Upon stimulation by microbial products through TLR, dendritic cells (DC) acquire the capacity to prime naive T cells and to initiate a proinflammatory immune response. Recently, we have shown that APC within the CNS of multiple sclerosis (MS) patients contain peptidoglycan (PGN), a major cell wall component of Gram-positive bacteria, which signals through TLR and NOD. In this study, we report that Staphylococcus aureus PGN as a single component can support the induction of experimental autoimmune encephalomyelitis (EAE) in mice, an animal model for MS. Mice immunized with an encephalitogenic myelin oligodendrocyte glycoprotein peptide in IFA did not develop EAE. In contrast, addition of PGN to the emulsion was sufficient for priming of autoreactive Th1 cells and development of EAE.
In vitro studies demonstrate that PGN stimulates DC-mediated processes,
reflected by increased Ag uptake, DC maturation, Th1 cell expansion,
activation, and proinflammatory cytokine production. These data indicate
that PGN-mediated interactions result in proinflammatory stimulation of
Ag-specific effector functions, which are important in the development of
EAE. These PGN-mediated processes may occur both within the peripheral
lymph nodes as well as in the CNS and likely involve recognition by TLR on
DC. Thus, PGN may provide a physiological trigger of DC maturation, and in
this way disrupt the normal tolerance to self Ag. As such, PGN signaling
pathways may serve as novel targets for the treatment of MS.