|Ph.D Student||Shira Yair-Sabag|
|Subject||The Role of HLA-B27 Peptidome in Ankylosing Spondylitis|
|Department||Department of Biology||Supervisor||Full Professor Admon Arie|
|Full Thesis text|
The HLA-B*27 has been known to be genetically associated with the inflammatory rheumatic disease Ankylosing Spondylitis (AS) since the beginning of the 1970. Yet, after years of extensive research, its role in the disease etiology remains unknown. The HLA molecules are transporters and presenters of endogenous peptides at the cells’ surface, thus enabling the immune system to scrutinize the health-state of the cells.
In autoimmune/inflammatory diseases, such as AS, it was suggested that presentation of HLA peptides resembling bacterial sequences may induce an anti-self immune response (arthritogenic peptide theory). For this reason, the peptidome of HLA-B*27 has drawn significant attention, aiming to gain better understanding of biological rational for this correlation. This study aims to expand the known binding motifs of the HLA-B*27 peptidome to facilitate selection and testing of new peptides, possibly involved with the disease.
In this study, large database was generated by using HeLa and C1R cell lines, stably transfected with the AS-associated HLA-B*27:05 allele or the non-associated HLA-B*27:09 allele. In addition, the HLA peptidomes of mutated, AS-associated and non-associated alleles, in which cysteine 67 was substituted by serine (C67S), were screened. Moreover, the peptidomes of HLA-B*27:05 and HLA-B*27:05-C67S were analyzed from the spleens of transgenic rats.
The results indicate that C67S mutation increased the percentages of bound peptides containing glutamine or lysine at their P2 position (P2-Lys), in both HLA-B*27:05 and HLA-B*27:09. These P2-Lys peptides were further investigated and found to be present at lower levels also in the wildtype B*27 peptidome, in which arginine (P2-Arg) is the most prominent amino acid. Glutamine (P2-Gln) follows it with lower percentages.
In addition, some of the identified P2-Lys containing peptides were assessed using binding assay and structure simulation, indicating that the HLA-B*27 molecules may indeed bind peptides containing Lys at their second position. These P2-Lys containing peptides were further examined for their resemblance to bacterial peptides and thus their potential to be arthritogenic peptides.
Overall, the data suggests that peptides with P2-Lys should be considered as potential ligands of the HLA-B*27 molecules and should be taken into account when looking for putative pathogenic peptides involved with AS.