Role Of TNF-α In Experimental Autoimmune Neuritis And KA Induced Central Neurodegenerative Disease

EAN is an animal model of Guillain-Barre syndrome (GBS), a demyelin ating autoimmune disease of peripheral nervous system (PNS) in humans. EAN can be induced in susceptible animal strains by active immunization with PNS tissue, the purified PNS myelin components P2 or PO proteins or their peptides, or passively transferred to naive animals by P2/PO peptides or active CD4+T cell. KA is an analog of excitotoxin glutamate. Administration of KA to rodents results in neuron death and seizures, which provides a well-characterized model for studies of human neurodegenerative diseases.TNF-a, originally identified as having anti-tumor activity, was later noticed that have pleiotropic functions although controversial. Its effects are mediated through two receptors, TNFR1 and TNFR2, mainly TNFR1. In recent studies, despite its pro-inflammatory activities, TNF-αhas been found to have beneficial effects on ischemia and autoimmunity by suppressing immune response. However, the role of TNF-αin EAN and KA induced neurodegeneration is not clear yet.Purposes:In present study, we investigated the role of TNF-αin autoimmune disease in peripheral nerve and excitotoxic neurdegeneration by using the models of EAN and KA-induced hippocampal injury in TNFR1-/- mice separately.Methods:(1) EAN was established in TNFRl-/-mice by subcutaneous injection of PO peptide 180-199. We evaluated the clinical symptoms and inflammatory cells infiltrations in the sciatic nerves by histopathological method. Specific PO- reactive T cell proliferation was detected and cells secreting IFN-y and IL-4 were also tested by ELISPOT. Using FACS, we measured the number of infiltrating macrophages within the PNS and MHCII and CCR3 expression on the infiltrating macrophages, as well as IFN-γand TNF-αsecretion and Swchwann cell apoptosis in Cauda equine.(2) An animal model of neurodegeneration in hippocampus was established in TNFR1-/- mice by giving KA through nose. Mice were monitored continuously for 5 hours to register the onset and extent of seizure activity. Open-field activity was measured one day before and seven days after KA administration. Histopathological changes of neurons in hippocampi were observed after 8 days of KA administration. Microglia activation and astrogliosis were tested by immune-histochemistry. Using FACS, we measured the number of activated microglia and CCR3 and TNFR2 expression on their membranes.Results:(1) Compared to wild type EAN mice, EAN in TNFR1-/- mice developed significantly more severe clinical signs, in parallel with enhanced numbers of inflammatory infiltrating cells in the peripheral nerves and splenic PO-reactve T proliferation and IFN-γsecretion, as well as increased obviously MHCII and CCR3 expression on the macrophages in the cauda equine.(2) Within 15-20 minutes after KA administration, both group of mice developed seizure, however, TNFR1-/-mice showed more severe seizures than the wild-type mice. In addition, obvious neurodegeneration, e.g. enhanced microglia activation, and astrogliosis in the hippocampus, as well as increased locomotor activity were found in TNFR1-/- mice, when compared with control wild type mice, although less microglia activation in the early stage.Conclusion:(1) Through TNFR1, TNF-αmight prevent the development of EAN via its anti-inflammtory effect.(2) TNF-αmight have inflammatory role in the early stage of KA induced-neurodegeneration by activation of microglia.(3) TNF-αmight have a protective role in the late phase of KA-induced neurodegeneration.