Interleukin-4 diminishes CD8(+) respiratory syncytial virus-specific cytotoxic T-lymphocyte activity in vivo

Exposure to lung-migrating helminth protects against murine SARS-CoV-2 infection through macrophage-dependent T cell activation

Helminth endemic regions report lower COVID-19 morbidity and mortality. Here, we show that lung remodeling from a prior infection with a lung-migrating helminth, Nippostrongylus brasiliensis, enhances viral clearance and survival of human-ACE2 transgenic mice challenged with SARS-CoV-2 (SCV2). This protection is associated with a lymphocytic infiltrate, including increased accumulation of pulmonary SCV2-specific CD8+ T cells, and anti-CD8 antibody depletion abrogated the N. brasiliensis-mediated reduction in viral loads. Pulmonary macrophages with a type 2 transcriptional and epigenetic signature persist in the lungs of N. brasiliensis-exposed mice after clearance of the parasite and establish a primed environment for increased CD8+ T cell recruitment and activation. Accordingly, depletion of macrophages ablated the augmented viral clearance and accumulation of CD8+ T cells driven by prior N. brasiliensis infection. Together, these findings support the concept that lung-migrating helminths can limit disease severity during SCV2 infection through macrophage-dependent enhancement of antiviral CD8+ T cell responses.

Helminth exposure protects against murine SARS-CoV-2 infection through macrophage dependent T cell activation

Helminth endemic regions report lower COVID-19 morbidity and mortality. Here, we show that lung remodeling from a prior infection with a lung migrating helminth, Nippostrongylus brasiliensis , enhances viral clearance and survival of human-ACE2 transgenic mice challenged with SARS-CoV-2 (SCV2). This protection is associated with a lymphocytic infiltrate including an increased accumulation of pulmonary SCV2-specific CD8+ T cells and anti-CD8 antibody depletion abrogated the N. brasiliensis -mediated reduction in viral loads. Pulmonary macrophages with a type-2 transcriptional signature persist in the lungs of N. brasiliensis exposed mice after clearance of the parasite and establish a primed environment for increased antigen presentation. Accordingly, depletion of macrophages ablated the augmented viral clearance and accumulation of CD8+ T cells driven by prior N. brasiliensis infection. Together, these findings support the concept that lung migrating helminths can limit disease severity during SCV2 infection through macrophage-dependent enhancement of anti-viral CD8+ T cell responses.

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Nasal Wash Cytokines during Respiratory Viral Infection in Pediatric Allogeneic Hematopoietic Cell-Transplant Recipients

Allogeneic hematopoietic cell-transplant (alloHCT) recipients are at increased risk of complications from viral respiratory-tract infections (vRTIs). We measured cytokine concentrations in nasal washes (NWs) from pediatric alloHCT recipients to better understand their local response to vRTI. Forty-one immunologic analytes were measured in 70 NWs, collected during and after vRTI, from 15 alloHCT recipients (median age, 11 yr) with 19 episodes of vRTI. These were compared with NW cytokine concentrations from an independent group of otherwise healthy patients. AlloHCT recipients are able to produce a local response to vRTI and produce IFN-α2 and IL-12p40 in significant quantities above an uninfected baseline early in infection. Compared with otherwise healthy comparator-group patients, alloHCT recipients have higher NW concentrations of IL-4 when challenged with vRTI. Further study of these immunologic analytes as well as of type 1 versus type 2 balance in the respiratory mucosa in the context of vRTI during immune reconstitution may be of future research interest in this vulnerable patient population.

Evaluation of the protective potential of antibody and T cell responses elicited by a novel preventative vaccine towards respiratory syncytial virus small hydrophobic protein

The small hydrophobic (SH) glycoprotein of human respiratory syncytial virus (RSV) is a transmembrane protein that is poorly accessible by antibodies on the virion but has an ectodomain (SHe) that is accessible and expressed on infected cells. The SHe from RSV strain A has been formulated in DPX, a unique delivery platform containing an adjuvant, and is being evaluated as an RSV vaccine candidate. The proposed mechanism of protection is the immune-mediated clearance of infected cells rather than neutralization of the virion. Our phase I clinical trial data clearly showed that vaccination resulted in robust antibody responses, but it was unclear if these immune responses have any correlation to immune responses to natural infection with RSV. Therefore, we embarked on this study to examine these immune responses in older adults with confirmed RSV infection. We compared vaccine-induced (DPX-RSV(A)) immune responses from participants in a Phase 1 clinical trial to paired acute and convalescent titers from older adults with symptomatic laboratory-confirmed RSV infection. Serum samples were tested for anti-SHe IgG titers and the isotypes determined. T cell responses were evaluated by IFN-γ ELISPOT. Anti-SHe titers were detected in 8 of 42 (19%) in the acute phase and 16 of 42 (38%) of convalescent serum samples. IgG1, IgG3, and IgA were the prevalent isotypes generated by both vaccination and infection. Antigen-specific T cell responses were detected in 9 of 16 (56%) of vaccinated participants. Depletion of CD4⁺ but not CD8⁺ T cells abrogated the IFN-γ ELISPOT response supporting the involvement of CD4⁺ T cells in the immune response to vaccination. The data showed that an immune response like that induced by DPX-RSV(A) could be seen in a subset of participants with confirmed RSV infection. These findings show that older adults with clinically significant infection as well as vaccinated adults generate a humoral response to SHe. The induction of both SHe-specific antibody and cellular responses support further clinical development of the DPX-RSV(A) vaccine.

Contribution of Dendritic Cells in Protective Immunity against Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is a major cause of severe respiratory disease in infants and the elderly. The socioeconomic burden of RSV infection is substantial because it leads to serious respiratory problems, subsequent hospitalization, and mortality. Despite its clinical significance, a safe and effective vaccine is not yet available to prevent RSV infection. Upon RSV infection, lung dendritic cells (DCs) detecting pathogens migrate to the lymph nodes and activate the adaptive immune response. Therefore, RSV has evolved various immunomodulatory strategies to inhibit DC function. Due to the capacity of RSV to modulate defense mechanisms in hosts, RSV infection results in inappropriate activation of immune responses resulting in immunopathology and frequent reinfection throughout life. This review discusses how DCs recognize invading RSV and induce adaptive immune responses, as well as the regulatory mechanisms mediated by RSV to disrupt DC functions and ultimately avoid host defenses.

Early Life Respiratory Syncytial Virus Infection and Asthmatic Responses

The infant's developing immune response is central to establishing a balanced system that reacts appropriately to infectious stimuli, but does not induce altered disease states with potential long-term sequelae. Respiratory syncytial virus may alter the immune system, affecting future responses. Early infection may have direct effects on the lung itself. Other early life processes contribute to the development of immune responses including assembly of the microbiome, which seems to have a particularly important role for establishing the immune environment. This review covers studies that have set up important paradigms and discusses recent data that direct research toward informative hypotheses.

Cytokines and CD8 T cell immunity during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection and hospitalization in infants. In spite of the enormous clinical burden caused by RSV infections, there remains no efficacious RSV vaccine. CD8 T cells mediate viral clearance as well as provide protection against a secondary RSV infection. However, RSV-specific CD8 T cells may also induce immunopathology leading to exacerbated morbidity and mortality. Many of the crucial functions performed by CD8 T cells are mediated by the cytokines they produce. IFN-γ and TNF are produced by CD8 T cells following RSV infection and contribute to both the acceleration of viral clearance and the induction of immunopathology. To prevent immunopathology, regulatory mechanisms are in place within the immune system to inhibit CD8 T cell effector functions after the infection has been cleared. The actions of a variety of cytokines, including IL-10 and IL-4, play a critical role in the regulation of CD8 T cell effector activity. Herein, we review the current literature on CD8 T cell responses and the functions of the cytokines they produce following RSV infection. Additionally, we discuss the regulation of CD8 T cell activation and effector functions through the actions of various cytokines.

Modulation of T-cell reactivity during equine pregnancy is antigen independent

PROBLEM

Pregnant mares demonstrate a reduction in cytotoxic T lymphocyte (CTL) reactivity against cells from the breeding stallion. We investigated whether this effect is limited to activity against paternal major histocompatibility complex (MHC) antigens, and whether it occurs during MHC-compatible pregnancy.

METHOD OF STUDY

Mares were mated to carry MHC-compatible or MHC-incompatible pregnancies. CTL activity of these mares when pregnant and non-pregnant was measured against cells from horses with MHC haplotypes unrelated to the mare or breeding stallion.

RESULTS

While carrying MHC-incompatible pregnancies, mares demonstrated reduced CTL activity against lymphocytes from third-party horses in addition to those from the breeding stallion. This effect was also observed in mares carrying MHC-compatible pregnancies.

CONCLUSIONS

The decrease in maternal T-cell reactivity characteristic of normal equine pregnancy is not restricted to paternal alloantigen, and occurs during MHC-matched matings. This suggests that antigen-independent mechanisms may be responsible for this reduction in cell-mediated immune activity.

Immunoprotectivity of HLA-A2 CTL peptides derived from respiratory syncytial virus fusion protein in HLA-A2 transgenic mouse

Identification of HLA-restricted CD8⁺ T cell epitopes is important to study RSV-induced immunity and illness. We algorithmically analyzed the sequence of the fusion protein (F) of respiratory syncytial virus (RSV) and generated synthetic peptides that can potentially bind to HLA-A*0201. Four out of the twenty-five 9-mer peptides tested: peptides 3 (F33–41), 13 (F214–222), 14 (F273–281), and 23 (F559–567), were found to bind to HLA-A*0201 with moderate to high affinity and were capable of inducing IFN-γ and IL-2 secretion in lymphocytes from HLA-A*0201 transgenic (HLA-Tg) mice pre-immunized with RSV or recombinant adenovirus expressing RSV F. HLA-Tg mice were immunized with these four peptides and were found to induce both Th1 and CD8⁺ T cell responses in in vitro secondary recall. Effector responses induced by these peptides were observed to confer differential protection against live RSV challenge. These peptides also caused better recovery of body weight loss induced by RSV. A significant reduction of lung viral load was observed in mice immunized with peptide 23, which appeared to enhance the levels of inflammatory chemokines (CCL17, CCL22, and IL-18) but did not increase eosinophil infiltration in the lungs. Whereas, significant reduction of infiltrated eosinophils induced by RSV infection was found in mice pre-immunized with peptide 13. Our results suggest that HLA-A2-restricted epitopes of RSV F protein could be useful for the development of epitope-based RSV vaccine.

Transforming growth factor beta is a major regulator of human neonatal immune responses following respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a major cause of morbidity and mortality. Previous studies have suggested that T-cell responses may contribute to RSV immunopathology, which could be driven by dendritic cells (DCs). DCs are productively infected by RSV, and during RSV infections, there is an increase of DCs in the lungs with a decrease in the blood. Pediatric populations are particularly susceptible to severe RSV infections; however, DC responses to RSV from pediatric populations have not been examined. In this study, primary isolated DCs from cord blood and adult peripheral blood were compared after RSV infection. Transcriptional profiling and biological network analysis identified transforming growth factor beta (TGF-β) and associated signaling molecules as differentially regulated in the two age groups. TGF-β1 was decreased in RSV-infected adult-blood DCs but increased in RSV-infected cord blood DCs. Coculture of adult RSV-infected DCs with autologous T cells induced secretion of gamma interferon (IFN-γ), interleukin 12p70 (IL-12p70), IL-2, and tumor necrosis factor alpha (TNF-α). Conversely, coculture of cord RSV-infected DCs and autologous T cells induced secretion of IL-4, IL-6, IL-1β, and IL-17. Addition of purified TGF-β1 to adult DC-T-cell cocultures reduced secretion of IFN-γ, IL-12p70, IL-2, and TNF-α, while addition of a TGF-β chemical inhibitor to cord DC-T-cell cocultures increased secretion of IL-12p70. These data suggest that TGF-β acts as a major regulator of RSV DC-T-cell responses, which could contribute to immunopathology during infancy.

Mucosal delivery of human papillomavirus pseudovirus-encapsidated plasmids improves the potency of DNA vaccination

Mucosal immunization may be important for protection against pathogens whose transmission and pathogenesis target the mucosal tissue. The capsid proteins of human papillomavirus (HPV) confer tropism for the basal epithelium and can encapsidate DNA during self-assembly to form pseudovirions (PsVs). Therefore, we produced mucosal vaccine vectors by HPV PsV encapsidation of DNA plasmids expressing an experimental antigen derived from the M and M2 proteins of respiratory syncytial virus (RSV). Intravaginal (IVag) delivery elicited local and systemic M-M2-specific CD8+ T-cell and antibody responses in mice that were comparable to an approximately 10,000-fold higher dose of naked DNA. A single HPV PsV IVag immunization primed for M-M2-specific-IgA in nasal and vaginal secretions. Based on light emission and immunofluorescent microscopy, immunization with HPV PsV-encapsidated luciferase- and red fluorescent protein (RFP)-expressing plasmids resulted in transient antigen expression (<5 days), which was restricted to the vaginal epithelium. HPV PsV encapsidation of plasmid DNA is a novel strategy for mucosal immunization that could provide new vaccine options for selected mucosal pathogens.

Skin inflammation arising from cutaneous regulatory T cell deficiency leads to impaired viral immune responses

Individuals with atopic dermatitis immunized with the small pox vaccine, vaccinia virus (VV), are susceptible to eczema vaccinatum (EV), a potentially fatal disseminated infection. Dysfunction of Forkhead box P3 (FoxP3)-positive regulatory T cells (Treg) has been implicated in the pathogenesis of atopic dermatitis. To test whether Treg deficiency predisposes to EV, we percutaneously VV infected FoxP3-deficient (FoxP3(KO)) mice, which completely lack FoxP3(+) Treg. These animals generated both fewer VV-specific CD8(+) effector T cells and IFN-gamma-producing CD8(+) T cells than controls, had higher viral loads, and exhibited abnormal Th2-polarized responses to the virus. To focus on the consequences of Treg deficiency confined to the skin, we generated mixed CCR4(KO) FoxP3(KO) bone marrow (CCR4/FoxP3) chimeras in which skin, but not other tissues or central lymphoid organs, lack Treg. Like FoxP3(KO) mice, the chimeras had impaired VV-specific effector T cell responses and higher viral loads. Skin cytokine expression was significantly altered in infected chimeras compared with controls. Levels of the antiviral cytokines, type I and II IFNs and IL-12, were reduced, whereas expression of the proinflammatory cytokines, IL-6, IL-10, TGF-beta, and IL-23, was increased. Importantly, infection of CCR4/FoxP3 chimeras by a noncutaneous route (i.p.) induced immune responses comparable to controls. Our findings implicate allergic skin inflammation resulting from local Treg deficiency in the pathogenesis of EV.

Characterization of respiratory syncytial virus M- and M2-specific CD4 T cells in a murine model

CD4 T cells have been shown to play an important role in the immunity and immunopathogenesis of respiratory syncytial virus (RSV) infection. We identified two novel CD4 T-cell epitopes in the RSV M and M2 proteins with core sequences M(213-223) (FKYIKPQSQFI) and M2(27-37) (YFEWPPHALLV). Peptides containing the epitopes stimulated RSV-specific CD4 T cells to produce gamma interferon (IFN-gamma), interleukin 2 (IL-2), and other Th1- and Th2-type cytokines in an I-A(b)-restricted pattern. Construction of fluorochrome-conjugated peptide-I-A(b) class II tetramers revealed RSV M- and M2-specific CD4 T-cell responses in RSV-infected mice in a hierarchical pattern. Peptide-activated CD4 T cells from lungs were more activated and differentiated, and had greater IFN-gamma expression, than CD4 T cells from the spleen, which, in contrast, produced greater levels of IL-2. In addition, M(209-223) peptide-activated CD4 T cells reduced IFN-gamma and IL-2 production in M- and M2-specific CD8 T-cell responses to D(b)-M(187-195) and K(d)-M2(82-90) peptides more than M2(25-39) peptide-stimulated CD4 T cells. This correlated with the fact that I-A(b)-M(209-223) tetramer-positive cells responding to primary RSV infection had a much higher frequency of FoxP3 expression than I-A(b)-M2(26-39) tetramer-positive CD4 T cells, suggesting that the M-specific CD4 T-cell response has greater regulatory function. Characterization of epitope-specific CD4 T cells by novel fluorochrome-conjugated peptide-I-A(b) tetramers allows detailed analysis of their roles in RSV pathogenesis and immunity.

Vaccination of calves using the BRSV nucleocapsid protein in a DNA prime-protein boost strategy stimulates cell-mediated immunity and protects the lungs against BRSV replication and pathology

Respiratory syncytial virus (RSV) is a major cause of respiratory disease in both cattle and young children. Despite the development of vaccines against bovine (B)RSV, incomplete protection and exacerbation of subsequent RSV disease have occurred. In order to circumvent these problems, calves were vaccinated with the nucleocapsid protein, known to be a major target of CD8⁺ T cells in cattle. This was performed according to a DNA prime–protein boost strategy. The results showed that DNA vaccination primed a specific T-cell-mediated response, as indicated by both a lymphoproliferative response and IFN-γ production. These responses were enhanced after protein boost. After challenge, mock-vaccinated calves displayed gross pneumonic lesions and viral replication in the lungs. In contrast, calves vaccinated by successive administrations of plasmid DNA and protein exhibited protection against the development of pneumonic lesions and the viral replication in the BAL fluids and the lungs. The protection correlated to the cell-mediated immunity and not to the antibody response.

Understanding the mechanisms of viral induced asthma: new therapeutic directions

Asthma is a common and debilitating disease that has substantially increased in prevalence in Western Societies in the last 2 decades. Respiratory tract infections by respiratory syncytial virus (RSV) and rhinovirus (RV) are widely implicated as common causes of the induction and exacerbation of asthma. These infections in early life are associated with the induction of wheeze that may progress to the development of asthma. Infections may also promote airway inflammation and enhance T helper type 2 lymphocyte (Th2 cell) responses that result in exacerbations of established asthma. The mechanisms of how RSV and RV induce and exacerbate asthma are currently being elucidated by clinical studies, in vitro work with human cells and animal models of disease. This research has led to many potential therapeutic strategies and, although none are yet part of clinical practise, they show much promise for the prevention and treatment of viral disease and subsequent asthma.

Interleukin-4 impairs granzyme-mediated cytotoxicity of Simian virus 40 large tumor antigen-specific CTL in BALB/c mice

In this report we analyzed the impact of interleukin-4 (IL-4) on tumor-associated simian virus 40 (SV40) large T-antigen (TAg)-specific CD8+ cytotoxic T cells during rejection of syngeneic SV40 transformed mKSA tumor cells in BALB/c mice. Strikingly, challenge of naïve mice with low doses of mKSA tumor cells revealed a CD8+ T cell-dependent prolonged survival time of naïve IL-4-/- mice. In mice immunized with SV40 TAg we observed in IL-4-/- mice, or in wild type mice treated with neutralizing anti-IL-4 monoclonal antibody, a strongly enhanced TAg-specific cytotoxicity of tumor associated CD8+ T cells. The enhanced cytotoxicity in IL-4-/- mice was accompanied by a significant increase in the fraction of CD8+ tumor associated T-cells expressing the cytotoxic effector molecules granzyme A and B and in granzyme B-specific enzymatic activity. The data suggest that endogenous IL-4 can suppress the generation of CD8+ CTL expressing cytotoxic effector molecules especially when the antigen induces only a very weak CTL response.

Virally delivered cytokines alter the immune response to future lung infections

Respiratory syncytial virus (RSV) is an important cause of infant morbidity and mortality worldwide and is increasingly recognized to have a role in the development and exacerbation of chronic lung diseases. There is no effective vaccine, and we reasoned that it might be possible to skew the immune system towards beneficial nonpathogenic responses by selectively priming protective T-cell subsets. We therefore tested recombinant RSV (rRSV) candidates expressing prototypic murine Th1 (gamma interferon [IFN-gamma]) or Th2 (interleukin-4 [IL-4]) cytokines, with detailed monitoring of responses to subsequent infections with RSV or (as a control) influenza A virus. Although priming with either recombinant vector reduced viral load during RSV challenge, enhanced weight loss and enhanced pulmonary influx of RSV-specific CD8+ T cells were observed after challenge in mice primed with rRSV/IFN-gamma. By contrast, rRSV/IL-4-primed mice were protected against weight loss during secondary challenge but showed airway eosinophilia. When rRSV/IL-4-primed mice were challenged with influenza virus, weight loss was attenuated but was again accompanied by marked airway eosinophilia. Thus, immunization directed toward enhancement of Th1 responses reduces viral load but is not necessarily protective against disease. Counter to expectation, Th2-biased responses were more beneficial but also influenced the pathological effects of heterologous viral challenge.

Local immune response to respiratory syncytial virus infection is diminished in senescence-accelerated mice

The effect of ageing on the local defence system against respiratory syncytial virus (RSV) infection was investigated using an aged mouse model of the senescence-accelerated mouse (SAM) strain P1. Following intranasal infection with RSV, SAM-P1 mice showed a marked loss in weight, with elevated virus growth in the lungs and prolonged virus shedding. The increased susceptibility to RSV infection was associated mainly with diminished cellular immunity by local virus-specific cytotoxic T lymphocytes and natural killer cells. The deficiency in cellular immune responses was due to a lack of clonal expansion of CD4+ and CD8+ T lymphocytes, together with an imbalance of T-helper type 1 (Th1)/Th2 cytokine production in the respiratory tract, including the lungs. Furthermore, the production of virus-specific local IgA antibody was restrained. Prolonged virus loading in the lungs of SAM-P1 mice caused a massive infiltration of CD16+/32+ inflammatory cells, which was one factor responsible for severe pneumonia. The adoptive transfer of immune-competent spleen cells achieved an appreciable protection for SAM-P1 mice against RSV challenge infection. These results suggested that age-related immune dysfunction, especially defects in cellular immune responses, accounts for the increased morbidity and mortality in RSV infection of the elderly.

Human and bovine respiratory syncytial virus vaccine research and development

Human (HRSV) and bovine (BRSV) respiratory syncytial viruses (RSV) are two closely related viruses, which are the most important causative agents of respiratory tract infections of young children and calves, respectively. BRSV vaccines have been available for nearly 2 decades. They probably have reduced the prevalence of RSV infection but their efficacy needs improvement. In contrast, despite decades of research, there is no currently licensed vaccine for the prevention of HRSV disease. Development of a HRSV vaccine for infants has been hindered by the lack of a relevant animal model that develops disease, the need to immunize immunologically immature young infants, the difficulty for live vaccines to find the right balance between attenuation and immunogenicity, and the risk of vaccine-associated disease. During the past 15 years, intensive research into a HRSV vaccine has yielded vaccine candidates, which have been evaluated in animal models and, for some of them, in clinical trials in humans. Recent formulations have focused on subunit vaccines with specific CD4+ Th-1 immune response-activating adjuvants and on genetically engineered live attenuated vaccines. It is likely that different HRSV vaccines and/or combinations of vaccines used sequentially will be needed for the various populations at risk. This review discusses the recent advances in RSV vaccine development.

Cutting Edge: Oseltamivir decreases T cell GM1 expression and inhibits clearance of respiratory syncytial virus: potential role of endogenous sialidase in antiviral immunity

The sialoglycosphingolipid GM1 is important for lipid rafts and immune cell signaling. T cell activation in vitro increases GM1 expression and increases endogenous sialidase activity. GM1 expression has been hypothesized to be regulated by endogenous sialidase. We tested this hypothesis in vivo using a mouse model of respiratory syncytial virus (RSV) infection. RSV infection increased endogenous sialidase activity in lung mononuclear cells. RSV infection increased lung CD8+ T cell surface GM1 expression. Activated CD8+ T cells in the lungs of RSV-infected mice were GM1(high). Treatment of RSV-infected mice with the sialidase/neuraminidase inhibitor oseltamivir decreased T cell surface GM1 levels. Oseltamivir treatment decreased RSV-induced weight loss and inhibited RSV clearance. Our data indicate a novel role for an endogenous sialidase in regulating T cell GM1 expression and antiviral immunity. Also, oseltamivir, an important anti-influenza drug, inhibits the clearance of a respiratory virus that lacks a neuraminidase gene, RSV.

Skin inflammation in RelB−/− mice leads to defective immunity and impaired clearance of vaccinia virus

BACKGROUND

Atopic dermatitis (AD) is an inflammatory skin disorder occurring in genetically predisposed individuals with a systemic T(H)2 bias. Atopic dermatitis patients exposed to the smallpox vaccine, vaccinia virus (VV), occasionally develop eczema vaccinatum (EV), an overwhelming and potentially lethal systemic infection with VV.

OBJECTIVE

To establish a murine model of EV and examine the effects of skin inflammation on VV immunity.

METHODS

The skin of RelB(-/-) mice, like that of chronic AD lesions in humans, exhibits thickening, eosinophilic infiltration, hyperkeratosis, and acanthosis. RelB(-/-) and wild-type (WT) control mice were infected with VV via skin scarification. Viral spread, cytokine levels, IgG2a responses and VV-specific T cells were measured.

RESULTS

Cutaneously VV-infected RelB(-/-), but not WT mice, exhibited weight loss, markedly impaired systemic clearance of the virus and increased contiguous propagation from the inoculation site. This was associated with a dramatically impaired generation of IFN-gamma-producing CD8(+) vaccinia-specific T cells along with decreased secretion of IFN-gamma by VV-stimulated splenocytes. The T(H)2 cytokines-IL-4, IL-5, IL-13, and IL-10-on the other hand, were overproduced. When infected intraperitoneally, RelB(-/-) mice generated robust T cell responses with good IFN-gamma production.

CONCLUSION

Allergic inflammation in RelB(-/-) mice is associated with dysregulated immunity to VV encountered via the skin. We speculate that susceptibility of AD patients to overwhelming vaccinia virus infection is similarly related to ineffective T cell responses.

CLINICAL IMPLICATIONS

The susceptibility of patients with AD to EV following cutaneous contact with VV is related to ineffective antiviral immune responses.

IL-13 is associated with reduced illness and replication in primary respiratory syncytial virus infection in the mouse

The role of IL-13 in respiratory syncytial virus (RSV) immunopathogenesis is incompletely described. To assess the effect of IL-13 on primary RSV infection, transgenic mice which either overexpress IL-13 in the lung (IL-13 OE) or non-transgenic littermates (IL-13 NT) were challenged intranasally with RSV. IL-13 OE mice had significantly decreased peak viral titers four days after infection compared to non-transgenic littermates. In addition, IL-13 OE mice had significantly lower RSV-induced weight loss and reduced lung IFN-γ protein expression compared with IL-13 NT mice. In contrast, primary RSV challenge of IL-13 deficient mice resulted in a small, but statistically significant increase in viral titers on day four after infection, no difference in RSV-induced weight loss compared to wild type mice, and augmented IFN-γ production on day 6 after infection. In STAT1-deficient (STAT1 KO) mice, where primary RSV challenge produced high levels of IL-13 production in the lungs, treatment with an IL-13 neutralizing protein resulted in greater peak viral titers both four and six days after RSV and greater RSV-induced weight loss compared to mice treated with a control protein. These results suggest that IL-13 modulates illness from RSV-infection.

IL-4 influences the differentiation and the susceptibility to activation-induced cell death of human naive CD8+ T cells

It is now well established that the cytokine environment influences the activation, differentiation, proliferation and death of T lymphocytes during the primary response to antigen. Using an in vitro model, we investigated the influence of IL-4, added at the onset of TCR stimulation, on phenotypic and functional markers of naive CD8+ T cell activation including the up-regulation of activation markers, proliferation as well as the susceptibility to activation-induced cell death (AICD). We report that IL-4, unlike IL-2 added at the onset of repeated TCR stimulation of naive CD8+ T cells prevents AICD, in part due to its ability to maintain the level of the survival-related protein Bcl-2. Moreover, TCR-triggered activation of naive CD8+ T cells in the presence of IL-4 leads to the development of a CD8+ T cell subset that proliferates normally, but which fails to exhibit characteristic activation parameters such as the up-regulation of CD25 and Granzyme B. Taken together, these results demonstrate that exposure to IL-4 during primary activation influences CD8+ T cell differentiation by inducing the development of a sub-population of AICD-resistant, proliferation-competent cells that do not show some of the typical features of CD8+ T cell activation.

The balance between influenza- and RSV-specific CD4 T cells secreting IL-10 or IFNgamma in young and healthy-elderly subjects

Respiratory syncytial virus (RSV) and influenza virus cause severe disease in elderly patients. The balance of pro- and anti-inflammatory cytokines may be critical in determining disease pathogenesis and outcome of infection. The frequencies of CD4 IL-10 (anti-inflammatory)- and CD4 and CD8 IFNgamma (pro-inflammatory)-secreting memory T cells specific for either RSV or influenza were not significantly different between young and elderly groups, although the ratio of IL-10/IFNgamma was significantly reduced in the elderly RSV response. A similar trend was seen for influenza. IFNgamma-secreting CD4 T cells contributed significantly more to anti-RSV than anti-influenza responses in both groups.

IL-2 production by dendritic cells is not critical for the activation of cognate and innate effectors in draining lymph nodes

Dendritic cells (DC) are unique antigen-presenting cells capable of triggering NK cell effector functions and priming naive T cells in vivo. Microbial stimulation induces early IL-2 production by mouse DC. Previous reports demonstrated that IL-2 is enriched at the site of DC/T cell interaction and promotes allogeneic T cell proliferation. However, the direct role of DC-derived IL-2 in the differentiation of cytotoxic T lymphocytes and in NK cell triggering in vivo has not been investigated. Lipopolysaccharide (LPS) stimulation of mouse bone marrow-derived DC results in early IL-2 production unless IL-4 is introduced in DC cultures. Here we show that IL-2 produced by LPS-activated DC is dispensable for cognate T cell responses since IL-2 loss of function DC elicit OVA-specific Tc1 effector and memory lymphocytes in draining lymph nodes in a setting where ex vivo cultured DC do not transfer antigens to host DC. Moreover, adoptively transferred IL-2 loss of function DC maintain their capacity to trigger NK cell proliferation/recruitment in lymph nodes. Therefore, immediate inducible IL-2 production by DC following microbial infection might play a regulatory role at ports of entry rather than in secondary lymphoid organs.

Expression of interleukin-4 by recombinant respiratory syncytial virus is associated with accelerated inflammation and a nonfunctional cytotoxic T-lymphocyte response following primary infection but not following challenge with wild-type virus

The outcome of a viral infection or of immunization with a vaccine can be influenced by the local cytokine environment. In studies of experimental vaccines against respiratory syncytial virus (RSV), an increased stimulation of Th2 (T helper 2) lymphocytes was associated with increased immunopathology upon subsequent RSV infection. For this study, we investigated the effect of increased local expression of the Th2 cytokine interleukin-4 (IL-4) from the genome of a recombinant RSV following primary infection and after a challenge with wild-type (wt) RSV. Mice infected with RSV/IL-4 exhibited an accelerated pulmonary inflammatory response compared to those infected with wt RSV, although the wt RSV group caught up by day 8. In the first few days postinfection, RSV/IL-4 was associated with a small but significant acceleration in the expansion of pulmonary T lymphocytes specific for an RSV CD8(+) cytotoxic T-lymphocyte (CTL) epitope presented as a major histocompatibility complex class I tetramer. However, by day 7 the response of tetramer-positive T lymphocytes in the wt RSV group caught up and exceeded that of the RSV/IL-4 group. At all times, the CTL response of the RSV/IL-4 group was deficient in the production of gamma interferon and was nonfunctional for in vitro cell killing. The accelerated inflammatory response coincided with an accelerated accumulation and activation of pulmonary dendritic cells early in infection, but thereafter the dendritic cells were deficient in the expression of B7-1, which governs the acquisition of cytolytic activity by CTL. Following a challenge with wt RSV, there was an increase in Th2 cytokines in the animals that had previously been infected with RSV/IL-4 compared to those previously infected with wt RSV, but the CD8(+) CTL response and the amount of pulmonary inflammation were not significantly different. Thus, a strong Th2 environment during primary pulmonary immunization with live RSV resulted in early inflammation and a largely nonfunctional primary CTL response but had a minimal effect on the secondary response.

The ‘supervirus’? Lessons from IL-4-expressing poxviruses

Members of the Poxviridae family are particularly adept at avoiding the host immune system, encoding a plethora of immunomodulatory proteins that subvert host defense. With their large genome, poxviruses are also useful for studying the effect of exogenous genes on virus-host interactions and immune responses. The insertion of the Th2 cytokine interleukin-4 (IL-4) into several poxviruses significantly increases the efficiency of the recombinant virus as a pathogen by directly inhibiting the development of Th1 immunity, which is crucial for viral clearance. In an age in which the fear of genetically modified weaponized pathogens exists, the understanding of how to make viruses more pathogenic further blurs the distinction between fundamental academic research and bioweapons development. Here, the extent of immune evasion by IL-4-expressing poxviruses will be explored, as will the consequences of this increased pathogenicity on protective immune responses.

Progressive differentiation and commitment of CD8+ T cells to a poorly cytolytic CD8low phenotype in the presence of IL-4

Exposure to IL-4 during activation of naive murine CD8+ T cells leads to generation of IL-4-producing effector cells with reduced surface CD8, low perforin, granzyme B and granzyme C mRNA, and poor cytolytic function. We show in this study that maximal development of these cells depended on exposure to IL-4 for the first 5 days of activation. Although IL-4 was not required at later times, CD8 T cell clones continued to lose surface CD8 expression with prolonged culture, suggesting commitment to the CD8low phenotype. This state was reversible in early differentiation. When single CD8low cells from 4-day cultures were cultured without IL-4, 65% gave rise to clones that partly or wholly comprised CD8high cells; the proportion of reverted clones was reduced or increased when the cells were cloned in the presence of IL-4 or anti-IL-4 Ab, respectively. CD8 expression positively correlated with perforin and granzyme A, B, and C mRNA, and negatively correlated with IL-4 mRNA levels among these clones. By contrast, most CD8low cells isolated at later time points maintained their phenotype, produced IL-4, and exhibited poor cytolytic function after many weeks in the absence of exogenous IL-4. We conclude that IL-4-dependent down-regulation of CD8 is associated with progressive differentiation and commitment to yield IL-4-producing cells with little cytolytic activity. These data suggest that the CD4-CD8- cells identified in some disease states may be the product of a previously unrecognized pathway of effector differentiation from conventional CD8+ T cells.

Modified vaccinia virus Ankara immunization protects against lethal challenge with recombinant vaccinia virus expressing murine interleukin-4

Recent events have raised concern over the use of pathogens, including variola virus, as biological weapons. Vaccination with Dryvax is associated with serious side effects and is contraindicated for many people, and the development of a safer effective smallpox vaccine is necessary. We evaluated an attenuated vaccinia virus, modified vaccinia virus Ankara (MVA), by use of a murine model to determine its efficacy against an intradermal (i.d.) or intranasal (i.n.) challenge with vaccinia virus (vSC8) or a recombinant vaccinia virus expressing murine interleukin-4 that exhibits enhanced virulence (vSC8-mIL4). After an i.d. challenge, 15 of 16 mice who were inoculated with phosphate-buffered saline developed lesions, one dose of intramuscularly administered MVA was partially protective (3 of 16 mice developed lesions), and the administration of two or three doses of MVA was completely protective (0 of 16 mice developed lesions). In unimmunized mice, an i.n. challenge with vSC8 caused a significant but self-limited illness, while vSC8-mIL4 resulted in lethal infections. Immunization with one or two doses of MVA prevented illness and reduced virus titers in mice who were challenged with either vSC8 or vSC8-mIL4. MVA induced a dose-related neutralizing antibody and vaccinia virus-specific CD8+-T-cell response. Mice immunized with MVA were fully protected from a low-dose vSC8-mIL4 challenge despite a depletion of CD4+ cells, CD8+ cells, or both T-cell subsets or an antibody deficiency. CD4+- or CD8+-T-cell depletion reduced the protection against a high-dose vSC8-mIL4 challenge, and the depletion of both T-cell subsets was associated with severe illness and higher vaccinia virus titers. Thus, MVA induces broad humoral and cellular immune responses that can independently protect against a molecularly modified lethal poxvirus challenge in mice. These data support the continued development of MVA as an alternative candidate vaccine for smallpox.

Prolonged production of TNF-alpha exacerbates illness during respiratory syncytial virus infection

CD8(+) CTL are the main effector cells responsible for resolving viral infections. However, the CTL response to respiratory syncytial virus (RSV) infection in mice facilitates viral clearance at the expense of significant immunopathology. Previous reports have shown a strong correlation between the mechanism of CTL activity and the severity of RSV-induced illness. Furthermore, experiments in perforin knockout mice revealed that antiviral cytokine production temporally correlated with RSV-induced illness. In the current study, we show that TNF-alpha is the dominant mediator of RSV-associated illness, and it is also important for clearance of virus-infected cells during the early stages of infection. We also demonstrate that IFN-gamma plays a protective role in conjunction with perforin/granzyme-mediated killing. Preliminary experiments in gld mice that express nonfunctional Fas ligand (FasL) revealed that RSV-induced illness is significantly reduced in the absence of FasL-mediated killing. Antiviral cytokine production was not elevated in the absence of FasL, suggesting a possible link between FasL and antiviral cytokine activity. This work shows that multiple phenotypic subsets of CD8(+) CTLs respond to RSV infection, each with varying capacities for clearance of virus-infected cells and the induction of illness. In addition, the revelation that TNF-alpha is the principal mediator of RSV-induced illness means that administration of TNF receptor antagonists, in combination with antiviral therapy, may be an effective method to treat RSV infections.

Pathogenesis of Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is recognized as the most important cause of serious lower respiratory tract illness in infants and young children worldwide causing repeat infections throughout life with serious complications occurring in the elderly and immune compromised patient. The level of disease pathogenesis associated with RSV infection is balanced between virus elimination and the nature of the immune response to infection. The innate and adaptive immune responses to RSV infection are not fully elucidated; however, significant progress has been made in understanding the virus-host relationship and mechanisms associated with disease pathogenesis. This review summarizes important aspects of these findings, and provides current perspective on processes that may contribute to RSV disease pathogenesis.

Treatment with anti-LFA-1 delays the CD8+ cytotoxic-T-lymphocyte response and viral clearance in mice with primary respiratory syncytial virus infection

Cytotoxic T lymphocytes (CTLs) play an important role in the immune response against respiratory syncytial virus (RSV) infection. The cell surface molecule lymphocyte function-associated antigen 1 (LFA-1) is an important contributor to CTL activation, CTL-mediated direct cell lysis, and lymphocyte migration. In an attempt to determine the role of LFA-1 during RSV infection, we treated BALB/c mice with monoclonal antibodies to LFA-1 at days -1, +1, and +4 relative to primary RSV infection. Anti-LFA-1 treatment during primary RSV infection led to reduced illness and delayed clearance of virus-infected cells. CTLs from RSV-infected mice that were treated with anti-LFA-1 exhibited diminished cytolytic activity and reduced gamma interferon production. In addition, studies with BrdU (5-bromo-2'-deoxyuridine)- and CFSE [5-(and 6)-carboxyfluorescein diacetate succinimidyl ester]-labeled lymphocytes showed that anti-LFA-1 treatment led to delayed proliferation during RSV infection. These results indicate that LFA-1 plays a critical role in the initiation of the immune response to RSV infection by facilitating CTL activation. These results may prove useful in the development of new therapies to combat RSV infection or other inflammatory diseases.

Profiling the CD8lowphenotype, an alternative career choice for CD8 T cells during primary differentiation

A CD8+ T cell of naive phenotype has multiple career choices during its primary differentiation into an effector cell population. One of these career options is becoming a CD8low T cell. We have previously shown by in vitro studies that CD8low T cells have lost expression of CD8 surface protein and mRNA and are poorly cytolytic. In line with poor cytolytic function, CD8low T cells express low levels of perforin and granzyme B and C, mediators of the granule-exocytosis machinery. However, CD8low T cells express IFN-gamma and substantial amounts of IL-4, the signature cytokines of type 1 and type 2 T-cell polarization, respectively. Here, we argue that the CD8low phenotype is an alternative career choice for any naive CD8+ T cell during primary activation but that the probability of choosing this option is greatly enhanced by both IL-4 and strong activation conditions. CD8low T cells have downregulated CD8 alpha/beta heterodimers and no preferential CD8 alpha/alpha homodimer expression. As shown by anti-CD8 Ab blocking experiments, surface CD8 substantially contributes to the CD8 T cell's effector function (i.e. cytokine expression and cytolytic activity). The distinct effector profile of CD8low T cells gives an example of the complexity of different CD8 T cell careers during primary effector differentiation.

Tetracycline-inducible packaging cell line for production of flavivirus replicon particles

We have previously developed replicon vectors derived from the Australian flavivirus Kunjin that have a unique noncytopathic nature and have been shown to direct prolonged high-level expression of encoded heterologous genes in vitro and in vivo and to induce strong and long-lasting immune responses to encoded immunogens in mice. To facilitate further applications of these vectors in the form of virus-like particles (VLPs), we have now generated a stable BHK packaging cell line, tetKUNCprME, carrying a Kunjin structural gene cassette under the control of a tetracycline-inducible promoter. Withdrawal of tetracycline from the medium resulted in production of Kunjin structural proteins that were capable of packaging transfected and self-amplified Kunjin replicon RNA into the secreted VLPs at titers of up to 1.6 x 10(9) VLPs per ml. Furthermore, secreted KUN replicon VLPs from tetKUNCprME cells could be harvested continuously for as long as 10 days after RNA transfection, producing a total yield of more than 10(10) VLPs per 10(6) transfected cells. Passaging of VLPs on Vero cells or intracerebral injection into 2- to 4-day-old suckling mice illustrated the complete absence of any infectious Kunjin virus. tetKUNCprME cells were also capable of packaging replicon RNA from closely and distantly related flaviviruses, West Nile virus and dengue virus type 2, respectively. The utility of high-titer KUN replicon VLPs was demonstrated by showing increasing CD8(+)-T-cell responses to encoded foreign protein with increasing doses of KUN VLPs. A single dose of 2.5 x 10(7) VLPs carrying the human respiratory syncytial virus M2 gene induced 1,400 CD8 T cells per 10(6) splenocytes in an ex vivo gamma interferon enzyme-linked immunospot assay. The packaging cell line thus represents a significant advance in the development of the noncytopathic Kunjin virus replicon-based gene expression system and may be widely applicable to the basic studies of flavivirus RNA packaging and virus assembly as well as to the development of gene expression systems based on replicons from different flaviviruses.

Cytokine pattern is solely influenced by priming vaccine but immunity and disease by both priming and boosting vaccines in mice challenged with respiratory syncytial virus

Vaccine formulation can influence cytokine and disease patterns in mice following respiratory syncytial virus (RSV) challenge. The influence of different live and killed dual-vaccine combinations on subsequent immune responses was investigated. BALB/c mice received either killed followed by killed (KV/KV), killed followed by live (KV/LV), live followed by killed (LV/KV), or live followed by live (LV/LV) RSV vaccines intramuscularly. Mouse weight loss, viral replication, cytokine expression patterns, immunoglobulin isotype antibody profiles, neutralizing antibody responses, and cytotoxicity T lymphocyte (CTL) activities in lungs were compared on subsequent live RSV challenge. On challenge, mice vaccinated initially with KV and boosted with either KV or LV expressed significantly skewed ratios of IL-4 to IFN-gamma mRNA and IgG1 to IgG2a antibody, when compared to those vaccinated initially with LV. Low levels of RSV replication were detected in lungs of mice vaccinated with KV/KV, KV/LV, and LV/KV, but not in mice vaccinated with LV/LV. Mice vaccinated with KV/LV, LV/KV, or LV/LV had RSV-specific CTL activity in lungs six days after RSV challenge, while no CTL activity was detected in KV/KV-vaccinated mice. Mice vaccinated with KV/KV had the greatest weight loss, while LV/LV-vaccinated mice resulted in the least. Mice vaccinated with either KV/LV or LV/KV had intermediate weight loss after challenge. These data indicate that an original antigenic sin-like phenomenon was exhibited in cytokine and immunoglobulin isotype responses in mice after challenge. T helper (Th)-like immune responses were determined solely by the initial vaccination, while weight loss, viral replication, neutralizing antibody responses, and CTL activities were also influenced by boosted vaccinations.

Are rhinovirus-induced airway responses in asthma aggravated by chronic allergen exposure?

Airway inflammation in asthma may represent a favorable environment for respiratory viral infections, augmenting virus-induced exacerbations in asthma. We postulated that repeated low-dose allergen exposure preceding experimental rhinovirus 16 (RV16) infection increases the severity of RV-induced airway obstruction and inflammation. Thirty-six house dust mite-allergic patients with mild to moderate asthma participated in a three-arm, parallel, placebo-controlled, double-blind study. Patients inhaled a low dose of house dust mite allergen for 10 subsequent working days (Days 1-5 and 8-12) and/or were subsequently infected with RV16 (Days 15 and 16). Allergen exposure resulted in a significant fall in FEV1 (p < 0.001) and provocative concentration of histamine causing a 20% fall in FEV1 (p < 0.001) and an increase in exhaled nitric oxide (p < 0.001) and percentage of sputum eosinophils (p < 0.001). RV16 infection led to a fall in FEV1 (p = 0.02) and increases in the percentage of sputum neutrophils (p = 0.01), sputum interleukin-8 (p = 0.04), and neutrophil elastase (p = 0.04). Successive allergen exposure and RV16 infection had no synergistic or additive effect on any of the clinical or inflammatory outcomes. In conclusion, repeated low-dose allergen exposure and RV16 infection induce distinct inflammatory profiles within the airways in asthma without apparent interaction between these two environmental triggers. This suggests that preceding allergen exposure, at the used dose and duration, is not a determinant of the severity of RV-induced exacerbations in patients with mild to moderate asthma.

Type 1 and type 2 cytokine imbalance in acute respiratory syncytial virus bronchiolitis

We examined the in vivo immune response of infants to natural respiratory syncytial virus (RSV) infection through analysis of cytokine levels in nasal lavage fluid and stimulated peripheral blood mononuclear cells. Eighty-eight babies with at least one parent with atopy and asthma were prospectively studied through their first winter. Twenty-eight infants had an upper respiratory tract infection where RSV was detected, of whom nine developed signs of acute bronchiolitis. Nasal lavage specimens were assayed for interferon-gamma, interleukin (IL)-4, IL-10, and IL-12 and the RSV load determined by quantitative polymerase chain reaction. Messenger RNA (mRNA) was extracted from stimulated peripheral blood mononuclear cells and interferon-gamma, IL-4, IL-12, and IL-18 mRNA levels determined by polymerase chain reaction. Cytokine profiles were analyzed in relation to clinical outcome. The IL-4/interferon-gamma ratio for infants with acute bronchiolitis was elevated in nasal lavage fluid on both Days 1-2 (p = 0.014) and Days 5-7 (p = 0.001) of the illness compared with infants with upper respiratory tract infection alone. Those with acute bronchiolitis demonstrated a higher IL-10/IL-12 ratio (p = 0.0015) on Days 1-2. IL-18 mRNA levels were reduced (p = 0.019) and the IL-4/interferon-gamma ratio elevated (p = 0.01) in stimulated peripheral blood mononuclear cells from infants with acute bronchiolitis. There was no difference in initial RSV load. These data strongly implicate excess type 2 and/or deficient type 1 immune responses in the pathogenesis of RSV bronchiolitis.

Interleukin-4-mediated downregulation of cytotoxic T lymphocyte activity is associated with reduced proliferation of antigen-specific CD8+ T cells

During virus infection, exogenous IL-4 strongly downregulates expression of antiviral cytokines and cytotoxic T lymphocyte (CTL) responses. In this study, we have employed a T cell receptor (TCR) transgenic system to more closely investigate the effect of IL-4 on CTL activity. This system involves mice transgenic for an H2-Kb restricted TCR recognising an ovalbumin (OVA)-specific peptide (OT-I mice), and recombinant vaccinia viruses expressing the gene for OVA (VV-OVA), or OVA together with IL-4 (VV-OVA-IL-4). Spleen cells from OT-I mice were adoptively transferred to irradiated C57BL/6 mice infected with VV-OVA or VV-OVA-IL-4. Five days following transfer, markedly stronger CTL activity was detected in VV-OVA- than in VV-OVA-IL-4-infected recipients. The reduction in CTL activity was associated with a reduction in the number of OVA-specific CD8+ T cells. Proliferation of cells from VV-OVA-IL-4-infected recipients was dramatically reduced, and this is a likely explanation for the IL-4-mediated reduction in the total number of OVA-specific cells and the reduced cytotoxic activity. On a per cell basis, the production of IFNgamma and cytotoxic activity of OVA-specific CD8+ cells was not influenced by IL-4. Taken together, our results indicate that the reduction in CTL activity by exogenous IL-4 is due to a reduced number of antigen-specific effectors, and does not involve a downregulation of effector function of these cells.

CD8 T cell responses to infectious pathogens

CD8 T cells respond to viral infections but also participate in defense against bacterial and protozoal infections. In the last few years, as new methods to accurately quantify and characterize pathogen-specific CD8 T cells have become available, our understanding of in vivo T cell responses has increased dramatically. Pathogen-specific T cells, once thought to be quite rare following infection, are now known to be present at very high frequencies, particularly in peripheral, nonlymphoid tissues. With the ability to visualize in vivo CD8 T cell responses has come the recognition that T cell expansion is programmed and, to a great extent, independent of antigen concentrations. Comparison of CD8 T cell responses to different pathogens also highlights the intricate relationship between microbially induced innate inflammatory responses and the kinetics, magnitude, and character of long-term T cell responses. This review describes recent progress in some of the major murine models of CD8 T cell-mediated immunity to viral, bacterial, and protozoal infection.

IL-13 is sufficient for respiratory syncytial virus G glycoprotein-induced eosinophilia after respiratory syncytial virus challenge

Although well studied in settings of helminth infection and allergen sensitization, the combined contributions of IL-4 and IL-13 and their signaling pathways in models of viral pathogenesis have not been reported. Using a murine model of respiratory syncytial virus (RSV) infection, we evaluated the contribution of IL-13, alone and in conjunction with IL-4, during immunization with recombinant vaccinia virus expressing RSV G glycoprotein (vvGs) or with formalin-inactivated RSV (FI-RSV). We showed that both IL-4 and IL-13 activity must be inhibited to modulate G-specific responses resulting in severe RSV-induced disease. Inhibition of IL-4 or IL-13 activity alone had minimal impact on disease in vvGs-immunized mice. However, treatment of IL-4-deficient mice with IL-13Ra during vvGs immunization reduced IL-5, IL-13, and eotaxin production and pulmonary eosinophilia after RSV challenge. In contrast, FI-RSV-induced immune responses were diminished when either IL-4 or IL-13 activity was blocked. After RSV challenge, these type 2 T cell responses were also diminished in vvGs-primed IL-4Ralpha-deficient mice. Our data suggest that secreted vvGs uses mechanisms requiring signaling through the IL-4Ralpha-chain by either IL-4 or IL-13 for induction of eosinophilia and is the first description of the relative contributions of IL-4, IL-13, and their receptors in viral pathogenesis.

Vaccination with minigenes encoding V(H)-derived major histocompatibility complex class I-binding epitopes activates cytotoxic T cells that ablate autoantibody-producing B cells and inhibit lupus

Current treatments for autoantibody-mediated diseases, such as lupus, can cause nonspecific immune suppression. In this paper, we used a bioinformatic approach to identify major histocompatibility complex class I-binding epitopes in the heavy chain variable region of anti-DNA antibodies from lupus-prone (NZB/NZW F1) mice. Vaccination of such mice with plasmid DNA vectors encoding these epitopes induced CD8(+) T cells that killed anti-DNA antibody-producing B cells, reduced serum anti-DNA antibody levels, retarded the development of nephritis, and improved survival. Vaccine-mediated induction of anti-V(H) cytotoxic T lymphocytes that ablate autoreactive B cells represents a novel approach to treat autoantibody-mediated diseases.

Enhanced type 1 immunity after secondary viral challenge in mice primed as neonates

The goal of infant immunization against viral infection is to develop protective long term memory responses. Priming neonatal mice with a low dose of Cas-Br-E murine leukemia virus (Cas) results in adult-like, type 1 protective responses. However, other studies suggest that Ag priming of neonates leads to an increase in type 2 secondary responses even when primary responses were type 1. We assessed whether type 1 CD8+ T cell-mediated responses developed in murine neonates are maintained after secondary challenge with Cas in adulthood. Despite the induction of significant anti-viral CD8+-mediated cytotoxic T lymphocyte and IFN-gamma responses, initial neonatal priming led to a lower frequency of virus-specific T cells compared with adult priming. Adult frequencies were reached in mice primed as neonates only after secondary challenge in adulthood. A nonspecific and transient CD4+-mediated IL-4 response was present in all groups after secondary challenge with Cas or medium, indicating that this rise in type 2 cytokine production was not unique to mice that had been primed as neonates. Rather, type 1 anti-viral memory CD8+ T cell responses developed in neonatal mice are stable, protective, and enhanced after secondary challenge.

Cationic liposome-mediated enhanced generation of human HLA-restricted RSV-specific CD8+ CTL+

Generation of human CD8+ cytotoxic T-lymphocyte (CTL) activity against respiratory syncytial virus (RSV) using peripheral blood leukocytes (PBL) in vitro is inefficient. Lipofectamine, a polycationic liposome, previously shown to enhance the transfection efficiency of DNA in cells, was evaluated for enhancing RSV CTL activity. Stimulator cells were prepared by infecting human PBL with RSV with or without Lipofectamine for 3 hr and then transferred to responder cells. After 8 days of incubation, CTL lysis of autologous target cells infected with RSV (also treated with Lipofectamine) was determined in a 4-hr 5'chromium release assay. Lipofectamine treatment significantly enhanced HLA-restricted RSV-specific CD8+ CTL activity (up to sevenfold, P < 0.05-0.001). Lipofectamine treatment also enhanced cell surface RSV antigen expression and increased the frequencies of HLA-A,B,C+/RSV+ and HLA-DR+/RSV+ leukocytes as demonstrated by flow cytometry. These results demonstrate the usefulness of cationic liposomes in augmenting cell surface antigen expression and increasing the efficiency of generation of human RSV-specific CD8+ CTL activity.

NK T cells contribute to expansion of CD8(+) T cells and amplification of antiviral immune responses to respiratory syncytial virus

CD1d-deficient mice have normal numbers of T lymphocytes and natural killer cells but lack Valpha14(+) natural killer T cells. Respiratory syncytial virus (RSV) immunopathogenesis was evaluated in 129xC57BL/6, C57BL/6, and BALB/c CD1d(-/-) mice. CD8(+) T lymphocytes were reduced in CD1d(-/-) mice of all strains, as shown by cell surface staining and major histocompatibility complex class I tetramer analysis, and resulted in strain-specific alterations in illness, viral clearance, and gamma interferon (IFN-gamma) production. Transient activation of NK T cells in CD1d(+/+) mice by alpha-GalCer resulted in reduced illness and delayed viral clearance. These data suggest that early IFN-gamma production and efficient induction of CD8(+)-T-cell responses during primary RSV infection require CD1d-dependent events. We also tested the ability of alpha-GalCer as an adjuvant to modulate the type 2 immune responses induced by RSV glycoprotein G or formalin-inactivated RSV immunization. However, immunized CD1-deficient or alpha-GalCer-treated wild-type mice did not exhibit diminished disease following RSV challenge. Rather, some disease parameters, including cytokine production, eosinophilia, and viral clearance, were increased. These findings indicate that CD1d-dependent NK T cells play a role in expansion of CD8(+) T cells and amplification of antiviral responses to RSV.

Immunity to polyoma virus infection and tumorigenesis

Because oncogenic DNA viruses establish persistent infections in humans, continuous immunosurveillance for neoplastic cells is required to prevent virus-induced tumors. Antigen-specific CD8+ T lymphocytes are critical in vivo effectors for eliminating virus-infected and virus-transformed cells. Investigation into the induction, regulation, and maintenance of CD8+ T cells specific for these viruses is hindered by the lack of tractable animal models that mimic natural infection. Resistance to tumors induced by polyoma virus, a persistent natural mouse DNA virus, is mediated by polyoma-specific CD8+ T cells. Mice susceptible to polyoma virus tumorigenesis mount a smaller, albeit still considerable, expansion of anti-polyoma CD8+ T cells; importantly, these antiviral CD8+ T cells lack cytotoxic activity while retaining the phenotype of cytotoxic T lymphocyte (CTL) effectors. In this review, we will discuss potential in vivo mechanisms that regulate the functional competence of anti-polyoma CD8+ T cells, particularly in the context of chronic antigenic stimulation provided by persistent viral infections and tumors.

A clonal culture system demonstrates that IL-4 induces a subpopulation of noncytolytic T cells with low CD8, perforin, and granzyme expression

Immune deviation of cytolytic T cell function, induced by type 2 cytokines like IL-4, is an attractive concept to explain failure of the immune system in some diseases. However, this concept is challenged by previous conflicting results on whether type 2 cytokine-producing CD8(+) T cells are cytolytic. Therefore, we have analyzed the relationship between cytolytic activity and cytokine production among large numbers of primary CD8(+) T cell clones. Single murine CD8(+) T cells of naive phenotype were activated at high efficiency with immobilized Abs to CD3, CD8, and CD11a in the presence of IL-2 (neutral conditions) or IL-2, IL-4, and anti-IFN-gamma Ab (type 2-polarizing conditions) for 8-9 days. Under neutral conditions, most clones produced IFN-gamma without IL-4 and were cytolytic. Under type 2-polarizing conditions, most clones produced IFN-gamma and IL-4 but displayed variable cytolytic activity and CD8 expression. Separation on the basis of surface CD8 levels revealed that, compared with CD8(high) cells from the same cultures, CD8(low) cells were poorly cytolytic and expressed low levels of perforin mRNA and protein and granzyme A, B, and C mRNA. A similar, smaller population of noncytolytic CD8(low) cells was identified among CD8(+) T cells activated in mixed lymphocyte reaction with IL-4. Variable efficiency of generation of the noncytolytic cells may account for the differing results of earlier studies. We conclude that IL-4 promotes the development of a noncytolytic CD8(low) T cell phenotype that might be important in tumor- or pathogen-induced immune deviation.

An aged mouse model for RSV infection and diminished CD8(+) CTL responses

Recent studies indicate that respiratory syncytial virus (RSV), like influenza, causes significant morbidity and mortality among elderly persons. There are currently no animal models to study the effects of aging on RSV disease and immunity. This manuscript provides an initial description of such a model. Aged and young BALB/c mice (22-24 and 2-4 months, respectively) were infected with 10(4) TCID(50) of RSV A2. RSV was detected by culture in lung and nose wash specimens obtained 4-6 days following infection at a slightly higher titer in old mice in comparison with young mice. RT-PCR assay detected RSV in the lungs and nose washes of all mice on 4, 8, and 21 days postinoculation, with only a slightly less frequency in young mice. Splenic lymphocytes from old mice exhibited significantly lower RSV-specific MHC class I-restricted CD8(+) CTL responses (P < 0.01-0001), and reduced IFN-production (P < 0.03) than young mice. Conversely, IL-4 production was somewhat elevated in old mice. These results demonstrate diminished RSV virus-specific CD8(+)CTL responses and IFN-gamma production in old mice in comparison with young. It is speculated that the deficient RSV-specific CTL responses may account for the increased morbidity and mortality from RSV infections in elderly persons. Although detailed histopathological, virological, and immunological analyses are incomplete at present, the old BALB/c RSV infection model described provides an opportunity to evaluate the role of CD8(+)CTL and cytokines in RSV disease in aging.

IL-2 during in vitro priming promotes subsequent engraftment and successful adoptive tumor immunotherapy by persistent memory phenotypic CD8(+) T cells

Adoptive T cell tumor immunotherapy potentially consists of two protective components by the transferred effector cells, the immediate immune response and the subsequent development of memory T cells. The extent by which adoptively transferred CD8(+) CTL are destined to become memory T cells is ambiguous as most studies focus on the acute effects on tumor shortly following adoptive transfer. In this study we show that a substantial fraction of the input CTL develop into memory cells that reject a s.c. tumor challenge. The use of exogenous IL-2 or a combination of IL-2 and IL-4, but not solely IL-4, during the ex vivo culture for the CTL inoculation was necessary for efficient development of CD8(+) memory T cells. Thus, an important component of adoptive immunotherapy using CTL is the production of CD8(+) Ag-specific memory cells which is primarily favored by IL-2 receptor signaling during ex vivo generation of the effector CTL.

Construction and characterization of recombinant vaccinia viruses co-expressing a respiratory syncytial virus protein and a cytokine

Recombinant vaccinia viruses are well-characterized tools that can be used to define novel approaches to vaccine formulation and delivery. While vector co-expression of immune mediators has enormous potential for optimizing the composition of vaccine-induced immune responses, the impact on antigen expression and vector antigenicity must also be considered. Co-expression of IL-4 increased vaccinia virus vector titres, while IFN-gamma co-expression reduced vaccinia virus replication in BALB/c mice and in C57BL/6 mice infected with some recombinant viruses. Protection against respiratory syncytial virus (RSV) challenge was similar in mice immunized with vaccinia virus expressing RSV G glycoprotein and IFN-gamma, even though the replication efficiency of the vector was diminished. These data demonstrate the ability of vector-expressed cytokine to influence the virulence of the vector and to direct the development of selected immune responses. This suggests that the co-expression of cytokines and other immunomodulators has the potential to improve the safety of vaccine vectors while improving the immunogenicity of vaccine antigens.