Lung dendritic cells in respiratory syncytial virus bronchiolitis

In Vivo Evidence of Respiratory Syncytial Virus Persistence in a Subset of Pulmonary Dendritic Cells Following a Primary Infection

Respiratory syncytial virus (RSV) causes annual epidemics of infections affecting the whole population. In vitro, it has been shown to infect and persist in human dendritic cells (DCs) for prolonged periods. Initially persistence is associated with low levels of replication before the virus becomes dormant. Reactivation of viral replication can be triggered many months later. Infection of DCs is likely to influence the host's ability to generate effective long-term memory responses. A well-established animal was utilized to confirm that RSV both infects and persists in pulmonary DCs in vivo. Mice were infected with a modified strain of RSV expressing red fluorescent protein (RSV-RFP) when replicating. Clinical symptoms of infection were monitored using weight change and inflammatory cell counts from bronchoalveolar lavage, which correlated with the RSV viral titer (quantitative polymerase chain reaction). Lung tissues were collected at 3, 5, 7, and 21 days postinfection (dpi) to assess leukocyte populations by flow cytometry. Clinical symptoms and RSV viral load peaked at 5 dpi. RSV-RFP was most prevalent in macrophages at 3 dpi and also observed in B cells and DCs. At 21 dpi, RSV-RFP remained evident in a subset of conventional DCs (CD103+CD11b+) even though both clinical symptoms and pulmonary inflammation had resolved. These results confirm that in this well-established mouse model, RSV persists in lung conventional DCs following resolution of the acute infection. Further work is required to explore whether the virus continues with low-level replication before becoming dormant in vivo, as has been described in vitro.

Early-Life Respiratory Syncytial Virus Infection, Trained Immunity and Subsequent Pulmonary Diseases

Respiratory syncytial virus (RSV) is often the first clinically relevant pathogen encountered in life, with nearly all children infected by two years of age. Many studies have also linked early-life severe respiratory viral infection with more pathogenic immune responses later in life that lead to pulmonary diseases like childhood asthma. This phenomenon is thought to occur through long-term immune system alterations following early-life respiratory viral infection and may include local responses such as unresolved inflammation and/or direct structural or developmental modifications within the lung. Furthermore, systemic responses that could impact the bone marrow progenitors may be a significant cause of long-term alterations, through inflammatory mediators and shifts in metabolic profiles. Among these alterations may be changes in transcriptional and epigenetic programs that drive persistent modifications throughout life, leaving the immune system poised toward pathogenic responses upon secondary insult. This review will focus on early-life severe RSV infection and long-term alterations. Understanding these mechanisms will not only lead to better treatment options to limit initial RSV infection severity but also protect against the development of childhood asthma linked to severe respiratory viral infections.

Airway Epithelial Derived Cytokines and Chemokines and Their Role in the Immune Response to Respiratory Syncytial Virus Infection

The airway epithelium is the primary target of respiratory syncytial virus infection. It is an important component of the antiviral immune response. It contributes to the recruitment and activation of innate immune cells from the periphery through the secretion of cytokines and chemokines. This paper provides a broad review of the cytokines and chemokines secreted from human airway epithelial cell models during respiratory syncytial virus (RSV) infection based on a comprehensive literature review. Epithelium-derived chemokines constitute most inflammatory mediators secreted from the epithelium during RSV infection. This suggests chemo-attraction of peripheral immune cells, such as monocytes, neutrophils, eosinophils, and natural killer cells as a key function of the epithelium. The reports of epithelium-derived cytokines are limited. Recent research has started to identify novel cytokines, the functions of which remain largely unknown in the wider context of the RSV immune response. It is argued that the correct choice of in vitro models used for investigations of epithelial immune functions during RSV infection could facilitate greater progress in this field.

NKG2D Regulation of Lung Pathology and Dendritic Cell Function Following Respiratory Syncytial Virus Infection

Background

Respiratory syncytial virus (RSV) is a common cause of respiratory tract infection in vulnerable populations. Natural killer (NK) cells and dendritic cells (DC) are important for the effector functions of both cell types following infection.

Methods

Wild-type and NKG2D-deficient mice were infected with RSV. Lung pathology was assessed by histology. Dendritic cell function and phenotype were evaluated by enzyme-linked immunosorbent assay and flow cytometry. The expression of NKG2D ligands on lung and lymph node DCs was measured by immunostaining and flow cytometry. Adoptive transfer experiments were performed to assess the importance of NKG2D-dependent DC function in RSV infection.

Results

NKG2D-deficient mice exhibited greater lung pathology, marked by the accumulation of DCs following RSV infection. Dendritic cells isolated from NKG2D-deficient mice had impaired responses toward Toll-like receptor ligands. Dendritic cells expressed NKG2D ligands on their surface, which was further increased in NKG2D-deficient mice and during RSV infection. Adoptive transfer of DCs isolated from wild-type mice into the airways of NKG2D-deficient mice ameliorated the enhanced inflammation in NKG2D-deficient mice after RSV infection.

Conclusion

NKG2D-dependent interactions with DCs control the phenotype and function of DCs and play a critical role in pulmonary host defenses against RSV infection.

Functional Impairment of Mononuclear Phagocyte System by the Human Respiratory Syncytial Virus

The mononuclear phagocyte system (MPS) comprises of monocytes, macrophages (MΦ), and dendritic cells (DCs). MPS is part of the first line of immune defense against a wide range of pathogens, including viruses, such as the human respiratory syncytial virus (hRSV). The hRSV is an enveloped virus that belongs to the Pneumoviridae family, Orthopneumovirus genus. This virus is the main etiological agent causing severe acute lower respiratory tract infection, especially in infants, children and the elderly. Human RSV can cause bronchiolitis and pneumonia and it has also been implicated in the development of recurrent wheezing and asthma. Monocytes, MΦ, and DCs significantly contribute to acute inflammation during hRSV-induced bronchiolitis and asthma exacerbation. Furthermore, these cells seem to be an important component for the association between hRSV and reactive airway disease. After hRSV infection, the first cells encountered by the virus are respiratory epithelial cells, alveolar macrophages (AMs), DCs, and monocytes in the airways. Because AMs constitute the predominant cell population at the alveolar space in healthy subjects, these cells work as major innate sentinels for the recognition of pathogens. Although adaptive immunity is crucial for viral clearance, AMs are required for the early immune response against hRSV, promoting viral clearance and controlling immunopathology. Furthermore, exposure to hRSV may affect the phagocytic and microbicidal capacity of monocytes and MΦs against other infectious agents. Finally, different studies have addressed the roles of different DC subsets during infection by hRSV. In this review article, we discuss the role of the lung MPS during hRSV infection and their involvement in the development of bronchiolitis.

The Interactive Roles of Lipopolysaccharides and dsRNA/Viruses on Respiratory Epithelial Cells and Dendritic Cells in Allergic Respiratory Disorders: The Hygiene Hypothesis

The original hygiene hypothesis declares "more infections in early childhood protect against later atopy". According to the hygiene hypothesis, the increased incidence of allergic disorders in developed countries is explained by the decrease of infections. Epithelial cells and dendritic cells play key roles in bridging the innate and adaptive immune systems. Among the various pattern-recognition receptor systems of epithelial cells and dendritic cells, including toll-like receptors (TLRs), nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) and others, TLRs are the key systems of immune response regulation. In humans, TLRs consist of TLR1 to TLR10. They regulate cellular responses through engagement with TLR ligands, e.g., lipopolysaccharides (LPS) acts through TLR4 and dsRNA acts through TLR3, but there are certain common components between these two TLR pathways. dsRNA activates epithelial cells and dendritic cells in different directions, resulting in allergy-related Th2-skewing tendency in epithelial cells, and Th1-skewing tendency in dendritic cells. The Th2-skewing effect by stimulation of dsRNA on epithelial cells could be suppressed by the presence of LPS above some threshold. When LPS level decreases, the Th2-skewing effect increases. It may be via these interrelated networks and related factors that LPS modifies the allergic responses and provides a plausible mechanism of the hygiene hypothesis. Several hygiene hypothesis-related phenomena, seemingly conflicting, are also discussed in this review, along with their proposed mechanisms.

Respiratory syncytial virus infection influences tight junction integrity

Respiratory syncytial virus (RSV) is an important risk factor of asthma development and is responsible for severe respiratory tract infections. However, the influence of RSV infection on barrier function of bronchial epithelial cells in vitro and in vivo is still unclear. The aim of this study was to analyse the role of RSV in tight junction (TJ) regulation and to compare epithelial integrity between asthmatic and healthy individuals upon RSV infection. Healthy and asthmatic human bronchial epithelial cells (HBECs) were differentiated at air-liquid interface (ALI) and infected with RSV and ultraviolet (UV)-irradiated RSV. TJ expression and their integrity were analysed by quantitative polymerase chain reaction (qPCR), transepithelial resistance (TER) and paracellular flux. To determine the effect in vivo, BALB/c mice were infected intranasally with RSV or UV-irradiated RSV A2. Bronchoalveolar lavage and TJ integrity were analysed on days 1, 2, 4 and 6 post-infection by qPCR, bioplex and confocal microscopy. RSV increased barrier integrity in ALI cultures of HBEC from healthy subjects, but no effect was found in HBECs from asthmatics. This was not associated with an increase in TJ mRNA expression. In vivo, RSV induced lung inflammation in mice and down-regulated claudin-1 and occludin mRNA expression in whole lungs. Surprisingly, RSV infection was not observed in bronchial epithelial cells, but was found in the lung parenchyma. Decreased expression of occludin upon RSV infection was visible in mouse bronchial epithelial cells in confocal microscopy. However, there was no regulation of claudin-1 and claudin-7 at protein level.

Human Respiratory Syncytial Virus: Role of Innate Immunity in Clearance and Disease Progression

Human respiratory syncytial virus (HRSV) infections have worldwide records. The virus is responsible for bronchiolitis, pneumonia, and asthma in humans of different age groups. Premature infants, young children, and immunocompromised individuals are prone to severe HRSV infection that may lead to death. Based on worldwide estimations, millions of cases were reported in both developed and developing countries. In fact, HRSV symptoms develop mainly as a result of host immune response. Due to inability to establish long lasting adaptive immunity, HRSV infection is recurrent and hence impairs vaccine development. Once HRSV attached to the airway epithelia, interaction with the host innate immune components starts. HRSV interaction with pulmonary innate defenses is crucial in determining the disease outcome. Infection of alveolar epithelial cells triggers a cascade of events that lead to recruitment and activation of leukocyte populations. HRSV clearance is mediated by a number of innate leukocytes, including macrophages, natural killer cells, eosinophils, dendritic cells, and neutrophils. Regulation of these cells is mediated by cytokines, chemokines, and other immune mediators. Although the innate immune system helps to clear HRSV infection, it participates in disease progression such as bronchiolitis and asthma. Resolving the mechanisms by which HRSV induces pathogenesis, different possible interactions between the virus and immune components, and immune cells interplay are essential for developing new effective vaccines. Therefore, the current review focuses on how the pulmonary innate defenses mediate HRSV clearance and to what extent they participate in disease progression. In addition, immune responses associated with HRSV vaccines will be discussed.

Ginseng protects against respiratory syncytial virus by modulating multiple immune cells and inhibiting viral replication

Ginseng has been used in humans for thousands of years but its effects on viral infection have not been well understood. We investigated the effects of red ginseng extract (RGE) on respiratory syncytial virus (RSV) infection using in vitro cell culture and in vivo mouse models. RGE partially protected human epithelial (HEp2) cells from RSV-induced cell death and viral replication. In addition, RGE significantly inhibited the production of RSV-induced pro-inflammatory cytokine (TNF-α) in murine dendritic and macrophage-like cells. More importantly, RGE intranasal pre-treatment prevented loss of mouse body weight after RSV infection. RGE treatment improved lung viral clearance and enhanced the production of interferon (IFN-γ) in bronchoalveolar lavage cells upon RSV infection of mice. Analysis of cellular phenotypes in bronchoalveolar lavage fluids showed that RGE treatment increased the populations of CD8⁺ T cells and CD11c⁺ dendritic cells upon RSV infection of mice. Taken together, these results provide evidence that ginseng has protective effects against RSV infection through multiple mechanisms, which include improving cell survival, partial inhibition of viral replication and modulation of cytokine production and types of immune cells migrating into the lung.

Responsiveness to respiratory syncytial virus in neonates is mediated through thymic stromal lymphopoietin and OX40 ligand

BACKGROUND

Recent studies revealed a critical role for thymic stromal lymphopoietin (TSLP) released from epithelial cells and OX40 ligand (OX40L) expressed on dendritic cells (DCs) in T(H)2 priming and polarization.

OBJECTIVES

We sought to determine the importance of the TSLP-OX40L axis in neonatal respiratory syncytial virus (RSV) infection.

METHODS

Mice were initially infected with RSV as neonates or adults and reinfected 5 weeks later. Anti-OX40L or anti-TSLP were administered during primary or secondary infection. Outcomes included assessment of airway function and inflammation and expression of OX40L, TSLP, and IL-12.

RESULTS

OX40L was expressed mainly on CD11c(+)MHC class II (MHCII)(+)CD11b(+) DCs but not CD103(+) DCs. Treatment of neonates with OX40L antibody during primary RSV infection prevented the subsequent enhancement of airway hyperresponsiveness and the development of airway eosinophilia and mucus hyperproduction on reinfection. Administration of anti-TSLP before neonatal RSV infection reduced the accumulation of lung DCs, decreased OX40L expression on lung DCs, and attenuated the enhancement of airway responses after reinfection.

CONCLUSIONS

In mice initially infected as neonates, TSLP expression induced by RSV infection is an important upstream event that controls OX40L expression, lung DC migration, and T(H)2 polarization, accounting for the enhanced response on reinfection.

Inflammatory responses to respiratory syncytial virus (RSV) infection and the development of immunomodulatory pharmacotherapeutics

Respiratory syncytial virus (RSV; Family Paramyxoviridae, Genus Pneumovirus) is a major respiratory pathogen of infants and children and an emerging pathogen of the elderly. Current management of RSV disease includes monoclonal antibody prophylaxis for infants identified as high risk and supportive care for those with active infection; there is no vaccine, although several are under study. In this manuscript, we review published findings from human autopsy studies, as well as experiments that focus on human clinical samples and mouse models of acute pneumovirus infection that elucidate basic principles of disease pathogenesis. Consideration of these data suggests that the inflammatory responses to RSV and related pneumoviral pathogens can be strong, persistent, and beyond the control of conventional antiviral and anti-inflammatory therapies, and can have profound negative consequences to the host. From this perspective, we consider the case for specific immunomodulatory strategies that may have the potential to alleviate some of the more serious sequelae of this disease.