R. Stokes Peebles

The Role of IFN in Respiratory Syncytial Virus Pathogenesis

Formalin-inactivated respiratory syncytial virus (RSV) vaccine preparations have been shown to cause enhanced disease in naive hosts following natural infection. In this study we demonstrate a similar pattern of enhanced disease severity following primary RSV infection of IFN-nonresponsive STAT1−/− mice. STAT1−/− mice showed markedly increased illness compared with wild-type BALB/c animals following RSV inoculation despite similar lung virus titers and rates of virus clearance. Histologically, STAT1−/− animals had eosinophilic and neutrophilic pulmonary infiltrates not present in wild-type or IFN-γ−/−-infected mice. In cytokine analyses of infected lung tissue, IFN-γ was induced in both STAT1−/− and wild-type mice, with preferential IL-4, IL-5, and IL-13 induction only in the STAT1−/− animals. Eotaxin was detected in the lungs of both wild-type and STAT1−/− mice following infection, with a 1.7-fold increase over wild-type in the STAT1−/− mice. Using a peptide epitope newly identified in the RSV fusion protein, we were able to demonstrate that wild-type memory CD4+ T cells stimulated by this peptide produce primarily IFN-γ, while STAT1−/−CD4+ cells produce primarily IL-13. These findings suggest that STAT1 activation by both type I (αβ) and type II (γ) IFNs plays an important role in establishing a protective, Th1 Ag-specific immune response to RSV infection.

Differential Type I Interferon Induction by Respiratory Syncytial Virus and Influenza A Virus In Vivo

ABSTRACT Type I interferon (IFN) induction is an immediate response to virus infection, and very high levels of these cytokines are produced when the Toll-like receptors (TLRs) expressed at high levels by plasmacytoid dendritic cells (pDCs) are triggered by viral nucleic acids. Unlike many RNA viruses, respiratory syncytial virus (RSV) does not appear to activate pDCs through their TLRs and it is not clear how this difference affects IFN-α/β induction in vivo. In this study, we investigated type I IFN production triggered by RSV or influenza A virus infection of BALB/c mice and found that while both viruses induced IFN-α/β production by pDCs in vitro, only influenza virus infection could stimulate type I IFN synthesis by pDCs in vivo. In situ hybridization studies demonstrated that the infected respiratory epithelium was a major source of IFN-α/β in response to either infection, but in pDC-depleted animals only type I IFN induction by influenza virus was impaired.

Prostaglandin I2 Analogs Inhibit Proinflammatory Cytokine Production and T Cell Stimulatory Function of Dendritic Cells

Signaling through the PGI2 receptor (IP) has been shown to inhibit inflammatory responses in mouse models of respiratory syncytial viral infection and OVA-induced allergic responses. However, little is known about the cell types that mediate the anti-inflammatory function of PGI2. In this study, we determined that PGI2 analogs modulate dendritic cell (DC) cytokine production, maturation, and function. We report that PGI2 analogs (iloprost, cicaprost, treprostinil) differentially modulate the response of murine bone marrow-derived DC (BMDC) to LPS in an IP-dependent manner. The PGI2 analogs decreased BMDC production of proinflammatory cytokines (IL-12, TNF-α, IL-1α, IL-6) and chemokines (MIP-1α, MCP-1) and increased the production of the anti-inflammatory cytokine IL-10 by BMDCs. The modulatory effect was associated with IP-dependent up-regulation of intracellular cAMP and down-regulation of NF-κB activity. Iloprost and cicaprost also suppressed LPS-induced expression of CD86, CD40, and MHC class II molecules by BMDCs and inhibited the ability of BMDCs to stimulate Ag-specific CD4 T cell proliferation and production of IL-5 and IL-13. These findings suggest that PGI2 signaling through the IP may exert anti-inflammatory effects by acting on DC.

Epidemiology of asthma: the year in review

Asthma is a worldwide problem, with more than 17 million persons in the United States estimated to have asthma, and there is evidence that the prevalence is increasing. This article reviews the latest epidemiologic evidence for an increase in asthma prevalence and morbidity, and the evidence that environment plays a significant role in this disease. This review focuses on five specific areas: prevalence, incidence, natural history, environmental factors, and morbidity and mortality.

Early infection with respiratory syncytial virus impairs regulatory T cell function and increases susceptibility to allergic asthma.

Immune tolerance is instituted early in life, during which time regulatory T (Treg) cells have an important role. Recurrent infections with respiratory syncytial virus (RSV) in early life increase the risk for asthma in adult life. Repeated infection of infant mice tolerized to ovalbumin (OVA) through their mothers milk with RSV induced allergic airway disease in response to OVA sensitization and challenge, including airway inflammation, hyper-reactivity and higher OVA-specific IgE, as compared to uninfected tolerized control mice. Virus infection induced GATA-3 expression and T helper type 2 (TH2) cytokine production in forkhead box P3 (FOXP3)+ Treg cells and compromised the suppressive function of pulmonary Treg cells in a manner that was dependent on interleukin-4 receptor α (IL-4Rα) expression in the host. Thus, by promoting a TH2-type inflammatory response in the lung, RSV induced a TH2-like effector phenotype in Treg cells and attenuated tolerance to an unrelated antigen (allergen). Our findings highlight a mechanism by which viral infection targets a host-protective mechanism in early life and increases susceptibility to allergic disease.

Human Metapneumovirus Infection Plays an Etiologic Role in Acute Asthma Exacerbations Requiring Hospitalization in Adults

We determined the prevalence of human metapneumovirus (hMPV) infection in adults with asthma who were prospectively enrolled after hospitalization for an acute asthma exacerbation. Nasal wash specimens collected at admission and 3 months after discharge were tested for hMPV by real-time reverse-transcription polymerase chain reaction assays. hMPV was detected in 7 (6.9%) of 101 subjects at hospitalization and in 1 (1.3%) of 75 subjects at follow-up (odds ratio, 7 [95% confidence interval, 0.9-312]; P=.03). None of the patients with hMPV infection at hospitalization tested positive at follow-up, strongly suggesting that hMPV plays a direct etiologic role in acute asthma exacerbations.

Differential Pathogenesis of Respiratory Syncytial Virus Clinical Isolates in BALB/c Mice

ABSTRACT Airway mucus is a hallmark of respiratory syncytial virus (RSV) lower respiratory tract illness. Laboratory RSV strains differentially induce airway mucus production in mice. Here, we tested the hypothesis that RSV strains differ in pathogenesis by screening six low-passage RSV clinical isolates for mucogenicity and virulence in BALB/cJ mice. The RSV clinical isolates induced variable disease severity, lung interleukin-13 (IL-13) levels, and gob-5 levels in BALB/cJ mice. We chose two of these clinical isolates for further study. Infection of BALB/cJ mice with RSV A2001/2-20 (2-20) resulted in greater disease severity, higher lung IL-13 levels, and higher lung gob-5 levels than infection with RSV strains A2, line 19, Long, and A2001/3-12 (3-12). Like the line 19 RSV strain, the 2-20 clinical isolate induced airway mucin expression in BALB/cJ mice. The 2-20 and 3-12 RSV clinical isolates had higher lung viral loads than laboratory RSV strains at 1 day postinfection (p.i.). This increased viral load correlated with higher viral antigen levels in the bronchiolar epithelium and greater histopathologic changes at 1 day p.i. The A2 RSV strain had the highest peak viral load at day 4 p.i. RSV 2-20 infection caused epithelial desquamation, bronchiolitis, airway hyperresponsiveness, and increased breathing effort in BALB/cJ mice. We found that RSV clinical isolates induce variable pathogenesis in mice, and we established a mouse model of clinical isolate strain-dependent RSV pathogenesis that recapitulates key features of RSV disease.

Immune-mediated disease pathogenesis in respiratory syncytial virus infection.

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

Respiratory syncytial virus infection prolongs methacholine-induced airway hyperresponsiveness in ovalbumin-sensitized mice

Severe respiratory syncytial virus (RSV)‐induced disease is associated with childhood asthma and atopy. We combined models of allergen sensitization and RSV infection to begin exploring the immunologic interactions between allergic and virus‐induced airway inflammation and its impact on airway hypersensitivity. Airway resistance was measured after methacholine challenge in tracheally intubated mice by whole body plethysmography. Lung inflammation was assessed by bronchoalveolar lavage (BAL) and histopathology. RSV infection alone did not cause significant airway hyperresponsiveness (AHR) to methacholine. Ovalbumin (OVA)‐induced AHR lasted only a few days past the discontinuance of OVA aerosol in mice that were ovalbumin sensitized and mock infected. In contrast, OVA‐sensitized mice infected with RSV during the OVA aerosol treatments (OVA/RSV) had AHR for more than 2 weeks after infection. However, 2 weeks after either RSV or mock infection, OVA/RSV mice had significantly more lymphocytes found during BAL than OVA mice, whereas the OVA and OVA/RSV groups had the same number of eosinophils. Histopathologic analysis confirmed an increased inflammation in the lungs of OVA/RSV mice compared with OVA mice. In addition, OVA/RSV mice had a more widespread distribution of mucus in their airways with increased amounts of intraluminal mucus pools compared with the other groups. Thus, prolonged AHR in RSV‐infected mice during ovalbumin‐sensitization correlates with increased numbers of lymphocytes in BAL fluid, increased lung inflammation, and mucus deposition in the airways, but not with airway eosinophilia. A further understanding of the immunologic consequences of combined allergic and virus‐induced airway inflammation will impact the management of diseases associated with airway hyperreactivity. J. Med. Virol. 57:186–192, 1999.

Th17-mediated inflammation in asthma

Asthma is a heterogeneous disease with many different phenotypes. Moderate and severe asthma phenotypes have been associated with increased neutrophils and increased Th17 cytokines, IL-17A, IL-17F, and IL-22, in the bronchoalveolar lavage fluid of patients. Th17 cytokines recruit neutrophils to the airway by increasing secretion of epithelial-derived neutrophilic chemokines. In addition, Th17 cytokines also induce mucous cell metaplasia and have pleotropic effects on airway smooth muscle resulting in airway narrowing. The role of Th17 cytokines in regulating Th2 cytokine expression and allergic airway inflammation remains unclear with conflicting reports. However, the role of Th17 cells in asthma will be answered in ongoing clinical trials with therapeutics targeting IL-17A and IL-17 receptor signaling.