T cells discriminate between differentially phosphorylated forms of alphaB-crystallin, a major central nervous system myelin antigen

Abstract

Factors such as developmental stage or physiological and infectious stress may change patterns of post-translational protein modification. In order to determine whether such regulated types of modification may influence T cell responsiveness to self proteins we examined the T cell response of SJL (H-2s) mice to alphaB-crystallin, a small heat shock protein that can exist in differentially phosphorylated forms. Epitope mapping revealed the presence of two T cell epitopes that are presented by I-As. One major epitope including residues 41-56 contains an amino acid residue (Ser45) that can be phosphorylated as the result of aging or stress. Accordingly, T cells from SJL mice discriminate between preparations of alphaB-crystallin that differ in their extent of phosphorylation at the level of whole protein as well as at the level of determinant-specific responses. Phosphorylation at Ser45 does not prevent binding of the peptide 41-56 to I-As and computer-assisted modelling of the peptide-MHC complex suggests that the phosphate group of the bound peptide extends outwards from the peptide-binding cleft and may thus be available for direct contact with TCR. Together, our data provide evidence that stress-inducible phosphorylation of alphaB-crystallin creates neo-determinants for T cells and, therefore, may contribute to the breakdown of peripheral tolerance to this self protein.

Identification of tumor-associated, MHC class II-restricted phosphopeptides as targets for immunotherapy

“…CD8 ϩ T cells immunized to specifically recognize these phosphopeptides are also capable of recognizing intact human tumor cells, suggesting that phosphopeptides may represent a new class of targets for cancer immunotherapy (5,6). In these studies and others, T cell discrimination of the phosphopeptide versus its nonphosphorylated counterpart was observed, indicating that phosphorylation can influence peptide immunogenicity (5)(6)(7)(8)(9)(10)(11)(12)(13). Recent crystal structural definition of phosphorylated peptide-HLA-A2 complexes demonstrated direct and indirect interactions of the phosphoresidue with the MHC molecule, often significantly increasing the affinity of the phosphopeptide for MHC I. Additionally, phosphoresidues were solvent-exposed, suggesting the potential for direct interactions with the T cell receptor (14,15).…”

Extracellular Matrix Remodeling: The Common Denominator in Connective Tissue DiseasesPossibilities for Evaluation and Current Understanding of the Matrix as More Than a Passive Architecture, but a Key Player in Tissue Failure

“…Many of these modifications have been implicated in the antigenicity of the proteins, as outlined in Table 4 (modified from Cloos and Christgau 15 ). 296,311,[319][320][321][322]346,347,[376][377][378][379][380][381][382][383][384][385][386][387][388][389] These observations have sparked a growing interest in the role and assessment of PTMs in autoimmune diseases as well as other pathological conditions associated with aging. Whether the presence of PTMs is merely a secondary phenomenon accompanying the disease or a primary event in disease initiation remains to be resolved.…”

An Immunoproteomic Approach for Identification of Clinical Biomarkers for Monitoring Disease

“…Even with sophisticated proteomic methodologies that incorporate a combination of sample preparation techniques, including depletion of high abundance proteins and/or prefractionation strategies, detection of protein biomarkers remains challenging (3,4). The use of circulating antibody repertoires from subjects suffering diseases such as inflammatory diseases, certain cancers, and autoimmune disorders represents a powerful means for detecting disease-associated antigenic proteins in protein macroarrays derived from body fluids, cell lines, tissue cells, or pathogens, which may be of prognostic/diagnostic value or may represent valuable drug targets (5)(6)(7)(8). Despite detection of disease-related antigenic proteins using immunoproteomic approaches (9), many of these antigens remain unidentifiable due to their low abundance (10,11).…”