The role of CNS TLR2 activation in mediating innate versus adaptive neuroinflammation.
Toll-like receptor 2 (TLR2) is expressed on immune cells in the periphery and the CNS and mediates both innate and adaptive immune responses. Recent studies have implicated TLR2 in systemic pathogenesis of adaptive immunity in experimental autoimmune encephalomyelitis (EAE). In addition, TLR2 is expressed on oligodendrocyte progenitor cells and its activation inhibits their differentiation and myelination. We investigated the roles of CNS TLR2 activation in mediating neuro-inflammatory responses in intact versus EAE animals. We examined the effects of intra-cerebro-ventricular (ICV) injection of Zymosan, a TLR2 agonist, on naive versus EAE animals. The neuro-inflammatory response was characterized by immune-fluorescent staining for IBA-1+ microglia/macrophages and CD3+ T cells, and by semi-quantitative real time PCR for TLR2 and immune cytokines. The nature of the immune cells isolated from EAE brain tissue was assessed by their proliferative response to the PLP peptide autoantigen. Survival and clinical scores were monitored; demyelination and axonal loss were quantified by Gold-Black and Bielschowsky stains. Our findings showed that Zymosan injection in naïve mice induced a massive neuro-inflammatory response without any clinical manifestations. In EAE mice, ICV Zymosan induced a severe acute toxic response with 80% mortality. Surviving animals returned to pre-injection clinical score, and their course of disease was not altered as compared to control EAE group. Demyelination and axonal loss were not affected by ICV Zymosan injection. Quantification of immune response in the brain by real time PCR, immunofluorescent stains and proliferative response to PLP peptide suggested that TLR2 activation induces innate but not adaptive immune response. We conclude that EAE mice are hypersensitive to CNS TLR2 activation with a severe toxic response. This might represent the susceptibility of multiple sclerosis patients to even trivial infections. As CNS TLR2 activation does not alter the clinical and pathological course of EAE, it implies that CNS TLR2 activation affects the innate but not adaptive brain immune responses.
Department of Neurology, The Agnes Ginges Center for Human Neurogenetics, Hadassah-Hebrew University Medical Center, Israel; Physiotherapy Department, School of Health Sciences, Ariel University, Israel. Electronic address: avital.luz@gmail.com.
Avital
A
Luz
Department of Neurology, The Agnes Ginges Center for Human Neurogenetics, Hadassah-Hebrew University Medical Center, Israel. Electronic address: nina.fainstein@mail.huji.ac.il.
Nina
N
Fainstein
Physiotherapy Department, School of Health Sciences, Ariel University, Israel. Electronic address: ofirae@ariel.ac.il.
Ofira
O
Einstein
Department of Neurology, The Agnes Ginges Center for Human Neurogenetics, Hadassah-Hebrew University Medical Center, Israel. Electronic address: tamir@hadassah.org.il.
Tamir
T
Ben-Hur
D056704:Adaptive Immunity / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D017252:CD3 Complex / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002490:Central Nervous System / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D004660:Encephalitis / Q000139:chemically induced / Q000276:immunology / Q000378:metabolism; D004681:Encephalomyelitis, Autoimmune, Experimental / Q000139:chemically induced / Q000473:pathology*; D005260:Female; D007113:Immunity, Innate / Q000187:drug effects / Q000502:physiology*; D007276:Injections, Intraventricular; D008264:Macrophages / Q000378:metabolism / Q000473:pathology; D051379:Mice; D017628:Microglia / Q000378:metabolism / Q000473:pathology; D018991:Myelin Proteolipid Protein / Q000633:toxicity; D010446:Peptide Fragments / Q000633:toxicity; D012333:RNA, Messenger / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism / Q000473:pathology; D013997:Time Factors; D051195:Toll-Like Receptor 2 / Q000819:agonists / Q000378:metabolism*; D015054:Zymosan / Q000633:toxicity
D017252:CD3 Complex; D016207:Cytokines; D018991:Myelin Proteolipid Protein; D010446:Peptide Fragments; D012333:RNA, Messenger; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2; C435023:myelin proteolipid protein (139-151); D015054:Zymosan
EAE; Neuroinflammation; TLR2; Zymosan