -9) and high constitutive expression of IRF-7 that allow them to respond to viruses with rapid and extremely robust IFN production; following activation and production of IFN, the pDC subsequently mature into antigen presenting cells that help to shape the adaptive immune response. However, like most cells in the body, the myeloid or conventional DC (mDC or cDC) also produce type I IFNs, albeit typically at a lower level than that observed with pDC, and this IFN is also important in innate and adaptive immunity induced by these classic antigen presenting cells. These two major DC subsets and their IFN products interact both with each other as well as with NK cells, monocytes, T helper cells, T cytotoxic cells, T regulatory cells and B cells to orchestrate the early immune response. This review discusses some of the converging history of DC and IFN as well as mechanisms for IFN induction in DC and the effects of this IFN on the developing immune response.

Plasmacytoid dendritic cells synergize with myeloid dendritic cells in the induction of antigen-specific antitumor immune responses

Plasmacytoid dendritic cells (pDC) are capable of producing high levels of type I IFNs upon viral stimulation, and play a central role in modulating innate and adaptive immunity against viral infections. Whereas many studies have assessed myeloid dendritic cells (mDC) in the induction of antitumor immune responses, the role of pDC in antitumor immunity has not been addressed. Moreover, the interaction of pDC with other dendritic cell subsets has not been evaluated. In this study, we analyzed the capacity of pDC in stimulating an Ag-specific T cell response. Immunization of mice with Ag-pulsed, activated pDC significantly augmented Ag-specific CD8(+) CTL responses, and protected mice from a subsequent tumor challenge. Immunization with a mixture of activated pDC plus mDC resulted in increased levels of Ag-specific CD8(+) T cells and an enhanced antitumor response compared with immunization with either dendritic cell subset alone. Synergy between pDC and mDC in their ability to activate T cells was dependent on MHC I expression by mDC, but not pDC, suggesting that pDC enhanced the ability of mDC to present Ag to T cells. Our results demonstrate that pDC and mDC can interact synergistically to induce an Ag-specific antitumor immune response in vivo.

Signaling Pathway Used by HSV-1 to Induce NF- B Activation: Possible Role of Herpes Virus Entry Receptor A

We have previously demonstrated that wild-type herpes simplex virus type 1 (HSV-1), as well as nonreplicating UV-inactivated HSV-1, promptly activates the nuclear factor-kappaB (NF-kappaB) in U937 monocytoid cells and that glycoprotein D (gD) of HSV-1 is sufficient by itself to exert a similar effect. We then investigated the signaling pathway used by HSV-1 to initiate NF-kappaB activation and, particularly, whether our observation could be related to the capability of HSV-1-gD to directly stimulate NF-kappaB through its interaction with the herpes virus entry receptor A (HveA). Here we report that: (a) co-cultivation of U937 cells with an adherent cell line expressing wild-type gD on its surface led to increased NF-kappaB activation, while co-cultivation with the same adherent cell line expressing a mutated form of gD, lacking the capability to bind HveA, did not cause the same effect; (b) exposure to UV-inactivated HSV-1 induced the activation of NF-kappaB in HveA-expressing U937 and THP-1 cells, but not in non-HveA-expressing HEp-2 cells; and (c) activation of NF-kappaB in U937 and THP-1 cells exposed to soluble gD was inhibited by an antibody able to interfere with gD-HveA interaction. These results suggest that HSV-1-gD-HveA interaction initiates a signal transduction pathway leading to NF-kappaB activation.

Herpes simplex virus encephalitis in human UNC-93B deficiency

Herpes simplex virus-1 (HSV-1) encephalitis (HSE) is the most common form of sporadic viral encephalitis in western countries. Its pathogenesis remains unclear, as it affects otherwise healthy patients and only a small minority of HSV-1-infected individuals. Here, we elucidate a genetic etiology for HSE in two children with autosomal recessive deficiency in the intracellular protein UNC-93B, resulting in impaired cellular interferon-alpha/beta and -lambda antiviral responses. HSE can result from a single-gene immunodeficiency that does not compromise immunity to most pathogens, unlike most known primary immunodeficiencies. Other severe infectious diseases may also reflect monogenic disorders of immunity.

Viral Vaccines for Cancer Immunotherapy

The understanding that tumor cells can be recognized and eliminated by the immune system has led to intense interest in the development of cancer vaccines. Viruses are naturally occurring agents that cause human disease but have the potential to prevent disease when attenuated forms or subunits are used as vaccines before exposure. A large number of viruses have been engineered as attenuated vaccines for the expression of tumor antigens, immunomodulatory molecules, and as vehicles for direct destruction of tumor cells or expression of highly specific gene products. This article focuses on the major viruses that are under development as cancer vaccines, including the poxviruses, adenoviruses, adeno-associated viruses, herpesviruses, retroviruses, and lentiviruses. The biology supporting these viruses as vaccines is reviewed and clinical progress is reported.

Sendai virus infection induces efficient adaptive immunity independently of type I interferons

Adaptive immunity in response to virus infection involves the generation of Th1 cells, cytotoxic T cells, and antibodies. This type of immune response is crucial for the clearance of virus infection and for long-term protection against reinfection. Type I interferons (IFNs), the primary innate cytokines that control virus growth and spreading, can influence various aspects of adaptive immunity. The development of antiviral immunity depends on many viral and cellular factors, and the extent to which type I IFNs contribute to the generation of adaptive immunity in response to a viral infection is controversial. Using two strains (Cantell and 52) of the murine respiratory Sendai virus (SeV) with differential abilities to induce type I IFN production from infected cells, together with type I IFN receptor-deficient mice, we examined the role of type I IFNs in the generation of adaptive immunity. Our results show that type I IFNs facilitate virus clearance and enhance the migration and maturation of dendritic cells after SeV infection in vivo; however, soon after infection, mice clear the virus from their lungs and efficiently generate cytotoxic T cells independently of type I IFN signaling. Furthermore, animals that are unresponsive to type I IFN develop long-term anti-SeV immunity, including CD8+ T cells and antibodies. Significantly, this memory response is able to protect mice against challenge with a lethal dose of virus. In conclusion, our results show that primary and secondary anti-SeV adaptive immunities are developed normally in the absence of type I IFN responsiveness.

Autocrine type I interferon amplifies dendritic cell responses to lipopolysaccharide via the nuclear factor-kappaB/p38 pathways

The central role of dendritic cells (DC) in the initiation of immune responses requires these cells to be able to determine the degree of danger in their microenvironment. Abrogating the activity of type I interferon (IFN) secreted after lipopolysaccharide (LPS) stimulation of DC inhibits CD86 and human leucocyte antigen-DR (HLA-DR) upregulation at a low LPS concentration. At a higher concentration of LPS, while changes in surface phenotype are not dependent on type I IFN, this cytokine is required for maximal secretion of interleukin-12 (IL-12) and tumour necrosis factor-alpha (TNFalpha) by DC. Thus, the secretion and autocrine activity of type I IFN after Toll-like receptor stimulation enables DC to orchestrate a hierarchical maturation response with regard to changes in surface phenotype and secretion of cytokines. In addition, the activation of nuclear factor-kappaB and p38 pathways in DC can occur either in an additive fashion when DC are exposed to dual stimulation or can be activated in discrete phases over time when DC are exposed to LPS alone. The differential activation of these pathways provides a mechanism for DC to integrate the activation by multiple stimuli and thus amplify responses to pathogen infection.