Expression of IFNγR2 mutated in a dileucine internalization motif reinstates IFNγ signaling and apoptosis in human T lymphocytes

Innate Immune System Activation and Neuroinflammation in Down Syndrome and Neurodegeneration: Therapeutic Targets or Partners?

Innate immune system activation and inflammation are associated with and may contribute to clinical outcomes in people with Down syndrome (DS), neurodegenerative diseases such as Alzheimer's disease (AD), and normal aging. In addition to serving as potential diagnostic biomarkers, innate immune system activation and inflammation may play a contributing or causal role in these conditions, leading to the hypothesis that effective therapies should seek to dampen their effects. However, recent intervention studies with the innate immune system activator granulocyte-macrophage colony-stimulating factor (GM-CSF) in animal models of DS, AD, and normal aging, and in an AD clinical trial suggest that activating the innate immune system and inflammation may instead be therapeutic. We consider evidence that DS, AD, and normal aging are accompanied by innate immune system activation and inflammation and discuss whether and when during the disease process it may be therapeutically beneficial to suppress or promote such activation.

Aberrations in circulating inflammatory cytokine levels in patients with Down syndrome: a meta-analysis

Evidence suggests that immune system alterations in Down syndrome (DS) may be early events that drive neuropathological and cognitive changes of Alzheimer's disease. The primary objective of this meta-analysis was to investigate whether there is an abnormal cytokine profile in DS patients when compared with healthy control (HC) subjects. A systematic search of Pubmed and Web of Science identified 19 studies with 957 DS patients and 541 HC subjects for this meta-analysis. Random effects meta-analysis demonstrated that patients with DS had significantly increased circulating tumor necrosis factor-α (Hedges’ g = 1.045, 95% confidence interval (CI) = 0.192 to 1.898, p = 0.016), interleukin (IL)-1β (Hedges’ g = 0.696, 95% confidence CI = 0.149 to 1.242, p = 0.013), interferon-γ (Hedges’ g = 0.978, 95% CI = 0.417 to 1.539, p = 0.001) and neopterin (Hedges’ g = 0.815, 95% CI = 0.423 to 1.207, p < 0.001) levels compared to HC subjects. No significant differences were found between patients with DS and controls for concentrations of IL-4, IL-6, IL8 and IL-10. In addition, most of the cytokine data in this meta-analysis were from children with DS and HC, and subgroup analysis showed that children with DS had elevated tumor necrosis factor-α, IL-1β and interferon-γ levels when compared with controls. Taken together, these results demonstrated that patients (children) with DS are accompanied by increased circulating cytokine tumor necrosis factor-α, IL-1β and interferon-γ levels, strengthening the clinical evidence that patients (children) with DS are accompanied by an abnormal inflammatory response.

Interferon gamma receptor: the beginning of the journey

Our view of endocytosis and membrane trafficking of transmembrane receptors has dramatically changed over the last 20 years. Several new endocytic routes have been discovered and mechanistically characterized in mammalian cells. Long considered as a passive means to terminate signaling through down-regulation of the number of activated receptors at the plasma membrane, it is now established that receptor endocytosis and endosomal sorting can be directly linked to the regulation of intracellular signaling pathways. The functional links between membrane trafficking of interferon receptors and JAK/STAT signaling have recently begun to be unraveled. These studies raise the exciting possibility that a certain level of signal specificity can be achieved through endocytosis and selective localization of the activated complexes within cellular membranes. The ongoing development of high-resolution cell imaging techniques with better spatial and temporal resolution gives new means of deciphering the inherent complexity of membrane trafficking and signaling. This should help to better comprehend the molecular mechanisms by which endocytosis and endosomal sorting of interferon receptors can orchestrate signaling selectivity within the JAK/STAT pathway that can be activated by as many as 60 different cytokines, growth factors, and hormones.

Down's syndrome, neuroinflammation, and Alzheimer neuropathogenesis

Down syndrome (DS) is the result of triplication of chromosome 21 (trisomy 21) and is the prevailing cause of mental retardation. In addition to the mental deficiencies and physical anomalies noted at birth, triplication of chromosome 21 gene products results in the neuropathological and cognitive changes of Alzheimer's disease (AD). Mapping of the gene that encodes the precursor protein (APP) of the β-amyloid (Aβ) present in the Aβ plaques in both AD and DS to chromosome 21 was strong evidence that this chromosome 21 gene product was a principal neuropathogenic culprit in AD as well as DS. The discovery of neuroinflammatory changes, including dramatic proliferation of activated glia overexpressing a chromosome 2 gene product--the pluripotent immune cytokine interleukin-1 (IL-1)--and a chromosome 21 gene product--S100B--in the brains of fetuses, neonates, and children with DS opened the possibility that early events in Alzheimer pathogenesis were driven by cytokines. The specific chromosome 21 gene products and the complexity of the mechanisms they engender that give rise to the neuroinflammatory responses noted in fetal development of the DS brain and their potential as accelerators of Alzheimer neuropathogenesis in DS are topics of this review, particularly as they relate to development and propagation of neuroinflammation, the consequences of which are recognized clinically and neuropathologically as Alzheimer's disease.

Chlamydophila pneumoniae in human immortal Jurkat cells and primary lymphocytes uncontrolled by interferon-γ

Lymphocytes are a potential host cell for Chlamydophila pneumoniae, although why the bacteria must hide in lymphocytes remains unknown. Meanwhile, interferon (IFN)-γ is a crucial factor for eliminating chlamydiae from infected cells through indoleamine 2,3-dioxygenase (IDO) expression, resulting in depletion of tryptophan. We therefore assessed if lymphocytes could work as a shelter for the bacteria to escape IFN-γ. C. pneumoniae grew normally in human lymphoid Jurkat cells, even in the presence of IFN-γ or under stimulation with phorbol myristate acetate plus ionomycin. Although Jurkat cells expressed IFN-γ receptor CD119, their lack of IDO expression was confirmed by RT-PCR and western blotting. Also, C. pneumoniae survived in enriched human peripheral blood lymphocytes, even in the presence of IFN-γ. Furthermore, C. pneumoniae in spleen cells obtained from IFN-γ knockout mice with C57BL/6 background was maintained in a similar way to wild-type mice, supporting a minimal role of IFN-γ-related response for eliminating C. pneumoniae from lymphocytes. Thus, we concluded that IFN-γ did not remove C. pneumoniae from lymphocytes, possibly providing a shelter for C. pneumoniae to escape from the innate immune response, which has direct clinical significance.

CD4+ CD25+ Foxp3+ IFNγ+ CD178+ human induced Treg (iTreg) contribute to suppression of alloresponses by apoptosis of responder cells

Induced Treg with the phenotype CD4(+)CD25(+)Foxp3(+)IFNγ(+) were shown to be associated with good long-term graft outcome in renal transplant recipients and inhibition of allogeneic T-cell responses in vitro. In the present study, we investigated whether apoptosis and Fas/FasL-dependent pathways contribute to the inhibition of T-cell activation. Early apoptosis and necrosis rates as well as co-expression of immunostimulatory and immunosuppressive proteins in/on CD4(+)CD25(+)Foxp3(+), CD4(+)IFNγ(+)Foxp3(+) and CD4(+)CD25(+)IFNγ(+) PBL were analyzed using cells from healthy controls and four-color flow cytometry, PMA/Ionomycin-stimulated PBL, and MLC. Sixteen hours PMA/Ionomycin stimulation induced iTreg subsets with the phenotype CD4(+)CD25(+)Foxp3(+), CD4(+)IFNγ(+)Foxp3(+) and CD4(+)CD25(+)IFNγ(+) co-expressing CD95, CD152, CD178, CD279, Granzyme A, Granzyme B, Perforin, IL-10, and TGFβ(1). CD178(+) iTreg increased within 3h after PMA/Ionomycin stimulation in parallel to early apoptotic Annexin(+)/PI(-) PBL, suggesting CD178-mediated apoptosis of responder cells by CD4(+)CD25(+)Foxp3(+)IFNγ(+)CD178(+) iTreg. CD4(+)CD25(+)IFNγ(+) and CD4(+)CD25(+)CD178(+) PBL separated from primary cell cultures and added to autologous PMA/Ionomycin stimulated secondary cell cultures induced apoptosis immediately. Early apoptosis was not antigen-specific as shown in secondary MLC with separated CD4(+)CD25(+)IFNγ(+) and CD4(+)CD25(+)CD178(+) PBL and third-party cells as stimulator. CD4(+)CD25(+)Foxp3(+)IFNγ(+)CD178(+) iTreg differentiate after cell stimulation and induce antigen-unspecific apoptosis of activated CD95(+) responder/effector cells in vitro that might contribute to iTreg-mediated inhibition of T-cell activation.

A novel internalization motif regulates human IFN-γ R1 endocytosis

This study tested the hypothesis that the IFN-γ R1 287-YVSLI-91 intracellular motif regulates its endocytosis. IFN-γ exerts its biological activities by interacting with a specific cell-surface RC composed of two IFN-γ R1 and two IFN-γ R2 chains. Following IFN-γ binding and along with the initiation of signal transduction, the ligand and IFN-γ R1 are internalized. Two major types of consensus-sorting signals are described in receptors, which are rapidly internalized from the plasma membrane to intracellular compartments: tyrosine-based and dileucine-based internalization motifs. Transfection of HEK 293 cells and IFN-γ R1-deficient fibroblasts with WT and site-directed, mutagenesis-generated mutant IFN-γ R1 expression vectors helped us to identify region IFN-γ R1 287-YVSLI-291 as the critical domain required for IFN-γ-induced IFN-γ R1 internalization and Y287 and LI290-291 as part of a common structure essential for receptor endocytosis and function. This new endocytosis motif, YxxLI, shares characteristics of tyrosine-based and dileucine-based internalization motifs and is highly conserved in IFN-γ Rs across species. The IFN-γ R1 270-LI-271 dileucine motif, previously thought to be involved in this receptor endocytosis, showed to be unnecessary for receptor endocytosis.

Neuroinflammation in the aging down syndrome brain; lessons from Alzheimer's disease

Down syndrome (DS) is the most genetic cause of mental retardation and is caused by the triplication of chromosome 21. In addition to the disabilities caused early in life, DS is also noted as causing Alzheimer's-disease-like pathological changes in the brain, leading to 50-70% of DS patients showing dementia by 60-70 years of age. Inflammation is a complex process that has a key role to play in the pathogenesis of Alzheimer's disease. There is relatively little understood about inflammation in the DS brain and how the genetics of DS may alter this inflammatory response and change the course of disease in the DS brain. The goal of this review is to highlight our current understanding of inflammation in Alzheimer's disease and predict how inflammation may affect the pathology of the DS brain based on this information and the known genetic changes that occur due to triplication of chromosome 21.