Langerhans cell density and activity in mouse skin and lymph nodes affect herpes simplex type 1 (HSV-1) pathogenicity

Role of Dendritic Cells in Viral Brain Infections

To gain access to the brain, a so-called immune-privileged organ due to its physical separation from the blood stream, pathogens and particularly viruses have been selected throughout evolution for their use of specific mechanisms. They can enter the central nervous system through direct infection of nerves or cerebral barriers or through cell-mediated transport. Indeed, peripheral lymphoid and myeloid immune cells can interact with the blood-brain and the blood-cerebrospinal fluid barriers and allow viral brain access using the "Trojan horse" mechanism. Among immune cells, at the frontier between innate and adaptive immune responses, dendritic cells (DCs) can be pathogen carriers, regulate or exacerbate antiviral responses and neuroinflammation, and therefore be involved in viral transmission and spread. In this review, we highlight an important contribution of DCs in the development and the consequences of viral brain infections.

Herpes Simplex Virus type 1 infects Langerhans cells and the novel epidermal dendritic cell, Epi-cDC2s, via different entry pathways

Skin mononuclear phagocytes (MNPs) provide the first interactions of invading viruses with the immune system. In addition to Langerhans cells (LCs), we recently described a second epidermal MNP population, Epi-cDC2s, in human anogenital epidermis that is closely related to dermal conventional dendritic cells type 2 (cDC2) and can be preferentially infected by HIV. Here we show that in epidermal explants topically infected with herpes simplex virus (HSV-1), both LCs and Epi-cDC2s interact with HSV-1 particles and infected keratinocytes. Isolated Epi-cDC2s support higher levels of infection than LCs in vitro, inhibited by acyclovir, but both MNP subtypes express similar levels of the HSV entry receptors nectin-1 and HVEM, and show similar levels of initial uptake. Using inhibitors of endosomal acidification, actin and cholesterol, we found that HSV-1 utilises different entry pathways in each cell type. HSV-1 predominantly infects LCs, and monocyte-derived MNPs, via a pH-dependent pathway. In contrast, Epi-cDC2s are mainly infected via a pH-independent pathway which may contribute to the enhanced infection of Epi-cDC2s. Both cells underwent apoptosis suggesting that Epi-cDC2s may follow the same dermal migration and uptake by dermal MNPs that we have previously shown for LCs. Thus, we hypothesize that the uptake of HSV and infection of Epi-cDC2s will stimulate immune responses via a different pathway to LCs, which in future may help guide HSV vaccine development and adjuvant targeting.

The Role of Dendritic Cells During Infections Caused by Highly Prevalent Viruses

Dendritic cells (DCs) are a type of innate immune cells with major relevance in the establishment of an adaptive response, as they are responsible for the activation of lymphocytes. Since their discovery, several reports of their role during infectious diseases have been performed, highlighting their functions and their mechanisms of action. DCs can be categorized into different subsets, and each of these subsets expresses a wide arrange of receptors and molecules that aid them in the clearance of invading pathogens. Interferon (IFN) is a cytokine -a molecule of protein origin- strongly associated with antiviral immune responses. This cytokine is secreted by different cell types and is fundamental in the modulation of both innate and adaptive immune responses against viral infections. Particularly, DCs are one of the most important immune cells that produce IFN, with type I IFNs (α and β) highlighting as the most important, as they are associated with viral clearance. Type I IFN secretion can be induced via different pathways, activated by various components of the virus, such as surface proteins or genetic material. These molecules can trigger the activation of the IFN pathway trough surface receptors, including IFNAR, TLR4, or some intracellular receptors, such as TLR7, TLR9, and TLR3. Here, we discuss various types of dendritic cells found in humans and mice; their contribution to the activation of the antiviral response triggered by the secretion of IFN, through different routes of the induction for this important antiviral cytokine; and as to how DCs are involved in human infections that are considered highly frequent nowadays.

Herpes Simplex Virus Type-2 Paralyzes the Function of Monocyte-Derived Dendritic Cells

Herpes simplex viruses not only infect a variety of different cell types, including dendritic cells (DCs), but also modulate important cellular functions in benefit of the virus. Given the relevance of directed immune cell migration during the initiation of potent antiviral immune responses, interference with DC migration constitutes a sophisticated strategy to hamper antiviral immunity. Notably, recent reports revealed that HSV-1 significantly inhibits DC migration in vitro. Thus, we aimed to investigate whether HSV-2 also modulates distinct hallmarks of DC biology. Here, we demonstrate that HSV-2 negatively interferes with chemokine-dependent in vitro migration capacity of mature DCs (mDCs). Interestingly, rather than mediating the reduction of the cognate chemokine receptor expression early during infection, HSV-2 rapidly induces β2 integrin (LFA-1)-mediated mDC adhesion and thereby blocks mDC migration. Mechanistically, HSV-2 triggers the proteasomal degradation of the negative regulator of β2 integrin activity, CYTIP, which causes the constitutive activation of LFA-1 and thus mDC adhesion. In conclusion, our data extend and strengthen recent findings reporting the reduction of mDC migration in the context of a herpesviral infection. We thus hypothesize that hampering antigen delivery to secondary lymphoid organs by inhibition of mDC migration is an evolutionary conserved strategy among distinct members of Herpesviridae.

HIV-1 border patrols: Langerhans cells control antiviral responses and viral transmission

Langerhans cells (LCs) reside in the mucosal epithelia and are refractory to HIV-1 infection; HIV-1 capture by C-type lectin receptor langerin and subsequent targeting to Birbeck granules prevents infection. Furthermore, LCs restrict transmission of CXCR4-using HIV-1 variants, which underscores the role of immature LCs as gatekeepers in the selection of HIV-1 variants. Interaction of langerin on LCs with hyaluronic acid on dendritic cells facilitates cross-presentation of HIV-1 to CD8+ T cells. Activation of LCs upon inflammation bypasses the langerin-dependent barrier, which favors cross-presentation and increases susceptibility of LCs to HIV-1 infection. These recent developments not only highlight the plasticity of LCs but also define an important role for LC-dendritic cell crosstalk at the periphery in directing adaptive immune responses to viruses.

A Dual Role for Corneal Dendritic Cells in Herpes Simplex Keratitis: Local Suppression of Corneal Damage and Promotion of Systemic Viral Dissemination

The cornea is the shield to the foreign world and thus, a primary site for peripheral infections. However, transparency and vision are incompatible with inflammation and scarring that may result from infections. Thus, the cornea is required to perform a delicate balance between fighting infections and preserving vision. To date, little is known about the specific role of antigen-presenting cells in viral keratitis. In this study, utilizing an established murine model of primary acute herpes simplex virus (HSV)-1 keratitis, we demonstrate that primary HSV keratitis results in increased conventional dendritic cells (cDCs) and macrophages within 24 hours after infection. Local depletion of cDCs in CD11c-DTR mice by subconjuntival diphtheria toxin injections, led to increased viral proliferation, and influx of inflammatory cells, resulting in increased scarring and clinical keratitis. In addition, while HSV infection resulted in significant corneal nerve destruction, local depletion of cDCs resulted in a much more severe loss of corneal nerves. Further, local cDC depletion resulted in decreased corneal nerve infection, and subsequently decreased and delayed systemic viral transmission in the trigeminal ganglion and draining lymph node, resulting in decreased mortality of mice. In contrast, sham depletion or depletion of macrophages through local injection of clodronate liposomes had neither a significant impact on the cornea, nor an effect on systemic viral transmission. In conclusion, we demonstrate that corneal cDCs may play a primary role in local corneal defense during viral keratitis and preserve vision, at the cost of inducing systemic viral dissemination, leading to increased mortality.

Langerhans Cell-Dendritic Cell Cross-Talk via Langerin and Hyaluronic Acid Mediates Antigen Transfer and Cross-Presentation of HIV-1

Human epidermal and mucosal Langerhans cells (LCs) express the C-type lectin receptor langerin that functions as a pattern recognition receptor. LCs are among the first immune cells to interact with HIV-1 during sexual transmission. In this study, we demonstrate that langerin not only functions as a pattern recognition receptor but also as an adhesion receptor mediating clustering between LCs and dendritic cells (DCs). Langerin recognized hyaluronic acid on DCs and removal of these carbohydrate structures partially abrogated LC-DC clustering. Because LCs did not cross-present HIV-1-derived Ags to CD8(+) T cells in a cross-presentation model, we investigated whether LCs were able to transfer Ags to DCs. LC-DC clustering led to maturation of DCs and facilitated Ag transfer of HIV-1 to DCs, which subsequently induced activation of CD8(+) cells. The rapid transfer of Ags to DCs, in contrast to productive infection of LCs, suggests that this might be an important mechanism for induction of anti-HIV-1 CD8(+) T cells. Induction of the enzyme hyaluronidase-2 by DC maturation allowed degradation of hyaluronic acid and abrogated LC-DC interactions. Thus, we have identified an important function of langerin in mediating LC-DC clustering, which allows Ag transfer to induce CTL responses to HIV-1. Furthermore, we showed this interaction is mediated by hyaluronidase-2 upregulation after DC maturation. These data underscore the importance of LCs and DCs in orchestrating adaptive immunity to HIV-1. Novel strategies might be developed to harness this mechanism for vaccination.

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.

Herpes simplex virus and varicella zoster virus, the house guests who never leave

Human alphaherpesviruses including herpes simplex viruses (HSV-1, HSV-2) and varicella zoster virus (VZV) establish persistent latent infection in sensory neurons for the life of the host. All three viruses have the potential to reactivate causing recurrent disease. Regardless of the homology between the different virus strains, the three viruses are characterized by varying pathologies. This review will highlight the differences in infection pattern, immune response, and pathogenesis associated with HSV-1 and VZV.

Combination of pet imaging with viral vectors for identification of cancer metastases

There are three main ways for dissemination of solid tumors: direct invasion, lymphatic spread and hematogenic spread. The presence of metastases is the most significant factor in predicting prognosis and therefore evidence of metastases will influence decision-making regarding treatment. Conventional imaging techniques are limited in the evaluation and localization of metastases due to their restricted ability to identify subcentimeter neoplastic disease. Hence, there is a need for an effective noninvasive modality that can accurately identify occult metastases in cancer patients. One such method is the combination of positron emission tomography (PET) with vectors designed for delivery of reporter genes into target cells. Vectors expressing the herpes simplex virus-1 thymidine kinase (HSV1-tk) reporter system have recently been shown to allow localization of micrometastases in animal models of cancer using non invasive imaging. Combination of HSV1-tk and PET imaging is based on the virtues of vectors which can carry and selectively express the HSV1-tk reporter gene in a variety of cancer cells but not in normal tissue. A radioactive tracer which is applied systemically is phosphorylated by the HSV1-tk enzyme, and as a consequence, the tracer accumulates in proportion to the level of HSV1-tk expression which can be imaged by PET. In this paper we review the recent developments in molecular imaging of micrometastases using replication-competent viral or nonviral vectors carrying the HSV1-tk gene using PET imaging. These diagnostic paradigms introduce an advantageous new concept in noninvasive molecular imaging with the potential benefits for improving patient care by providing guidance for therapy to patients with risk for metastases.

Defining the herpes simplex virus-specific CD8+ T cell repertoire in C57BL/6 mice

HSV type 1 (HSV-1) expresses its genes sequentially as immediate early (α), early (β), leaky late (γ1), and true late (γ2), where viral DNA synthesis is an absolute prerequisite only for γ2 gene expression. The γ1 protein glycoprotein B (gB) contains a strongly immunodominant CD8(+) T cell epitope (gB(498-505)) that is recognized by 50% of both the CD8(+) effector T cells in acutely infected trigeminal ganglia (TG) and the CD8(+) memory T cells in latently infected TG. Of 376 predicted HSV-1 CD8(+) T cell epitopes in C57BL/6 mice, 19 (gB(498-505) and 18 subdominant epitopes) stimulated CD8(+) T cells in the spleens and TG of HSV-1 acutely infected mice. These 19 epitopes identified virtually all CD8(+) T cells in the infected TG that represent all or the vast majority of the HSV-specific CD8(+) TCR repertoire. Only 11 of ∼84 HSV-1 proteins are recognized by CD8(+) T cells, and most (∼80%) are expressed before viral DNA synthesis. Neither the immunodominance of gB(498-505) nor the dominance hierarchy of the subdominant epitopes is due solely to MHC or TCR affinity. We conclude that the vast majority of CD8(+) T cells in HSV-1 acutely infected TG are HSV specific, that HSV-1 β and γ1 proteins that are expressed before viral DNA synthesis are favored targets of CD8(+) T cells, and that dominance within the TCR repertoire is likely due to the frequency or expansion and survival characteristics of CD8(+) T cell precursors.

Viruses and Langerhans cells

Langerhans cells (LCs) are the resident dendritic cells (DCs) of epidermis in human mucosal stratified squamous epithelium and the skin. A phenotypically similar DC has recently been discovered as a minor population in the murine dermis. In epidermis, LCs function as sentinel antigen-presenting cells that can capture invading viruses such as herpes simplex virus (HSV), varicella-zoster virus (VZV) and human immunodeficiency virus (HIV). This interaction between LCs and viruses results in highly variable responses, depending on the virus as discussed in this review. For example, HSV induces apoptosis in LCs but HIV does not. LCs seem to be the first in a complex chain of antigen presentation to T cells in lymph nodes for HSV and possibly VZV, or they transport virus to T cells, as described for HIV and maybe VZV. Together with epidermal keratinocytes they may also have a role in the initial innate immune response at the site of infection in the epidermis, although this is not fully known. The full spectrum of biological responses of LCs even to these viruses has yet to be understood and will require complementary studies in human LCs in vitro and in murine models in vivo.

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.

Imaging of lymph node micrometastases using an oncolytic herpes virus and [F]FEAU PET

Background

In patients with melanoma, knowledge of regional lymph node status provides important information on outlook. Since lymph node status can influence treatment, surgery for sentinel lymph node (SLN) biopsy became a standard staging procedure for these patients. Current imaging modalities have a limited sensitivity for detection of micrometastases in lymph nodes and, therefore, there is a need for a better technique that can accurately identify occult SLN metastases.

Methodology/Principal Findings

B16-F10 murine melanoma cells were infected with replication-competent herpes simplex virus (HSV) NV1023. The presence of tumor-targeting and reporter-expressing virus was assessed by [¹⁸F]-2′-fluoro-2′-deoxy-1-β-D-β-arabinofuranosyl-5-ethyluracil ([¹⁸F]FEAU) positron emission tomography (PET) and confirmed by histochemical assays. An animal foot pad model of melanoma lymph node metastasis was established. Mice received intratumoral injections of NV1023, and 48 hours later were imaged after i.v. injection of [¹⁸F]FEAU. NV1023 successfully infected and provided high levels of lacZ transgene expression in melanoma cells. Intratumoral injection of NV1023 resulted in viral trafficking to melanoma cells that had metastasized to popliteal and inguinal lymph nodes. Presence of virus-infected tumor cells was successfully imaged with [¹⁸F]FEAU-PET, that identified 8 out of 8 tumor-positive nodes. There was no overlap between radioactivity levels (lymph node to surrounding tissue ratio) of tumor-positive and tumor-negative lymph nodes.

Conclusion/Significance

A new approach for imaging SLN metastases using NV1023 and [¹⁸F]FEAU-PET was successful in a murine model. Similar studies could be translated to the clinic and improve the staging and management of patients with melanoma.

Langerhans cells and viral immunity

Langerhans cells (LC) are a unique dendritic cell subset that are located in mucosal stratified squamous epithelium and skin epidermis. Their location is ideally suited for their function as antigen presenting cells that capture invading viruses and induce anti-viral immunity. However, it is becoming evident that the interaction between LC and viruses can result in different responses, depending on the virus and the receptors involved. Here we will discuss the recent data on the similarities and differences in roles of LC in viral immunity to and infection with HIV, herpes simplex and varicella-zoster virus. Although all three viruses interact with LC during initial infection, the effects can be quite different, reflecting differences in biology and pathogenesis.

Critical role of dendritic cells in mouse mammary tumor virus in vivo infection

Mouse mammary tumor virus (MMTV) is a milk-transmitted betaretrovirus that causes mammary tumors in mice. Although mammary epithelial cells are the ultimate targets of MMTV, the virus utilizes components of the host immune system to establish infection. Previous studies indicated that dendritic cells play a role in MMTV infection. Here we show that dendritic cells are the first cells to be infected by MMTV in vivo and that they are capable of producing infectious virus that can be transmitted to other cell types. Moreover, upon contact with the virus, dendritic cells became more mature and migrated in response to the chemokine macrophage inflammatory protein 3beta. Finally, we demonstrate that targeted ablation of dendritic cells in vivo dramatically attenuated MMTV infection. These data indicate that MMTV infection of dendritic cells is critical to initial propagation of the virus in vivo.

Dendritic cells in viral pathogenesis: protective or defective?

Dendritic cells (DC) are potent antigen-presenting cells that are critical in the initiation of immune responses to control and/or eliminate viral infections. Recent studies have investigated the effects of virus infection on the biology of DC. This review summarizes these changes, focusing on both the DC parameters affected and the viral factors involved. In addition, the central role of DC biology in the pathogenesis of several viral families, including herpesviruses, paramyxoviruses and retroviruses, is explored. The field of pathogen recognition by DC is addressed, focusing on its role in protecting the host from viral infection, as well as the ability of viruses to exploit such host receptor ligation and signalling to their replicative advantage. The hypothesis is proposed that virus and host have evolved a symbiotic relationship to ensure both viral transmission and host survival.

Herpes simplex virus infection of human dendritic cells induces apoptosis and allows cross-presentation via uninfected dendritic cells

HSV efficiently infects dendritic cells (DCs) in their immature state and induces down-regulation of costimulatory and adhesion molecules. As in mice, HSV infection of human DCs also leads to their rapid and progressive apoptosis, and we show that both early and late viral proteins contribute to its induction. Because topical HSV infection is confined to the epidermis, Langerhans cells are expected to be the major APCs in draining lymph nodes. However, recent observations in murine models show T cell activation to be mediated by nonepidermal DC subsets, suggesting cross-presentation of viral Ag. In this study we provide an explanation for this phenomenon, demonstrating that HSV-infected apoptotic DCs are readily phagocytosed by uninfected bystander DCs, which, in turn, stimulate virus-specific CD8+ T cell clones.

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

Adaptive cellular immunity is required to clear HSV-1 infection in the periphery. Myeloid dendritic cells (DCs) are the first professional Ag-presenting cell to encounter the virus after primary and secondary infection and thus the consequences of their infection are important in understanding the pathogenesis of the disease and the response to the virus. Following HSV-1 infection, both uninfected and infected human DCs acquire a more mature phenotype. In this study, we demonstrate that type I IFN secreted from myeloid DC mediates bystander activation of the uninfected DCs. Furthermore, we confirm that this IFN primes DCs for elevated IL-12 p40 and p70 secretion. However, secretion of IFN is not responsible for the acquisition of a mature phenotype by HSV-1-infected DC. Rather, virus binding to a receptor on the cell surface induces DC maturation directly, through activation of the NF-kappaB and p38 MAPK pathways. The binding of HSV glycoprotein D is critical to the acquisition of a mature phenotype and type I IFN secretion. The data therefore demonstrate that DCs can respond to HSV exposure directly through recognition of viral envelope structures. In the context of natural HSV infection, the coupling of viral entry to the activation of DC signaling pathways is likely to be counterbalanced by viral disruption of DC maturation. However, the parallel release of type I IFN may result in paracrine activation so that the DCs are nonetheless able to mount an adaptive immune response.

The host response to herpes simplex virus infection

PURPOSE OF REVIEW

Infection with herpes simplex virus remains a significant cause of disease. The host immune system plays an important role in containing viral replication, and there has been considerable progress in defining which components of immunity are key to the resolution of infection. Nevertheless, effective immunoprophylaxis or immunotherapy has not yet been achieved.

RECENT FINDINGS

Recent work has focused on understanding the early events leading to the herpes simplex virus-specific immune response, in particular on the role of antigen-presenting dendritic cells. Herpes simplex virus has evolved a number of ways of interfering with antigen presentation by dendritic cells, thus presumably impeding or delaying the host immune response. Nevertheless, herpes simplex virus triggers strong cellular and humoral immunity. The ability of dendritic cells to take up dead or dying infected cells and cross-present them to cognate T cells may be the key to resolving this apparent paradox. Interaction between dendritic cell subsets, and particularly the virus-induced release of type I interferons may be essential to drive efficient antigen cross-presentation and subsequent T-cell activation.

SUMMARY

A greater understanding of the importance of dendritic cells in driving viral immunity, and of the ligands that activate these cells and the cytokines they secrete, has provided novel vaccination strategies. The delivery of immunomodulatory genes together with viral antigens, for example by DNA vaccination, may harness the full potential of dendritic cells, and achieve the goal of effective immunological control of herpes simplex virus.

Depletion of Langerhans cells in human papillomavirus type 16-infected skin is associated with E6-mediated down regulation of E-cadherin

Human papillomavirus type 16 (HPV16) is an oncogenic virus that causes persistent infections in cervical epithelium. The chronic nature of HPV16 infections suggests that this virus actively evades the host immune response. Intraepithelial Langerhans cells (LC) are antigen-presenting cells that are critical in T-cell priming in response to viral infections of the skin. Here we show that HPV16 infection is directly associated with a reduction in the numbers of LC in infected epidermis. Adhesion between keratinocytes (KC) and LC, mediated by E-cadherin, is important in the retention of LC in the skin. Cell surface E-cadherin is reduced on HPV16-infected basal KC, and this is directly associated with the reduction in numbers of LC in infected epidermis. Expression of a single viral early protein, HPV16 E6, in KC reduces levels of cell surface E-cadherin thereby interfering with E-cadherin-mediated adhesion. Through this pathway, E6 expression in HPV16-infected KC may limit presentation of viral antigens by LC to the immune system, thus preventing the initiation of a cell-mediated immune response and promoting survival of the virus.

Targeting epidermal Langerhans cells by epidermal powder immunization

Immune reactions to foreign or self-antigens lead to protective immunity and, sometimes, immune disorders such as allergies and autoimmune diseases. Antigen presenting cells (APC) including epidermal Langerhans cells (LCs) play an important role in the course and outcome of the immune reactions. Epidermal powder immunization (EPI) is a technology that offers a tool to manipulate the LCs and the potential to harness the immune reactions towards prevention and treatment of infectious diseases and immune disorders.

Expression of human immunodeficiency virus type 1 gp120 from herpes simplex virus type 1-derived amplicons results in potent, specific, and durable cellular and humoral immune responses

Herpes simplex virus type 1 (HSV-1) infects a wide range of cells, including dendritic cells. Consequently, HSV-1 vectors may be capable of eliciting strong immune responses to vectored antigens. To test this hypothesis, an HSV-1 amplicon plasmid encoding human immunodeficiency virus type 1 gp120 was constructed, and murine immune responses to helper virus-free amplicon preparations derived from this construct were evaluated. Initial studies revealed that a single intramuscular (i.m.) injection of 10(6) infectious units (i.u.) of HSV:gp120 amplicon particles (HSV:gp120) elicited Env-specific cellular and humoral immune responses. A potent, CD8(+)-T-cell-mediated response to an H-2D(d)-restricted peptide from gp120 (RGPGRAFVTI) was measured by a gamma interferon ELISPOT and was confirmed by standard cytotoxic-T-lymphocyte assays. Immunoglobulin G enzyme-linked immunosorbent assay analysis showed the induction of a strong, Env-specific antibody response. An i.m. or an intradermal administration of HSV:gp120 at the tail base elicited a more potent cellular immune response than did an intraperitoneal (i.p.) inoculation, although an i.p. introduction generated a stronger humoral response. The immune response to HSV:gp120 was durable, with robust cellular and humoral responses persisting at 171 days after a single 10(6)-i.u. inoculation. The immune response to HSV:gp120 was also found to be dose dependent: as few as 10(4) i.u. elicited a strong T-cell response. Finally, HSV:gp120 elicited significant Env-specific cellular immune responses even in animals that had been previously infected with wild-type HSV-1. Taken together, these data strongly support the use of helper-free HSV-1 amplicon particles as vaccine delivery vectors.

Herpes simplex virus evolved to use the human defense mechanisms to establish a lifelong infection in neurons--a review and hypothesis

The review of recent studies using DNA microarrays shed new light on herpes simplex virus (HSV) replicative cycle, the response of immature dendritic cells (DCs) to pathogens and the response of neurons in trigeminal ganglia to virus reactivation. These studies provided a better understanding of the molecular biology of HSV during infection, latency and reactivation. The research on the sensory trigeminal neurons and the neuronal axons (type C fibers) that transverse the skin basal membrane, enter the skin epidermis and interact with the cell membrane of the skin resident immature DCs provided an insight on the connection between the nervous system and the host immune system. Based on these studies a hypothesis is presented suggesting that HSV evolved to use the human host defense systems (pain signals, the immune system cells and sensory neurons) to ensure its entry from the skin epithelium into the sensory neurons. Reactivated HSV in the neurons utilizes the same host defense systems to return to the skin epithelium.

Phenotypic Identification of Antigen-Dependent and Antigen-Independent CD8 CTL Precursors in the Draining Lymph Node During Acute Cutaneous Herpes Simplex Virus Type 1 Infection

Optimal immunological control of cutaneous herpes simplex virus type 1 (HSV-1) infections initiated in the hind footpad of C57BL/6 (B6, H-2b) mice is dependent upon the presence of functional HSV-1-specific T lymphocytes. The class I MHC-restricted, CD8+ T cell subpopulation is involved in the clearance of infectious HSV-1 from the skin and limiting HSV-1 replication and spread within the peripheral nervous system. However, the frequency of HSV-1-specific CTL precursors (CTLp), as a measure of potential anti-viral CD8+ T cell function, is relatively low compared with other acute viral infections. To gain insight into the basis for this low functional frequency, changes in the CD8+ T cell subpopulation phenotype associated with activation and differentiation were investigated. Analysis of the phenotypic changes showed that HSV-1-specific CTLp were found predominantly within a subpopulation of CD8+ T cells expressing high levels of CD44 (CD44high) and high levels of the IL-2 receptor α-chain (CD25high). A second activated subpopulation of CD8+ T cells expressing the CD44high CD25low phenotype did not contain detectable HSV-1-specific CTLp, even after the addition of HSV-1-infected stimulator cells as a source of an exogenous Ag. These data suggested that HSV-1-specific CD8+ T cells must increase expression of CD25 before attaining the potential to become CTL effector cells. These findings also indicated that the up-regulation of CD44 alone is not sufficient to identify precisely HSV-1-specific CD8+ T cells.

Phenotypic characteristics associated with the acquisition of HSV-specific CD8 T-lymphocyte-mediated cytolytic function in vitro

Class I MHC-restricted, HSV-1-specific CD8(+) cytolytic T lymphocyte (CTL) function is rarely detected in lymphocytes isolated directly from the lymph node draining the site of infection. However, culture in vitro for 24 to 72 h in the absence of exogenous antigen results in the development of easily detectable levels of HSV-1-specific CTL effectors. The inability to detect virus-specific CTL in HSV-1-infected mice is not well understood. However, since the in vitro culture of HSV-1-immune lymphocytes results in the transition to CTL function, studies of the changes occurring to the CD8(+) T cell subpopulation may provide important insights into the development of virus-specific CTL. Therefore, the phenotypic changes taking place in the CD8(+) population of T cells from draining popliteal lymph nodes of HSV-1-infected C57BL/6 (B6) mice were investigated, focusing on changes in the expression of cell surface markers associated with T lymphocyte activation. The results demonstrate an increase in the percentage of CD8(+) T cells expressing the activation markers CD44 and CD25 in parallel with the acquisition of HSV-specific CTL effector function. Cytolytic function was found exclusively within the CD8(+) CD44(hi) CD25(hi) fraction of cells in culture, but, surprisingly, was not detectable in CD8(+) CD44(hi) CD25(lo) T cells. This suggested that the acquisition of high levels of the high-affinity IL-2 receptor was closely linked to cytolytic function and may define an important developmental stage in the transition from noncytolytic to cytolytic effector cell. In support of this, CD8(+) CD25(hi) T cells isolated from the regional lymph node exhibited direct ex vivo cytolytic function, indicating that cytolytic effector cells were present in the lymph node, but must emigrate rapidly after attaining this level of differentiation.

An analysis of the role of skin Langerhans cells (LC) in the cytoplasmic processing of HIV-1 peptides after "peplotion" transepidermal transfer and HLA class I presentation to CD8+ CTLs--an approach to immunization of humans

Skin Langerhans cells (LC) are antigen-presenting cells capable of expressing MHC class I and class II molecules on the plasma membrane. This molecular activity was reviewed to combine the knowledge of peptide presentation by MHC and HLA class I and class II molecules to prime CD8+ cytotoxic T cells (CTLs) and CD4+ T helper cells, respectively. The possible utilization of the skin dendritic cells for the development of antiviral CTLs and antibodies by synthetic peptides modeled according to the motifs of peptides that naturally interact with the peptide binding grooves of the various HLA haplotypes is discussed and evaluated. It may be possible that the introduction of synthetic viral peptides with motifs to fit the HLA class I haplotypes of a human population to the skin dendritic cells will prime selectively the cellular or the humoral immune responses. This approach may provide a new vaccination technique that applies synthetic virus peptides as vaccines for the immunization of humans. The neuropeptide CGRP interacts with LC and modulates antigen presentation.

Role of Langerhans cells and other dendritic cells in viral diseases

Langerhans cells are part of a vast system of potent antigen-presenting cells known under the name of dendritic cells. During the last decade, much has been learned on dendritic cell involvement in the immune response to infectious diseases. This review briefly summarizes our current understanding of the role played by Langerhans cells and other dendritic cells in the pathogenesis of DNA and RNA virus infections. These data may form the basis for the development of innovative approaches in the diagnosis, prevention, and treatment of viral diseases.

Internalization of Ia molecules into Birbeck granule-like structures in murine dendritic cells

Dendritic cells isolated from the draining lymph nodes of mice sensitized epicutaneously with hapten are potent antigen-presenting cells and contain Birbeck granules and cored tubules characteristic of antigen-activated epidermal Langerhans cells. We used immunogold labeling and transmission electron microscopy to follow the internalization of Ia molecules in these antigen-presenting cells. We found that Ia molecules were internalized into Birbeck granule-like structures in the antigen-activated dendritic cells. Computer reconstruction of serial sections of the dendritic cells demonstrated that these structures span the cytoplasm from the cell membrane to the nuclear membrane and are associated with lysosomes. The internalization of Ia molecules into these structures supports the hypothesis that the Birbeck granule-like structures are derived from the cell membrane and are involved in the antigen-processing/presenting function of the dendritic cells.

Detection of IL-1 beta, TNF-alpha, and IL-6 gene transcription by the polymerase chain reaction in keratinocytes, Langerhans cells and peritoneal exudate cells during infection with herpes simplex virus-1

Interleukin-1, tumour necrosis factor-alpha and interleukin-6 are considered to be major mediators of inflammatory processes. In the present study, cytokine gene transcription was detected by the polymerase chain reaction technique during cutaneous and intraperitoneal infection with herpes simplex virus-1. Epidermal cell suspensions obtained from mice infected with herpes simplex virus-1 in the ear pinna were enriched or depleted in Langerhans cells by immunomagnetic fractionation. Herpes simplex virus-1 infection in the skin was found to induce interleukin-1 beta, tumour necrosis factor-alpha and interleukin-6 gene transcription in keratinocytes at 24 hours post-infection. Gene transcription declined by 48 hours post-infection. Induction of interleukin-1 beta and tumour necrosis factor-alpha but not of IL-6 gene transcription was detected in Langerhans cells obtained from infected mice at 24 hours post-infection. In order to study cytokine gene transcription during intraperitoneal infection with herpes simplex virus-1, peritoneal exudate cells were obtained from infected mice. Maximal levels of interleukin-1 beta, tumour necrosis factor-alpha, and interleukin-6 mRNA were found in peritoneal exudate cells 6 hours after infection. RNA transcription declined at 24 hours post-infection and was no longer detectable at 48 hours post-infection. Since the higher susceptibility of newborn mice to intraperitoneal herpes simplex virus-1 infection has been suggested to be related to defective cytokine production, cytokine gene transcription was compared in peritoneal exudate cells obtained from infected newborn and adult mice. No significant differences in interleukin-1 beta, tumour necrosis factor-alpha and interleukin-6 gene expression were observed in peritoneal exudate cells obtained from newborn mice as compared with adult mice. In conclusion, cutaneous and intraperitoneal infection with herpes simplex virus-1 induces interleukin-1 beta, tumour necrosis factor-alpha and interleukin-6 gene transcription in epidermal and peritoneal exudate cells.

Dendritic cells and dinitrochlorobenzene (DNCB): a new treatment approach to AIDS

Recent studies suggest that antigen-presenting cells (dendritic cells) may play a key role in the pathogenesis of human immunodeficiency virus (HIV) infection. This observation makes new immunomodulatory treatment strategies desirable. Topical dinitrochlorobenzene (DNCB) is discussed as a possible treatment modality in the context of its proven therapeutic uses and its immunomodulatory effect on dendritic cells. DNCB may be a safe, inexpensive, and widely available treatment option for HIV disease.

Computer analysis of antigenic domains and RGD-like sequences (RGWG) in the E glycoprotein of flaviviruses: an approach to vaccine development

Antigenic domains and RGD-like sequences in the E glycoprotein of the flaviviruses Japanese encephalitis virus, yellow fever virus, West Nile virus, dengue type 4 virus, and tick-borne encephalitis virus were analyzed by computer programs that provide information on the physical properties of the polypeptides. The use of computer programs for the development of vaccines based on the synthesis of antigenic peptides is discussed. Synthetic viral peptides are proposed to be used for topical application so as to interfere with the virus-cell interaction. Viral peptides with antigenic epitopes to protect against dengue virus infection without enhancing pathogenesis may also be developed on the basis of the computer analysis.

Mouse footpad Langerhans cells as an indicator for safety of foot and mouth disease virus vaccines

The effect of various vaccines against foot and mouth disease virus (FMDV) was tested on Langerhans cell density in the footpad epidermis of mice. Injection of monovalent, bivalent and trivalent FMDV vaccines caused a reduction in Langerhans cell density in the murine skin, which was more marked at the center of the footpad, the site of injection, than at the periphery. Testing of the various components of the vaccine showed that saponin caused a marked reduction in Langerhans cells while injection of aluminium hydroxide had a lesser effect and the virus alone had no effect on these cells. Thus Langerhans cell density could serve as an efficient marker to test the safety of vaccines to FMDV since the integrity of Langerhans cells, which are the antigen-presenting cells in the skin epidermis, is needed for an effective immune response to the vaccine.