Natalia Ziętara

Novel reporter mouse reveals constitutive and inflammatory expression of IFN-beta in vivo.

Type I IFN is a major player in innate and adaptive immune responses. Besides, it is involved in organogenesis and tumor development. Generally, IFN responses are amplified by an autocrine loop with IFN-β as the priming cytokine. However, due to the lack of sensitive detection systems, where and how type I IFN is produced in vivo is still poorly understood. In this study, we describe a luciferase reporter mouse, which allows tracking of IFN-β gene induction in vivo. Using this reporter mouse, we reveal strong tissue-specific induction of IFN-β following infection with influenza or La Crosse virus. Importantly, this reporter mouse also allowed us to visualize that IFN-β is expressed constitutively in several tissues. As suggested before, low amounts of constitutively produced IFN might maintain immune cells in an activated state ready for a timely response to pathogens. Interestingly, thymic epithelial cells were the major source of IFN-β under noninflammatory conditions. This relatively high constitutive expression was controlled by the NF Aire and might influence induction of tolerance or T cell development.

Loss-of-function mutations in the IL-21 receptor gene cause a primary immunodeficiency syndrome

A primary immunodeficiency syndrome caused by loss-of-function mutations in the IL-21 receptor exhibits impaired B, T, and NK cell function.

Temporal and Spatial Resolution of Type I and III Interferon Responses In Vivo

ABSTRACT Although the action of interferons (IFNs) has been extensively studied in vitro, limited information is available on the spatial and temporal activation pattern of IFN-induced genes in vivo. We created BAC transgenic mice expressing firefly luciferase under transcriptional control of the Mx2 gene promoter. Expression of the reporter with regard to onset and kinetics of induction parallels that of Mx2 and is thus a hallmark for the host response. Substantial constitutive expression of the reporter gene was observed in the liver and most other tissues of transgenic mice, whereas this expression was strongly reduced in animals lacking functional type I IFN receptors. As expected, the reporter gene was induced not only in response to type I (α and β) and type III (λ) IFNs but also in response to a variety of IFN inducers such as double-stranded RNA, lipopolysaccharide (LPS), and viruses. In vivo IFN subtypes show clear differences with respect to their kinetics of action and to their spatial activation pattern: while the type I IFN response was strong in liver, spleen, and kidney, type III IFN reactivity was most prominent in organs with mucosal surfaces. Infection of reporter mice with virus strains that differ in their pathogenicity shows that the IFN response is significantly altered in the strength of IFN action at sites which are not primarily infected as well as by the onset and duration of gene induction.

Critical role for miR-181a/b-1 in agonist selection of invariant natural killer T cells

T-cell receptor (TCR) signal strength determines selection and lineage fate at the CD4+CD8+ double-positive stage of intrathymic T-cell development. Members of the miR-181 family constitute the most abundantly expressed microRNA at this stage of T-cell development. Here we show that deletion of miR-181a/b-1 reduced the responsiveness of double-positive thymocytes to TCR signals and virtually abrogated early invariant natural killer T (iNKT) cell development, resulting in a dramatic reduction in iNKT cell numbers in thymus as well as in the periphery. Increased concentrations of agonist ligand rescued iNKT cell development in miR-181a/b-1−/− mice. Our results define a critical role of miR-181a/b-1 in early iNKT cell development and show that miR-181a/b-1 sets a TCR signaling threshold for agonist selection.

In vivo RNAi-mediated silencing of TAK1 decreases inflammatory Th1 and Th17 cells through targeting of myeloid cells.

Cells from the mononuclear phagocyte system (MPS) act as systemic and local amplifiers that contribute to the progression of chronic inflammatory disorders. Transforming growth factor-β-activated kinase 1 (TAK1) is a pivotal upstream mitogen-activated protein kinase-kinase-kinase acting as a mediator of cytokine expression. It remains critical to determine in vivo the implication of TAK1 in controlling the innate immune system. Here, we describe a vehicle tailored to selectively deliver siRNAs into MPS cells after intravenous administration, and validate in vivo the potential of the RNAi-mediated TAK1 knock down for immunomodulation. In a mouse model of immune-mediated inflammatory disorder, we show that anti-TAK1 siRNA lipoplexes efficiently alleviate inflammation, severely impair the downstream c-Jun N-terminal kinase and nuclear factor-κB signaling pathways, and decrease the expression of proinflammatory mediators. Importantly, the systemic TAK1 gene silencing decreases the frequency of Th1 and Th17 cells, both mediating autoimmunity in experimental arthritis, demonstrating the immunomodulatory potential of TAK1. Finally, in vitro inhibition of TAK1 in myeloid cells decreases interferon-γ-producing T cells, suggesting that a delivery system able to target MPS cells and to silence TAK1 impacts on pathogenic T effector cells in autoimmunity.

Absence of IFN-β Impairs Antigen Presentation Capacity of Splenic Dendritic Cells via Down-Regulation of Heat Shock Protein 70

Type I IFNs play a key role in linking the innate and adaptive arms of the immune system. Although produced rapidly in response to pathogens, IFNs are also produced at low levels in the absence of infection. In the present study, we demonstrate that constitutively produced IFNs are necessary in vivo to maintain dendritic cells in an “Ag presentation-competent” state. Conventional dendritic cells (cDCs) isolated from spleens of IFN-β or IFNAR-deficient mice exhibit a highly impaired ability to present Ag and activate naive T cells. Microarray analysis of mRNA isolated from IFN-β−/− and IFNAR−/− cDCs revealed diminished expression of two genes that encoded members of the heat shock protein 70 (Hsp70) family. Consistent with this observation, pharmacological inhibition of Hsp70 in cDCs from wild-type mice impaired their T cell stimulatory capacity. Similarly, the Ag presentation ability of splenic cDCs isolated from Hsp70.1/3−/− mice was also severely impaired in comparison to wild-type cDCs. Thus, constitutive IFN-β expression regulates Hsp70 levels to help maintain dendritic cells in a competent state for efficient priming of effector T cells in vivo.

Human IL-21 and IL-21R deficiencies: two novel entities of primary immunodeficiency.

Purpose of review This review highlights the recent identification of human interleukin-21 (IL-21) and interleukin-21 receptor (IL-21R) deficiencies as novel entities of primary immunodeficiency. Recent findings We recently described the first patients with IL-21R deficiency who had cryptosporidial infections associated with chronic cholangitis and liver disease. All IL-21R-deficient patients suffered from recurrent respiratory tract infections. Immunological work-up revealed impaired B cell proliferation and immunoglobulin class-switch, reduced T cell effector functions, and variable natural killer cell dysfunctions. Recently, these findings have been extended by the discovery of one patient with a mutation in the IL21 gene. This patient predominantly manifested with very early onset inflammatory bowel disease and recurrent respiratory infections. Laboratory examination showed reduced circulating B cells and impaired B cell class-switch. Summary Human IL-21 and IL-21R deficiencies cause severe, primary immunodeficiency reminiscent of common variable immunodeficiency. Early diagnosis is critical to prevent life-threatening complications, such as secondary liver failure. In view of the critical role of IL-21 in controlling immune homeostasis, early hematopoietic stem cell transplantation might be considered as therapeutic intervention in affected children.

Listeria monocytogenes Induces T Cell Receptor Unresponsiveness through Pore-Forming Toxin Listeriolysin O

BACKGROUND The success of many pathogens relies on their ability to circumvent the innate and adaptive immune defenses. How bacterial pathogens subvert adaptive immune defenses is not clear. Cholesterol-dependent cytolysins (CDCs) represent an expansive family of homologous pore-forming toxins that are produced by more than 20 gram-positive bacterial species. Listeriolysin O (LLO), a prototype CDC, is the main virulence factor of Listeria monocytogenes. METHODS We employed flow cytometric and microarray techniques to analyze the effect of LLO on T cell activation in vitro and in vivo. RESULTS In vivo and in vitro proliferation of CD4(+) T cells upon T cell receptor (TCR) activation was highly diminished in the presence of LLO or wild-type L. monocytogenes but not in the presence of LLO-deficient L. monocytogenes. This block in T cell proliferation was specific to T cell activation via the TCR and not by phorbol 12-myristate 13-acetate-ionomycin, which bypasses the proximal TCR signaling event. The results of microarray analysis suggest that LLO-induced T cell unresponsiveness is due to the induction of a calcium-nuclear factor of activated T cells-dependent transcriptional program that drives the expression of negative regulators of TCR signaling. CONCLUSION These findings provide important insights into how bacterial toxins silence adaptive immune responses and thus enable prolonged survival of the pathogen in the host.

Multicongenic fate mapping quantification of dynamics of thymus colonization

Ziętara et al demonstrate with multicongenic fate mapping that thymus seeding is directly restricted to the duration of niche occupancy rather than long-range effects.

ICOS‐dependent stimulation of NKT cells by marginal zone B cells

Marginal zone (MZ) B cells express high levels of CD1d molecules. In accordance, MZ B cells, like splenic conventional DCs (cDCs), efficiently trigger NKT‐cell proliferation. Importantly, MZ B cells exclusively induced production of IL‐4 and IL‐13 by such cells whereas cDCs induced robust production of mainly IFN‐γ. NKT‐cell proliferation, IL‐4 and IL‐13 production induced by MZ B cells were dependent on ICOS/ICOS ligand interaction while IFN‐γ and IL‐17 induction by cDCs required glucocorticoid‐induced TNF receptor/glucocorticoid‐induced TNF receptor ligand interplay. Our data illustrate that both MZ B cells and cDCs act as efficient APCs for NKT cells and might differentially influence the quality of the subsequent immune response.