Non-alcoholic Wernicke's Encephalopathy Masquerading As CNS Relapse of Acute Myeloid Leukemia.

While Wernicke's encephalopathy (WE) is mostly caused by thiamine deficiency secondary to chronic alcohol use, other conditions that may affect one's nutritional status, such as bariatric surgery, hyperemesis gravidarum, chronic gastrointestinal disease, HIV/AIDS, and certain malignancies, may also lead to this outcome. We are discussing one such case, WE, in a young man with acute myeloid leukemia (AML) who underwent chemotherapy. The patient presented with blurred vision, paresthesia, weakness, and vomiting. Although he denied alcohol abuse, his symptoms, physical exam findings, and MRI results were consistent with WE. Treatment with thiamine resulted in a significant improvement in his visual disturbances and mental status. The authors highlight the importance of recognizing WE in non-alcoholic patients, particularly those undergoing prolonged hospitalization and chemotherapy, as nutritional deficiencies can develop. They recommend thiamine supplementation for patients receiving chemotherapy and those with poor oral intake. The case underscores the need for high clinical suspicion and early intervention in atypical cases of WE.

Influence of vaccination with CVI988/Rispens on load and replication of a very virulent Marek's disease virus strain in feathers of chickens.

Several highly efficacious vaccines are currently available for control of Marek's disease, a lymphoproliferative disease in chickens. However, these vaccines are unable to prevent infection with Marek's disease virus (MDV) in vaccinated birds. This leads to shedding of virulent MDV from feather follicle epithelium and skin epithelial cells of vaccinated and infected chickens. The objective of the present study was to study the interactions between a vaccine strain (CVI988/Rispens) and a very virulent strain of MDV (RB1B) in feathers. We examined genome load and replication of CVI988 and MDV-RB1B strains at various time points post infection. Moreover, we evaluated cytokine expression in feathers as indicators of immunity generated in response to vaccines against MDV. Analysis of feathers collected between 4 and 21 days post infection (d.p.i.) revealed a steady level of CVI988 genome load in the presence or absence of RB1B. Infection with MDV resulted in a significant increase in RB1B genome load peaking at 14 d.p.i. Importantly, vaccination with CVI988 resulted in a significant reduction in accumulation of MDV-RB1B in feathers. RB1B genome accumulation in feather tips was associated with increased expression of interferon-α at 14 d.p.i. and interferon-Sγ at earlier time points, 4 and 7 d.p.i. compared with 10 and 14 d.p.i. Interleukin-10 and interleukin-6 were up-regulated at 14 d.p.i. in the infected groups. This study expands our understanding of the dynamics of replication of vaccine and virulent MDV strains in the feathers and illuminates mechanisms associated with immunity to Marek's disease.

Establishment of an aerosol-based Marek's disease virus infection model.

Marek's disease virus (MDV), which is the causative agent of Marek's disease (MD), is shed by infected chickens and transmitted to other chickens through the respiratory route. Experimental reproduction of MD has been commonly done either by intra-abdominal inoculation of cell-associated MDV or by exposure to MDV-infected 'seeder' chickens. The former method does not mimic the natural route of MDV infection, whereas the latter method suffers from lack of uniformity in the timing and amount of virus transmission from seeder chickens to susceptible birds. The aim of the present study was to establish an infection model of MDV that mimics the natural route of infection. Here we report that when chickens were exposed for 20 min to aerosols (particle size 1.91 microm) of cell-free MDV suspensions containing 1280 plaque-forming units/ml, which were generated using a nebulizer, pathological and clinical signs of MD were observed in 95%-100% of the aerosol-exposed chickens by 21 days post-infection (dpi). Chickens that were exposed to aerosols and sampled at 1, 2, 3, 10, and 21 dpi showed MDV replication as early as 1 dpi in lungs as well as in other tissues such as spleen and bursa of Fabricius. This infection model will facilitate the studies directed to elucidate MDV-host interaction at the site of virus entry.

Evaluation of recombinant adenovirus vectors and adjuvanted protein as a heterologous prime-boost strategy using HER2 as a model antigen.

Induction of strong antigen-specific cell-mediated and humoral responses are critical to developing a successful therapeutic vaccine. Herein, using HER2 as a model antigen, we aim to evaluate a therapeutic vaccine protocol that elicits anti-tumor antibody and cytotoxic T cells to HER2/neu antigen. Replication-competent (ΔPS AdV) and non-replicating recombinant adenoviral vectors (AdV) expressing a rat HER2/neu (ErbB2) oncogene, were generated and compared for four different doses and over four time points for their ability to induce antigen-specific T and B cell responses in mice. Although ΔPS AdV:Her2 vector was shown to induce more durable antigen-specific CD8+ T cell responses, overall, the AdV:Her2 vector induced broader T and B cell responses. Hence the AdV:Her2 vector was used to evaluate a heterologous prime-boost vaccination regimen using rat HER2 protein encapsulated in archaeosomes composed of a semi-synthetic glycolipid (sulfated S-lactosylarchaeol, SLA; and lactosylarchaeol, LA) (SLA/LA:HER2enc) or admixed with archaeosomes composed of SLA alone (SLA:HER2adm). We first tested AdV:Her2 using a prime-boost approach with SLA/LA:HER2enc, and thereafter evaluated a sub-optimal AdV:Her2 dose in a heterologous prime-boost approach with SLA:HER2adm. A single administration of AdV:Her2 alone induced strong cell-mediated immune responses, whereas SLA/LA:HER2enc alone induced strong antigen-specific IgG titers. In mice primed with a suboptimal dose of AdV:Her2, strong CD8+ T-cell responses were observed after a single dose which were not further augmented by protein boost. AdV:Her2 induced CD4+ specific T-cell responses were augmented by SLA:HER2adm. Homologous vaccination using SLA:HER2adm induced strong antigen-specific antibody responses. However, the overall magnitude of the responses was similar with three doses of SLA:HER2adm or Ad:HER2 prime followed by two doses of SLA:HER2adm. We demonstrate that AdV:Her2 is capable of inducing strong antigen-specific CD8+ T cell responses, even at a low dose, and that these responses can be broadened to include antigen-specific antibody responses by boosting with SLA adjuvanted proteins without compromising CD8 T cell responses elicited by AdV priming.

Cytomegalovirus Seropositivity Predicts a Decline in the T Cell But Not the Antibody Response to Influenza in Vaccinated Older Adults Independent of Type 2 Diabetes Status.

Type 2 diabetes mellitus (T2DM) and persistent cytomegalovirus (CMV) infection are postulated contributors to inflammatory processes that impact on the age-related decline in T-cell responses to influenza vaccination. Older subjects with T2DM (n = 30) and healthy aged controls (n = 40) were enrolled and received influenza vaccination in this study. Serum inflammatory markers and CMV serostatus were measured. Pre- to post-vaccination changes in serum antibody titers to the A/H3N2 strain, and levels of granzyme B (GrB, cytotoxic T lymphocytes) in lysates and cytokines in supernatants from influenza A/H3N2-challenged peripheral blood mononuclear cells were measured. We found no difference between the T2DM and healthy groups in the immune responses measured. However, CMV serostatus was a key determinant of the GrB response to influenza challenge; CMV+ subjects had low levels of inducible GrB (iGrB) activity in response to influenza challenge. In contrast, the serum antibody response to the A/H3N2 vaccine strain did not differ with CMV serostatus, and serum levels of the inflammatory marker, ß2-microglobulin, were positively correlated with age, T2DM, and serum IL-10 levels. In conclusion, CMV seropositivity associated with a decline in GrB responses to influenza may predict increased susceptibility to influenza in older adults.

Effects of interferon-γ knockdown on vaccine-induced immunity against Marek's disease in chickens.

Interferon (IFN)-γ has been shown to be associated with immunity to Marek's disease virus (MDV). The overall objective of this study was to investigate the causal relationship between IFN-γ and vaccine-conferred immunity against MDV in chickens. To this end, 3 small interfering RNAs (siRNAs) targeting chicken IFN-γ, which had previously been shown to reduce IFN-γ expression in vitro, and a control siRNA were selected to generate recombinant avian adeno-associated virus (rAAAV) expressing short-hairpin small interfering RNAs (shRNAs). An MDV challenge trial was then conducted: chickens were vaccinated with herpesvirus of turkey (HVT), administered the rAAAV expressing shRNA, and then challenged with MDV. Tumors were observed in 4 out of 10 birds that were vaccinated with HVT and challenged but did not receive any rAAAV, 5 out of 9 birds that were administered the rAAAV containing IFN-γ shRNA, and 2 out of 10 birds that were administered a control enhanced green fluorescent protein siRNA. There was no significant difference in MDV genome load in the feather follicle epithelium of the birds that were cotreated with the vaccine and the rAAAV compared with the vaccinated MDV-infected birds. These results suggest that AAAV-based vectors can be used for the delivery of shRNA into chicken cells. However, administration of the rAAAV expressing shRNA targeting chicken IFN-γ did not seem to fully abrogate vaccine-induced protection.

Il a été démontré que l'interféron (INF)-γ est associé à l'immunité contre le virus de la maladie de Marek (VMM). L'objectif général de la présente étude était d'examiner la relation causale entre l'IFN-γ et l'immunité conférée par le vaccin contre le VMM chez les poulets. Pour y parvenir, trois petits ARN interférant (siARN) ciblant l'IFN-γ, et qui avaient préalablement été montré comme étant capable de réduire l'expression in vitro de l'IFN-γ, et un siARN témoin furent choisis afin de générer du virus adéno-associé aviaire recombinant (rAAAV) exprimant de courtes boucles de siRNA (shRNA). Un essai d'infection par VMM fut alors réalisé : des poulets furent vaccinés avec de l'herpèsvirus de dinde (HVT), reçurent le rAAAV exprimant les shRNA, et par la suite challengés avec le VMM. Des tumeurs furent observées chez 4 des 10 poulets qui avaient été vacciné avec HVT et challengés mais qui n'avaient pas reçu aucun rAAAV, 5 des 9 oiseaux qui avaient reçu le rAAAV contenant l'IFN-γ avec les shRNA, et 2 des 10 oiseaux témoins qui avaient reçu un siRNA qui augmentait la protéine fluorescente verte. Il n'y avait aucune différence significative dans la charge de génome de VMM dans l'épithélium du follicule des plumes des oiseaux qui avaient été co-traités avec le vaccin et le rAAAV comparativement aux oiseaux non-vaccinés avec MMV et infectés. Ces résultats suggèrent que les vecteurs à base d'AAAV peuvent être utilisés pour la livraison de shRNA dans les cellules des oiseaux. Toutefois, l'administration de rAAAV exprimant des shRNA ciblant l'IFN-γ des oiseaux n'a pas semblé complètement abrogé la protection induite par le vaccin.(Traduit par Docteur Serge Messier).

Ageing and respiratory infections: the airway of ageing.

Respiratory infections are a leading cause of infectious disease burden worldwide especially among the elderly. Furthermore, a direct relationship between ageing and susceptibility to infections has been reported, which may be caused by impaired immune function, frailty and degree of exposure to infectious diseases. Many complex changes, including structural and age-associated decline in immunity are associated with increased pulmonary diseases worldwide and result in a high age-related disease burden. The common respiratory infections that present serious risks for the elderly include influenza, respiratory syncytial virus, and a number of bacterial pathogens including pneumococcus and tuberculosis. Vaccines are available for a limited number of these pathogens including influenza, pneumococcal and pertussis vaccines. This mini review article examines the age-related changes in immune function that predispose the elderly population to respiratory infections and potential loss of vaccine efficacy with a focus on ageing and influenza infections.

Immunosenescence: Influenza vaccination and the elderly.

Aging is associated with a decline in the normal function of the immune system, both cellular and humoral, which often leads to a state of 'immunosenescence'. It is necessary that we understand the fundamental cellular and molecular basis of immune senescence and immune responsiveness to prevent age-related diseases, such as viral and bacterial infections, in order to develop appropriate preventative and novel therapeutic measures. Vaccination has been a highly effective prophylactic in protecting vulnerable populations worldwide from many pathogens. Novel vaccine research to enhance protection against these diseases remains a global area of innovation and improvement. This review discusses the impact of immune senescence on the response to influenza vaccines, and the recent progress in translating the knowledge into developing effective influenza vaccines for the elderly to promote healthy aging.

The effects of administration of ligands for Toll-like receptor 4 and 21 against Marek's disease in chickens.

Ligands for Toll-like receptors (TLRs) are known to stimulate immune responses, leading to protection against bacterial and viral pathogens. Here, we aimed to examine the effects of various TLR ligands on the development of Marek's disease in chickens. Specific-pathogen free chickens were treated with a series of TLR ligands that interact with TLR3, TLR9 and TLR21. In a pilot study, it was determined that TLR4 and TLR21 ligands are efficacious, in that they could reduce the incidence of Marek's disease tumors in infected birds. Hence, in a subsequent study, chickens were treated with lipopolysaccharide (LPS) as a TLR4 and CpG oligodeoxynucleotides (ODN) as TLR21 agonists before being challenged with the RB1B strain of Marek's disease virus (MDV) via the respiratory route. The results demonstrated that the administration of LPS or CpG ODN, but not PBS or non-CpG ODN, delayed disease onset and reduced MDV genome copy number in the spleens of infected chickens. Taken together, our data demonstrate that TLR4 and 21 agonists modulate anti-virus innate immunity including cytokine responses in MD-infected chicken and this response can only delay, but not inhibit, disease progression.

Immunity to Marek's disease: where are we now?

Marek's disease (MD) in chickens was first described over a century ago and the causative agent of this disease, Marek's disease virus (MDV), was first identified in the 1960's. There has been extensive and intensive research over the last few decades to elucidate the underlying mechanisms of the interactions between the virus and its host. We have also made considerable progress in terms of developing efficacious vaccines against MD. The advent of the chicken genetic map and genome sequence as well as development of approaches for chicken transcriptome and proteome analyses, have greatly facilitated the process of illuminating underlying genetic mechanisms of resistance and susceptibility to disease. However, there are still major gaps in our understanding of MDV pathogenesis and mechanisms of host immunity to the virus and to the neoplastic events caused by this virus. Importantly, vaccines that can disrupt virus transmission in the field are lacking. The current review explores mechanisms of host immunity against Marek's disease and makes an attempt to identify the areas that are lacking in this field.

Small interfering RNA-mediated knockdown of chicken interferon-γ expression.

Interferon (IFN)-γ is a cytokine with a variety of functions, including direct antiviral activities and the capacity to polarize T-cells. However, there is limited information available about the function of this cytokine in the avian immune system. To gain a better understanding of the biological relevance of IFN-γ in chicken immunity, gain-of-function (upregulation) and loss-of-function (downregulation) studies need to be conducted. RNA interference (RNAi), a technique employed for downregulating gene expression, is mediated by small interfering RNA (siRNA), which can trigger sequence-specific gene silencing. In this regard, sequence specificity and delivery of siRNA molecules remain critical issues, especially to cells of the immune system. Various direct and indirect approaches have been employed to deliver siRNA, including the use of viral vectors. The objectives of the present study were to determine whether RNAi could effectively downregulate expression of chicken IFN-γ in vitro, and investigate the feasibility of recombinant adeno-associated virus to deliver siRNA in vitro as well. Three 27-mer Dicer substrate RNAs were selected based on the chicken IFN-γ coding sequence and transfected into cells or delivered using a recombinant avian adeno-associated virus (rAAAV) into a chicken fibroblast cell line expressing chIFN-γ. The expression of chIFN-γ transcripts was significantly downregulated when a cocktail containing all three siRNAs was used. Expression of endogenous IFN-γ was also significantly downregulated in primary cells after stimulation with a peptide. Further, significant suppression of IFN-γ transcript was also observed in vitro in cells that were treated with rAAAV, expressing siRNA targeting IFN-γ. Off-target effects in the form of triggering IFN responses by RNAi, including expression of chicken 2',5'-oligoadenylate synthetase and IFN-α, were also examined. Our results suggest that siRNAs selected were effective at downregulating IFN-γ in vitro both when delivered directly as well as when expressed by an rAAAV-based vector.

A Toll-like receptor 3 agonist (polyI:C) elicits innate host responses in the spleen and lungs of chickens.

Double-stranded (ds) RNA interacts with host Toll-like receptor (TLR-3), leading to the induction of anti-viral host responses. The present study was designed to compare different routes of administration of a synthetic dsRNA (polyI:C) for induction of innate responses in chicken spleen and lungs. Chickens were treated with polyI:C via the aerosol, intra-air sac (i.a.s.), and intramuscular (IM) routes. Spleen and lungs were collected at 0, 2, 6, 12, and 24 h post-treatment and the expression of innate defence genes was quantified by real-time reverse transcriptase polymerase chain reaction (RT-PCR). There was an up-regulation of interferon (IFN)-ß, TLR-3, and Toll/interleukin 1 receptor domain-containing adaptor protein inducing IFN-ß (TRIF) at 6 h post-treatment in the spleen via IM administration of polyI:C. There was also an increase in the expression of TLR-3 and TRIF in the spleen at 2 h post-treatment via the i.a.s. route. The expression of IFN-α and TRIF was upregulated at 6 h post-treatment via the i.a.s. route in the lungs. Overall, our results indicate that administration of polyI:C can locally and systemically induce the expression of innate response genes depending on the route.

A toll-like receptor 3 ligand enhances protective effects of vaccination against Marek's disease virus and hinders tumor development in chickens.

Marek's disease (MD) is caused by Marek's disease virus (MDV). Various vaccines including herpesvirus of turkeys (HVT) have been used to control this disease. However, HVT is not able to completely protect against very virulent strains of MDV. The objective of this study was to determine whether a vaccination protocol consisting of HVT and a Toll-like receptor (TLR) ligand could enhance protective efficacy of vaccination against MD. Hence, chickens were immunized with HVT and subsequently treated with synthetic double-stranded RNA polyriboinosinic polyribocytidylic [poly(I:C)], a TLR3 ligand, before or after being infected with a very virulent strain of MDV. Among the groups that were HVT-vaccinated and challenged with MDV, the lowest incidence of tumors was observed in the group that received poly(I:C) before and after MDV infection. Moreover, the groups that received a single poly(I:C) treatment either before or after MDV infection were better protected against MD tumors compared to the group that only received HVT. No association was observed between viral load, as determined by MDV genome copy number, and the reduction in tumor formation. Overall, the results presented here indicate that poly(I:C) treatment, especially when it is administered prior to and after HVT vaccination, enhances the efficacy of HVT vaccine and improves protection against MDV.

Interferon-γ influences immunity elicited by vaccines against very virulent Marek's disease virus.

Vaccination of chickens with herpesvirus of turkey (HVT) confers only partial protection against challenge with a very virulent Marek's disease virus (MDV). Here, we evaluated the ability of recombinant chicken interferon-gamma (rChIFN-γ) to enhance protective efficacy of HVT against the very virulent MDV strain, RB1B. The bioactivity of IFN-γ expressed by a plasmid expression vector was confirmed by its ability to stimulate a chicken macrophage cell line (HD11) to produce nitric oxide (NO) in vitro. The administration of HVT with 5µg of pcDNA:chIFN-γ plasmid reduced the incidence of tumor development significantly when compared to vaccinated birds (77.7% in the HVT+empty vector group and 80% in HVT group versus 33.3% in the HVT+chIFN-γ group) and significantly increased IFN-γ expression in the splenocytes of the protected group, suggesting that rChIFN-γ increases the potency of HVT against MDV. Further analysis demonstrated that the protected birds that received HVT vaccine and/or plasmid had lower MDV genome load and lower amounts of transcripts for meq and vIL-8 than in the birds without lesions. Similarly, lower expression of IL-10, IL-18 and IL-6 was observed in the chickens without lesions compared to the chickens that had lesions, suggesting an inverse association between up-regulation of these cytokines and vaccine-induced immunity. In conclusion, IFN-γ can positively influence immunity conferred by HVT vaccination against challenge with a very virulent Marek's disease virus (vvMDV) in chickens.

Assessment of bioactivity of a recombinant chicken interferon-gamma expressed using a baculovirus expression system.

The full-length coding sequence of chicken interferon-γ (ChIFN-γ) was cloned into a baculovirus nonfusion vector, pFastBacDual, and expressed in Sf21 insect cells. Recombinant ChIFN-γ (rChIFN-γ) protein was found to be expressed both intracellularly as well as in the culture supernatants. The affinity-purified rChIFN-γ contained 14, 17, and 28 kDa proteins, possibly representing both glycosylated and nonglycosylated protein forms of ChIFN-γ. The bioactivity of rChIFN-γ was confirmed in vitro by production of nitric oxide in a chicken macrophage cell line (HD11) and antiviral activity against vesicular stomatitis virus in primary chicken embryonic fibroblast cells. Further, HD11 cells stimulated with rChIFN-γ showed significant upregulation of inducible nitric oxide synthases, IFN-γ, interleukin-1ß, interleukin-12p35, signal transducers and activators of transcription 1, class II, major histocompatibility complex, transactivator, and major histocompatibility complex II-ß chain (BL-B) transcripts. In conclusion, the present study provides information on the ability of functionally active rChIFN-γ expressed in a baculovirus system in inducing significant transcriptional upregulation of various immune system-related genes, including those that encode cytokines, antigen-presenting molecules, and transcription factors involved in the major histocompatibility complex and IFN-signaling pathway.

In vivo administration of ligands for chicken toll-like receptors 4 and 21 induces the expression of immune system genes in the spleen.

Toll-like receptors (TLRs) are a group of conserved proteins that play an important role in pathogen recognition in addition to the initiation and regulation of innate and adaptive immune responses. To date, several TLRs have been identified in chickens, each recognizing different ligands. TLR stimulation in chickens has been shown to play a role in host-responses to pathogens. However, the mechanisms through which TLRs modulate the chicken immune system have not been well examined. The present study was conducted to characterize the kinetics of responses to TLR4 and TLR21 stimulation in chickens following intramuscular injections of their corresponding ligands, lipopolysaccharide (LPS) and CpG oligodeoxynucleotides (ODNs), respectively. To this end, relative expression of cytokine genes in the spleen was determined at 2, 6, 12 and 24 h after injection of TLR ligands. The results indicated that LPS strongly induced the up-regulation of some immune system genes early on in the response to treatment, including interferon (IFN)-γ, interleukin (IL)-10, and IL-1ß. Furthermore, treatment with CpG ODN promoted the up-regulation of major histocompatibility complex (MHC)-II, IFN-γ and IL-10. The response to CpG ODN appeared to be somewhat delayed compared to the response to LPS. Moreover, we found a significant increase in IFN-α gene expression in response to LPS but not CpG ODNs. Future studies may be aimed to further characterize the molecular mechanisms of TLR activation in chickens or to exploit TLR agonists as vaccine adjuvants.

Transcriptome and proteome profiling of host responses to Marek's disease virus in chickens.

Marek's disease (MD) is an immunosuppressive and proliferative disease of domestic chickens caused by a highly oncogenic cell-associated alpha-herpesvirus, named Marek's disease virus (MDV). Despite the availability of highly efficacious vaccines for control of MD and existence of lines of chickens which display differential genetic susceptibility or resistance to this disease, little is known about the underlying mechanisms of MDV-host interactions. The recent advent of global or targeted gene and protein expression profiling has paved the way towards gaining a better understanding of host responses to MDV. The main objective of this review is to discuss some of the recent advancements made in relation to elucidating the mechanisms of MDV pathogenesis, host responses to MDV, genetic resistance/susceptibility to MD, and immunity conferred by vaccines. In this regard, particular emphasis has been placed on studies employing proteome and transcriptome profiling approaches. Finally, the utility of microRNA and RNA interference (RNAi) technologies for functional analysis of genes, proteins, and pathways that play a role in the complex interactions between MDV and its host is discussed.

Vaccine-induced host responses against very virulent Marek's disease virus infection in the lungs of chickens.

The aim of this study was to investigate the kinetics of virus replication and cellular responses in the lungs following infection with Marek's disease virus (MDV) and/or vaccination with herpesvirus of turkey (HVT) via the respiratory route. Chickens vaccinated with HVT and challenged with MDV had a higher accumulation of MDV and HVT genomes in the lungs compared to the chickens that received HVT or MDV alone. This increase in virus load was associated with augmented expression of interferon (IFN)-gamma and interleukin (IL)-10, and increased T cell infiltration. These findings shed more light on the immunological events that occur in the lungs after vaccination or infection with MDV.

Immune responses against Marek's disease virus.

It is more than a century since Marek's disease (MD) was first reported in chickens and since then there have been concerted efforts to better understand this disease, its causative agent and various approaches for control of this disease. Recently, there have been several outbreaks of the disease in various regions, due to the evolving nature of MD virus (MDV), which necessitates the implementation of improved prophylactic approaches. It is therefore essential to better understand the interactions between chickens and the virus. The chicken immune system is directly involved in controlling the entry and the spread of the virus. It employs two distinct but interrelated mechanisms to tackle viral invasion. Innate defense mechanisms comprise secretion of soluble factors as well as cells such as macrophages and natural killer cells as the first line of defense. These innate responses provide the adaptive arm of the immune system including antibody- and cell-mediated immune responses to be tailored more specifically against MDV. In addition to the immune system, genetic and epigenetic mechanisms contribute to the outcome of MDV infection in chickens. This review discusses our current understanding of immune responses elicited against MDV and genetic factors that contribute to the nature of the response.

Induction of innate host responses in the lungs of chickens following infection with a very virulent strain of Marek's disease virus.

The natural route of entry of Marek's disease virus (MDV) is via the respiratory system. However, little is known about host-virus interactions in the lungs. The objective of the present study was to examine MDV replication and induction of innate host responses in the lungs of chickens infected through inhalation. Replication of MDV in lungs was detectable as early as 12 hours post-infection (hpi). The expression of Toll-like receptor (TLR)3 and TLR7 genes was enhanced in response to MDV infection in the lungs. This was associated with the up-regulation of interleukin (IL)-1beta and IL-8 genes. In response to MDV infection, the number of macrophages in lungs of infected chickens was significantly higher compared to uninfected control chickens. The expression of inducible nitric oxide synthase (iNOS) gene was also significantly higher in the lungs at 72 hpi following MDV infection. In conclusion, the present study demonstrates induction of innate host responses to MDV infection in the respiratory system. Further studies are needed to characterize other host responses generated in the lungs following MDV infection.