A single non-synonymous polymorphism of TLR2 is sufficient to recapitulate the variability of Experimental Multiple Sclerosis

In the pathogenesis of Multiple Sclerosis a growing body of evidence is directing the attention also to bacteria. It is known that TLRs are involved in maintaining tolerance and inducing inflammation against the pathogens. We showed (1) that M tb-derived motives play an essential role in the induction of the experimental model of Multiple Sclerosis (EAE). To examine TLR2 (the main receptor for M tb) in the development of EAE we crossed different strains of mice, SJL and B6, in both of which is possible to induce EAE after immunization with myelin derived proteins. These two strains display a non-synonymous SNP of TLR2 that condition mobility of encephalitogenic T cells, with the allele of B6 dominant over that of SJL. Using of a strain lacking for TLR2 expression (B6tlr2-) we observed that a single NSP of TLR2 has a complex effect on clinical and histology of EAE. Although TLR2 haplotype does not influence incidence of disease, it is crucial for the course of EAE (more severe in F1 SJL x B6tlr2- than in F1 SJL x B6wt mice), significant for remission of EAE symptoms and involved in localization of infiltrates and demyelination in frontal lobes. The polymorphic site of TLR2 influences polarization of T cells by the expression of cytokines modifying the bias towards Th1/Th17, while no effect was seen in FoxP3 expression. Objective: In Multiple Sclerosis pathogenesis a growing body of evidence is directing the attention to bacteria. We showed that M tuberculosis (Mtb)-derived motives play an essential role in the induction of the experimental model of Multiple Sclerosis (EAE). TLR2 is the main receptor for Mtb. SJL and B6 mouse strains, in both of which is possible to induce EAE, display a non-synonymous SNP of TLR2 that condition mobility of encephalitogenic T cells, with the B6 allele dominant over the SJL one. To investigate the role of TLR2 in EAE development we crossed SJL mice with wild type B6 mice (B6wt) or B6 that fail to express TLR2 (B6tlr2-). Methods: F1(SJLxB6wt) and F1(SJLxB6tlr2-) female, mice 8-10 week old, were immunized with an emulsion of IFA enriched with 4mg/ml of killed and heat dried Mtb and different doses of PLP139-151 for immunization and EAE induction. At day 0 and 3 after EAE induction we treated a part of mice with Pertussis Toxin (PTx). Clinical score and body weight was recorded daily. CNS from mice was removed after reperfusion with PBS and paraformaldehyde. Sections from the brains and the spinal cords were processed for histological analysis to assess for inflammatory lesions and demyelination. Cytokines expression was evaluated by real-time PCR. Results: F1(SJLxB6tlr2-) mice displayed a more severe EAE compared to F1(SJLxB6wt) mice, in absence of PTx. F1(SJLxB6wt) mice were more sensitive to PTx administration than F1(SJLxB6tlr2-) mice. Severity of the disease appeared to be correlated to higher levels of pro-inflammatory cytokines IFN-g and IL-17 in F1(SJLxB6tlr2-) mice, while the level of FoxP3 mRNA is similar. The EAE in F1(SJLxB6wt) mice had a progressive/chronic course, while F1(SJLxB6tlr2-) mice consistently showed signs of symptoms remission, promoted by PTx. F1(SJLxB6tlr2-) mice showed a greater tendency to a rostral distribution of lesions. Conclusions: TLR2 haplotype does not influence disease incidence, but it is crucial for the course of EAE, significant for remission of EAE symptoms and involved in localization of infiltrates and demyelination in frontal lobes. The SNP on TLR2 influences polarization of T cells by the expression of cytokines modifying the bias towards Th1/Th17, while no effect was seen in FoxP3 expression. Thus, a single polymorphism of TLR2 is able to modify clinical and histology of EAE, reproducing a wide spectrum of the variability of experimental Multiple Sclerosis.