Naturally Presented Peptides on Major Histocompatibility Complex I and II Molecules Eluted from Central Nervous System of Multiple Sclerosis Patients

Tandem mass spectrometry was used to identify naturally processed peptides bound to major histocompatibility complex (MHC) I and MHC II molecules in central nervous system (CNS) of eight patients with multiple sclerosis (MS). MHC molecules were purified from autopsy CNS material by immunoaffinity chromatography with monoclonal antibody directed against HLA-A, -B, -C, and -DR. Subsequently peptides were separated by reversed-phase HPLC and analyzed by mass spectrometry. Database searches revealed 118 amino acid sequences from self-proteins eluted from MHC I molecules and 191 from MHC II molecules, corresponding to 174 identified source proteins. These sequences define previously known and potentially novel autoantigens in MS possibly involved in disease induction and antigen spreading. Taken together, we have initiated the characterization of the CNS-expressed MHC ligandome in CNS diseases and were able to demonstrate the presentation of naturally processed myelin basic protein peptides in the brain of MS patients.T cells recognize antigen bound to MHC¹ molecules (1). CD4 as well as CD8 T cells have been shown to play a pathogenic role in various autoimmune diseases (2). Pathogenic T cells infiltrate the target organs and locally secrete proinflammatory cytokines and chemokines leading to tissue inflammation and possibly subsequent tissue destruction (3–5). Local presentation of autoantigens by MHC molecules in the target tissue of the autoimmune attack, i.e. the central nervous system (CNS) in multiple sclerosis (MS) or the pancreas in diabetes, is therefore a prerequisite for local immune amplification (6). MS is an inflammatory and neurodegenerative disease of the CNS leading to myelin and axonal loss (7). There are different disease courses, i.e. relapsing-remitting, secondary chronic progressive, and primary progressive disease. Potential autoantigens in MS include myelin basic protein (MBP), proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein (MOG). It is thought that T cells enter the CNS from the systemic circulation and that they are subsequently reactivated in the CNS on MHC I and MHC II molecules expressed on local antigen-presenting cells (APC) (8).To date, naturally presented HLA-bound peptides from patients with MS thus far have not been isolated and identified. So far, only circumstantial evidence exists for the local presentation of autoantigens such as MBP on MHC molecules in CNS (9). The aim of this study consisted of the characterization of the MHC-bound peptide repertoire derived from brains of patients with MS. Cutting edge technology combining HPLC and tandem mass spectrometry has recently allowed us to define peptides presented on APC from bronchoalveolar lavage from lungs of sarcoidosis patients (10). Applying a similar method on autopsy material of MS patients, for the first time we demonstrated local presentation of previously known and potential novel autoantigens in MS.