|M.Sc Student||Haimovich Yael|
|Subject||The HLA-B27 Immunopeptidome and the Immune-mediated|
Inflammatory Disease Ankylosing Spondylitis
|Department||Department of Biology||Supervisor||Professor Emeritus Arie Admon|
|Full Thesis text|
The human leukocyte antigen (HLA) class I molecule presents endogenous protein fragments on the cell surface of nucleated cells for surveillance by cytotoxic T lymphocytes (CTLs). The presented HLA class I peptides may originate from normal or abnormal proteins and can signal the existence of a disease or infection to the immune system’s CD8 cells. Soluble HLA class I (sHLA) molecules are also present in the plasma of all individuals, and is appears at altered levels during different pathologies.
Ankylosing spondylitis (AS) is a painful inflammatory arthritis that affects the spine, pelvis, and sometimes joints. This condition often progresses to variable degrees of fusion of the vertebrae in severe cases, resulting in a rigid spine. This condition is currently incurable but early diagnosis combined with pain and stiffness reduction treatment might reduce or prevent deformity.
Susceptibility to AS is correlated with the presence of the HLA-B27 allele. There are currently three main theories to the disease’s etiology. 1. The arthritogenic peptide hypothesis suggesting the disease is the result of an auto-reactive CTL in the patients’ bodies reacting to a self-peptide bound by HLA-B27. This is the result of enhanced immunity to previous disease, which involved exposure to bacterial or viral peptides mimicking in their sequences the body’s arthritogenic peptides; 2. The misfolding hypothesis proposes that HLA-B27 is unusually slow to fold and causes cellular stress and activates the unfolded protein response, which leads to activation and secretion of pro-inflammatory cytokines. 3. The surface homodimer hypothesis is based on the observation that HLA-B27 can form cell-surface homodimers. This homodimer may form a structure recognized by proinflammatory innate immune cells.
A novel disease diagnostic approach was developed in our lab, based on the purification and mass spectrometry identification of the peptides bound to the plasma sHLA molecules. We implemented this method on the plasma (and spleens) of rats transgenic for HLA-B27 to model the disease, and also on the plasma of AS patients and healthy controls.
We identified very few typical HLA-B27, this phenomenon may be a characteristic of sHLA-B27. We also discovered several peptides that appear mainly in the sick rats, and another set of peptides that mainly appears in the AS patients. These peptides may serve as disease biomarkers. We also found peptides with high mimicry to known arthritogenic bacteria. These peptides need to be further studied to verify their immunogenicity.