Anti-IL-4 treatment at immunization modulates cytokine expression, reduces illness, and increases cytotoxic T lymphocyte activity in mice challenged with respiratory syncytial virus

Atypical measles and enhanced respiratory syncytial virus disease (ERD) made simple

Atypical measles and enhanced respiratory syncytial virus disease (ERD) were serious diseases that resulted from exposure of children immunized with inactivated vaccines against measles virus (MV) and respiratory syncytial virus (RSV) to the respective wild-type agents in the 1960s. Although the clinical manifestations of both illnesses were different, the immune responses elicited and primed for by the vaccines shared important similarities. Both vaccines failed to elicit long-lived protective antibody and to promote cytotoxic T lymphocyte responses. In both cases, postvaccination exposure to wild type virus during community outbreaks was associated with immune complex deposition in affected tissues, vigorous CD4 T lymphocyte proliferative responses, and a Th2 bias of the immune response. No relapses of atypical measles or ERD were ever reported. In this manuscript, the pathogeneses of both enhanced diseases and the requirements for the generation of protective antibodies against MV and RSV are discussed, to contribute to the development of newer safe and effective vaccines against these important pathogens.

Distinct gene subsets are induced at different time points after human respiratory syncytial virus infection of A549 cells

cDNA microarray technology was applied to time course analysis of differentially expressed genes in A549 cells following human respiratory syncytial virus (HRSV) infection. Both up- and down-regulation of cellular genes were observed in a time-dependent manner. However, gene up-regulation prevailed over gene down-regulation. Virus infectivity was required as UV-inactivated virus failed to up-regulate/down-regulate those genes. At early times post-infection (0-6 h p.i.) 85 genes were up-regulated. Some of those genes were involved in cell growth/proliferation, cellular protein metabolism and cytoskeleton organization. Among the most strongly up-regulated genes at that time were the urokinase plasminogen activator (PLAU) and its receptor (PLAUR), a pleiotropic system involved in many biological processes, including chemotaxis and inflammation. Functionally related genes encoding the alpha- and beta-chains of several integrins were also up-regulated within the first 12 h of infection. Genes up-regulated between 6 and 12 h p.i. included interferon-stimulated genes (ISGs), genes related to oxidative stress and genes of the non-canonical NF-kappaB pathway. At later times, genes involved in the immune response became predominant among the up-regulated genes, most of them being ISGs. Different up-regulation kinetics of cytokine and cytokine-signalling-related genes were also observed. These results highlight the dynamic interplay between the virus and the host cell and provide a general picture of changes in cellular gene expression along the HRSV replicative cycle.

The cysteine-rich region and secreted form of the attachment G glycoprotein of respiratory syncytial virus enhance the cytotoxic T-lymphocyte response despite lacking major histocompatibility complex class I-restricted epitopes

The cytotoxic T-lymphocyte (CTL) response is important for the control of viral replication during respiratory syncytial virus (RSV) infection. The attachment glycoprotein (G) of RSV does not encode major histocompatibility complex class I-restricted epitopes in BALB/c mice (H-2(d)). Furthermore, studies to date have described an absence of significant CTL activity directed against this protein in humans. Therefore, G previously was not considered necessary for the generation of RSV-specific CTL responses. In this study, we demonstrate that, despite lacking H-2(d)-restricted epitopes, G enhances the generation of an effective CTL response against RSV. Furthermore, we show that this stimulatory effect is independent of virus titers and RSV-induced inflammation; that it is associated primarily with the secreted form of G; and that the effect depends on the cysteine-rich region of G (GCRR), a segment conserved in wild-type isolates worldwide. These findings reveal a novel function for the GCRR with potential implications for the generation of protective cellular responses and vaccine development.

Pathogenesis of respiratory syncytial virus infection in the murine model

There is a wide spectrum of illness caused by respiratory syncytial virus (RSV) infection that is caused in large part by host-related factors, such as age of the patient and degree of host immunocompetency. Although the vast majority of persons infected with RSV experience symptoms of mild upper respiratory tract infection, in some people these infections cause significant morbidity and are sometimes fatal. Although a great deal of investigation in both humans and animals has explained the timing and tropism of RSV infection and the general principles by which the immune system responds to this infection, at present we only partially understand the disparity in illness severity that can occur. This article briefly reviews the clinical sequelae of RSV infection and then focuses on the mechanisms of viral pathogenesis.

New approaches to vaccine adjuvants: inhibiting the inhibitor

Graham discusses a study that explores new approaches to enhancing vaccine-induced immune responses.

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.

Role of CCL11 in eosinophilic lung disease during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a major viral pathogen of infants and the elderly. Significant morbidity is caused by an overexuberant mixed lung cell infiltrate, which is thought to be driven by chemokines. One of the main chemotactic mediators responsible for the movement of eosinophils is CCL11 (eotaxin). Using a mouse model of eosinophilic bronchiolitis induced by RSV, we show here that treatment in vivo with a blocking antibody to CCL11 greatly reduces lung eosinophilia and disease severity. In addition, anti-CCL11 caused a striking inhibition of CD4-T-cell influx and shifted cytokine production away from interleukin-5 without reducing the resistance to viral replication. These results suggest that in addition to influencing eosinophil diapedesis and survival, anti-CCL11 has an action on T cells. These studies strengthen the case for anti-CCL11 treatment of Th2-driven diseases.

Respiratory syncytial virus-induced immunoprotection and immunopathology

Respiratory syncytial virus (RSV), a member of the Paramyxoviridae family, is a major clinical problem causing yearly epidemics of severe lower airway disease in both infants and the elderly. Attempts at vaccination have been frustrated by both the poor immunogenicity of this virus, and the severe immunopathology observed in early vaccine trials. Primary infection generally occurs in infancy, with approximately 5% of infected infants requiring hospitalization. Equally problematic is the apparent link between severe RSV disease and the later development of allergy and asthma. While there is no evidence that natural infection promotes Th2 predominance, development of enhanced eosinophilic disease in children receiving inactivated virus administered with a commonly used adjuvant demonstrated how easily the balance between immune-mediated protection and immune-mediated pathology can be perturbed. In this review we have focused on studies carried out in the mouse model aimed at determining the correlates of RSV protection and explaining the mechanism of vaccine enhanced immunopathology.

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.

Vbeta14(+) T cells mediate the vaccine-enhanced disease induced by immunization with respiratory syncytial virus (RSV) G glycoprotein but not with formalin-inactivated RSV

Mice immunized with respiratory syncytial virus (RSV) G glycoprotein or with formalin-inactivated RSV (FI-RSV) exhibit severe disease following RSV challenge. This results in type 2 cytokine production and pulmonary eosinophilia, both hallmarks of vaccine-enhanced disease. RSV G-induced T-cell responses were shown to be restricted to CD4(+) T cells expressing Vbeta14 in the T-cell receptor (TCR), and the deletion of these T cells resulted in less severe disease. We therefore examined the role of Vbeta14(+) T cells in FI-RSV-induced disease. BALB/c mice were immunized with vaccinia virus expressing secreted RSV G (vvGs) or with FI-RSV. At the time of challenge with live RSV, mice were injected with antibody to the Vbeta14 component of the TCR. vvGs-immunized mice treated with anti-Vbeta14 had reduced cytokine levels in the lung. Eosinophil recruitment to the lung was also significantly reduced. In contrast, depletion of Vbeta14(+) T cells in FI-RSV-immunized mice had little impact on cytokine production or pulmonary eosinophilia. An analysis of TCR Vbeta chain usage confirmed a bias toward Vbeta14 expression on CD4(+) T cells from vvGs-immunized mice, whereas the CD4(+) T cells in FI-RSV-immunized mice expressed a diverse array of Vbeta chains. These data show that although FI-RSV and vvGs induce responses resulting in similar immunopathology, the T-cell repertoire mediating the response is different for each immunogen and suggest that the immune responses elicited by RSV G are not the basis for FI-RSV vaccine-enhanced disease.

Respiratory syncytial virus (RSV) G glycoprotein is not necessary for vaccine-enhanced disease induced by immunization with formalin-inactivated RSV

Following respiratory syncytial virus (RSV) challenge, mice immunized with RSV G or with formalin-inactivated RSV (FI-RSV) exhibit severe disease associated with type 2 cytokine production and pulmonary eosinophilia. This has led to the proposal that the presence of RSV G is the factor in FI-RSV that induces disease-enhancing T-cell responses. Therefore, we evaluated the role of RSV G and its immunodominant region in the induction of aberrant immune responses during FI-RSV immunization. BALB/c mice were immunized with FI preparations of wild-type (wt) RSV or recombinant RSV (rRSV) containing deletions of (i) the entire G gene, (ii) the region of the G gene encoding amino acids 187 to 197 of the immunodominant region, or (iii) the entire SH gene. After challenge, illness, RSV titers, cytokine levels, and pulmonary eosinophilia were measured. Peak RSV titers postchallenge were significantly greater in mice immunized with FI preparations of the deletion viruses than in those immunized with FI-rRSV wt, suggesting that the absence of G or SH in FI-RSV reduced its protective efficacy. Deletion of G or its epitope did not reduce illness, cytokine production, or eosinophilia relative to that in mice immunized with FI-rRSV wt. While cytokine levels and eosinophilia were similar, illness was reduced in mice immunized with SH-deleted FI-RSV. These data suggest that G-specific immune responses may be important for vaccine-induced protection and are not solely the basis for FI-RSV vaccine-enhanced illness. These data suggest that the method of RSV antigen delivery, rather than the protein composition, influences the phenotype of the induced immune responses and that RSV G should not necessarily be excluded from potential vaccine strategies.

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.

Theiler's virus infection: a model for multiple sclerosis

Both genetic background and environmental factors, very probably viruses, appear to play a role in the etiology of multiple sclerosis (MS). Lessons from viral experimental models suggest that many different viruses may trigger inflammatory demyelinating diseases resembling MS. Theiler's virus, a picornavirus, induces in susceptible strains of mice early acute disease resembling encephalomyelitis followed by late chronic demyelinating disease, which is one of the best, if not the best, animal model for MS. During early acute disease the virus replicates in gray matter of the central nervous system but is eliminated to very low titers 2 weeks postinfection. Late chronic demyelinating disease becomes clinically apparent approximately 2 weeks later and is characterized by extensive demyelinating lesions and mononuclear cell infiltrates, progressive spinal cord atrophy, and axonal loss. Myelin damage is immunologically mediated, but it is not clear whether it is due to molecular mimicry or epitope spreading. Cytokines, nitric oxide/reactive nitrogen species, and costimulatory molecules are involved in the pathogenesis of both diseases. Close similarities between Theiler's virus-induced demyelinating disease in mice and MS in humans, include the following: major histocompatibility complex-dependent susceptibility; substantial similarities in neuropathology, including axonal damage and remyelination; and paucity of T-cell apoptosis in demyelinating disease. Both diseases are immunologically mediated. These common features emphasize the close similarities of Theiler's virus-induced demyelinating disease in mice and MS in humans.

Contribution of respiratory syncytial virus G antigenicity to vaccine-enhanced illness and the implications for severe disease during primary respiratory syncytial virus infection

BACKGROUND

Immunization of BALB/c mice with vaccinia virus expressing the G glycoprotein (vvG) of respiratory syncytial virus (RSV) or with formalin-inactivated alum-precipitated RSV (FI-RSV) predisposes for severe illness, type 2 cytokine production and pulmonary eosinophilia after challenge with live RSV. This similar disease profile has led to the proposal that the presence of the G glycoprotein in the FI-RSV preparation was the immunologic basis for the vaccine-associated enhancement of disease observed in the failed clinical trials of the 1960s. However, processes of disease pathogenesis observed in FI-RSV- and vvG-immunized mice suggest that FI-RSV and vvG immunizations induce immune responses of different compositions and requirements that converge to produce similar disease outcomes upon live virus challenge.

METHODS

The potential role of RSV G present in FI-RSV preparations in increasing postimmunization disease severity was explored in mice.

RESULTS

The absence of RSV G or its immunodominant epitope during FI-RSV immunization does not reduce disease severity after RSV challenge. Furthermore although depletion of V beta 14+ T cells during RSV challenge modulates disease in G-primed mice, minimal impact on disease in FI-RSV-immunized mice is observed.

CONCLUSION

FI-RSV vaccine-enhanced illness is not attributable to RSV G. Furthermore formulation of a safe and effective RSV vaccine must ensure RSV antigen production, processing and presentation via the endogenous pathways. Thus gene delivery by vector, by DNA or by live attenuated virus are attractive vaccine approaches.

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.

Cytokine production patterns and antibody response to measles vaccine

Cytokines play an important role in the immune response to live measles virus immunization. To gain further insight into the cytokine production profile in response to measles vaccination, we studied interferon-gamma (IFN-gamma), tumor necrosis factor (TNF-alpha), soluble IL-2 receptor (sIL-2R), interleukin-2 (IL-2), interleukin-4 (IL-4), and interleukin-6 (IL-6) in both supernatants from peripheral blood mononuclear cells (PBMC) stimulated with phytohaemagglutinin (PHA), and plasma. We enrolled 57 healthy infants and children residing in an area where no measles virus circulated in their lifetimes. Overall analysis of cytokines in supernatants from PBMC showed that a predominant Th1 cytokine pattern occurs after the second dose of measles immunization. However, plasma levels of Th1 cytokines (IFN-gamma, sIL-2R and TNF-alpha) were preferentially activated by measles virus after the first dose of measles vaccination. Median IFN-gamma plasma levels were 1.73 pg/ml for infants compared to 0.63 pg/ml for older children (P = 0.003). These data suggest that after the first and the second dose of measles virus immunization, there is a predominant Th1-type directed immune response, but the Th1 cytokine pattern seems to be stronger in previously unvaccinated children. There was no correlation between cytokine production by PBMC supernatants after PHA stimulation and circulating levels of plasma cytokines. No relationship was found between any specific cytokine level and measles antibody level.

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.

Production of interferon-gamma and interleukin-10 after inactivated hepatitis A immunization

STUDY OBJECTIVE

To assess helper T cell function by measuring cytokine production over time after hepatitis A immunization.

DESIGN

Open-label, single-dose study.

SETTING

General clinical research center of a university hospital.

SUBJECTS

Twenty-five healthy adults.

INTERVENTION

Each subject was immunized with inactivated hepatitis A vaccine; blood was drawn on day 0 (the day of immunization) and days 2, 5, 7, 10, and 28 after immunization.

MEASUREMENTS AND MAIN RESULTS

Production of interferon (IFN)-gamma and interleukin (IL)-10 by peripheral blood mononuclear cells stimulated in culture with hepatitis A virus was measured by enzyme-linked immunosorbent assay. Concentrations of hepatitis A antibody were measured on day 28. Both IFN-gamma and IL-10 production peaked on day 10 after immunization (IFN-gamma day 0 median = 7.35 pg/ml, interquartile ratio [IQR] = 20.8 vs day 10 median = 22.35 pg/ml, IQR = 42.4, p < 0.05; IL-10 day 0 median = 1.00, IQR = 7.4 vs day 10 median = 11.75 pg/ml, IQR = 92.3, p < 0.02, Wilcoxon signed rank test). The IL-10:IFN-gamma ratio on day 10 correlated with antibody production (Pearson product moment correlation 0.46, p < 0.05). This ratio was used as a measure of helper T cell phenotype.

CONCLUSION

Both IFN-gamma and IL-10 are produced in response to hepatitis A vaccine. The parallel production after immunization may contribute to the high efficacy of these vaccine preparations in inducing both cell-mediated immune response and a protective antibody response.

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.

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.

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.

Macrophage defences against respiratory tract infections

Pulmonary macrophages with a key role in defence against respiratory infection are a heterogeneous family of cells with phagocytic, antigen processing and immunomodulatory functions. Macrophages are important in both innate and acquired immunity in the respiratory tract, and have a role in lung defence against viruses, bacteria, mycobacteria and fungi. Interactions of pathogens with lung macrophages is strongly influenced by soluble immune components including complement, collectins and immunoglobulins. Macrophage function can be modulated by cytokines, environmental exposures, recent and chronic infection including HIV infection, drug therapy and gene transfer.

Rhinovirus-induced airway inflammation in asthma: effect of treatment with inhaled corticosteroids before and during experimental infection

Asthma exacerbations are frequently linked to rhinovirus infections. However, the associated inflammatory pathways are poorly understood, and treatment of exacerbations is often unsatisfactory. In the present study we investigated whether antiinflammatory treatment with inhaled corticosteroids prevents any rhinovirus-induced worsening of lower airway inflammation. To that end, we selected 25 atopic patients with mild asthma who underwent experimental rhinovirus 16 (RV16) infection, while receiving double-blind, placebo-controlled treatment with the inhaled corticosteroid budesonide (800 microg twice a day) throughout the study period, starting 2 wk before infection. We assessed inflammatory cell numbers in the bronchial mucosa as obtained by bronchial biopsies 2 d before and 6 d after RV16 infection, and analyzed those in relation to cold symptoms, changes in blood leukocyte counts, airway obstruction, and airway hyperresponsiveness. RV16 colds induced an increase in CD3(+) cells in the lamina propria (p = 0.03) and tended to decrease the numbers of epithelial eosinophils (p = 0.06) in both groups analyzed as a whole. The T cell accumulation was positively associated with cold symptoms. Budesonide pretreatment improved airway hyperresponsiveness (p = 0.02) and eosinophilic airways inflammation (p = 0.04). Yet it did not significantly affect the RV16-associated changes in the numbers of any of the inflammatory cell types. We conclude that RV16 infection by itself induces only subtle worsening of airway inflammation in asthma, which is not improved (or worsened) by inhaled corticosteroids. The latter finding is in keeping with the limited protection of inhaled corticosteroids against acute asthma exacerbations.

Increased replication of respiratory syncytial virus (RSV) in pulmonary infiltrates is associated with enhanced histopathological disease in bonnet monkeys (Macaca radiata) pre-immunized with a formalin-inactivated RSV vaccine

The pathology of respiratory syncytial virus (RSV) disease in bonnet monkeys parallels findings with human RSV disease. RSV-infected animals pre-immunized with a formalin-inactivated (FI) RSV vaccine develop inflammation in peribronchiolar, perivascular, interstitial and intra-alveolar sites with lung inflammation scores significantly higher than animals with a primary RSV infection and those pre-immunized with an FI-Vero cell control vaccine (P=0.05). Animals previously infected and re-exposed to RSV had significantly lower alveolar, interstitial and total lung inflammation scores than in primary infection (P=0.05). Immunization with two intra-muscular doses of 0.5 ml of the FI-RSV vaccine administered 21 days apart resulted in little serum-neutralizing and ELISA antibody, low levels of secretory IgA and a low lymphocyte proliferative response that was significantly lower than the response observed in animals that were previously infected with live RSV. Higher RSV virus titres were detected in the lungs and lung lavage fluid of monkeys immunized with the FI-RSV vaccine than in those with a primary infection (P=0.001). RSV was detected by in situ hybridization in pulmonary inflammatory infiltrates, where the single most abundant infiltrating cellular species was macrophages, so it may be these cells that support the enhanced virus replication that contributes to the enhanced pulmonary pathology of FI-RSV immunization.

Viral rhinitis

Viral rhinitis is a common, morbid, and costly malady, often complicated by otitis media, sinusitis, and asthma. Current therapies are relatively ineffective and aimed at reducing symptoms rather than moderating underlying mechanisms. Nasal elevations of proinflammatory cytokines track symptom expression during viral rhinitis, and it is hypothesized that these chemicals orchestrate a common response to infection with many different viruses that cause rhinitis. Also, recent evidence supports a role for neurogenic inflammation in the development of complications. Future studies should dissect the role of proinflammatory cytokines and neuropeptides in the expression of symptoms, signs, pathophysiologies, and complications of viral rhinitis.

Differential expression of TGF-beta, IL-2, and other cytokines in the CNS of Theiler's murine encephalomyelitis virus-infected susceptible and resistant strains of mice

Intracranial inoculation of susceptible SJL mice with Theiler's murine encephalomyelitis virus (TMEV) results in biphasic disease consisting of early acute disease, followed by late chronic demyelinating disease, associated with mononuclear infiltrates and demyelinating lesions. In contrast, resistant C57BL/6 (B6) mice develop only early acute disease. We employed cytokine-specific RT-PCR to determine the expression of cytokine transcripts in the CNS of TMEV-infected SJL and B6 mice. During early acute disease, we have found a strong proinflammatory (Th1) cytokine response in the CNS of both TMEV-infected SJL and B6 mice, demonstrated by the expression of transcripts for IFN-gamma, IL-1, IL-6, IL-12p40, and TNF-alpha. At 8 days postinfection (p.i.), TGF-beta1 and TNF-alpha transcripts were present at significantly higher levels (P < 0.01) in the CNS of SJL susceptible mice in comparison to those found in the CNS of B6 mice. Immunohistochemical staining revealed that TGF-beta protein was expressed in leptomeningeal mononuclear inflammatory cell infiltrates in the brain of SJL mice but not in B6 mice, at 8 days p.i. TGF-beta may be responsible for the failure of SJL mice to develop an effective anti-TMEV CTL response. During late chronic demyelinating disease, high levels of proinflammatory Th1 cytokines were found in the CNS of SJL mice, but not B6 mice. Significantly higher levels (P < 0.01) of anti-inflammatory cytokine transcripts (IL-4, IL-5, and IL-10 (Th2 cytokines) and TGF-beta) were found in the spinal cord of TMEV-infected SJL mice with chronic demyelinating disease than in the spinal cord of B6 mice during the same time period (39 or 60 days p.i.). These anti-inflammatory cytokines may contribute to the downregulation of the proinflammatory response in SJL mice. High levels of IL-2 transcripts and protein appeared transiently in the spinal cord of TMEV-infected SJL mice before the onset of demyelinating disease and coincided with an influx of new T cells into the CNS and/or expansion of remaining T cells that have not been eliminated after viral clearance.

The attachment (G) glycoprotein of respiratory syncytial virus contains a single immunodominant epitope that elicits both Th1 and Th2 CD4+ T cell responses

BALB/c mice immunized with a vaccinia virus expressing the attachment (G) glycoprotein of respiratory syncytial virus (RSV) develop a virus-specific CD4(+) T cell response that consists of a mixture of Th1 and Th2 CD4(+) T cells following intranasal infection with live RSV. Recent work has shown that both Th1 and Th2 CD4(+) T cells are elicited to a single region comprising aa 183-197 of the G protein. To more precisely define the CD4(+) T cell epitope(s) contained within this region, we created a panel of amino- and carboxyl-terminal truncated as well as single alanine-substituted peptides spanning aa 183-197. These peptides were used to examine the ex vivo cytokine response of memory effector CD4(+) T cells infiltrating the lungs of G-primed RSV-infected mice. Analysis of lung-derived memory effector CD4(+) T cells using intracellular cytokine staining and/or ELISA of effector T cell culture supernatants revealed a single I-E(d)-restricted CD4(+) T cell epitope with a core sequence mapping to aa 185-193. In addition, we examined the T cell repertoire of the RSV G peptide-specific CD4(+) T cells and show that the CD4(+) T cells directed to this single immunodominant G epitope use a restricted range of TCR Vss genes and predominantly express Vss14 TCR.

Predominant type-2 response in infants with respiratory syncytial virus (RSV) infection demonstrated by cytokine flow cytometry

Acute RSV infection in infancy may produce some asthma-like symptoms and may be followed by a recurrent wheeze later in childhood. It has been proposed that RSV infection stimulates type-2 cytokine responses, resembling those found in atopy and asthma. Peripheral blood cells were obtained from RSV-infected infants (n = 30) and healthy controls (n = 10). After in vitro restimulation of the cells, intracellular IL-4 and interferon-gamma (IFN-gamma) were measured by flow cytometry. The cells from RSV-infected infants produced more IL-4 and less IFN-gamma than those from healthy controls. IL-4 production was more frequent in CD8 than in CD4 cells, and the bias toward IL-4 production was greatest in infants with mild infections, whereas IFN-gamma production increased with disease severity. Our conclusions are that RSV infection is associated with IL-4 production in peripheral T cells, and that peripheral blood in infants with severe disease may be depleted of cytokine-producing cells.

Immune-mediated disease pathogenesis in respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is an important cause of severe respiratory disease in persons at both extremes of age. Wheezing is a cardinal sign of infection and the illness is associated with an increased incidence of childhood asthma. Data from both humans and animal models have linked severe disease in infants and the syndrome of vaccine-enhanced illness with an aberrant composition of CD4+ T cells, suggestive of an exaggerated Th2 response. Studies in murine models have shown that prior vaccination, coexisting allergic inflammation, or direct modulation of the cytokine milieu can profoundly influence the immune response to RSV and thereby affect the expression of disease. In addition, there are intrinsic antigenic properties of the RSV G glycoprotein that promote Th2 responses and eosinophilia. This paper proposes an integrated working model of how host and virus factors interact to determine the characteristics of RSV-induced illness. This model suggests strategies for the development of new vaccine and immunotherapeutic interventions, and creates a framework for asking additional questions about the immunopathogenesis of RSV.

Cellular immune responses in neonates

Reduced numbers of lymphocytes and antigen presenting cells have been described as some of the main factors responsible for antigenic tolerance or low responsiveness in neonates. However, by changing the parameters of immunization, such as dose of antigen and frequency of antigen presenting cells we and others have shown that neonates have the option of developing the same variety of immune responses seen in adults. Several aspects of the development of cellular immunity in human and murine neonates are reviewed in this article, with a special focus on the development of T cell mediated responses, from ontogeny to effector function.

Bovine respiratory syncytial virus-specific IgE is associated with interleukin-2 and -4, and interferon-gamma expression in pulmonary lymph of experimentally infected calves

OBJECTIVE

To study the local immune response of calves to bovine respiratory syncytial virus (BRSV) infection with emphasis on IgE production and cytokine gene expression in pulmonary lymph.

ANIMALS

Twelve 6- to 8-week-old Holstein bull calves. Six similar control calves were mock infected to obtain control data.

PROCEDURE

Lymphatic cannulation surgery was performed on 12 calves to create a long-term thoracic lymph fistula draining to the exterior. Cannulated calves were exposed to virulent BRSV by aerosol. Lymph fluid collected daily was assayed for BRSV and isotype-specific IgE antibody, total IgG, IgA, IgM, and protein concentrations. Interleukin-4 (IL-4), interleukin-2 (IL-2), and interferon-gamma were semi-quantitated by reverse transcription-polymerase chain reaction (RT-PCR). Cell counts and fluorescence-activated cell scanner (FACSCAN) analysis of T-cell subsets were performed on lymph cells.

RESULTS

Calves had clinical signs of respiratory tract disease during days 5 to 10 after infection and shed virus. Bovine respiratory syncytial virus-specific IgE in infected calves was significantly increased over baseline on day 9 after infection. Mean virus-specific IgE concentrations strongly correlated with increases in severity of clinical disease (r = 0.903). Expression of IL-2, IL-4, and interferon-gamma was variably present in infected and control calves, with IL-4 expression most consistent during early infection.

CONCLUSIONS AND CLINICAL RELEVANCE

Infection with BRSV was associated with production of BRSV-specific IgE, and IL-4 message was commonly found in lymph cells of infected calves. This finding supports the concept that BRSV-induced pathophysiology involves a T helper cell type-2 response. Effective therapeutic and prophylactic strategies could, therefore, be developed using immunomodulation to shift the immune response more toward a T helper cell type-1 response.

Immunology of Varicella Immunization in the elderly

OBJECTIVE

To review the varicella-zoster virus (VZV) and herpes zoster disease and to summarize published reports on the use of the live-attenuated varicella zoster vaccine to enhance cell-mediated immunity in elderly individuals.

DATA SOURCE

A MEDLINE search (1966-August 1999) for English-language clinical studies and review articles pertaining to VZV and the live-attenuated varicella vaccine was conducted; references obtained from these publications were subsequently reviewed for additional relevant articles.

STUDY SELECTION AND DATA EXTRACTION

Representative clinical trials were summarized and relevant information was selected to assist in the understanding of VZV, the subsequent immune response, and the live-attenuated varicella vaccine.

DATA SYNTHESIS

The physiologic, age-related decline in VZV cell-mediated immunity has been shown to be restored on administration of live-attenuated varicella vaccine. Various studies report serum anti-VZV antibody concentrations, and production of interferon-gamma were increased following vaccination. Concentrations subsequently returned to baseline one year after vaccination. Increase in responder cell frequency, a measure of cell-mediated immunity, has been reported to last up to four years after vaccination, at concentrations similar or superior to those observed following herpes zoster.

CONCLUSIONS

Enhancement of cell-mediated immune response in elderly individuals through vaccination with live-attenuated varicella vaccine is a possible measure to protect this population from herpes zoster and to attenuate its complications. A summary of immunogenicity studies to identify the immune response to live-attenuated varicella vaccine in the elderly is presented. The absolute clinical significance, as well as appropriate administration guidelines of this prophylactic intervention, will become evident following forthcoming large, masked, placebo-controlled trials.

IL-4 and IL-10 antagonize IL-12-mediated protection against acute vaccinia virus infection with a limited role of IFN-gamma and nitric oxide synthetase 2

Resistance or susceptibility to most infectious diseases is strongly determined by the balance of type 1 vs type 2 cytokines produced during infection. However, for viruses, this scheme may be applicable only to infections with some cytopathic viruses, where IFN-gamma is considered as mandatory for host defense with little if any participation of type 2 responses. We studied the role of signature Th1 (IL-12, IFN-gamma) and Th2 (IL-4, IL-10) cytokines for immune responses against vaccinia virus (VV). IL-12-/- mice were far more susceptible than IFN-gamma-/- mice, and primary CTL responses against VV were absent in IL-12-/- mice but remained intact in IFN-gamma-/- mice. Both CD4+ and CD8+ T cells from IL-12-/- mice were unimpaired in IFN-gamma production, although CD4+ T cells showed elevated Th2 cytokine responses. Virus replication was impaired in IL-4-/- mice and, even more strikingly, in IL-10-/- mice, which both produced elevated levels of the proinflammatory cytokines IL-1alpha and IL-6. Thus, IL-4 produced by Th2 cells and IL-10 produced by Th2 cells and probably also by macrophages counteract efficient anti-viral host defense. Surprisingly, NO production, which is considered as a major type 1 effector pathway inhibited by type 2 cytokines, appears to play a limited role against VV, because NO sythetase 2-deficient mice did not show increased viral replication. Thus, our results identify a new role for IL-12 in defense beyond the induction of IFN-gamma and show that IL-4 and IL-10 modulate host protective responses to VV.

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

Although interleukin-4 (IL-4) has been implicated in respiratory syncytial virus (RSV)-enhanced disease, the mechanism by which it modulates immune responses to primary RSV infection remains unclear. We have developed a system to investigate the effect of IL-4 on RSV epitope-specific cytotoxic T-lymphocyte (CTL) effector function in vivo, using an H-2K(d)-restricted RSV M2 epitope. BALB/c mice were infected with recombinant vaccinia virus (rVV) constructed to express RSV M2 protein (vvM2) alone or coexpress M2 and IL-4 (vvM2/IL-4). Splenocytes were assessed for M2-specific CTL activity in a direct (51)Cr release assay and intracellular gamma interferon (IFN-gamma) production by fluorescence-activated cell sorting analysis. Mice infected with vvM2/IL-4 had less M2-specific primary CTL activity than those infected with vvM2. M2-specific CTL frequency, as measured by M2 peptide-induced intracellular IFN-gamma production, was diminished in the vvM2/IL-4 group, partially accounting for the reduction of CTL activity. Mice immunized with either construct were challenged intravenously with RSV 4 weeks postimmunization, and direct CTL were measured. These results demonstrate that local expression of IL-4, at the time of antigen presentation, diminishes the cytolytic activity of primary and memory CD8(+) RSV-specific CTL responses in vivo.

Reduced interferon-gamma expression in peripheral blood mononuclear cells of infants with severe respiratory syncytial virus disease

We examined the in vivo cell-mediated immune response in infants with respiratory syncytial virus (RSV) infection in order to gain information about the pathogenesis of severe RSV disease in infancy. Semiquantitative reverse transcription-polymerase chain reaction and three-color flow cytometry were used to determine the levels of messenger RNA (mRNA) for interferon (IFN)-gamma in peripheral blood mononuclear cells, and the distribution of lymphocyte subsets in infants with acute RSV infection. The findings were correlated with the severity of the patients' illness and the production of RSV-specific IgE antibodies (RSV-IgE). Significantly lower IFN-gamma levels and T-lymphocyte counts in the acute phase of illness were observed in infants with severe RSV disease than in those with a milder clinical course of illness. The induction of RSV-IgE was not related to IFN-gamma levels in the acute phase of illness, but rather correlated with IFN-gamma expression during convalescence. The data indicate that reduced IFN-gamma expression may be an important factor in the pathogenesis of severe RSV disease in infancy.

Secreted respiratory syncytial virus G glycoprotein induces interleukin-5 (IL-5), IL-13, and eosinophilia by an IL-4-independent mechanism

The attachment glycoprotein G of respiratory syncytial virus (RSV) is produced as both membrane-anchored and secreted forms by infected cells. Immunization with secreted RSV G (Gs) or formalin-inactivated alumprecipitated RSV (FI-RSV) predisposes mice to immune responses involving a Th2 cell phenotype which results in more severe illness and pathology, decreased viral clearance, and increased pulmonary eosinophilia upon subsequent RSV challenge. These responses are associated with increased interleukin-4 (IL-4) production in FI-RSV-primed mice, and the responses are IL-4 dependent. RNase protection assays demonstrated that similar levels of IL-4 mRNA were induced after RSV challenge in mice primed with vaccinia virus expressing Gs (vvGs) or a construct expressing only membrane-anchored G (vvGr). However, upon RSV challenge, vvGs-primed mice produced significantly greater levels of IL-5 and IL-13 mRNA and protein than vvGr-primed mice. Administration of neutralizing anti-IL-4 antibody 11.B11 during vaccinia virus priming did not alter the levels of vvGs-induced IL-5, IL-13, pulmonary eosinophilia, illness, or RSV titers upon RSV challenge, although immunoglobulin G (IgG) isotype profiles revealed that more IgG2a was produced. vvGs-priming of IL-4-deficient mice demonstrated that G-induced airway eosinophilia was not dependent on IL-4. In contrast, airway eosinophilia induced by FI-RSV priming was significantly reduced in IL-4-deficient mice. Thus we conclude that, in contrast to FI-RSV, the secreted form of RSV G can directly induce IL-5 and IL-13, producing pulmonary eosinophilia and enhanced illness in RSV-challenged mice by an IL-4-independent mechanism.

Induction of Th-1 and Th-2 responses by respiratory syncytial virus attachment glycoprotein is epitope and major histocompatibility complex independent

In BALB/c mice, sensitization to respiratory syncytial virus (RSV) attachment (G) glycoprotein leads to the development of lung eosinophilia upon challenge infection with RSV, a pathology indicative of a strong in vivo induction of a Th-2-type response. In this study, we found that a strong, RSV G-specific, Th-1-type cytokine response occurred simultaneously with a Th-2-type response in G-primed mice after RSV challenge. Both Th-1 and Th-2 effector CD4(+) T cells recognized a single immunodominant site on this protein, implying that the differentiation of memory CD4(+) T cells along the Th-1 or Th-2 effector pathway was independent of the epitope specificity of the T cells. A similar observation was made in G-primed H-2(b) haplotype mice after RSV challenge, further suggesting that this process is not dependent on the peptide epitope presented. On the other hand, genes mapping to loci outside of the major histocompatibility complex region are crucial regulators of the development of a Th-2-type response and lung eosinophilia. The implication of these findings for the immune mechanisms underlying the pathogenesis of RSV is discussed.

Antibody repertoire against HIV-1 gp120 triggered in nude and normal mice by GM-CSF/gp120 immunization

Granulocyte-macrophage colony stimulating factor (GM-CSF) facilitates the induction of primary immune responses by activating and recruiting antigen-presenting cells (APC), which efficiently present antigen determinants to Th cells. We have derived a functional GM-CSF/gp120 chimeric protein that, following immunization in soluble, adjuvant-independent form in normal mice, triggers highly specific, high affinity anti-gp120 antibodies. In contrast, nude mice respond with mutated, polyreactive, low affinity antibodies that mature further and increase in affinity in T cell-reconstituted nude mice. Anti-gp120 antibody production in nude mice is mediated principally by GM-CSF/gp120-triggered IL-4 production, since neutralizing anti-IL-4 abrogates the in vivo response. The anti-gp120 antibody response in normal, nude and T cell-reconstituted nude mice is encoded at a remarkably high frequency by the VH81X and VH7183 genes, a family used notably during fetal life and, when expressed at the adult stage, associated with autoimmune disease. We conclude that HIV gp120 binds and selects a subpopulation of developing B cells expressing a set of VH genes associated with immunodeficiency and autoimmunity.

Diminished IL-10 production in subjects with allergy after infection with influenza A virus

BACKGROUND

Recent studies have documented a link between respiratory viral infections and the expression of asthma and other allergic disorders. Results from other studies have suggested that diminished production of IL-10, an anti-inflammatory cytokine, may contribute to the pathophysiologic features of these diseases.

OBJECTIVE

The objective of this study was to determine whether diminished IL-10 production and TH2 cytokine skewing occur in allergic, as compared with nonallergic, subjects after experimental infection with the influenza A virus.

METHODS

PBMCs were isolated from 11 subjects with allergy and 14 subjects with no allergy before and after influenza A infection and stimulated with either mitogen (PHA) or antigen (influenza A). Supernatants were assayed for IL-10, IL-4, and IFN-gamma by ELISA.

RESULTS

PBMC IL-10 production was significantly diminished in subjects with allergy, as compared with subjects with no allergy, after experimental infection with influenza A virus. However, significant TH2 skewing and enhanced airway symptoms were not observed in these same subjects.

CONCLUSIONS

These data provide further support that subjects with allergy have an intrinsic inability to upregulate IL-10 production in response to inflammatory stimuli and extend this observation to include respiratory viral infections. Future studies in this area could lead to a better understanding of the pathogenesis of asthma and other allergic disorders

CD8 T Cells Are Essential in the Development of Respiratory Syncytial Virus-Induced Lung Eosinophilia and Airway Hyperresponsiveness

Viral respiratory infections can cause bronchial hyperresponsiveness and exacerbate asthma. In mice, respiratory syncytial virus (RSV) infection results in airway hyperresponsiveness (AHR) and eosinophil influx into the airways. The immune cell requirements for these responses to RSV infection are not well defined. To delineate the role of CD8 T cells in the development of RSV-induced AHR and lung eosinophilia, we tested the ability of mice depleted of CD8 T cells to develop these symptoms of RSV infection. BALB/c mice were depleted of CD8 T cells using anti-CD8 Ab treatment before intranasal administration of infectious RSV. Six days postinfection, airway responsiveness to inhaled methacholine was assessed by barometric body plethysmography, and numbers of lung eosinophils and levels of IFN-γ, IL-4, and IL-5 in bronchoalveolar lavage fluid were monitored. RSV infection resulted in airway eosinophilia and AHR in control mice, but not in CD8-depleted animals. Further, whereas RSV-infected mice secreted increased amounts of IL-5 into the airways as compared with noninfected controls, no IL-5 was detectable in both bronchoalveolar lavage fluid and culture supernatants from CD8-depleted animals. Treatment of CD8-depleted mice with IL-5 fully restored both lung eosinophilia and AHR. We conclude that CD8 T cells are essential for the influx of eosinophils into the lung and the development of AHR in response to RSV infection.

Enhanced Cytotoxic T Cell Activity in IL-4-Deficient Mice

CD8+ effectors are critical components of type 1 responses against viral infections as well as for antiviral vaccines. IL-4 plays a clear role as an inhibitor of CD4+ Th1 cells; however, its role in CD8+ T cell regulation appears to be more complex. Thus, IL-4 may augment CD8+ T cell growth, but also limit effector function. Moreover, abundant IL-4 is inhibitory for viral clearance, but the lack of IL-4 appears not to affect CTL-mediated immunity. This report investigates these disparate roles of IL-4 in CD8+ T lymphocyte regulation by comparing T cell responses specific for a single HIV-IIIIB gp120-derived epitope in BALB/c mice deficient in IL-4 to those in wild-type controls. CTL activation was monitored during the acute and memory phases following immunization with recombinant vaccinia virus. Similar frequencies of gp120-specific CTL precursors in splenocytes from both groups indicated that IL-4 plays no significant role in either CTL priming or the establishment of memory. However, cytolytic activity in cultures derived from IL-4-deficient mice developed earlier and was strikingly enhanced following in vitro restimulation, an effect exhibited by both primary and memory T cells. Secretion of IL-2 and IFN-γ by CD8+ T cells from IL-4-deficient mice was also elevated, reflecting their enhanced activation. Thus, IL-4 appears to limit the activation, expansion, and differentiation of CD8+ T cells with high cytolytic potential.

Evolution of the type-1 (Th1)-type-2 (Th2) cytokine paradigm

During the past 12 years, since the discovery of murine Th1 and Th2 clones, increasing numbers of cells that make type-1 and type-2 cytokines have been recognized, and a growing number of these cytokines have been described. Emphasis has shifted from the CD4+ T cell, as the source of Th1-Th2 cytokines, to the functional effect of the type-1 and type-2 cytokines, independent of their cell of origin. Appreciation of the complex interactions of CMI and humoral immune responses continues to evolve. If this new paradigm provides insight into infectious disease pathogenesis and prevention, then it should allow development of new vaccines and vaccine adjuvants against these diseases.

Host Genetic Determinants of Vaccine-Induced Eosinophilia During Respiratory Syncytial Virus Infection

In BALB/c mice, sensitization with the attachment protein (G) of respiratory syncytial virus (RSV) leads to CD4+ T cell-mediated lung eosinophilia during subsequent challenge with RSV. To determine the host genetic influences on this model of lung eosinophilia, we tested 15 different inbred mouse strains. Eosinophilia developed in all H-2d (BALB/c, DBA/2n, and B10.D2), but not in H-2k (CBA/Ca, CBA/J, C3H, BALB.K, or B10.BR) mouse strains. Among H-2b mice, 129 and BALB.B developed eosinophilia, whereas C57BL/6 and C57BL/10 did not. Testing first generation crosses between sensitive and resistant strains showed that eosinophilia developed in all H-2dxk (n = 5), irrespective of background genes, but not in H-2dxb (n = 2) mice. In vivo depletion of CD8+ T cells or IFN-γ rendered C57BL/6, but not BALB.K mice, susceptible to eosinophilia. Analysis of B10 recombinant mice showed that the Dd allele (in B10.A(5R) mice) prevented CD8+ T cell accumulation in the lung, resulting in intense lung eosinophilia. However, the Db allele (in B10.A(2R) and B10.A(4R) mice) supported CD8+ T cell expansion and prevented eosinophilia. Intracellular cytokine staining showed that lung eosinophilia correlated with reduced IFN-γ and increased IL-10 expression in lung T cells. These results are compatible with the unifying model that Th2 cells mediate the disease but can be inhibited by CD8+ T cells secreting IFN-γ. Our findings have important implications for the development of protective, nonpathogenic vaccines for RSV disease.

Respiratory syncytial virus (RSV) disease and prospects for its control

Respiratory syncytial virus (RSV) is a major virus pathogen of infants and young children, an important cause of disease in adults and is responsible for a significant amount of excess morbidity and mortality in the elderly. It also can be devastating in immunosuppressed populations. Vaccines are being developed, but none are currently licensed. Moreover, even if one or more are approved, they may not be suitable for some populations vulnerable to RSV (e.g. very young infants and the immunosuppressed). Ribavirin and immunoglobulin preparations with high titers of RSV-specific neutralizing antibodies are currently approved for use to treat and prevent RSV infection. However, neither of these is cost-effective or simple to administer. New agents are needed to reduce the impact of RSV. This review is concerned with the means currently available for controlling RSV, the search for new agents effective against this virus, and future prospects for preventing and treating RSV infections.

Recombinant vaccinia virus coexpressing the F protein of respiratory syncytial virus (RSV) and interleukin-4 (IL-4) does not inhibit the development of RSV-specific memory cytotoxic T lymphocytes, whereas priming is diminished in the presence of high levels of IL-2 or gamma interferon

In order to investigate if immune responses to the fusion (F) protein of respiratory syncytial virus (RSV) could be influenced by cytokines, recombinant vaccinia viruses (rVV) carrying both the F gene of RSV and the gene for murine interleukin-2 (IL-2), IL-4, or gamma interferon (IFN-gamma) were constructed. In vitro characterization of rVV revealed that insertion of the cytokine gene into the VP37 locus of the vaccinia virus genome resulted in 100- to 1,000-fold higher expression than insertion of the same gene into the thymidine kinase (TK) locus. In comparison, only a two- to fivefold difference in the level of expression of the F protein was observed when the gene was inserted into either of these two loci. Mice vaccinated with rVV expressing the F protein and high levels of IL-2 or IFN-gamma cleared rVV more rapidly than mice inoculated with a control rVV and developed only low levels of RSV-specific serum antibody. In addition, these recombinants were much less effective at priming RSV-specific memory cytotoxic T lymphocytes (CTL) and IFN-gamma production by spleen cells than rVV expressing the F protein alone. In contrast, mice vaccinated with rVV expressing high levels of IL-4 showed signs of delayed rVV clearance. RSV-specific serum antibody responses were biased in favor of immunoglobulin G1 (IgG1) in these mice, as there was a significant reduction in IgG2a antibody responses compared with serum antibody responses in mice vaccinated with rVV expressing the F protein alone. However, vaccination with rVV expressing the F protein together with high levels of IL-4 did not alter the development of RSV-specific memory CTL or IFN-gamma production by RSV-restimulated splenocytes.

Priming with secreted glycoprotein G of respiratory syncytial virus (RSV) augments interleukin-5 production and tissue eosinophilia after RSV challenge

The respiratory syncytial virus (RSV) G glycoprotein promotes differentiation of type 2 CD4+ T lymphocytes and induces an eosinophilic response in lungs of RSV-infected mice. A unique feature of G is that a second initiation codon in the transmembrane region of the glycoprotein results in secretion of soluble protein from infected cells. Recombinant vaccinia viruses that express wild-type G (vvWT G), only secreted G (vvM48), or only membrane-anchored G (vvM48I) were used to define the influence of G priming on immunopathogenesis. Mice immunized with vvM48 had more severe illness following RSV challenge than did mice primed with vvWT G or vvM48I. Coadministration of purified G during priming with the construct expressing membrane-anchored G shifted immune responses following RSV challenge to a more Th2-like response. This was characterized by increased interleukin-5 in lung supernatants and an increase in G-specific immunoglobulin G1 antibodies. Eosinophils were present in the infiltrate of all mice primed with G-containing vectors but were greatest in mice primed with regimens including secreted G. These data suggest the form of G protein available for initial antigen processing and presentation is an important factor in promoting Th2-like immune responses, including the induction of lung eosinophilia. The ability of RSV to secrete G protein may therefore represent a viral strategy for immunomodulation and be a key determinant of disease pathogenesis.