Effect of influenza A infection on maturation and function of neonatal monocyte-derived dendritic cells

Functional Heterogeneity of Umbilical Cord Blood Monocyte-Derived Dendritic Cells

Human umbilical cord blood (UCB) represents a unique resource for hematopoietic stem cell transplantation for children and patients lacking suitable donors. UCB harbors a diverse set of leukocytes such as professional APCs, including monocytes, that could act as a novel source for cellular therapies. However, the immunological properties of UCB monocytes and monocyte-derived dendritic cells (MoDCs) are not fully characterized. In this study, we characterized the phenotype and functions of UCB-MoDCs to gauge their potential for future applications. UCB exhibited higher frequencies of platelets and lymphocytes as well as lower frequencies of neutrophils in comparison with adult whole blood. Leukocyte subset evaluation revealed significantly lower frequencies of granulocytes, NK cells, and CD14+CD16- monocytes. Surface marker evaluation revealed significantly lower rates of costimulatory molecules CD80 and CD83 while chemokine receptors CCR7 and CXCR4, as well as markers for Ag presentation, were similarly expressed. UCB-MoDCs were sensitive to TLR1-9 stimulation and presented quantitative differences in the release of proinflammatory cytokines. UCB-MoDCs presented functional CCR7-, CXCR4-, and CCR5-associated migratory behavior as well as adequate receptor- and micropinocytosis-mediated Ag uptake. When cocultured with allogeneic T lymphocytes, UCB-MoDCs induced weak CD4+ T lymphocyte proliferation, CD71 expression, and release of IFN-γ and IL-2. Taken together, UCB-MoDCs present potentially advantageous properties for future medical applications.

PA-X protein assists H9N2 subtype avian influenza virus in escaping immune response of mucosal dendritic cells

H9N2 subtype low pathogenicity avian influenza virus (AIV) poses a potential zoonotic risk. PA-X, a novel protein generated by PA gene ribosomal frameshift, is considered to be the virulence factor of H9N2 subtype AIVs. Our study found that rTX possessing PA-X protein enhanced the mammalian pathogenicity of H9N2 subtype AIVs compared with PA-X-deficient virus (rTX-FS). Furthermore, PA-X protein inhibited H9N2 subtype AIVs to infect dendritic cells (DCs), but not nonimmune cells (MDCK cells). Meanwhile, PA-X protein suppressed the phenotypic expression (CD80, CD86, CD40 and MHCII), early activation marker (CD69) and pro-inflammatory cytokines (IL-6 and TNF-α), whereas increased anti-inflammatory cytokine (IL-10) in DCs. After intranasally viral infection in mice, we found that PA-X protein of H9N2 subtype AIVs reduced CD11b+ and CD103+ subtype mucosal DCs recruitment to the nasal submucosa by inhibiting CCL20 expression. Moreover, PA-X protein abolished the migratory ability of CD11b+ and CD103+ DCs into draining cervical lymph nodes by down-regulating CCR7 expression. The rTX-infected DCs significantly impaired the allogeneic CD4+ T cell proliferation, suggesting PA-X protein suppressed the immune functions of DCs for hindering the downstream immune activation. These findings indicated that PA-X protein assisted H9N2 subtype AIVs in escaping immune response of mucosal DCs for enhancing the pathogenicity.

Challenges for the Newborn Immune Response to Respiratory Virus Infection and Vaccination

The initial months of life reflect an extremely challenging time for newborns as a naïve immune system is bombarded with a large array of pathogens, commensals, and other foreign entities. In many instances, the immune response of young infants is dampened or altered, resulting in increased susceptibility and disease following infection. This is the result of both qualitative and quantitative changes in the response of multiple cell types across the immune system. Here we provide a review of the challenges associated with the newborn response to respiratory viral pathogens as well as the hurdles and advances for vaccine-mediated protection.

The effect of age on foal monocyte-derived dendritic cell (MoDC) maturation and function after exposure to killed bacteria

Neonatal foals are uniquely susceptible to certain infections early in life. Dendritic cells (DC) are vital in the transition between the innate and adaptive immune response to infection, but DC biology in foals is not fully characterized. Monocyte-derived DC represent a suitable in vitro model similar to DC that differentiate from monocytes recruited from circulation. We hypothesized that foal monocyte-derived DC (MoDC) would exhibit age-dependent phenotypic and functional differences compared to adult horse MoDC. MoDC generated from 9 horses (collected once) and from 8 foals (collected at 1, 7, and 30 days-of-age) were exposed to killed whole cell Escherichia coli or Staphylococcus aureus bacteria. MoDC expression of MHC class II (MHC class-II), CD86, and CD14 were measured by flow cytometry, and supernatant cytokine concentrations of IL-4, IL-17, IFN-γ, and IL-10 were quantified with a validated immunoassay. The percentage of MoDC expressing MHC class-II and CD86 was lower and CD14 was higher for cells generated from 1-day-old foals compared to cells generated from adult horses (P < 0.0001). Bacterial exposure increased the percentage of cells expressing CD86 at all ages (P < 0.0001). Bacteria-exposed MoDC from 1-day-old foals produced significantly less IL-4, IL-17, and IFN-γ than adult MoDC produced in response to bacterial exposure (P ≤ 0.04). Following bacterial exposure, foal MoDC phenotype and cytokine secretion were different than those of mature horses. These differences could reduce the ability of foals to generate a protective immune response against bacterial infection.

Respiratory Mononuclear Phagocytes in Human Influenza A Virus Infection: Their Role in Immune Protection and As Targets of the Virus

Emerging viruses have become increasingly important with recurrent epidemics. Influenza A virus (IAV), a respiratory virus displaying continuous re-emergence, contributes significantly to global morbidity and mortality, especially in young children, immunocompromised, and elderly people. IAV infection is typically confined to the airways and the virus replicates in respiratory epithelial cells but can also infect resident immune cells. Clearance of infection requires virus-specific adaptive immune responses that depend on early and efficient innate immune responses against IAV. Mononuclear phagocytes (MNPs), comprising monocytes, dendritic cells, and macrophages, have common but also unique features. In addition to being professional antigen-presenting cells, MNPs mediate leukocyte recruitment, sense and phagocytose pathogens, regulate inflammation, and shape immune responses. The immune protection mediated by MNPs can be compromised during IAV infection when the cells are also targeted by the virus, leading to impaired cytokine responses and altered interactions with other immune cells. Furthermore, it is becoming increasingly clear that immune cells differ depending on their anatomical location and that it is important to study them where they are expected to exert their function. Defining tissue-resident MNP distribution, phenotype, and function during acute and convalescent human IAV infection can offer valuable insights into understanding how MNPs maintain the fine balance required to protect against infections that the cells are themselves susceptible to. In this review, we delineate the role of MNPs in the human respiratory tract during IAV infection both in mediating immune protection and as targets of the virus.

Differential immune response of influenza A virus-infected dendritic cells and association with autophagy

Aim: We sought to study the responses of dendritic cells (DCs) after direct stimulation by different influenza A viruses. Materials & methods: Using bone marrow-derived DCs (BMDCs) as a model, we measured the expression of surface markers, cytokine production and the priming effect on CD4+ naive T cells. Results & conclusion: We found that all of the tested viruses induced BMDC maturation. Cytokine expression assays also demonstrated that activated BMDCs secrete higher levels of cytokines. Similar to the maturation degree, well-stimulated BMDCs induced higher levels of naive CD4+ T-cell activation. Furthermore, we found that the PR8 and WSN influenza A viruse-induced BMDC functional activation was at least partially influenced by autophagy.

Azithromycin modulates immune response of human monocyte-derived dendritic cells and CD4+ T cells

Azithromycin (AZM) is a macrolide antibiotic that exhibits anti-inflammatory activity aside from its antimicrobial effect, a feature that may ameliorate certain inflammatory disorders and prevent graft-versus-host disease in patients receiving stem cell transplantation. In the present study, we investigated the ability of AZM to influence the function of human monocyte-derived dendritic cells (DCs) and CD4⁺ T cells. We found that AZM down-regulated CD80, CD86, and HLA-DR expression in lipopolysaccharide (LPS)-stimulated DCs and suppressed interleukin (IL)-6, IL-10, IL-12, and tumor necrosis factor-alpha production in these cells. In addition, AZM increased endocytosis and/or expression of Toll-like receptor (TLR)2, TLR4, and TLR9 in DCs and suppressed anti-CD3/CD28-induced CD4⁺ T cell proliferation and interferon-gamma production, an effect that was synergistic with dexamethasone. Finally, AZM suppressed DC-induced allogeneic T cell proliferation and cytokine production. Our study demonstrates that AZM modulates DC and CD4⁺ T cell function and may be of therapeutic benefit in various inflammatory disorders.

Influenza A Virus Infection, Innate Immunity, and Childhood

Infection with influenza A virus is responsible for considerable morbidity and mortality in children worldwide. While it is apparent that adequate activation of the innate immune system is essential for pathogen clearance and host survival, an excessive inflammatory response to infection is detrimental to the young host. A review of the literature indicates that innate immune responses change throughout childhood. Whether these changes are genetically programmed or triggered by environmental cues is unknown. The objectives of this review are to summarize the role of innate immunity in influenza A virus infection in the young child and to highlight possible differences between children and adults that may make children more susceptible to severe influenza A infection. A better understanding of age-related differences in innate immune signaling will be essential to improve care for this high-risk population.