Mecanismos de procesamiento y presentación antigénica en autoinmunidad

Abstract

HLA molecules are peptide-presenting molecules, which show to T lymphocytes the state of the cell and environment, what allows to activate the specific immune response in case of infection or tumoral tranformation. There are two types of HLA molecules, class I (HLA-A, -B and -C) and class II (HLA-DR, -DP and -DQ). Class I molecules show peptides derived from the catabolism of endogenous proteins, while class II molecules show peptides derived from exogenous, membrane or vesicle proteins. The strong genetic association of many autoimmune diseases are with some HLA alleles. Among these disorders are rheumatoid arthritis, associated with DR1, several subtypes of DR4 and DR10, but not with DR15. HLA-DR15 is a complex haplotype associated with multiple sclerosis which expresses two functional genes, HLA-DRB1*15:01 (DR2b) and HLA-DRB5*01:01 (DR2a). On the other hand, several peptides can bind to multiple class II molecules, what has been denominated promiscuity of HLA class II molecules._x000D_ On the other hand, the proteasome is an abundant multicatalytic complex which is the main degradative system in the cytosol and nucleus. Three major types of proteasome have been described: the constitutive proteasom with the catalytic subunits β1,β2 y β5; the immunoproteasome (β1i, β2i y β5i) and the thymoproteasome (β1i, β2i y β5t). Recently, intermediate proteasome have been described. These contain β1, β2 and β5i or β1i, β2 and β5i._x000D_ In this thesis we have studied, using biochemical and mass spectrometry techniques, several points of the antigenic processing and presentation. First, the peptide repertoires bound to HLA-DR molecules differentially associated with rheumatoid arthritis have been analyzed. Second, we have studied the peptide repertoires associated to DR2a and DR2b, molecules simultaneously expressed in cells with the haplotype HLA-DR15. Finally, we have characterized the specificity of the intermediate proteasome β5i and its role in the generation of HLA class I peptide ligands._x000D_ Our data indicate that, among the allotypes associated with the disease, the most similar peptide repertoires are DR1 and DR10, and many common peptides contain leucine in P4 core position and basic residues in P8. The peptide repertoires bound to DR2a and DR2b allowed the refinement of their binding motifs. Both repertoires are complimentary and with a low degree of overlap. Furthermore, we estimated that both molecules contribute similarly to the global peptide repertoire presented by HLA-DR15. The fact that all peptide repertoires analyzed showed a low degree or overlap indicate that, although the HLA-DR promiscuity exists, it occurs in a low number of peptide ligands._x000D_ On the other hand, a new protocol for the rapid and efficient purification of an active and pure 20S proteasome has been developed. The data indicate that the intermediate proteasome β5i has a decreased chymotrypsin-like activity, a similar caspase-like and an increased trypsin-like activity than the standard proteasome. Finally, in vitro digestions with purified 20S proteasomes of peptide precursor of HLA class I-ligands has allowed to explain the generation of several HLA- class I peptide ligands.

Date of Award	7 Jul 2017
Original language	Undefined/Unknown
Supervisor	Iñaki Alvarez (Director)