Role of T lymphocyte subsets in the pathogenesis of primary infection and rechallenge with respiratory syncytial virus in mice

The role of CD4+ and CD8+ T lymphocytes in terminating respiratory syncytial virus (RSV) replication, causing disease, and protecting from reinfection was investigated using a BALB/c mouse model in which CD4+ or CD8+ lymphocytes or both were depleted by injections of Mab directed against the respective mouse lymphocyte determinants. Kinetics of RSV replication, illness, and pathology were assessed after primary infection and rechallenge. Both CD4+ and CD8+ lymphocyte subsets were involved in terminating RSV replication after primary infection. When both T lymphocyte subsets were depleted RSV replication was markedly prolonged, yet no illness was evident, suggesting that host immune response rather than viral cytocidal effect was the primary determinant of disease in mice. Both CD4+ and CD8+ lymphocytes contributed to illness, although CD8+ lymphocytes appeared to play the dominant role in this particular system. Analysis of histological responses suggested that CD4+ lymphocytes were required for the appearance of peribronchovascular lymphocytic aggregates seen in normal mice after rechallenge, and that the presence of alveolar lymphocytes was correlated with illness. It is postulated that antibody is an illness-sparing mechanism for protecting mice from RSV infection, and that T lymphocytes are an important determinant of illness. Further delineation of RSV-induced immunopathogenesis in primary infection and reinfection will provide important information for the development of vaccine strategies.

Cytotoxic T cells clear virus but augment lung pathology in mice infected with respiratory syncytial virus

We have examined the function of class I MHC-restricted cytotoxic T cells in experimental respiratory syncytial virus (RSV) infection of BALB/c mice by transfer of T cell line MJC-A2 and CTL clone E8a into RSV-infected mice. The T cell line cleared pulmonary RSV infection within 5 d in persistently infected gamma-irradiated mice, but caused acute respiratory disease. This was only seen in infected mice and was often lethal after transfer of greater than 3 x 10(6) CTL. Lower numbers of CTL produced less severe disease but still cleared lung RSV, albeit over a longer time course (up to 10 d). Clearance of lung RSV in immunocompetent mice by the T cell line and CTL clone was again accompanied by acute and sometimes lethal respiratory disease. Bronchoalveolar lavage showed severe lung hemorrhage and frequent neutrophil efflux in mice with CTL-augmented disease.

Primary respiratory syncytial virus infection in mice

A mouse model of respiratory syncytial virus (RSV) infection is described. A high-titered, large-volume inoculum results in replication of RSV to a high titer in lungs of BALB/c mice. Mice older than 15 weeks of age are more susceptible to RSV infection. Titers up to 10(6.9) plaque-forming units (pfu)/gram lung can be attained in 32-week-old mice. Older mice experience a clinical illness manifested by ruffled fur, reduced activity, and weight loss. Lung histology of older mice infected with RSV shows bronchiolitis and increased number of lymphocytes and macrophages in alveolar spaces compared with that of mice less than 8 weeks old. This model will serve as the basis for investigating immunodeterminants of recovery and protection from RSV infection.

Syncytial giant-cell hepatitis. Sporadic hepatitis with distinctive pathological features, a severe clinical course, and paramyxoviral features

BACKGROUND AND METHODS

We describe a new form of hepatitis, occurring in 10 patients over a period of six years, characterized clinically by manifestations of severe hepatitis, histologically by large syncytial giant hepatocytes, and ultrastructurally by intracytoplasmic structures consistent with paramyxoviral nucleocapsids.

RESULTS

The patients ranged in age from 5 months to 41 years. The tentative clinical diagnosis before biopsy was non-A, non-B hepatitis in five patients and autoimmune chronic active hepatitis in the others. Five patients underwent liver transplantation; the others died. The diagnosis of syncytial giant-cell hepatitis was established pathologically. The liver cords were replaced in all 10 patients by syncytial giant cells with up to 30 nuclei. In 8 of the 10 the cytoplasm contained pleomorphic particles of 150 to 250 microns, filamentous strands, and particles of 14 to 17 nm with peripherally disposed spikes resembling paramyxoviral nucleocapsids. Structures resembling degenerated forms were found in the other two patients. One of two chimpanzees injected with a liver homogenate from the index patient had an increase in the titer of paramyxoviral antibodies, probably an anamnestic reaction to previous paramyxoviral infection, suggesting that a paramyxoviral antigen but not viable virus was present in the liver homogenate.

CONCLUSIONS

Although further virologic studies will be required for precise classification, we believe that paramyxoviruses should be considered in patients with severe sporadic hepatitis.

Pulmonary eosinophilic response to respiratory syncytial virus infection in mice sensitized to the major surface glycoprotein G

To investigate the contribution of immunity to individual respiratory syncytial (RS) virus proteins to the augmentation of pulmonary pathology, mice were scarified with recombinant vaccinia viruses (rVV) expressing individual RS virus proteins. The pulmonary response to infection with RS virus was monitored by bronchoalveolar lavage (BAL). In mice vaccinated with the major surface glycoprotein (G), 14-25% of BAL cells were eosinophils; these comprised less than 3% of BAL cells from other groups of mice after RS virus challenge. Mice sensitized to the G or fusion (F) proteins developed lung haemorrhage and those sensitized to G, F or nucleoprotein (N) showed pulmonary polymorphonucleocyte efflux. To investigate the concomitant changes in local T-cell subsets, BAL cells were stained with mAbs to CD4, CD8, CD45RB, alpha beta and gamma delta T cell receptor (TCR) proteins. Three colour flow cytometry showed that most cells were CD3+CD4+ alpha beta+gamma delta+ or CD3+CD8+ alpha beta+gamma delta-, although some CD4-CD8-SIg- cells were also identified. Most of these 'null' cells lacked CD3, but CD3+ null cells from rVV-G or -F primed mice bore either alpha beta and gamma delta TCR in approximately equal numbers. The intensity of staining for CD45RB declined rapidly after infection with RS virus on both CD4 and CD8 cells. The rate of loss of CD45RB on CD4 T cells was accelerated by prior sensitization with rVV-G, consistent with conversion to helper T cell subsets producing eosinophil-promoting cytokines. The eosinophilic reaction to RS virus infection therefore specifically reflects sensitization to G protein, but sensitization to other proteins can also cause distinct pathological effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathologic and immunocytochemical studies of morbillivirus infection in striped dolphins (Stenella coeruleoalba)

Hundreds of striped dolphins (Stenella coeruleoalba) died along the Spanish Mediterranean coast during the second half of 1990. We necropsied 58 dolphins. Partial collapse of the lungs with patchy atelectasis, subcutaneous edema, icterus, and stomatitis were the most prominent gross morphologic changes. Histologically, a bronchiolo-interstitial pneumonia was the most frequent lesion (72% of the animals). It was characterized by hyperplasia of alveolar epithelial type II cells and formation of multinucleate syncytia in alveolar and bronchiolar lumina. Other prominent lesions were encephalitis (69%), lymphoid depletion, and formation of multinucleate syncytia in the cortex of lymph nodes. The distribution of morbillivirus antigen was investigated in 23 well-preserved dolphins using a monoclonal antibody against the hemagglutinin glycoprotein of phocine distemper virus. Positive immunostaining was found in brain (77%), in lung (70%), and in mesenteric (61%), mediastinal (47%), and prescapular (45%) lymph nodes. Phocine distemper virus antigen was demonstrated less frequently in trachea, stomach, biliary epithelium, intestine, kidney, and mammary gland. Necrotizing-hemorrhagic pneumonia and encephalitis due to Aspergillus fumigatus were seen in three dolphins, whereas two animals had lesions of toxoplasmosis. Changes in our dolphins were similar to those caused by distemper in seals and porpoises. The origin of the dolphin virus and the relationships among dolphin, seal, and porpoise morbilli viruses are unknown.

Respiratory syncytial virus-induced acute lung injury in adult patients with bone marrow transplants: a clinical approach and review of the literature

Acute lung injury induced by respiratory syncytial virus (RSV) is a major cause of morbidity and mortality in patients who have undergone bone marrow transplantation. Twenty-nine of the 74 patients who received bone marrow transplants at the University of Minnesota during a 1-year period developed evidence of acute lung injury, and RSV was identified as the cause in 8. We discuss the clinical course of these 8 patients and offer a clinical approach to RSV infection occurring after bone marrow transplantation. We also review the immune response to infection with RSV and relate this information to the nature and degree of immunosuppression present in patients undergoing this type of transplantation. We found bronchoalveolar lavage with rapid antigen detection to be particularly useful for the prompt diagnosis of this serious infection. The virus was obtained from the lower respiratory tract of each patient and was identified in lavage effluent by culture and by antigen detection (ELISA). The mean time to a positive culture was 6 days, while detection of antigens of respiratory syncytial virus by ELISA was completed within 18 hours in all cases. The clinical progression of the illness in immunocompromised patients appears to be the same as in non-immunocompromised persons: upper respiratory tract infection and illness precede lower respiratory tract infection and acute lung injury. Seven of our 8 patients had upper respiratory tract symptoms or abnormal sinus radiographs, and upper respiratory specimens (cultures and ELISA from nasopharynx, throat, and sputum) were positive in 5 of 8 patients. Six patients developed RSV-induced lung injury before marrow engraftment; 4 of them had respiratory failure requiring mechanical ventilation and died, including 3 in whom RSV was eliminated from the lower respiratory tract following treatment with ribavirin aerosol. Two additional pre-engraftment patients had only relatively mild lung injury 4 days after beginning treatment with ribavirin for RSV infection in the upper respiratory tract. Their recovery suggests that early treatment may ameliorate RSV-induced lung injury. The remaining 2 patients developed lung injury after marrow engraftment. Both of these patients had clear chest radiographs, responded clinically to ribavirin, and survived. RSV is a potentially treatable cause of life-threatening lung injury, if the physician is aggressive in identifying the virus in the upper respiratory tract before evidence of lung injury appears. Rapid detection methods are essential when bone marrow transplant patients have fever along with signs, symptoms, or radiographic indications of nasal or sinus disorders.(ABSTRACT TRUNCATED AT 400 WORDS)

Defective viral genomes arising in vivo provide critical danger signals for the triggering of lung antiviral immunity

The innate immune response to viruses is initiated when specialized cellular sensors recognize viral danger signals. Here we show that truncated forms of viral genomes that accumulate in infected cells potently trigger the sustained activation of the transcription factors IRF3 and NF-κB and the production type I IFNs through a mechanism independent of IFN signaling. We demonstrate that these defective viral genomes (DVGs) are generated naturally during respiratory infections in vivo even in mice lacking the type I IFN receptor, and their appearance coincides with the production of cytokines during infections with Sendai virus (SeV) or influenza virus. Remarkably, the hallmark antiviral cytokine IFNβ is only expressed in lung epithelial cells containing DVGs, while cells within the lung that contain standard viral genomes alone do not express this cytokine. Together, our data indicate that DVGs generated during viral replication are a primary source of danger signals for the initiation of the host immune response to infection.

Cotton rats previously immunized with a chimeric RSV FG glycoprotein develop enhanced pulmonary pathology when infected with RSV, a phenomenon not encountered following immunization with vaccinia--RSV recombinants or RSV

In studies conducted in the 1960s, children previously immunized with a formalin-inactivated respiratory syncytial virus (RSV) vaccine (FI-RSV) developed a greater incidence and severity of pulmonary disease during subsequent natural RSV infection than did controls. It was previously shown that cotton rats immunized with FI-RSV or immunoaffinity-purified fusion (F) glycoprotein developed enhanced pulmonary histopathology following intranasal challenge with RSV. In the present studies, various forms of immunization, including parenteral inoculation of an immunoaffinity-purified F glycoprotein or a chimeric FG glycoprotein produced in insect cells using a baculovirus vector (Bac-FG), intradermal infection with a vaccinia-F recombinant (Vac-F) or intranasal infection with an adenovirus-F recombinant (Ad-F) or RSV, were compared for immunogenicity, efficacy and ability to alter the host so that enhanced pulmonary histopathology developed during RSV infection 3 months after immunization. Immunization of cotton rats with F glycoprotein, Bac-FG, Vac-F, Ad-F or infection with RSV induced high levels of ELISA-F antibodies, but the antibodies induced by purified F glycoprotein of Bac-FG had low levels of neutralizing activity. Immunization with Vac-F or Ad-F, or infection with RSV induced a high level of resistance to pulmonary RSV replication, whereas animals immunized with Bac-FG or FI-RSV were only partially protected. Following RSV challenge, animals immunized with purified F glycoprotein or Bac-FG developed the highest levels of bronchiolar and alveolar histopathology, those immunized with FI-RSV had intermediate levels, and those immunized with Vac-F or RSV had histopathology scores at control levels. Ad-F immunized animals had elevated scores of bronchiolar but not alveolar histopathology; however, this finding was not reproducible. Passive transfer of pooled immune sera from animals infected with RSV or Vac-F and Vac-G was highly protective, whereas pooled sera from animals immunized with Bac-FG failed to protect the lungs against RSV challenge. Increased pulmonary histopathology was not observed in the passively immunized animals following RSV challenge, suggesting that the histopathology was mediated by RSV-specific T cells. These data indicate that subunit F glycoprotein or chimeric FG vaccines share with FI-RSV the properties of (i) induction of F antibodies with low neutralizing activity and (ii) enhancement of pulmonary histopathology during subsequent RSV infection. These observations confirm the need for caution in studies involving the administration of RSV subunit vaccines to seronegative humans.

CXCR3 directs antigen-specific effector CD4+ T cell migration to the lung during parainfluenza virus infection

Effector T cells are a crucial component of the adaptive immune response to respiratory virus infections. Although it was previously reported that the chemokine receptors CCR5 and CXCR3 affect trafficking of respiratory virus-specific CD8+ T cells, it is unclear whether these receptors govern effector CD4+ T cell migration to the lungs. To assess the role of CCR5 and CXCR3 in vivo, we directly compared the migration of Ag-specific wild-type and chemokine receptor-deficient effector T cells in mixed bone marrow chimeric mice during a parainfluenza virus infection. CXCR3-deficient effector CD4+ T cells were 5- to 10-fold less efficient at migrating to the lung compared with wild-type cells, whereas CCR5-deficient effector T cells were not impaired in their migration to the lung. In contrast to its role in trafficking, CXCR3 had no impact on effector CD4+ T cell proliferation, phenotype, or function in any of the tissues examined. These findings demonstrate that CXCR3 controls virus-specific effector CD4+ T cell migration in vivo, and suggest that blocking CXCR3-mediated recruitment may limit T cell-induced immunopathology during respiratory virus infections.

Effectiveness of topically administered neutralizing antibodies in experimental immunotherapy of respiratory syncytial virus infection in cotton rats

Initial studies of the prophylactic effect of parenterally administered respiratory syncytial virus (RSV)-neutralizing antibodies in cotton rats indicated that virus replication in lung tissues was restricted when animals with preexisting antibody titers in serum of 1:100 or more (as measured by plaque reduction) were challenged intranasally with 10(4) PFU of virus. Subsequently, a therapeutic effect of parenterally administered RSV antibodies (present in human gamma globulin) was demonstrated in both cotton rats and owl monkeys. Parenteral inoculation of RSV-infected cotton rats or owl monkeys with purified human immunoglobulin licensed for intravenous administration in humans (IVIG) effected a 10(-1.7) to 10(-2.7) reduction in the level of pulmonary virus at the height of infection. Because of these encouraging results, we examined topical administration of IVIG to determine whether it was also effective and whether it offered an advantage over the parenteral route with regard to simplicity and the dose required for full therapeutic effect. IVIG (0.025 g/kg) administered topically by the intranasal route to anesthetized cotton rats at the height of RSV infection effected a 10(2.2)-fold reduction in viral titers of pulmonary tissues and a complete clearance of detectable virus in 92% of the animals within 24 h. In contrast, 4 g of IVIG per kg was required to produce a comparable therapeutic effect when the material was administered parenterally. Thus, the therapeutic effect of IVIG was 160 times greater by the topical route than by parenteral inoculation.

Demonstration of respiratory syncytial virus in an autopsy series

Respiratory syncytial virus (RSV) antigen was demonstrated in formalin-fixed, paraffin-embedded autopsy tissue using an immunoperoxidase technique. Eighteen autopsy cases were selected on the basis of one of the following criteria: a positive culture for RSV, antemortem or postmortem; positive ELISA test for RSV, antemortem or postmortem; or postmortem histology suggestive of paramyxovirus infection. Controls included three cases from which parainfluenza or influenza virus had been cultured and a case in which the clinical diagnosis of measles was firmly established. Sections of formalin-fixed, paraffin-embedded tissue were stained with a rabbit anti-RSV antibody (Dako) using an immunoperoxidase technique. Staining was achieved in 12 cases. This included 6 of 7 cases selected because of positive cultures or ELISA tests for RSV. The other 6 cases in which RSV was identified by the described technique lacked culture or ELISA confirmation. Granular and globular staining was seen in the cytoplasm of respiratory epithelial cells and syncytial giant cells. None of the control cases stained for RSV. The histology of RSV lungs was consistent with changes described in the literature for RSV infection, although pneumonic consolidation and syncytial giant cells were more prominent in this series.

IFN-alpha regulates Toll-like receptor-mediated IL-27 gene expression in human macrophages

IL-27 is a novel member of the IL-12 cytokine family. IL-27 has pro- and anti-inflammatory properties, and it controls the responses of adaptive immunity. It promotes the differentiation of naïve Th cells and suppresses the effector functions of Th17 cells. Biologically active IL-27 is a heterodimer composed of EBV-induced gene 3 (EBI3) and p28 proteins. We report that TLR-dependent expression of IL-27 in human macrophages is mediated by IFN-alpha. Stimulation of macrophages with agonists for TLR3 {polyinosinic:polycytidylic acid [poly(I:C)]}, TLR4 (LPS), or TLR7/8 (R848) results in concurrent expression of EBI3 and p28. The p28 expression is inhibited with neutralizing anti-IFN-alpha antibodies. Unlike poly(I:C), LPS, and R848, TLR2 agonist (S)-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-N-palmitoyl-(R)-Cys-(S)-Ser(S)-Lys4-OH trihydrochloride does not stimulate macrophages to produce IFN-alpha, and therefore, it is not able to turn on the expression of p28. There is an IFN-stimulated response element (ISRE) in the p28 gene promoter. IFN-alpha enhances the expression of IFN regulatory factor 1 (IRF-1) in macrophages and induces binding of IRF-1 to the p28 ISRE site. The data provide a mechanistic basis for the IFN-alpha-mediated activation of IL-27. The data emphasize a role of IFN-alpha in immune responses, which rely on the recognition of pathogens by TLRs.

An epidemic of respiratory syncytial virus in elderly people: clinical and serological findings

In 1984-1985, an outbreak of respiratory syncytial virus (RSV) infection occurred in two geriatric wards. Among 68 patients (mean age +/- SD = 82.5 +/- 12.5 with respiratory signs, 52 had signs caused by RSV infection. Among all patients, the clinical and serological attack rates were 61.2% and 75.0%, respectively. The most frequent clinical presentation was intensive coughing (96.1%) and fever (96.1%) associated with expectorate (63.5%). The duration of the respiratory symptoms was 5 to 7 days. The disease gradually resolved, although in eight (15.4%) patients complications occurred. For periods of up to 1 year after infection, 172 sera were obtained and tested by complement fixation test (CFT), fluorescent assays for titrating specific IgG, IgA, and IgM, and Western blotting. Specific IgM appeared in six (11.5%) of the infected patients and peaked 2 to 6 months after infection, and there was no significant correlation with severity of clinical symptoms. However, higher peak G and A antibody responses were observed in persons with rales (CFT: P = 0.008; IgG: P = 0.042; IgA: P = 0.020), cough (IgG: P = 0.034), sputum (IgG: P = 0.030), dyspnea (CFT: P = 0.024), conjunctivitis (CFT: P = 0.025), and bronchitis (CFT: P = 0.018). The temporal patterns of IgA and CFT results were found to be similar, whereas IgG peaked later, i.e., between 2 and 6 months. The patients with the most severe symptoms had the highest antibody titers obtained by conventional tests and by Western blots. Thus, RSV can be an epidemic pathogen among elderly persons, although this illness is usually mild.

Immunization of cotton rats with the fusion (F) and large (G) glycoproteins of respiratory syncytial virus (RSV) protects against RSV challenge without potentiating RSV disease

A formalin-inactivated respiratory syncytial virus (RSV) vaccine tested 22 years ago failed to protect infant vaccinees against RSV infection or disease. Instead, lower respiratory tract disease was enhanced during subsequent infection by RSV. Enhancement of pulmonary pathology is also observed when cotton rats are immunized with formalin-inactivated RSV and subsequently infected with this virus. A major question that must be addressed for each new paramyxovirus vaccine is whether the immunogen possesses the capacity to potentiate disease. In the present study, we evaluated a newly developed purified F and G glycoprotein vaccine over a wide dosage range for immunogenicity, efficacy and capacity to potentiate pulmonary pathology in cotton rats. In addition, a formalin-inactivated RSV vaccine, which served as a positive control for enhancement of pulmonary pathology, was evaluated simultaneously. The results of these comparisons indicate that the purified F and G glycoprotein vaccine was highly immunogenic and was efficacious even in animals that developed low levels of serum-neutralizing antibodies. Furthermore, the F and G vaccine did not induce potentiation of pulmonary pathology. In contrast, formalin-inactivated RSV potentiated RSV pulmonary histopathology, but there was a sparing of potentiation at high and low doses. Both the formalin-inactivated RSV and purified F and G preparations induced a high level of serum antibodies capable of binding to purified F and G glycoproteins but both sets of antibodies had significantly reduced neutralizing activity. These results are encouraging because they suggest that purified paramyxovirus glycoproteins might be used safely as a vaccine.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutrophils in respiratory viral infections

Viral respiratory infections are a common cause of severe disease, especially in infants, people who are immunocompromised, and in the elderly. Neutrophils, an important innate immune cell, infiltrate the lungs rapidly after an inflammatory insult. The most well-characterized effector mechanisms by which neutrophils contribute to host defense are largely extracellular and the involvement of neutrophils in protection from numerous bacterial and fungal infections is well established. However, the role of neutrophils in responses to viruses, which replicate intracellularly, has been less studied. It remains unclear whether and, by which underlying immunological mechanisms, neutrophils contribute to viral control or confer protection against an intracellular pathogen. Furthermore, neutrophils need to be tightly regulated to avoid bystander damage to host tissues. This is especially relevant in the lung where damage to delicate alveolar structures can compromise gas exchange with life-threatening consequences. It is inherently less clear how neutrophils can contribute to host immunity to viruses without causing immunopathology and/or exacerbating disease severity. In this review, we summarize and discuss the current understanding of how neutrophils in the lung direct immune responses to viruses, control viral replication and spread, and cause pathology during respiratory viral infections.

Controls for lung dendritic cell maturation and migration during respiratory viral infection

Dendritic cells are ideally suited to orchestrate the innate and adaptive immune responses to infection, but we know little about how these cells respond to infection with common respiratory viruses. Paramyxoviral infections are the most frequent cause of serious respiratory illness in childhood and are associated with an increased risk of asthma. We therefore used a high-fidelity mouse model of paramyxoviral respiratory infection triggered by Sendai virus to examine the response of conventional and plasmacytoid dendritic cells (cDCs and pDCs, respectively) in the lung. We found that pDCs are scarce at baseline but become the predominant population of lung dendritic cells during infection. This recruitment allows for a source of IFN-alpha locally at the site of infection. In contrast, cDCs rapidly differentiate into myeloid cDCs and begin to migrate from the lung to draining lymph nodes within 2 h after viral inoculation. These events cause the number of lung cDCs to decrease rapidly and remain decreased at the site of viral infection. Maturation and migration of lung cDCs depends on Ccl5 and Ccr5 signals because these events are significantly impaired in Ccl5(-/-) and Ccr5(-/-) mice. cDCs failure to migrate to draining lymph nodes in Ccl5(-/-) or Ccr5(-/-) mice is associated with impaired up-regulation of CCR7 that would normally direct this process. Our results indicate that pDCs and cDCs respond distinctly to respiratory paramyxoviral infection with patterns of movement that should serve to coordinate the innate and adaptive immune responses, respectively.

A human respiratory syncytial virus (RSV) primate model of enhanced pulmonary pathology induced with a formalin-inactivated RSV vaccine but not a recombinant FG subunit vaccine

Human respiratory syncytial virus (RSV) is the leading cause of severe bronchiolitis and pneumonia in infants. RSV vaccine development has been stifled for the past 23 years because infants vaccinated with formalin-inactivated (FI) RSV have experienced exacerbated disease upon RSV infection. This exacerbated disease phenomenon is poorly understood, in part because of the lack of a primate model that exhibits a similar exacerbated disease state. Vaccination of African green monkeys with either FI RSV or a genetically engineered subunit vaccine termed FG glycoprotein reduced replication of challenge virus. However, only vaccination with FI RSV induced an enhanced pulmonary pathologic response to RSV infection. Pulmonary inflammatory scores in the FG glycoprotein-vaccinated monkeys were no greater than in monkeys vaccinated with adjuvant alone. This is the first demonstration of RSV vaccine-induced enhanced pathology in a primate and illustrates that a subunit vaccine has the potential of circumventing this exacerbated disease phenomenon.

Encephalomyelitis, reproductive failure and corneal opacity (blue eye) in pigs, associated with a paramyxovirus infection

A new clinicopathological disorder associated with a paramyxovirus infection in pigs is described. Central nervous system manifestations and corneal opacity are the main features in piglets two to 21 days old. Older pigs seem to be more resistant and only corneal opacity is commonly observed. In pregnant sows the virus appears to be responsible for reproductive disturbances such as stillbirth, mummification and a return to oestrus. The changes are mainly microscopic and characterised by a non-suppurative encephalomyelitis, interstitial pneumonia and anterior uveitis with corneal oedema. Experimental infection of one-day-old piglets with the virus reproduced clinical signs similar to those described in naturally infected piglets. The virus was recovered from the tonsils, lung and brain of the experimentally infected piglets between the fourth and 20th day after infection.

Cutting edge: virus-specific CD4+ memory T cells in nonlymphoid tissues express a highly activated phenotype

Recent studies have shown that CD4(+) memory T cells persist in nonlymphoid organs following infections. However, the development and phenotype of these peripheral memory cells are poorly defined. In this study, multimerized MHC-Ig fusion proteins, with a covalently attached peptide sequence from the Sendai virus hemagglutinin/neuraminidase gene, have been used to identify virus-specific CD4(+) T cells during Sendai virus infection and the establishment of peripheral CD4(+) memory populations in the lungs. We show declining frequencies of virus-specific CD4(+) T cells in the lungs over the course of approximately 3 mo after infection. Like peripheral CD8(+) T cells, the CD4(+) have an acutely activated phenotype, suggesting that a high level of differentiation is required to reach the airways and persist as memory cells. Differences in CD25 and CD11a expression indicate that the CD4(+) cells from the lung airways and parenchyma are distinct memory populations.

Inflammatory infiltration of the upper airway epithelium during Sendai virus infection: involvement of epithelial dendritic cells

We undertook the present study to determine the nature of the cellular inflammatory response within the epithelial lining of the rat trachea during a Sendai virus infection. In particular, we aimed to investigate changes in the resident population of epithelial dendritic cells. Rats were infected with Sendai virus, and tracheal tissue was examined immunohistochemically at various times with a panel of cell-specific monoclonal antibodies. We found that Sendai virus infection was restricted to only the lumenal layer of epithelial cells and that virus nucleoprotein was present from days 2 to 5 postinfection. Starting around day 2 or 3, there was a large cellular influx consisting of macrophages, neutrophils, NK cells, and T cells; this coincided with expression of high levels of ICAM-1 on the basal (uninfected) layers of the epithelium. The T cells were mostly alphabeta T-cell receptor positive; however, a smaller influx of gammadelta T cells also took place. The number of resident dendritic cells increased markedly during infection, with numbers peaking around day 5 and remaining elevated 14 days later. The peak of the inflammatory response occurred on day 5 and declined thereafter, with the exception of dendritic cell and alphabeta T-cell numbers, which remained elevated. Starting around day 3, the tracheal epithelial cells expressed increasing levels of major histocompatibility complex class II antigen. This expression was maximal at day 5 and declined rapidly thereafter. In vitro culture of tracheal segments demonstrated that viral infection was not per se responsible for the upregulation of class II expression and that when cultured in the presence of gamma interferon, class II antigen was induced on epithelial cells.

Antigen-nonspecific recruitment of Th2 cells to the lung as a mechanism for viral infection-induced allergic asthma

Respiratory viral infections have been shown to trigger exacerbations of asthma; however, the mechanism by which viral Th1-type inflammation exacerbates an allergic Th2-type disease remains unclear. We have previously shown that although adoptively transferred Th2 cells are inefficiently recruited to the lung in response to Ag, cotransfer of Th1 cells can increase accumulation of Th2 cells. In this study, we show that respiratory viral infection increases recruitment of resting Th2 cells specific for OVA even in the absence of OVA challenge. These findings suggest that the mechanism by which Th1-type inflammation enhances allergy is via an effect on recruitment. To study the role of the antigenic specificity of Th1 cells in the enhancement of Th2 cell recruitment and to determine whether virus-induced recruitment of OVA-specific Th2 cells may involve Th1 cells specific to a different Ag, we tested whether hen egg lysozyme-specific Th1 cells could synergize with OVA-specific Th2 cells. Challenge of mice that had received adoptively transferred Th1 cells plus Th2 cells induced the expression of inflammatory chemokines in the lung and increased both recruitment and activation of Th2 cells, leading to eosinophil recruitment, even in the absence of challenge with the Th2 Ag. Interestingly, as IL-5 supports eosinophilia, culture of resting Th2 cells with fresh APC induced production of IL-5 in the absence of specific Ag. Thus, Ag-specific activation of Th1 cells enhances the recruitment potential of the lung leading to recruitment and activation of Th2 cells. This implies that circulating Th2 cells in allergic individuals could enter the lungs in response to infection or inflammation and become activated to trigger allergy.

Cutting Edge: Effector Memory CD8+ T Cells in the Lung Airways Retain the Potential to Mediate Recall Responses

Previous studies have shown that long-lived memory CD8(+) T cells persist in the lung airways following the resolution of a murine Sendai virus infection. These cells are CD11a(low), noncytolytic, and do not proliferate in the lung airways raising the possibility that they are "end stage" or terminally differentiated memory cells. In this current report, we investigated the functional characteristics of these cells by analyzing their capacity to respond to secondary viral infection outside of the lung environment. We show that, after transfer into the bloodstream, CD11a(low) memory T cells from the lung airways can return to the secondary lymphoid tissue and respond to a secondary viral challenge. Furthermore, these cells re-express CD11a, which may contribute to their migratory and proliferative capacity. These data demonstrate that lung airway memory CD8(+) T cells are not terminally differentiated cells and retain the capacity to mediate recall responses to infection.

MyD88-Mediated Instructive Signals in Dendritic Cells Regulate Pulmonary Immune Responses during Respiratory Virus Infection

Respiratory syncytial virus (RSV) is the leading cause of respiratory disease in infants worldwide. The induction of innate immunity and the establishment of adaptive immune responses are influenced by the recognition of pathogen-associated molecular patterns by TLRs. One of the primary pathways for TLR activation is by MyD88 adapter protein signaling. The present studies indicate that MyD88 deficiency profoundly impacts the pulmonary environment in RSV-infected mice characterized by the accumulation of eosinophils and augmented mucus production. Although there was little difference in CD4 T cell accumulation, there was also a significant decrease in conventional dendritic cells recruitment to the lungs of MyD88(-/-) mice. The exacerbation of RSV pathophysiology in MyD88(-/-) mice was associated with an enhanced Th2 cytokine profile that contributed to an inappropriate immune response. Furthermore, bone marrow-derived dendritic cells (BMDC) isolated from MyD88(-/-) mice were incapable of producing two important Th1 instructive signals, IL-12 and delta-like4, upon RSV infection. Although MyD88(-/-) BMDCs infected with RSV did up-regulate costimulatory molecules, they did not up-regulate class II as efficiently and stimulated less IFN-gamma from CD4(+) T cells in vitro compared with wild-type BMDCs. Finally, adoptive transfer of C57BL/6 BMDCs into MyD88(-/-) mice reconstituted Th1 immune responses in vivo, whereas transfer of MyD88(-/-) BMDCs into wild-type mice skewed the RSV responses toward a Th2 phenotype. Taken together, our data indicate that MyD88-mediated pathways are essential for the least pathogenic responses to this viral pathogen through the regulation of important Th1-associated instructive signals.