CD8+ T cells control Th2-driven pathology during pulmonary respiratory syncytial virus infection

Regulatory T cells promote early influx of CD8+ T cells in the lungs of respiratory syncytial virus-infected mice and diminish immunodominance disparities

In addition to regulating autoimmunity and antitumor immunity, CD4(+) CD25(+) FoxP3(+) natural regulatory T (Treg) cells are global regulators of adaptive immune responses. Depletion of these cells with the anti-CD25 antibody PC61 prior to primary respiratory syncytial virus (RSV) infection was partial but had several effects on the RSV-specific CD8(+) response in a hybrid mouse model. Mediastinal lymph node and spleen epitope-specific CD8(+) T-cell responses were enhanced in Treg-cell-depleted mice at all time points following infection, but responses of Treg-cell-depleted lung show a strikingly different pattern than lymphoid organ responses, with an initial delay in the CD8(+) T-cell response. The delay in the CD8(+) T-cell response correlated with a delay both in the early phase of viral clearance and in illness in Treg-cell-depleted mice compared to isotype-treated controls. The lungs of Treg-cell-depleted mice were shown to have increased lung chemokine and cytokine levels 7 days postinfection despite lower CD8(+) T-cell responses. Following the early delay in the lung response, CD8(+) T-cell responses at later infection time points were enhanced and increased the severity of illness in depleted mice. Finally, decreasing regulatory T-cell control of the CD8(+) T-cell response had a greater effect on response of the dominant K(d)-restricted M2 epitope consisting of amino acids 82 to 90 (K(d)M2(82-90)) than on the subdominant D(b)M(187-195) epitope response, indicating that regulatory T cells modulate immunodominance disparities in epitope-specific CD8(+) T-cell responses following primary RSV infection.

The number of respiratory syncytial virus (RSV)-specific memory CD8 T cells in the lung is critical for their ability to inhibit RSV vaccine-enhanced pulmonary eosinophilia

Children that were administered a formalin-inactivated respiratory syncytial virus (FI-RSV) vaccine experienced enhanced respiratory disease, including pulmonary eosinophilia, after contracting a natural RSV infection. RSV vaccine-enhanced disease can be mimicked in BALB/c mice immunized with either FI-RSV or with a recombinant vaccinia virus (vacv) expressing the RSV attachment (G) protein. We have recently demonstrated that memory CD8 T cells directed against the RSV immunodominant M2(82-90) epitope inhibit the development of pulmonary eosinophilia in either vacvG- or FI-RSV-immunized mice by reducing the total number of Th2 cells in the lung after RSV challenge. In this study, we show that memory CD8 T cells specific to a subdominant epitope within the RSV fusion (F) protein fail to inhibit the development of pulmonary eosinophilia after RSV challenge of mice previously co-immunized with vacvF and with either vacvG or FI-RSV. We observed that the inability of RSV F(85)-specific memory CD8 T cells to inhibit the development of pulmonary eosinophilia was largely due to an inadequate total number of F(85)-specific memory CD8 T cells in the lung at early times after RSV challenge. Increasing the number of F(85)-specific memory CD8 T cells after immunization grants these cells the ability to inhibit RSV vaccine-enhanced pulmonary eosinophilia. Moreover, we demonstrate that RSV-specific memory CD8 T cells, when present in sufficient numbers, inhibit the production of the Th2-associated chemokines CCL17 and CCL22. Taken together, these results indicate that RSV-specific memory CD8 T cells may alter the trafficking of Th2 cells and eosinophils into the lung.

Lack of antibody affinity maturation due to poor Toll-like receptor stimulation leads to enhanced respiratory syncytial virus disease

Respiratory syncytial virus (RSV) is a leading cause of hospitalization in infants. A formalin-inactivated RSV vaccine was used to immunize children in 1966 and elicited non-protective, pathogenic antibody. Two immunized infants died and 80% were hospitalized after subsequent RSV exposure. No vaccine was licensed since.

A widely accepted hypothesis attributed vaccine failure to formalin disruption of protective antigens. Instead, we show that lack of protection was not due to alterations caused by formalin, but to low antibody avidity for protective epitopes. Lack of antibody affinity maturation followed poor Toll-like receptor stimulation. This study explains why the inactivated RSV vaccine failed to protect and consequently led to severe disease, hampering vaccine development for forty-two years. Also, it suggests that inactivated RSV vaccines may be rendered safe and effective by inclusion of TLR-agonists in their formulation. In addition, it identifies affinity maturation as a critical factor for the safe immunization of infants.

Pulmonary immunity and immunopathology: lessons from respiratory syncytial virus

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory disease in infants and is an important source of morbidity and mortality in the elderly and immunocompromised. This review will discuss the humoral and cellular adaptive immune responses to RSV infection and how these responses are shaped in the immature immune system of the infant and the aged environment of the elderly. Furthermore, we will provide an overview of our current understanding of the role the various arms of the adaptive immune response play in mediating the delicate balance between the successful elimination of the virus from the host and the induction of immunopathology. Efficacious immunization against RSV remains a high priority within the field and we will highlight recent advances made in vaccine design.

RNA interference inhibits respiratory syncytial virus replication and disease pathogenesis without inhibiting priming of the memory immune response

Respiratory syncytial virus (RSV) is a major cause of morbidity in infants, young children, and the elderly worldwide. Currently, there is no effective vaccine, and antiviral drugs to control infection are limited. RNA interference is a powerful tool amenable to development of antiviral drugs. Using small interfering RNA (siRNA) targeting the RSV P gene (siRNA-P), RSV replication can be silenced both in vitro and in a BALB/c model of RSV infection. In this study, we examine the effect of siRNA prophylaxis on the primary and memory immune response to RSV infection in mice. We show that mice prophylactically treated with siRNA-P to decrease but not eliminate RSV replication exhibit reduced pulmonary inflammation and lung pathogenesis and produce a robust anti-RSV memory response when subsequently challenged with RSV. The pulmonary T-cell memory response was characterized by high numbers of CD44(hi) CD62L(lo) CD4(+) and CD8(+) T cells, M2 peptide tetramer(+) CD8(+) T cells expressing gamma interferon, and an RSV-specific antibody response. The results support the hypothesis that siRNAs can be developed as effective antiviral drugs that can be used to reduce the viral load and parameters of pathogenesis without limiting the induction of the memory immune response.

Regulation of immunity to respiratory syncytial virus by dendritic cells, toll-like receptors, and notch

The activation and maintenance of pulmonary viral disease is regulated at multiple levels and determined by the early innate response to the pathogenic stimuli. Subsequent activation events that rely directly and indirectly on the virus itself can alter the development and severity of the ensuing immunopathologic responses. In the present review we outline several interconnected mechanisms that rely on the early recognition of viral nucleic acid for the most appropriate anti-viral immune responses, including TLRs and Notch activation in DCs and T cells. Deviation or persistence of the immune response to respiratory viruses may impact significantly on the severity of the responses. While these mechanisms are likely similar in most respiratory viral infections, this review will focus on findings with respiratory syncytial virus (RSV) infections.

Overcoming T cell-mediated immunopathology to achieve safe RSV vaccination

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract disease in young children. Premature infants, immunocompromised individuals, and the elderly exhibit an increased risk for the development of severe disease after RSV infection. Currently, there is not a safe and effective RSV vaccine available, in part due to our incomplete understanding of how severe immunopathology was induced following RSV infection of children previously immunized with a formalin-inactivated RSV vaccine. Much of our current understanding of RSV vaccine-enhanced disease can be attributed to the establishment of multiple mouse models of RSV vaccination. Studies analyzing the RSV-specific immune response in mice have clearly demonstrated that both CD4 and CD8 memory T cells contribute to RSV-induced immunopathology. In this review we will focus our discussion on data generated from the mouse models of RSV immunization that have advanced our understanding of how virus-specific T cells mediate immunopathology and RSV vaccine-enhanced disease.

Proliferative expansion and acquisition of effector activity by memory CD4+ T cells in the lungs following pulmonary virus infection

The memory CD4+ T cell response to the respiratory syncytial virus (RSV) attachment (G) protein in the lungs of primed BALB/c mice undergoing challenge pulmonary RSV infection is dominated by effector T cells expressing a single Vbeta-chain, Vbeta14. We have used Vbeta14 expression to examine the kinetics of the activation, accumulation, and acquisition of the effector activity of memory CD4+ T cells responding to pulmonary infection. This analysis revealed that proliferative expansion and effector CD4+ T cell differentiation preferentially occur in the respiratory tract following rapid activation within and egress from the lymph nodes draining the respiratory tract. These findings suggest that, in response to natural infection at a peripheral mucosal site such as the lungs, memory CD4+ T cell expansion and differentiation into activated effector T cells may occur predominantly in the peripheral site of infection rather than exclusively in the lymph nodes draining the site of infection.

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

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

Pulmonary eosinophilia requires interleukin-5, eotaxin-1, and CD4+ T cells in mice immunized with respiratory syncytial virus G glycoprotein

Severe illness, type 2 cytokine production, and pulmonary eosinophilia are adverse immune responses resulting from respiratory syncytial virus (RSV) challenge of vvGs-immunized mice. We have shown IL-4 and IL-13 activity must be simultaneously inhibited to reduce disease severity. We now address the contributions of IL-5, eotaxin-1, and CD4+ and CD8+ T cells to the induction of disease-enhancing immune responses. Depletion of CD4+ T cells during immunization prevented IL-4, IL-13, and eotaxin-1 production, diminished eosinophilia, and reduced weight loss. Conversely, CD8+ T cell depletion did not decrease eosinophilia, weight loss, or type 2 cytokines but did dramatically reduce mucus production and increase eotaxin production. Anti-IL-5 administration at immunization or challenge significantly decreased pulmonary eosinophilia. Strikingly, there were not concomitant decreases in weight loss. Following RSV challenge eotaxin-1-deficient mice immunized with vvGs exhibited significantly less eosinophilia without decreased weight loss or type 2 cytokine production. We conclude CD4+ T cell production of IL-5 and induction of eotaxin-1 are required for vvGs-induced eosinophilia following RSV challenge, while CD8+ T cells appear to down-regulate eotaxin-1 and mucus production. In summary, we demonstrate that pulmonary eosinophilia 1) is a by-product of memory CD4+ T cell activation, 2) does not necessarily correlate with mucus production, and, most importantly, 3) is not required for the RSV G-induced illness in mice. These findings have important implications for the evaluation of candidate RSV vaccines.

Sub-nucleocapsid nanoparticles: a nasal vaccine against respiratory syncytial virus

BACKGROUND

Bronchiolitis caused by the respiratory syncytial virus (RSV) in infants less than two years old is a growing public health concern worldwide, and there is currently no safe and effective vaccine. A major component of RSV nucleocapsid, the nucleoprotein (N), has been so far poorly explored as a potential vaccine antigen, even though it is a target of protective anti-viral T cell responses and is remarkably conserved between human RSV A and B serotypes. We recently reported a method to produce recombinant N assembling in homogenous rings composed of 10-11 N subunits enclosing a bacterial RNA. These nanoparticles were named sub-nucleocapsid ring structure (N SRS).

METHODOLOGY AND PRINCIPAL FINDINGS

The vaccine potential of N SRS was evaluated in a well-characterized and widely acknowledged mouse model of RSV infection. BALB/c adult mice were immunized intranasally with N SRS adjuvanted with the detoxified E. coli enterotoxin LT(R192G). Upon RSV challenge, vaccinated mice were largely protected against virus replication in the lungs, with a mild inflammatory lymphocytic and neutrophilic reaction in their airways. Mucosal immunization with N SRS elicited strong local and systemic immunity characterized by high titers of IgG1, IgG2a and IgA anti-N antibodies, antigen-specific CD8(+) T cells and IFN-gamma-producing CD4(+) T cells.

CONCLUSIONS/SIGNIFICANCE

This is the first report of using nanoparticles formed by the recombinant nucleocapsid protein as an efficient and safe intra-nasal vaccine against RSV.

Understanding the mechanisms of viral induced asthma: new therapeutic directions

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

The role of T cells in the enhancement of respiratory syncytial virus infection severity during adult reinfection of neonatally sensitized mice

Respiratory syncytial virus (RSV) is the major cause of infantile bronchiolitis and hospitalization. Severe RSV disease is associated with the development of wheezing in later life. In a mouse model of the delayed effects of RSV, the age at primary infection determines responses to reinfection in adulthood. During primary RSV infection, neonatal BALB/c mice developed only mild disease and recruited CD8 cells that were defective in gamma interferon production. Secondary reinfection of neonatally primed mice caused enhanced inflammation and profuse lung T-cell recruitment. CD4 cell depletion during secondary RSV challenge attenuated disease (measured by weight loss); depletion of CD8 cells also markedly attenuated disease severity but enhanced lung eosinophilia, and depletion of both CD4 and CD8 cells together completely abrogated weight loss. Depletion of CD8 (but not CD4) cells during primary neonatal infection was protective against weight loss during adult challenge. Therefore, T cells, in particular CD8 T cells, play a central role in the outcome of neonatal infection by enhancing disease during secondary challenge. These findings demonstrate a crucial role for T cells in the regulation of immune responses after neonatal infection.

Understanding respiratory syncytial virus (RSV) vaccine-enhanced disease

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection in infants and children worldwide. In addition, RSV causes serious disease in elderly and immune compromised individuals. RSV infection of children previously immunized with a formalin-inactivated (FI)-RSV vaccine is associated with enhanced disease and pulmonary eosinophilia that is believed to be due to an exaggerated memory Th2 response. As a consequence, there is currently no licensed RSV vaccine and detailed studies directed towards prevention of vaccine-associated disease are a critical first step in the development of a safe and effective vaccine. The BALB/c mouse model of RSV infection faithfully mimics the human respiratory disease. Mice previously immunized with either FI-RSV or a recombinant vaccinia virus (vv) that expresses the attachment (G) glycoprotein exhibit extensive lung inflammation and injury, pulmonary eosinophilia, and enhanced disease following challenge RSV infection. CD4 T cells secreting Th2 cytokines are necessary for this response because their depletion eliminates eosinophilia. Intriguing recent studies have demonstrated that RSV-specific CD8 T cells can inhibit Th2-mediated pulmonary eosinophilia in vvG-primed mice by as yet unknown mechanisms. Information gained from the animal models will provide important information and novel approaches for the rational design of a safe and efficacious RSV vaccine.

Polylactide-co-glycolide (PLG) microparticles modify the immune response to DNA vaccination

Priming with the major surface glycoprotein G of respiratory syncytial virus (RSV) expressed by recombinant vaccinia leads to strong Th2 responses and lung eosinophilia during viral challenge. We now show that DNA vaccination in BALB/c mice with plasmids encoding G attenuated RSV replication but also enhanced disease with lung eosinophilia and increased IL-4/5 production. However, formulating the DNA with PLG microparticles reduced the severity of disease during RSV challenge without significantly lessening protection against viral replication. PLG formulation greatly reduced lung eosinophilia and prevented the induction of IL-4 and IL-5 during challenge, accompanied by a less marked CD4+ T cell response and a restoration of the CD8+ T cell recruitment seen during infection of non-vaccinated animals. After RSV challenge, lung eosinophilia was enhanced and prolonged in mice vaccinated with DNA encoding a secreted form of G; this effect was virtually prevented by PLG formulation. Therefore, PLG microparticulate formulation modifies the pattern of immune responses induced by DNA vaccination boosts CD8+ T cell priming and attenuates Th2 responses. We speculate that PLG microparticles affect antigen uptake and processing, thereby influencing the outcome of DNA vaccination.

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-gamma), RSV F(51-66)-specific CD4 T cells secreted interleukin-5, and mice developed pulmonary eosinophilia after RSV challenge. IFN-gamma-deficient mice exhibited decreased weight loss compared to wild-type controls, suggesting that IFN-gamma exacerbates systemic disease. These data demonstrate that IFN-gamma can have both beneficial and detrimental effects during a secondary RSV infection.

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.

Serum mannose-binding lectin levels are linked with respiratory syncytial virus (RSV) disease

The innate immune response facilitates the quality of the adaptive immune response and is critical to an individual's susceptibility to infection and disease. Mannose-binding lectin (MBL) is a plasma protein with anti-microbial properties that binds a wide range of pathogens to flag them for immune destruction independent of antibodies. In this study, serum MBL levels were measured in 81 children <5 years old experiencing acute respiratory syncytial virus infection and in 40 control children to determine the association with disease severity. Almost 70% of all RSV-infected children had low to intermediate MBL levels (<500 ng/ml) compared to controls, and most of the <6 months old RSV interned patients had low to intermediate levels. No differences were detected in MBL levels between case and control children <1 month old. Analysis of the T-cell compartment in peripheral blood mononuclear cells (PBMC) from acute RSV-infected and control children showed that the percent CD4+ T cells was statistically lower in RSV-infected children > or =6 months old compared to controls, while the percent CD8+ T cells in RSV-infected and control PBMC was generally similar. These results suggest that low serum MBL levels may be a marker of RSV disease severity in children and that MBL may be important in limiting RSV disease pathogenesis.

Human and bovine respiratory syncytial virus vaccine research and development

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

Mapping and characterization of the primary and anamnestic H-2(d)-restricted cytotoxic T-lymphocyte response in mice against human metapneumovirus

Cytotoxic T lymphocytes (CTLs) are important for the control of virus replication during respiratory infections. For human metapneumovirus (hMPV), an H-2(d)-restricted CTL epitope in the M2-2 protein has been described. In this study, we screened the hMPV F, G, N, M, M2-1, and M2-2 proteins using three independent algorithms to predict H-2(d) CTL epitopes in BALB/c mice. A dominant epitope (GYIDDNQSI) in positions 81 to 89 of the antitermination factor M2-1 and a subdominant epitope (SPKAGLLSL) in N(307-315) were detected during the anti-hMPV CTL response. Passive transfer of CD8(+) T-cell lines against M2-1(81-89) and N(307-315) protected Rag1(-/-) mice against hMPV challenge. Interestingly, diversification of CTL targets to include multiple epitopes was observed after repetitive infections. A subdominant response against the previously described M2-2 epitope was detected after the third infection. An understanding of the CTL response against hMPV is important for developing preventive and therapeutic strategies against the 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.

Immunogenicity and efficacy of recombinant RSV-F vaccine in a mouse model

RSV vaccine development has constraints due to safety issues encountered by formalin-inactivated FI-RSV vaccines. A desirable vaccine should induce Th(1) responses and a strong mucosal immunity to provide complete protection from RSV infection. In the present paper, we developed and evaluated a mucosal vaccine against RSV in a mouse model. The antigenic regions corresponding to residues 412-524 of RSV-F protein were amplified by RT-PCR and cloned into a vector containing the ctxA(2)B gene of the cholera toxin. The recombinant protein was expressed in E. coli and properties of the recombinant protein were analyzed by SDS-PAGE, Western blot and G(M1)-ELISA. The purified recombinant protein (rRF-412) was used to immunize BALB/c mice intranasally. The results from our studies show that the rRF-412 immunogen induced mucosal (IgA) and systemic antibody (IgG, IgG1, IgG2a, and IgG2b) responses which neutralized RSV. The IgG1/IgG2a ratios indicated a Th(1)-biased antibody response. The Th(1) (TNF-alpha, IL-12p70, IFN-gamma, IL-2) and Th(2) (IL-10, IL-4 and IL-5) cytokine profiles were analyzed after stimulation of spleen cells from mice immunized with purified RF-412 protein. Similar to the antibody response, we observed that the rRF-412 immunogen induced a mixed Th(1)/Th(2) cytokine immune response with a Th(1)-bias response. Serum antibodies were capable of neutralizing RSV and mice immunized with rRF-412 were significantly protected from live RSV challenge. Our data provides evidence that the rRF-412 immunogen may be a potential mucosal vaccine candidate against RSV.

Respiratory Syncytial Virus Recombinant F Protein (Residues 255–278) Induces a Helper T Cell Type 1 Immune Response in Mice

We have developed and evaluated an immunodominant respiratory syncytial virus (RSV) F antigen in a mouse model. The antigenic region corresponding to amino acids 255-278 of the RSV F protein was cloned into a vector containing the ctxA(2)B gene of cholera toxin (CT). The recombinant protein was expressed in Escherichia coli and analyzed on sodium dodecyl sulfate-polyacrylamide gels. The purified protein was evaluated by immunoblot and ganglioside GM(1) enzyme-linked immunosorbent assay to confirm the expression of the RSV F protein and to correct association of the recombinant protein to form a holotoxin-like chimera, respectively. We hypothesized that genetic fusion of modified CT-based adjuvant with RSV F immunodominant epitopes (rRF-255) would induce protective humoral and cellular immune responses in mice. Intranasal immunization of mice with rRF-255 overall induced higher concentrations of anti-RSV F-specific antibodies in both serum and saliva as compared with mice immunized intranasally with RSV or phosphate-buffered saline (PBS). Antibody isotype analysis (IgA, IgG1, IgG2a, and IgG2b) was also performed. The predominant IgG2a antibody isotype response in combination with cytokine analysis of helper T cell type 1 (interferon-gamma, interleukin [IL]-2, IL-12 p70, and tumor necrosis factor-alpha) and helper T cell type 2 (IL-4 and IL-10) responses revealed that rRF-255 antigen induces a prominent helper T cell type 1 immune response in mice. The rRF-255 antigen also induced serum neutralizing antibodies in immunized mice. Analysis of RSV load in lungs showed that rRF-255 immunization provided significant protection compared with PBS control animals.

DNA immunization with plasmids encoding fusion and nucleocapsid proteins of bovine respiratory syncytial virus induces a strong cell-mediated immunity and protects calves against challenge

Respiratory syncytial viruses (RSV) are one of the most important respiratory pathogens of humans and cattle, and there is currently no safe and effective vaccine prophylaxis. In this study, we designed two codon-optimized plasmids encoding the bovine RSV fusion (F) and nucleocapsid (N) proteins and assessed their immunogenicity in young calves. Two administrations of both plasmids elicited low antibody levels but primed a strong cell-mediated immunity characterized by lymphoproliferative response and gamma interferon production in vitro and in vivo. Interestingly, this strong cellular response drastically reduced viral replication, clinical signs, and pulmonary lesions after a highly virulent challenge. Moreover, calves that were further vaccinated with a killed-virus vaccine developed high levels of neutralizing antibody and were fully protected following challenge. These results indicate that DNA vaccination could be a promising alternative to the classical vaccines against RSV in cattle and could therefore open perspectives for vaccinating young infants.

Respiratory Syncytial Virus Infection in Adults

Originally considered as only a paediatric pathogen, respiratory syncytial virus (RSV) has recently been shown to be a significant cause of respiratory illness among elderly and high-risk adults. Approximately 170,000 hospitalizations and 10,000 deaths associated with RSV occur annually in people over the age of 65 years in the United States. Although rhinorrhoea and wheezing are common symptoms among adults, the clinical syndrome associated with RSV is not distinctive and thus laboratory methods are required for specific diagnosis. Presently, the combination of reverse transcription PCR and enzyme immunoassay serology offers the best sensitivity and specificity for diagnosis of RSV. Treatment options are limited at present, with inhaled ribavirin being the only licensed drug for use in hospitalized children. Vaccines against RSV remain an unachieved goal. Promising new agents that inhibit the virus-cell fusion, cell-cell fusion, or viral gene expression are currently in development.

C5 modulates airway hyperreactivity and pulmonary eosinophilia during enhanced respiratory syncytial virus disease by decreasing C3a receptor expression

Enhanced respiratory syncytial virus disease, a serious pulmonary disorder that affected recipients of an inactivated vaccine against respiratory syncytial virus in the 1960s, has delayed the development of vaccines against the virus. The enhanced disease was characterized by immune complex-mediated airway hyperreactivity and a severe pneumonia associated with pulmonary eosinophilia. In this paper, we show that complement factors contribute to enhanced-disease phenotypes. Mice with a targeted disruption of complement component C5 affected by the enhanced disease displayed enhanced airway reactivity, lung eosinophilia, and mucus production compared to wild-type mice and C5-deficient mice reconstituted with C5. C3aR expression in bronchial epithelial and smooth muscle cells in the lungs of C5-deficient mice was enhanced compared to that in wild-type and reconstituted rodents. Treatment of C5-deficient mice with a C3aR antagonist significantly attenuated airway reactivity, eosinophilia, and mucus production. These results indicate that C5 plays a crucial role in modulating the enhanced-disease phenotype, by affecting expression of C3aR in the lungs. These findings reveal a novel autoregulatory mechanism for the complement cascade that affects the innate and adaptive immune responses.

Differential immune responses and pulmonary pathophysiology are induced by two different strains of respiratory syncytial virus

In this study we performed comparisons of pulmonary responses between two different respiratory syncytial virus (RSV) antigenic subgroup A strains, A2 and Line 19. Line 19 strain induced significant dose-responsive airway hyperreactivity (AHR) in BALB/c mice at days 6 and 9 after infection, whereas the A2 strain induced no AHR at any dose. Histological examination indicated that A2 induced no goblet cell hyper/metaplasia, whereas the Line 19 induced goblet cell expansion and significant increases in gob5 and MUC5AC mRNA and protein levels in vivo. When examining cytokine responses, A2 strain induced significant interleukin (IL)-10 expression, whereas Line 19 strain induced significant IL-13 expression. When IL-13-/- mice were infected with Line 19 RSV, the AHR responses were abrogated along with gob5 gene expression. There was little difference in viral titer throughout the infection between the line 19- and A2-infected mice. However, the A2 strain grew to significantly higher titers than the Line 19 strain in HEp-2 cells in vitro. Thus, RSV Line 19-induced airway dysfunction does not correlate with viral load in vivo. These data demonstrate that different RSV strains of the same antigenic subgroup can elicit differential immune responses that impact the phenotypic expression of RSV-induced illness.

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.

A novel flow cytometric assay focusing on perforin release mechanisms of cytotoxic T lymphocytes

CD8(hi+) cytotoxic T lymphocytes (CTL) are major players in immune defense. In addition, they contribute to the maintenance of immune homeostasis. We now describe a hitherto unavailable, but simple assay to determine ex vivo lytic granule-based cytotoxic functions of human CD8(hi+) CTL subgroups in a clinical setting, under target cell free conditions. Ficoll-isolated peripheral blood lymphocytes from 17 healthy volunteers were stimulated either by phorbol 12-myristate 13-acetate (PMA) in combination with ionomycin or by antibody mediated crosslinking of the CD3 molecule on the T cell surface. Using perforin as a marker for lytic granules, the reduction of CTL granules over time intervals up to 120 min was quantified by FACScan flow cytometry. The kinetics of perforin reduction were compared to the kinetics of NA-CBZ-L-lysine-thiobenzyl ester hydrochloride (BLT)-esterase release and of CD63 upregulation. The reduction in the perforin(+) portion of CD8(hi+) CTLs was correlated inversely with BLT-esterase release and CD63 upregulation. At 30 and 120 min after PMA/ionomycin stimulation, 55 +/- 14% and 42 +/- 14%, respectively, of CD8(hi+) CTLs still stained perforin(+) (time point 0 min = 100%). Perforin-granule release induced by CD3-crosslinking occurred as fast within 30 min (55 +/- 17%), but over the 120 min time interval it was not as complete when compared to PMA/ionomycin-stimulated perforin-reduction. Thus, the combination of an established degranulation assay with the power of immuno flow cytometry allows one to investigate the cytotoxic capability of CTL-subtypes and the kinetics of perforin-granule release. In addition, the assay may prove useful in the elucidation of intracellular signaling cascades governing the perforin-granule release process.

Bases celulares e bioquímicas da doença pulmonar obstrutiva crônica

A doença pulmonar obstrutiva crônica é uma doença inflamatória com participação ativa de macrófagos, neutrófilos e linfócitos CD8+ em sua patogênese, associada a estímulos oxidantes diretos das estruturas pulmonares, que desencadeiam reações bioquímicas, levando a progressiva desorganização das pequenas vias aéreas e ao remodelamento estrutural não reversível. A liberação de substâncias provenientes das células recrutadas e do estresse oxidativo leva ao desequilíbrio inicialmente temporário dos mecanismos de defesa pulmonar. A permanência desse desequilíbrio é uma das chaves da fisiopatogenia atual. Os autores descrevem as alterações celulares e bioquímicas da doença pulmonar obstrutiva crônica.

Characterization of the CD8+ T cell responses directed against respiratory syncytial virus during primary and secondary infection in C57BL/6 mice

The BALB/c mouse model for human respiratory syncytial virus infection has contributed significantly to our understanding of the relative role for CD4+ and CD8+ T cells to immune protection and pathogenic immune responses. To enable comparison of RSV-specific T cell responses in different mouse strains and allow dissection of immune mechanisms by using transgenic and knockout mice that are mostly available on a C57BL/6 background, we characterized the specificity, level and functional capabilities of CD8+ T cells during primary and secondary responses in lung parenchyma, airways and spleens of C57BL/6 mice. During the primary response, epitopes were recognized originating from the matrix, fusion, nucleo- and attachment proteins, whereas the secondary response focused predominantly on the matrix epitope. C57BL/6 mice are less permissive for hRSV infection than BALB/c mice, yet we found CD8+ T cell responses in the lungs and bronchoalveolar lavage, comparable to the responses described for BALB/c mice.

Differential chemokine expression following respiratory virus infection reflects Th1- or Th2-biased immunopathology

Respiratory syncytial virus (RSV) is a major viral pathogen of infants that also reinfects adults. During RSV infection, inflammatory host cell recruitment to the lung plays a central role in determining disease outcome. Chemokines mediate cell recruitment to sites of inflammation and are influenced by, and influence, the production of cytokines. We therefore compared chemokine production in a mouse model of immunopathogenic RSV infection in which either Th1 or Th2 immunopathology is induced by prior sensitization to individual RSV proteins. Chemokine expression profiles were profoundly affected by the nature of the pulmonary immunopathology: "Th2" immunopathology in BALB/c mice was associated with increased and prolonged expression of CCL2 (MCP-1), CXCL10 (IP-10), and CCL11 (eotaxin) starting within 24 h of challenge. C57BL/6 mice with "Th2" pathology (enabled by a deficiency of CD8+ cells) also showed increased CCL2 production. No differences in chemokine receptor expression were detected. Chemokine blockers may therefore be of use for children with bronchiolitis.

CD8 T cells modulate CD4 T-cell and eosinophil-mediated pulmonary pathology in pneumocystis pneumonia in B-cell-deficient mice

Pneumocystis spp. pneumonia (PCP) in humans and in surrogate animal species typically occurs in the absence of CD4 T cells, as takes place during acquired immune deficiency syndrome. However, patients treated with highly active anti-retroviral therapy sometimes exhibit an exacerbation of diseases such as PCP that coincides with resurgent CD4 T cells, a phenomenon known as immune reconstitution disease. We used an animal model of PCP using the B-cell-deficient muMT mouse together with antibody-mediated depletion of various T-cell subsets to examine the role of CD4 and CD8 T cells in the development of pathology in PCP. Although overt pathology occurs in the presence of CD4 T cells only, CD8 T cells only, or both, pulmonary injury occurs via different paths, depending on the complement of T cells present. Surprisingly, profound damage occurred when only CD4 T cells were present, and this pathology coincided with enhanced recruitment and activation of eosinophils and strong type 2 cytokine polarization in the alveolar environment. In addition, CD8 T cells can act to moderate this CD4 T cell-mediated pathology, possibly by increasing the ratio of putative CD25+ suppressor CD4 T cells to CD25- effector CD4 T cells.

UVA1 radiation (340–400nm) interferes with the perforin-granule system of CD8hi+ cytotoxic T lymphocytes in vitro

UVA1-irradiation was introduced as an innovative and effective phototherapy of atopic dermatitis (AD) and other skin diseases. In AD, a defect of a central apoptosis inducing effector system involved in immunoregulation and immune defense, i.e., the system of perforin-granules in cytotoxic T lymphocytes (CTL), was recently reported: perforin-reduction and perforin-hyperreleasability. We now investigated UVA1-effects on the perforin-granule system in vitro. Peripheral blood CTLs were exposed in vitro to 10-100 J/cm2 UVA1 (340-400 nm), and to 30-150 mJ/cm2 UVB (280-315 nm) as a control. A time-dependent perforin-granule release was induced by phorbol 12-myristate 13-acetate (PMA) and ionomycin. This release was inhibited dose-dependently by UVA1, but not by UVB. An UVA1-dose dependent pattern of sensitive (80%) and insensitive (20%) individuals was found. The kinetics of perforin release in AD-CTLs, i.e. hyperreleasability, was normalized by 50 J/cm2 UVA1 in vitro. Sodium azide as a quencher of reactive oxygen species prevented the UVA1-mediated inhibition of perforin-granule release. Our data demonstrate for the first time a dose- and wavelength-dependent UVA1-effect in vitro on a major effector system of cytotoxic lymphocytes, the system of perforin-granules. This might contribute to the further understanding of immunomodulatory UVA1-effects in vivo.

CD8+ T-cell-mediated killing of donor dendritic cells prevents alloreactive T helper type-2 responses in vivo

Accumulating evidence indicates that, in absence of CD8+ T-cell activation, CD4+ T-cell-mediated allograft rejection is associated with a dominant Th2-cell response and eosinophil infiltrates. In this study, we analyzed the mechanisms by which CD8+ T cells regulate alloreactive CD4+ T-cell priming and differentiation into interleukin 4 (IL-4)-producing cells. We showed that interferon gamma (IFN-gamma) production by CD8+ T cells was dispensable for the inhibition of Th2-cell development, as well as tissue eosinophilia and type 2 cytokine production in the rejected grafts. Since we noticed that CD8+ T cells not only suppressed Th2 differentiation, but also down-modulated the overall priming of alloreactive CD4+ T cells, we evaluated whether CD8+ T cells act by limiting the accumulation of donor-derived dendritic cells (DCs) in lymph nodes. We found that indeed, alloreactive CD8+ T cells rapidly eliminated allogeneic DCs from T-cell areas of draining lymph nodes, through a perforin-dependent mechanism. Thus, our data demonstrate that cytotoxic T lymphocyte (CTL)-mediated clearance of allogeneic DCs is a negative feedback mechanism that limits the duration of alloantigen presentation in draining lymph nodes, thereby modulating the amplitude and polarization of the primary alloreactive CD4+ T-cell responses.

Respiratory Syncytial Virus G Protein and G Protein CX3C Motif Adversely Affect CX3CR1+T Cell Responses

Interactions between fractalkine (CX3CL1) and its receptor, CX3CR1, mediate leukocyte adhesion, activation, and trafficking. The respiratory syncytial virus (RSV) G protein has a CX3C chemokine motif that can bind CX3CR1 and modify CXCL1-mediated responses. In this study, we show that expression of the RSV G protein or the G protein CX3C motif during infection is associated with reduced CX3CR1+ T cell trafficking to the lung, reduced frequencies of RSV-specific, MHC class I-restricted IFN-gamma-expressing cells, and lower numbers of IL-4- and CX3CL1-expressing cells. In addition, we show that CX3CR1+ cells constitute a major component of the cytotoxic response to RSV infection. These results suggest that G protein and the G protein CX3C motif reduce the antiviral T cell response to RSV infection.

Carriers for the delivery of a vaccine against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a major cause of bronchiolitis and pneumonia in young children and the elderly. Despite its clinical importance, there is no licensed vaccine available at present. Vaccine development has been hampered by observations of increased pathology after RSV infection in infants vaccinated with formalin-inactivated RSV; incomplete immunity following natural infection; and the need to be effective during the neonatal period when levels of maternal antibody are high. Four categories of RSV vaccine carriers--live-attenuated RSVs, recombinant vectors expressing the protective antigens of RSV, DNA vaccines and subunit vaccines--have been evaluated in animal models and/or clinical trials. So far, studies with live-attenuated virus vaccines highlight the need to improve immunogenicity whilst maintaining a suitable level of attenuation. Studies with recombinant vectors, DNA and subunit vaccines illustrate the pivotal nature of the vaccine carrier in determining the balance between immune-mediated protection against infection and the induction of immune-mediated pulmonary pathology.

Regulatory Role of Host CD8+ T Lymphocytes in Experimental Graft-versus-Host Disease across a Single Major Histocompatibility Complex Class II Incompatibility

BACKGROUND

CD8+ T cells are known to regulate type 2 helper T cell (Th2) alloreactive immune responses but their mode of activation is unclear. We investigated the role of host CD8+ T cells in experimental Th2-type graft-versus-host disease (GVHD) where donor/recipient disparity is restricted to a single major histocompatibility complex (MHC) class II antigen.

METHODS

Immunoglobulin (Ig) E serum levels, eosinophilia and lymphoid tissue hyperplasia were compared after injection of bm12 CD4+ T cells in either wild-type or CD8+ T cell-deficient (CD8-/-) C57BL/6 mice. In vitro, we explored effects of the addition of CD8+ T cells from wild-type or IFN-gamma-/- mice in mixed leukocyte cultures prepared with beta2 microglobulin-deficient (beta2m-/-) CD4+ T cells as responders or beta2m dendritic cells as stimulators.

RESULTS

HyperIgE resolved after 3 weeks in wild-type hosts whereas it persisted for 6 weeks in CD8-/- hosts. Eosinophil infiltrates in lymph nodes were significantly enhanced in CD8-/- hosts. Increased serum levels of IL-5 and IL-13 in CD8-/- hosts confirmed the enhancement of Th2-type responses in the context of recipient CD8+ T cell deficiency. Hyperplasia of lymph nodes and spleen were similar in both groups, as well as in vivo proliferation of donor CD4+ T cells. In vitro, CD8+ T cell regulation of the alloreactive Th2 response depended on their production of IFN-gamma and did not require expression of beta2m on CD4+ T cells or antigen-presenting cells.

CONCLUSIONS

Host CD8+ T cells regulate alloreactive Th2 responses during graft-versus-host disease through an IFN-gamma dependent pathway, independently of the recognition of beta2m-associated MHC class I molecules.

Induction of balanced immunity in BALB/c mice by vaccination with a recombinant fusion protein containing a respiratory syncytial virus G protein fragment and a CTL epitope

Respiratory syncytial virus (RSV), an important pathogen of the lower respiratory tract, is responsible for severe illness both in new born and young children and in elderly people. However, development of a RSV vaccine has been hampered by the outcome of the infant trials in the 1960s with a formalin-inactivated RSV (FI-RSV) preparation. Previous studies in mice indicated that G protein immunization resulted in antibody and Th2-type response and failed to induce MHC I-restricted CD8(+) T-cell response. Vaccines designed to induce CD8(+) T-cell along with antibody response might be ideal. In the present report, a fusion protein G1F/M2 containing a RSV-G protein fragment (G: 125-225 amino acid) and a CD8(+) T-cell epitope from RSV-M2 protein was investigated. G1F/M2 was cloned, expressed in E. coli, purified and renaturated. In BALB/c mice, G1F/M2 induced not only humoral immunity but also cellular immunity. In addition, interestedly, G1F/M2 elicited balanced IgG1/IgG2a response. These results suggest that the fusion protein G1F/M2 is potential as a RSV subunit vaccine.

Immune responses and disease enhancement during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is one of the commonest and most troublesome viruses of infancy. It causes most cases of bronchiolitis, which is associated with wheezing in later childhood. In primary infection, the peak of disease typically coincides with the development of specific T- and B-cell responses, which seem, in large part, to be responsible for disease. Animal models clearly show that a range of immune responses can enhance disease severity, particularly after vaccination with formalin-inactivated RSV. Prior immune sensitization leads to exuberant chemokine production, an excessive cellular influx, and an overabundance of cytokines during RSV challenge. Under different circumstances, specific mediators and T-cell subsets and antibody-antigen immune complex deposition are incriminated as major factors in disease. Animal models of immune enhancement permit a deep understanding of the role of specific immune responses in RSV disease, assist in vaccine design, and indicate which immunomodulatory therapy might be beneficial to children with bronchiolitis.

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.

Chinchilla and murine models of upper respiratory tract infections with respiratory syncytial virus

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in infants and the elderly. While the primary infection is the most serious, reinfection of the upper airway throughout life is the rule. Although relatively little is known about either RSV infection of the upper respiratory tract or host mucosal immunity to RSV, recent literature suggests that RSV is the predominant viral pathogen predisposing to bacterial otitis media (OM). Herein, we describe mouse and chinchilla models of RSV infection of the nasopharynx and Eustachian tube. Both rodent hosts were susceptible to RSV infection of the upper airway following intranasal challenge; however, the chinchilla proved to be more permissive than the mouse. The chinchilla model will likely be extremely useful to test the role of RSV in bacterial OM and the efficacy of RSV vaccine candidates designed to provide mucosal and cytotoxic T-lymphocyte immunity. Ultimately, we hope to investigate the relative ability of these candidates to potentially protect against viral predisposal to bacterial OM.

CD8+ alphabeta T cells can mediate late airway responses and airway eosinophilia in rats

BACKGROUND

The function of CD8+ T-cell subsets in mediating late allergic responses is incompletely understood.

OBJECTIVE

We sought to test the hypothesis that CD8+ alphabeta T cells are proinflammatory in the airways in vivo by using a well-characterized animal model and the technique of adoptive transfer.

METHODS

Brown Norway rats were administered CD8 + alphabeta T cells (10 6 ) intraperitoneally purified from lymph node cells of either naive or ovalbumin (OVA)-sensitized rats and were challenged with aerosolized OVA 2 days later. Control rats were sensitized to 100 mug of OVA in Al(OH) 3 subcutaneously or sham sensitized to saline and were OVA challenged 2 weeks later.

RESULTS

The OVA-sensitized and OVA-challenged group and the recipients of OVA-primed CD8+ alphabeta T cells had significant late airway responses calculated from lung resistance measured for an 8-hour period after challenge compared with the naive CD8 + alphabeta T cell-transferred group and the sham-sensitized control group. The number of eosinophils in bronchoalveolar lavage fluid increased in the OVA-sensitized group and the OVA-primed CD8+ alphabeta T-cell recipients compared with numbers in the naive CD8+ alphabeta T-cell recipients and the sham-sensitized control group. IL-4 and IL-5 cytokine mRNA expression in bronchoalveolar lavage fluid increased in the OVA-sensitized group and the OVA-primed CD8+ alphabeta T-cell recipients compared with that in the sham-sensitized group.

CONCLUSION

We conclude that antigen-primed CD8 + alphabeta T cells might have a proinflammatory role in allergen-driven airway responses in the rat.

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.

Gene-gun DNA vaccination aggravates respiratory syncytial virus-induced pneumonitis

A CD8+ T-cell memory response to respiratory syncytial virus (RSV) was generated by using a DNA vaccine construct encoding the dominant Kd-restricted epitope from the viral transcription anti-terminator protein M2 (M282–90), linked covalently to human β 2-microglobulin (β 2m). Cutaneous gene-gun immunization of BALB/c mice with this construct induced an antigen-specific CD8+ T-cell memory. After intranasal RSV challenge, accelerated CD8+ T-cell responses were observed in pulmonary lymph nodes and virus clearance from the lungs was enhanced. The construct induced weaker CD8+ T-cell responses than those elicited with recombinant vaccinia virus expressing the complete RSV M2 protein, but stronger than those induced by a similar DNA construct without the β 2m gene. DNA vaccination led to enhanced pulmonary disease after RSV challenge, with increased weight loss and cell recruitment to the lung. Depletion of CD8+ T cells reduced, but did not abolish, enhancement of disease. Mice vaccinated with a construct encoding a class I-restricted lymphocytic choriomeningitis virus epitope and β 2m suffered more severe weight loss after RSV infection than unvaccinated RSV-infected mice, although RSV-specific CD8+ T-cell responses were not induced. Thus, in addition to specific CD8+ T cell-mediated immunopathology, gene-gun DNA vaccination causes non-specific enhancement of RSV disease without affecting virus clearance.

Recombinant respiratory syncytial virus lacking secreted glycoprotein G is attenuated, non-pathogenic but induces protective immunity

Respiratory syncytial virus (RSV) causes intense pulmonary inflammatory responses in some infected infants. The surface attachment protein 'G' of RSV has membrane-bound and secreted forms and shows homology to the CX3C chemokine fractalkine. Using recombinant techniques, we generated replication-competent recombinant clonal RSV expressing normal G proteins ('rRSV') or only the membrane-bound form of G ('Gmem rRSV'). Both recombinants grew well in HEp-2 cells, but after primary intranasal infection in mice, pulmonary Gmem rRSV replication was reduced tenfold compared to parental or rRSV; moreover, CCL2 and CCL5 production was greatly reduced and no apparent disease or pulmonary cellular infiltration was observed. However, Gmem rRSV-infected mice developed good antibody responses and were fully protected against subsequent intranasal challenge with parental virus. Even in mice sensitized to G by cutaneous infection with recombinant vaccinia expressing G, intranasal challenge with Gmem rRSV caused insignificant disease. We conclude that secreted G is a key viral product assisting virus replication in vivo, enhancing CCL2 and CCL5 production and promoting illness. Engineered RSV mutants lacking the ability to secrete G are thus promising vaccine candidates.