Molecular basis for the MHC class II association in rat experimental autoimmune encephalomyelitis

Sammanfattning: This thesis investigates the functional and structural aspects of rat MHC class 11 molecules and studies their influence on MBP- and MOG-peptide induced experimental autoimmune encephalomylitis (EAE) in LEW MHC congenic rat strains. EAE is an animal model for multiple sclerosis (MS) and can be induced in rats with components of the myelin sheath . As in MS, the MHC exerts a strong influence on the susceptibility or the resistance to EAE. We established an ELISA-based MHC class 11 peptide binding assay, which allowed us to determine in vitro what myelin peptides bind to different allelic variants of purified rat MHC class 11 molecules. We found that differences in disease susceptibility to certain MBP peptides observed in the different rat strains were partially reflected in the allelic diversity of the peptide binding profiles. Although intermediate to strong binding of MBP and MOG peptides to the restricting MHC class 11 molecule was a prerequisite, it was only one of the many requirements to be met in order for a peptide to be encephalitogenic. We also used the peptide binding ELISA in conjunction with combinatorial peptide libraries to study the peptide binding pattern of the RT1.Dn molecule. To our knowledge, this is the first description of the peptide binding properties of a rat DR-like molecule. We studied the requirements for dominant expression of TCRBV8S2 in LEW rats after immunization with MBP63-88. We found that the preferential recruitment of TCRVB38S2+ T cells was strictly dependent on MHC haplotype and on the heterologous origin of the peptide. Moreover, by varying the peptide of immunization and thus, the pathogenic T-cell repertoire, we could show that the suppressive effect of naked DNA vaccination was highly specific. Beside DNA vaccination, we tested three more approaches targeting the trimolecular complex in order to treat or to prevent EAE: T-cell depletion with a TCRBV8S2 specific monoclonal antibody, nasal tolerance and coimmunization with a high affinity MHC class 11 ligand all led to suppression of EAE. In MOG-peptide induced EAE, we demonstrated a lack of correlation between 1) immunodominance and encephalitogenicity. Instead, in LEW.1N rats, the cryptic MOG 91-108 epitope was disease driving. Immunogenic responses against this peptide were only detectable in the CNS, underscoring the importance of analyzing immune responses in the target organ 2) immunogenicity and encephalitogenicity i.e. some immunodominant MOG peptides raised a peripheral IFN-gamma response accompanied by a B-cell response without causing encephalitogenicity. In conclusions, these studies suggest that efficient binding and presentation of an encephalitogen by its restricting MHC molecule in the peripheral lymphoid tissue undoubtedly plays an fundamental role in the initiation of the autoimmune response. But the influence of the MHC on the T-cell repertoire, both in selecting potentially encephalitogenic T cells as well as in the selection of a regulatory repertoire might also have an enormous impact on the development of autoimmune disease.