Enhanced pulmonary histopathology induced by respiratory syncytial virus (RSV) challenge of formalin-inactivated RSV-immunized BALB/c mice is abrogated by depletion of interleukin-4 (IL-4) and IL-10.

In previous studies, children immunized with a formalin-inactivated respiratory syncytial virus vaccine (FI-RSV) developed severe pulmonary disease with greater frequency than did controls during subsequent natural RSV infection. In earlier efforts to develop an animal model for this phenomenon, extensive pulmonary histopathology developed in FI-RSV-immunized cotton rats and mice subsequently challenged with RSV. In mice, depletion of CD4+ T cells at the time of RSV challenge completely abrogated this histopathology. Furthermore, the predominant cytokine mRNA present in lungs of FI-RSV-immunized mice during subsequent infection with RSV was that characteristically secreted by Th2 T cells, namely interleukin-4 (IL-4). In the present studies, we sought to determine the relative contributions of gamma interferon (IFN-gamma), IL-2, IL-4, and IL-10 to the lymphocytic infiltration into the lungs observed following RSV challenge of mice previously immunized with FI-RSV. Mice previously immunized with FI-RSV or infected with RSV were depleted of IFN-gamma, IL-2, IL-4, or IL-10 immediately before RSV challenge, and the magnitude of inflammatory cell infiltration around bronchioles and pulmonary blood vessels was quantified. The phenomenon of pulmonary-histopathology potentiation by FI-RSV was reproduced in the present study, thereby allowing us to investigate the effect of cytokine depletion on the process. Simultaneous depletion of both IL-4 and IL-10 completely abrogated pulmonary histopathology in FI-RSV-immunized mice. Depletion of IL-4 alone significantly reduced bronchiolar, though not perivascular, histopathology. Depletion of IL-10 alone had no effect. Depletion of IFN-gamma, IL-2, or both together had no effect on the observed histopathology. These data indicate that FI-RSV immunization primes for a Th2-, IL-4-, and IL-10-dependent inflammatory response to subsequent RSV infection. It is possible that this process played a role in enhanced disease observed in infants and children immunized with FI-RSV.     

Priming with live respiratory syncytial virus (RSV) prevents the enhanced pulmonary inflammatory response seen after RSV challenge in BALB/c mice immunized with formalin-inactivated RSV.

To investigate enhanced disease associated with a formalin-inactivated (FI) respiratory syncytial virus (RSV) vaccine, we studied the pulmonary inflammatory response to RSV in BALB/c mice immunized with live RSV, FI-RSV, or combinations of the two. After RSV challenge, the number of granular cells, the ratio of CD4+/CD8+ lymphocytes, and the level of Th2-like cytokine mRNAs in the bronchoalveolar lavage specimens in mice immunized first with live RSV and then with FI-RSV were lower than that in FI-RSV-immunized mice and close to that in live RSV-immunized mice. These data suggest that prior live RSV infection prevents most of the enhanced inflammatory response seen in FI-RSV-immunized mice and might explain lack of enhanced disease in older FI-RSV-immunized children. A live RSV vaccine might similarly decrease the risk of enhanced disease with non-live RSV vaccines.     

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 synctial virus infection in BALB/c mice previously immunized with formalin-inactivated virus induces enhanced pulmonary inflammatory response with a predominant Th2-like cytokine pattern.

Vaccination with formalin-inactivated respiratory syncytial virus (FI-RSV) caused excessive disease in infants upon subsequent natural infection with RSV. Recent studies with BALB/c mice have suggested that T cells are important contributors to lung immunopathology during RSV infection. In this study, we investigated vaccine-induced enhanced disease by immunizing BALB/c mice with live RSV intranasally or with FI-RSV intramuscularly. The mice were challenged with RSV 6 weeks later, and the pulmonary inflammatory response was studied by analyzing cells obtained by bronchoalveolar lavage 4 and 8 days after challenge. FI-RSV-immunized mice had an increased number of total cells, granulocytes, eosinophils, and CD4+ cells but a decreased number of CD8+ cells. The immunized mice also had a marked increase in the expression of mRNA for the Th2-type cytokines interleukin-5 (IL-5) and IL-13 as well as some increase in the expression of IL-10 (a Th2-type cytokine) mRNA and some decrease in the expression of IL-12 (a Th1-type cytokine) mRNA. The clear difference in the pulmonary inflammatory response to RSV between FI-RSV- and live-RSV-immunized mice suggests that this model can be used to evaluate the disease-enhancing potential of candidate RSV vaccines and better understand enhanced disease.     

CD8 T cells inhibit respiratory syncytial virus (RSV) vaccine-enhanced disease

Vaccination of children with a formalin-inactivated (FI) respiratory syncytial virus (RSV) vaccine led to exacerbated disease including pulmonary eosinophilia following a natural RSV infection. Immunization of BALB/c mice with FI-RSV or a recombinant vaccinia virus (vv) expressing the RSV attachment (G) protein (vvG) results in a pulmonary Th2 response and eosinophilia after RSV challenge that closely mimics the RSV vaccine-enhanced disease observed in humans. The underlying causes of RSV vaccine-enhanced disease remain poorly understood. We demonstrate here that RSV M2-specific CD8 T cells reduce the Th2-mediated pathology induced by vvG-immunization and RSV challenge in an IFN-gamma-independent manner. We also demonstrate that FI-RSV immunization does not induce a measurable RSV-specific CD8 T cell response and that priming FI-RSV-immunized mice for a potent memory RSV-specific CD8 T cell response abrogates pulmonary eosinophilia after subsequent RSV challenge. Our results suggest that the failure of the FI-RSV vaccine to induce a CD8 T cell response may have contributed to the development of pulmonary eosinophilia and augmented disease that occurred in vaccinated individuals.     

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.     

Enhanced disease and pulmonary eosinophilia associated with formalin-inactivated respiratory syncytial virus vaccination are linked to G glycoprotein CX3C-CX3CR1 interaction and expression of substance P

Vaccination with formalin-inactivated respiratory syncytial virus (FI-RSV) vaccine or RSV G glycoprotein results in enhanced pulmonary disease after live RSV infection. Enhanced pulmonary disease is characterized by pulmonary eosinophilia and is associated with a substantial inflammatory response. We show that the absence of the G glycoprotein or G glycoprotein CX3C motif during FI-RSV vaccination or RSV challenge of FI-RSV-vaccinated mice, or treatment with anti-substance P or anti-CX3CR1 antibodies, reduces or eliminates enhanced pulmonary disease, modifies T-cell receptor Vbeta usage, and alters CC and CXC chemokine expression. These data suggest that the G glycoprotein, and in particular the G glycoprotein CX3C motif, is key in the enhanced inflammatory response to FI-RSV vaccination, possibly through the induction of substance P.     

IL-13 is required for eosinophil entry into the lung during respiratory syncytial virus vaccine-enhanced disease

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in children. Children previously vaccinated with a formalin-inactivated RSV vaccine experienced enhanced morbidity and mortality upon natural RSV infection. Histological analysis revealed the presence of eosinophils in the pulmonary infiltrate of the vaccinated children. Eosinophils are characteristic of Th2 responses, and Th2 cells are known to be necessary to induce pulmonary eosinophilia in RSV-infected BALB/c mice previously immunized with a recombinant vaccinia virus (vv) expressing the RSV G protein (vvG). Using IL-13-deficient mice, we find that IL-13 is necessary for eosinophils to reach the lung parenchyma and airways of vvG-immunized mice undergoing RSV challenge infection. IL-13 acts specifically on eosinophils as the magnitude of pulmonary inflammation, RSV G protein-specific CD4 T cell responses, and virus clearance were not altered in IL-13-deficient mice. After RSV challenge, eosinophils were readily detectable in the blood and bone marrow of vvG-immunized IL-13-deficient mice, suggesting that IL-13 is required for eosinophils to transit from the blood into the lung. Pulmonary levels of CCL11 and CCL22 protein were significantly reduced in IL-13-deficient mice indicating that IL-13 mediates the recruitment of eosinophils into the lungs by inducing the production of chemokines important in Th2 cell and eosinophil chemotaxis.     

Decrease in Formalin-Inactivated Respiratory Syncytial Virus (FI-RSV) Enhanced Disease with RSV G Glycoprotein Peptide Immunization in BALB/c Mice

Respiratory syncytial virus (RSV) is a high priority target for vaccine development. One concern in RSV vaccine development is that a non-live virus vaccine would predispose for enhanced disease similar to that seen with the formalin inactivated RSV (FI-RSV) vaccine. Since a mAb specific to RSV G protein can reduce pulmonary inflammation and eosinophilia seen after RSV infection of FI-RSV vaccinated mice, we hypothesized that RSV G peptides that induce antibodies with similar reactivity may limit enhanced disease after subunit or other non-live RSV vaccines. In support of this hypothesis, we show that FI-RSV vaccinated mice administered RSV G peptide vaccines had a significant reduction in enhanced disease after RSV challenge. These data support the importance of RSV G during infection to RSV disease pathogenesis and suggest that use of appropriately designed G peptide vaccines to reduce the risk of enhanced disease with non-live RSV vaccines merits further study.     

Resistance to respiratory syncytial virus (RSV) challenge induced by infection with a vaccinia virus recombinant expressing the RSV M2 protein (Vac-M2) is mediated by CD8+ T cells, while that induced by Vac-F or Vac-G recombinants is mediated by antibodies.

It was previously demonstrated that the vaccinia virus recombinants expressing the respiratory syncytial virus (RSV) F, G, or M2 (also designated as 22K) protein (Vac-F, Vac-G, or Vac-M2, respectively) induced almost complete resistance to RSV challenge in BALB/c mice. In the present study, we sought to identify the humoral and/or cellular mediators of this resistance. Mice were immunized by infection with a single recombinant vaccinia virus and were subsequently given a monoclonal antibody directed against CD4+ or CD8+ T cells or gamma interferon (IFN-gamma) to cause depletion of effector T cells or IFN-gamma, respectively, at the time of RSV challenge (10 days after immunization). Mice immunized with Vac-F or Vac-G were completely or almost completely resistant to RSV challenge after depletion of both CD4+ and CD8+ T cells prior to challenge, indicating that these cells were not required at the time of virus challenge for expression of resistance to RSV infection induced by the recombinants. In contrast, the high level of protection of mice immunized with Vac-M2 was completely abrogated by depletion of CD8+ T cells, whereas depletion of CD4+ T cells or IFN-gamma resulted in intermediate levels of resistance. These results demonstrate that antibodies are sufficient to mediate the resistance to RSV induced by the F and G proteins, whereas the resistance induced by the M2 protein is mediated primarily by CD8+ T cells, with CD4+ T cells and IFN-gamma also contributing to resistance.     

RSV Vaccine-Enhanced Disease Is Orchestrated by the Combined Actions of Distinct CD4 T Cell Subsets

There is no currently licensed vaccine for respiratory syncytial virus (RSV) despite being the leading cause of lower respiratory tract infections in children. Children previously immunized with a formalin-inactivated RSV (FI-RSV) vaccine exhibited enhanced respiratory disease following natural RSV infection. Subsequent studies in animal models have implicated roles for CD4 T cells, eosinophils and non-neutralizing antibodies in mediating enhanced respiratory disease. However, the underlying immunological mechanisms responsible for the enhanced respiratory disease and other disease manifestations associated with FI-RSV vaccine-enhanced disease remain unclear. We demonstrate for the first time that while CD4 T cells mediate all aspects of vaccine-enhanced disease, distinct CD4 T cell subsets orchestrate discrete and specific disease parameters. A Th2-biased immune response, but not eosinophils specifically, was required for airway hyperreactivity and mucus hypersecretion. In contrast, the Th1-associated cytokine TNF-α was necessary to mediate airway obstruction and weight loss. Our data demonstrate that individual disease manifestations associated with FI-RSV vaccine-enhanced disease are mediated by distinct subsets of CD4 T cells.     

Differential Histopathology and Chemokine Gene Expression in Lung Tissues following Respiratory Syncytial Virus (RSV) Challenge of Formalin-Inactivated RSV- or BBG2Na-Immunized Mice

A BALB/c mouse model of enhanced pulmonary pathology following vaccination with formalin-inactivated alum-adsorbed respiratory syncytial virus (FI-RSV) and live RSV challenge was used to determine the type and kinetics of histopathologic lesions induced and chemokine gene expression profiles in lung tissues. These data were compared and contrasted with data generated following primary and/or secondary RSV infection or RSV challenge following vaccination with a promising subunit vaccine, BBG2Na. Severe peribronchiolitis and perivascularitis coupled with alveolitis and interstitial inflammation were the hallmarks of lesions in the lungs of FI-RSV-primed mice, with peak histopathology evident on days 5 and 9. In contrast, primary RSV infection resulted in no discernible lesions, while challenge of RSV-primed mice resulted in rare but mild peribronchiolitis and perivascularitis, with no evidence of alveolitis or interstitial inflammation. Importantly, mice vaccinated with a broad dose range (20 to 0.02 microg) of a clinical formulation of BBG2Na in aluminium phosphate demonstrated histopathology similar to that observed in secondary RSV infection. At the molecular level, FI-RSV priming was characterized by a rapid and strong up-regulation of eotaxin and monocyte chemotactic protein 3 (MCP-3) relative gene expression (potent lymphocyte and eosinophil chemoattractants) that was sustained through late time points, early but intermittent up-regulation of GRO/melanoma growth stimulatory activity gene and inducible protein 10 gene expression, while macrophage inflammatory protein 2 (MIP-2) and especially MCP-1 were up-regulated only at late time points. By comparison, primary RSV infection or BBG2Na priming resulted in considerably lower eotaxin and MCP-3 gene expression increases postchallenge, while expression of lymphocyte or monocyte chemoattractant chemokine genes (MIP-1beta, MCP-1, and MIP-2) were of higher magnitude and kinetics at early, but not late, time points. Our combined histopathologic and chemokine gene expression data provide a basis for differentiating between aberrant FI-RSV-induced immune responses and normal responses associated with RSV infection in the mouse model. Consequently, our data suggest that BBG2Na may constitute a safe RSV subunit vaccine for use in seronegative infants.     

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.     

Transfer of the enhancing effect of respiratory syncytial virus infection on subsequent allergic airway sensitization by T lymphocytes.

In mice, respiratory syncytial virus (RSV) infection enhances allergic airway sensitization, resulting in lung eosinophilia and in airway hyperresponsiveness (AHR). The mechanisms by which RSV contributes to development of asthma and its effects on allergic airway sensitization in mice are not known. We tested whether these consequences of RSV infection can be adoptively transferred by T cells and whether depletion of T cell subsets prevents the effects of RSV infection on subsequent airway sensitization. Mononuclear cells, T lymphocytes, or CD4 or CD8 T cells from peribronchial lymph nodes (PBLN) of RSV-infected mice were transferred into naive BALB/c mice which were then exposed to OVA via the airways. Additionally, RSV-infected mice were depleted of CD4 or CD8 T cells following acute RSV infection but prior to airway sensitization. Following sensitization, airway responsiveness to inhaled methacholine, numbers of lung eosinophils, and levels of IFN-gamma, IL-4, and IL-5 in PBLN cell cultures were monitored. Transfer of T cells from RSV-infected mice resulted in increased eosinophil influx into the lungs, increased IL-5 production, and development of AHR following airway sensitization to allergen. Transfer of CD8 but not CD4 T cells from the PBLN of RSV-infected mice also resulted in AHR following 10 days of OVA exposure. Further, depletion of CD8 T cells prevented these consequences of RSV infection while CD4 T cell depletion reduced them. We conclude that T cells, in particular CD8 T cells, are critical in mediating RSV-induced development of lung eosinophilia and AHR following allergic airway sensitization.     

The cytolytic activity of pulmonary CD8+ lymphocytes, induced by infection with a vaccinia virus recombinant expressing the M2 protein of respiratory syncytial virus (RSV), correlates with resistance to RSV infection in mice.

Previous studies demonstrated that the pulmonary resistance to respiratory syncytial virus (RSV) challenge induced by immunization with a recombinant vaccinia virus expressing the M2 protein of RSV (vac-M2) was significantly greater 9 days after immunization than at 28 days and was mediated predominantly by CD8+ T cells. In this study, we have extended these findings and sought to determine whether the level of CD8+ cytotoxic T-lymphocyte (CTL) activity measured in vitro correlates with the resistance to RSV challenge in vivo. Three lines of evidence documented an association between the presence of pulmonary CTL activity and resistance to RSV challenge. First, vac-M2 immunization induced pulmonary CD8+ CTL activity and pulmonary resistance to RSV infection in BALB/c (H-2d) mice, whereas significant levels of pulmonary CTL activity and resistance to RSV infection were not seen in BALB.K (H-2k) or BALB.B (H-2b) mice. Second, pulmonary CD8+ CTL activity was not induced by infection with other vaccinia virus-RSV recombinants that did not induce resistance to RSV challenge. Third, the peak of pulmonary CTL activity correlated with the peak of resistance to RSV replication (day 6), with little resistance being observed 45 days after immunization. An accelerated clearance of virus was not observed when mice were challenged with RSV 45 days after immunization with vac-M2. The results indicate that resistance to RSV induced by immunization with vac-M2 is mainly mediated by primary pulmonary CTLs and that this resistance decreases to very low levels within 2 months following immunization. The implications for inclusion of CTL epitopes into RSV vaccines are discussed in the context of these observations.     

Cytotoxic T cells specific for a single peptide on the M2 protein of respiratory syncytial virus are the sole mediators of resistance induced by immunization with M2 encoded by a recombinant vaccinia virus.

We have studied the immunobiology of respiratory syncytial virus (RSV), a major cause of respiratory tract morbidity in children. As part of these studies, it was previously found that immunization of BALB/c (H-2d) mice with a recombinant vaccinia virus (rVV) which encoded the M2 protein of RSV provided complete protection against infection with RSV. This protection was transient and associated with M2-specific CD8+ T-cell (TCD8+) responses. In this study, we used two approaches to demonstrate that expression of an H-2Kd-restricted nonameric peptide (Ser Tyr Ile Gly Ser Ile Asn Asn Ile) corresponding to M2 residues 82 to 90 is necessary and sufficient to induce protective TCD8+ responses. First, infection of mice with an rVV which encoded the peptide M2Met82-90 induced levels of primary pulmonary TCD8+ and resistance to RSV challenge equivalent to that induced by infection with an rVV which expressed the complete M2 protein. Second, elimination of peptide binding to Kd by the replacement of Tyr with Arg at amino acid position 83 of the full-length protein completely abrogated the ability of an rVV-expressing full-length M2 to induce either M2-specific TCD8+ responses or resistance to RSV infection. These findings demonstrate that the M2(82-90) peptide is the sole determinant of immunity induced in BALB/c mice by the M2 protein and that a remarkably high level of transient resistance to infection with pulmonary virus is associated with TCD8+ responses to a single determinant.     

Effects of Formalin-Inactivated Respiratory Syncytial Virus (FI-RSV) in the Perinatal Lamb Model of RSV

Respiratory syncytial virus (RSV) is the most frequent cause of bronchiolitis in infants and children worldwide. There are currently no licensed vaccines or effective antivirals. The lack of a vaccine is partly due to increased caution following the aftermath of a failed clinical trial of a formalin-inactivated RSV vaccine (FI-RSV) conducted in the 1960’s that led to enhanced disease, necessitating hospitalization of 80% of vaccine recipients and resulting in two fatalities. Perinatal lamb lungs are similar in size, structure and physiology to those of human infants and are susceptible to human strains of RSV that induce similar lesions as those observed in infected human infants. We sought to determine if perinatal lambs immunized with FI-RSV would develop key features of vaccine-enhanced disease. This was tested in colostrum-deprived lambs immunized at 3–5 days of age with FI-RSV followed two weeks later by RSV infection. The FI-RSV-vaccinated lambs exhibited several key features of RSV vaccine-enhanced disease, including reduced RSV titers in bronchoalveolar lavage fluid and lung, and increased infiltration of peribronchiolar and perivascular lymphocytes compared to lambs either undergoing an acute RSV infection or naïve controls; all features of RSV vaccine-enhanced disease. These results represent a first step proof-of-principle demonstration that the lamb can develop altered responses to RSV following FI-RSV vaccination. The lamb model may be useful for future mechanistic studies as well as the assessment of RSV vaccines designed for infants.     

Respiratory syncytial virus infection of human lung endothelial cells enhances selectively intercellular adhesion molecule-1 expression

Respiratory syncytial virus (RSV) is worldwide the most frequent cause of bronchiolitis and pneumonia in infants requiring hospitalization. In the present study, we supply evidence that human lung microvascular endothelial cells, human pulmonary lung aorta endothelial cells, and HUVEC are target cells for productive RSV infection. All three RSV-infected endothelial cell types showed an enhanced cell surface expression of ICAM-1 (CD54), which increased in a time- and RSV-dose-dependent manner. By using noninfectious RSV particles we verified that replication of RSV is a prerequisite for the increase of ICAM-1 cell surface expression. The up-regulated ICAM-1 expression pattern correlated with an increased cellular ICAM-1 mRNA amount. In contrast to ICAM-1, a de novo expression of VCAM-1 (CD106) was only observed on RSV-infected HUVEC. Neither P-selectin (CD62P) nor E-selectin (CD62E) was up-regulated by RSV on human endothelial cells. Additional experiments performed with neutralizing Abs specific for IL-1alpha, IL-1beta, IL-6, and TNF-alpha, respectively, excluded an autocrine mechanism responsible for the observed ICAM-1 up-regulation. The virus-induced ICAM-1 up-regulation was dependent on protein kinase C and A, PI3K, and p38 MAPK activity. Adhesion experiments using polymorphonuclear neutrophil granulocytes (PMN) verified an increased ICAM-1-dependent adhesion rate of PMN cocultured with RSV-infected endothelial cells. Furthermore, the increased adhesiveness resulted in an enhanced transmigration rate of PMN. Our in vitro data suggest that human lung endothelial cells are target cells for RSV infection and that ICAM-1 up-regulated on RSV-infected endothelial cells might contribute to the enhanced accumulation of PMN into the bronchoalveolar space.     

Differential role of gamma interferon in inhibiting pulmonary eosinophilia and exacerbating systemic disease in fusion protein-immunized mice undergoing challenge infection with respiratory syncytial virus

Secondary exposure to respiratory syncytial virus (RSV) can lead to immunopathology and enhanced disease in vaccinated individuals. Vaccination with individual RSV proteins influences the type of secondary RSV-specific immune response that develops upon challenge RSV infection, as well as the extent of immunopathology. RSV-specific memory CD4 T cells can directly contribute to immunopathology through their cytokine production. Immunization of BALB/c mice with a recombinant vaccinia virus (vv) expressing the attachment (G) protein of RSV results in pulmonary eosinophilia upon RSV challenge, whereas immunization of mice with a vv expressing the fusion (F) protein does not. We analyzed the CD4 T-cell response to an I-E^d-restricted CD4 T-cell epitope within the F protein of RSV corresponding to amino acids 51 to 66 in an effort to better understand the similarities and differences in the immune response elicited by the G versus the F protein. Vaccination with the G protein induces a mixture of RSV G-specific Th1 and Th2 cells with a restricted T-cell receptor repertoire. In contrast, we demonstrate here that immunization with the F protein elicits a broad repertoire of RSV F-specific CD4 T cells that predominantly exhibit a Th1 phenotype. However, in the absence of gamma interferon (IFN-γ), RSV F_51-66-specific CD4 T cells secreted interleukin-5, and mice developed pulmonary eosinophilia after RSV challenge. IFN-γ-deficient mice exhibited decreased weight loss compared to wild-type controls, suggesting that IFN-γ exacerbates systemic disease. These data demonstrate that IFN-γ can have both beneficial and detrimental effects during a secondary RSV infection.     

Role of T-lymphocyte subsets in recovery from respiratory syncytial virus infection in calves.

The role of T-cell subsets in respiratory syncytial virus (RSV) infection was investigated by using monoclonal antibodies (MAbs) to selectively deplete gnotobiotic calves of CD4+, CD8+, or WC1+ gamma delta T-cell receptor+ lymphocytes. Injection of these MAbs produced specific reductions of the target cell populations in the circulation and tissues. Ten days after RSV infection, immunoglobulin M (IgM), IgG1, and IgA antibodies were detected in sera and lung washings from control calves. Depletion of CD8+ T cells had no effect on either the serum or local antibody responses to RSV, whereas depletion of CD4+ T cells suppressed the antibody responses in two of three calves. The IgM and IgA responses were significantly increased in the lung washings of calves from which WC1+ T cells were depleted. Depletion of CD4+ or WC1+ T cells caused no significant delay in virus clearance, although an increase in the extent of pneumonic consolidation was observed in anti-CD4-treated calves. Nasopharyngeal excretion of RSV was prolonged in calves depleted of CD8+ T cells, and virus was isolated in high titers from lung washings of these animals 10 days after infection, whereas virus had been cleared from lung washings of all other animals. The delayed virus clearance was associated with an increase in the severity of pneumonic consolidation in three of four of the calves from which CD8+ T cells were depleted. This study shows that CD8+ T cells play a dominant role in the recovery of calves from RSV infection.