Recent data have indicated that an important instructive class of signals regulating the immune response is Notch ligand–mediated activation. Using quantitative polymerase chain reaction, we observed that only Delta-like 4 (dll4) was up-regulated on bone marrow–derived dendritic cells after respiratory syncytial virus (RSV) infection, and that it was dependent on MyD88-mediated pathways. Using a polyclonal antibody specific for dll4, the development of RSV-induced disease was examined. Animals treated with anti-dll4 had substantially increased airway hyperresponsiveness compared with control antibody-treated animals. When the lymphocytic lung infiltrate was examined, a significant increase in total CD4+ T cells and activated (perforin+) CD8+ T cells was observed. Isolated lung CD4+ T cells demonstrated significant increases in Th2-type cytokines and a decrease in interferon γ, demonstrating an association with increased disease pathogenesis. Parellel in vitro studies examining the integrated role of dll4 with interleukin-12 demonstrated that, together, both of these instructive signals direct the immune response toward a more competent, less pathogenic antiviral response. These data demonstrate that dll4-mediated Notch activation is one regulator of antiviral immunity.

Natural killer (NK) cells are equipped to innately produce the cytokine gamma interferon (IFN-γ) in part because they basally express high levels of the signal transducer and activator of transcription 4 (STAT4). Type 1 interferons (IFNs) have the potential to activate STAT4 and promote IFN-γ expression, but concurrent induction of elevated STAT1 negatively regulates access to the pathway. As a consequence, it has been difficult to detect type 1 IFN stimulation of NK cell IFN-γ during viral infections in the presence of STAT1 and to understand the evolutionary advantage for maintaining the pathway. The studies reported here evaluated NK cell responses following infections with lymphocytic choriomeningitis virus (LCMV) in the compartment handling the earliest events after infection, the peritoneal cavity. The production of type 1 IFNs, both IFN-α and IFN-β, was shown to be early and of short duration, peaking at 30 h after challenge. NK cell IFN-γ expression was detected with overlapping kinetics and required activating signals delivered through type 1 IFN receptors and STAT4. It took place under conditions of high STAT4 levels but preceded elevated STAT1 expression in NK cells. The IFN-γ response reduced viral burdens. Interestingly, increases in STAT1 were delayed in NK cells compared to other peritoneal exudate cell (PEC) populations. Taken together, the studies demonstrate a novel mechanism for stimulating IFN-γ production and elucidate a biological role for type 1 IFN access to STAT4 in NK cells.

Chemokines are important mediators of the immune response to pathogens, but can also promote chronic inflammatory states. Chemokine receptor 6 (CCR6) is found on immature DC and effector/memory T cells, and binds a single ligand, CCL20, with high affinity. Here, we investigated the role of CCL20 and CCR6 in a pulmonary viral infection caused by RSV, a ubiquitous virus that can cause severe pulmonary complications. Neutralization of CCL20 during RSV infection significantly reduced lung pathology and favored a Th1 effector response. CCR6-deficient animals recapitulated this phenotype, and additionally showed enhanced viral clearance when compared with WT mice. No differences were observed in migration of T cells to the lungs of CCR6 À/À animals; however, a significant reduction was observed in numbers of conventional DC (cDC), but not plasmacytoid DC, in CCR6 À/À mice. A pathogenic phenotype could be reconstituted in CCR6 À/À mice by supplying cDC into the airway, indicating that mere number of cDC dictates the adverse response. Our data suggest that blockade of the CCL20/CCR6 pathway provides an environment whereby the attenuated recruitment of cDC alters the balance of innate immune cells and mediates the efficient antiviral response to RSV.Key words: Chemokines . DC . Mucosal immunity IntroductionRSV is a pervasive virus that is the most common cause of hospitalization in children under the age of 2 [1]. RSV can also adversely affect the elderly and immunocompromised individuals, causing severe lower respiratory tract infection [2]. Although both Th1 and Th2 effector responses may be generated, Th2 immunity is responsible for RSV-associated pathology, including airway damage and mucus hypersecretion [3]. RSV represents a recurrent problem throughout life because immunologic memory never fully develops [4]. Furthermore, studies have demonstrated a correlation between early exposure to RSV and the later development of asthma [5,6]. No vaccine currently exists, and early attempts to develop a vaccine proved detrimental, as individuals inoculated with a formalin-inactivated form of virus demonstrated enhanced pulmonary eosinophilia and Th2 responses [7]. Clearly, further investigation is needed to clarify the fine balance between immune protection and pathology during RSV infection.Chemokines are key mediators of leukocyte recruitment during pathogenic insult, and also play a prominent role in homeostasis [8]. Most chemokines are promiscuous in that they can bind multiple receptors. CC chemokine receptor 6 (CCR6) is unique in the latter regard in that it binds a single chemokine, CCL20 [9]. CCL20 is a homeostatic chemokine, with a prominent role in organizing lymphoid tissue in the gut [10], but is also upregulated upon pro-inflammatory stimulation [11]. This dual function of CCL20 is evident in the cells expressing its corresponding receptor, CCR6, and contributes to a role for these cells in various immune settings.CCR6 is found on immature DC, B cells, effector/memory T cells and T regulatory cells [12][13][14][...

BackgroundRespiratory syncytial virus (RSV) is a leading cause of bronchiolitis and pneumonia in young children worldwide, and no vaccine is currently available. Inactivated RSV vaccines tested in the 1960's led to vaccine-enhanced disease upon viral challenge, which has undermined RSV vaccine development. RSV infection is increasingly being recognized as an important pathogen in the elderly, as well as other individuals with compromised pulmonary immunity. A safe and effective inactivated RSV vaccine would be of tremendous therapeutic benefit to many of these populations.Principal FindingsIn these preclinical studies, a mouse model was utilized to assess the efficacy of a novel, nanoemulsion-adjuvanted, inactivated mucosal RSV vaccine. Our results demonstrate that NE-RSV immunization induced durable, RSV-specific humoral responses, both systemically and in the lungs. Vaccinated mice exhibited increased protection against subsequent live viral challenge, which was associated with an enhanced Th1/Th17 response. In these studies, NE-RSV vaccinated mice displayed no evidence of Th2 mediated immunopotentiation, as has been previously described for other inactivated RSV vaccines.ConclusionsThese studies indicate that nanoemulsion-based inactivated RSV vaccination can augment viral-specific immunity, decrease mucus production and increase viral clearance, without evidence of Th2 immune mediated pathology.