טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHalevi Lilach
SubjectThe HLA-B27 Peptidome in Autoimmunity and Cancer
DepartmentDepartment of Biology
Supervisor Professor Arie Admon
Full Thesis textFull thesis text - English Version


Abstract

The HLA-B27 allele confers a 20-fold increased risk of developing a group of diseases termed spondyloarthropathies, autoimmune rheumatoid cartilage diseases. The molecular mechanism underlying this linkage is yet unkown. Ankylosing spondylitis is the most frequent spondyloarthropathy, 95% of the patients carry the B27. Reactive arthritis is another subtype that emerges following specific intracellular infections; 80% of the patients are B27 positive. The cartilage is considered the primary target for autoimmune response of CD8+ T cells previously activated by infection. Disease is probably initiated by a pathogen's peptide presented on HLA-B27, mimicking peptides normally presented by chondrocytes.

Developing treatments based on specifically targeting the disease causing T-cells without disrupting the entire immune system is the goal of this research. This has been demonstrated in animal models and HLA-B27 peptides were also administered to patients with encouraging preliminary results.

This research is the first large scale study of the HLA-B27 peptidome, it is based on recovery of peptides from soluble HLA-B27 molecules followed by analysis with advanced mass spectrometry and bioinformatics. We examined the HLA-B27 peptidomes of cells used as cartilage models, and of bacteria infected cells. We identified about 2500 natural ligands, over ten times the number known to date.

Human cell lines were retrovirally transfected with the sHLA-B27, the soluble molecules were affinity purified from the growth media , their peptides separated by ultrafiltration and chromatography and identified by mass spectrometry. Natural B27 ligands derived from cartilage specific proteins were identified for the first time. 

Bioinformatics was used to search for mimicry between the sequenced peptides and sequences from arthritogenic bacteria. Some cartilage peptides identified here were found as highly similar to amino acid sequences common to many arthritogenic pathogens.

We then tested whether non-phagocytic cells can present peptides derived from these pathogens within their HLA class-I. The cells were infected with the arthritogenic bacteria Salmonella and Mycoplasma. Post-infection changes in the peptidome were detected, some similar to both bacteria. B27 peptides derived from bacterial proteins were also identified, these were found to be shared by many arthritogenic strains. Our findings are the first to biochemically show presentation of bacterial antigens on HLA class-I, and the first to show it in non-phagocytic cells.

Since HLA-B27 is a prevalent allele, found in 10% of the population, its cancer-related peptides were also investigated. We have identified over 180 such ligands with potential to become targeted immunotherapeutic anti-cancer drugs for HLA-B27 positive pateints.