TLR2 tolerance in EAE

Abstract

Abstract TLR2 expression is enhanced in MS and EAE, but its role in these diseases is controversial. In adoptive transfer EAE, exogenous TLR ligands are not administered yet TLR2-deficient mice have been reported to develop attenuated disease. Despite this evidence for a disease-promoting function of TLR2, others have shown the opposite, i.e. that administration of TLR2 ligands can inhibit EAE in WT mice. To understand this paradox we tested the postulate that although TLR2 signaling may be EAE-promoting, repeated TLR2 ligand administration can lead to diminished TLR2 responsiveness (tolerance) and attenuated disease. To establish our approach, we administered Pam2Cys to SJL/J mice for 5 days and induced TLR2 tolerance that persisted for 4–5 days, reflected in decreased serum TNFα in response to a second TLR2 ligand (p<0.0001 day 1; p<0.01 day 3; p=0.069 day 5). Next, we used this approach to induce TLR2 tolerance in the context of EAE. SJL/J mice received EAE-causing, PLP-reactive LNCs on day 0 and tolerance was induced at various time points. Surprisingly, initiating the TLR2 tolerance protocol at day −2 or day +8 showed no effect on disease. In contrast, initiating the protocol between day +4 and +6 lead to significant inhibition of EAE onset and severity that lasted at least 5 days (p=0.025) and was associated with TLR2 tolerance (p<0.0001). In sum, we have used TLR tolerance as a novel probe to identify a narrow kinetic window in which TLR2 is required for EAE. Additionally, we have demonstrated the potential use of TLR tolerance as a new therapeutic approach in EAE and MS. Ongoing studies will characterize the relevant TLR2-expressing cells in EAE and the potential role of the microbiome in inducing homeostatic TLR tolerance that regulates autoimmunity.