| Abstract |
Title: TNF-Related Apoptosis Inducing Ligand (TRAIL) Expression in Natural Killer (NK) cells and their role in Experimental Autoimmune Encephalomyelitis (EAE)
Introduction: Multiple Sclerosis (MS) is a CD4+ T cell mediated, demyelinating autoimmune disease of the central nervous system (CNS). TRAIL, a 281amino acid homotrimeric member of the TNF/NGF superfamily is expressed as soluble and membrane-bound form by activated T cells, B cells, macrophages and NK cells both in human and mouse and induces caspase-mediated cell death in transformed and non-transformed cells. 1,2 However, it has been shown that TRAIL acts not only as an apoptotic ligand but exerts also an immunoregulatory function.
In the animal model of MS, the EAE, it has been demonstrated that, when applied intracerebrally, TRAIL induces neuronal death and exacerbates the disease.3 However, when applied in the periphery, it reduces severity by inhibiting autoreactive T cells. 4 So far, the cell population which mediates the modulation of EAE through TRAIL is undefined.
In MS patients, an increased amount of soluble TRAIL in the peripheral blood has been linked to clinical response (stable EDSS score) to IFN-β treatment at the relapsing remitting (RR-MS) form of the disease during the first year of treatment. 5 Additionally, TRAIL induction on NK cells of MS patients after in vitro culture with IFN-β is less pronounced compared to healthy controls (Infante-Duarte, unpublished data).
NK cells are members of the innate immune system, but also capable of regulating cells of the adaptive system as autoreactive T cells and dendritic cells. 7 Furthermore, a reduced functional activity of NK cells has been linked to MS relapses and NK cell depletion has been shown to exacerbate EAE. 7-9
Aims:
1. To investigate which factors, e.g. IFN-β, are able to modulate TRAIL-expression in murine NK cells.
2. To investigate the role of TRAIL-expressing NK cells in modulating the clinical course and histopathology of EAE.
Methods: Induction of TRAIL on NK cells of wild-type (wt) C57BL/6 mice by IFN-β was investigated at the gene level by Taq-Man analysis and at the protein level through antibody detection using flow cytometry (FACS).
EAE was induced in wt C57BL/6 mice through subcutaneous (s.c.) injection of Myelin Oligodendrocyte Glycoprotein (MOG 35-55) peptide in Complete Freund’s Adjuvant (CFA).
Shortly after immunisation, “naive” NK cells or TRAIL-expressing NK cells (which were pre-incubated with IFN-β) were injected to the aforementioned mice. Clinical course, severity of disease and histopathological landmarks of mice receiving either NK cells or TRAIL expressing-NK cells were compared with those of control mice (injected with PBS alone).
Results: IFN-β induced an increase of TRAIL mRNA expression on murine NK cells at concentrations of 500U/ml and 1000U/ml. An induction of surface TRAIL expression on NK cells with the same concentrations of IFN-β was also confirmed at the protein level.
The optimal concentration and incubation time of 1000U/ml for 18 hours was used for TRAIL induction on ‘naïve’ NK cells.
In C57BL/6 mice, which received the TRAIL-expressing NK cells intravenously (i.v.), a reduced incidence of EAE induction was observed compared to mice, which received untouched NK cells or PBS alone.
Discussion: NK cells represent a putative target of IFN-β treatment in EAE. IFN-β-induction of TRAIL in NK cells may be an important mechanism of action of this drug. TRAIL-expressing NK cells could play a regulatory role during the induction phase of the disease by influencing the priming of T cells or neuron survival in the CNS. Thus, generation of NK cells with immunoregulatory properties may represent a therapeutic strategy for EAE and MS.
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TNF-Related Apoptosis Inducing Ligand (TRAIL) expression in natural killer (NK) and their role in Experimental Autoimmune Encephalomyelitis (EAE)
