Autoimmune T cell responses to antigenic peptides presented by bronchoalveolar lavage cell HLA-DR molecules in sarcoidosis.

The etiology of sarcoidosis remains unknown. Recently, by mass spectrometric sequencing of peptides eluted from HLA-DR molecules of bronchoalveolar lavage (BAL) cells from DRB10301(pos) patients, we identified potential self-antigens in sarcoidosis. The aim of the present study was to investigate the capacity of selected peptides to stimulate lung and blood T cells of sarcoidosis patients using an interferon-gamma ELISPOT assay. In peripheral blood, there were strong T cell responses to a peptide derived from the cytoskeletal protein vimentin in 6 out of 11 DRB10301(pos) patients with active disease but not in patients with other HLA types. BAL T cell responses against peptides derived from ATP synthase or from lysyl-tRNA synthetase were detected in DRB10301(pos) as well as DRB10301(neg) patients. By using antigenic peptides presented in vivo in the lungs of sarcoidosis patients, we have identified blood and lung T cell autoimmune responses that may help sustain the inflammation in this disease.

Identification of HLA-DR-bound peptides presented by human bronchoalveolar lavage cells in sarcoidosis.

Sarcoidosis is an inflammatory disease of unknown etiology, most commonly affecting the lungs. Activated CD4+ T cells accumulate in the lungs of individuals with sarcoidosis and are considered to be of central importance for inflammation. We have previously shown that Scandinavian sarcoidosis patients expressing the HLA-DR allele DRB1*0301 are characterized by large accumulations in the lungs of CD4+ T cells expressing the TCR AV2S3 gene segment. This association afforded us a unique opportunity to identify a sarcoidosis-specific antigen recognized by AV2S3+ T cells. To identify candidates for the postulated sarcoidosis-specific antigen, lung cells from 16 HLA-DRB1*0301pos patients were obtained by bronchoalveolar lavage. HLA-DR molecules were affinity purified and bound peptides acid eluted. Subsequently, peptides were separated by reversed-phase HPLC and analyzed by liquid chromatography-mass spectrometry. We identified 78 amino acid sequences from self proteins presented in the lungs of sarcoidosis patients, some of which were well-known autoantigens such as vimentin and ATP synthase. For the first time, to our knowledge, we have identified HLA-bound peptides presented in vivo during an inflammatory condition. This approach can be extended to characterize HLA-bound peptides in various autoimmune settings.

Peptide motif for the rat MHC class II molecule RT1.Da: similarities to the multiple sclerosis-associated HLA-DRB1*1501 molecule.

Experimental autoimmune encephalomyelitis induced with myelin proteins in DA and LEW.1AV1 rats is a model of multiple sclerosis (MS). It reproduces major aspects of this detrimental disease of the central nervous system. MS is associated with the HLA-DRB1*1501, DRB5*0101, and DQB1*0602 haplotype. DA and LEW.1AV1 rats share the RT1av1 haplotype. So far, no MHC class II peptide motif of RT1.Da molecules has been described. Sequence alignment of the beta chain of the rat MHC class II molecule RT1.Da with human HLA class II molecules revealed strong similarity in the peptide-binding groove of RT1.Da and HLA-DRB1*1501. According to the putative peptide-binding pockets of RT1.Da, after comparison with the pockets of HLA-DRB1*1501, we predicted the peptide motif of RT1.Da. To verify the predicted motif, naturally processed peptides were eluted by acidic treatment from immunoaffinity-purified RT1.Da molecules of lymphoid tissue of DA rats and subsequently analyzed by ESI tandem mass spectrometry. In addition, we performed binding studies with combinatorial nonapeptide libraries to purified RT1.Da molecules. Based on these studies we could define a peptide-binding motif for RT1.Da characterized by aliphatic amino acid residues (L, I, V, M) and of F for the peptide pocket P1, aromatic residues (F, Y, W) for P4, basic residues (K, R) for P6, aliphatic residues (I, L, V) for P7, and aromatic residues (F, Y, W) and L for P9. Both methods revealed similar binding characteristics for peptides to RT1.Da. This data will allow epitope predictions for analysis of peptides, relevant for experimental autoimmune diseases.