ABSTRACT
Peptides derived from amino acid sequence 60-80 of HLA-B27 (B27PA, aa 60-72 and B2702PA, aa 60-80) mimic cytokeratin and are able to induce in vitro proliferation of human peripheral blood lymphocytes as well as arthritis in Lewis rats. Here we show that the pathogenic epitope recognized by autoaggressive rat T cells is located at the N-terminus of the sequence, between aa 60 and 72. A C-terminally elongated 25mer peptide (B2702.60-84) showed increased pathogenicity, indicating either a second arthritogenic epitope or an immunomodulatory region within this peptide. B2702.60-84 has been described to inhibit murine and human CD8 + cytotoxic T cells (CTL) and was even successfully used for the treatment of allograft rejection. In addition to pathogenicity we have investigated the immunomodulatory effect of peptide B2702.60-84 in our rat model of experimental autoimmune uveitis (EAU), induced with retinal S-Antigen peptide PDSAg. We found that disease exacerbated following coimmunization of PDSAg with B2702.60-84. In vitro, the B27-peptide enhanced the proliferation of CD4+ T cell lines specific for retinal autoantigen peptides during coincubation of B2702.60-84 with the respective antigen. Oral tolerance induction, an effective mechanism to prevent uveitis in Lewis rats, is abrogated by cofeeding peptide B2702.60-84 with the tolerogen PDSAg. In rat EAU, naturally occurring regulatory T cells and orally induced gamma deltaTCR+ suppressor cells are CD8+ which might be impeded by peptide B2702.60-84. As a consequence of their abrogated suppressive capacity disease was exacerbated. We propose a similar role of HLA-B27 in man: disturbing the mechanisms down-regulating self-responses might lead to autoimmune diseases. This could explain the high association of HLA-B27 with a variety of autoimmune diseases targeting different organs or tissues.
Subject(s)
Autoimmune Diseases/immunology , Disease Models, Animal , HLA-B27 Antigen/chemistry , HLA-B27 Antigen/immunology , Peptide Fragments/immunology , Peptide Fragments/pharmacology , Amino Acid Sequence , Animals , Arthritis/chemically induced , Cell Proliferation/drug effects , Female , HLA-B27 Antigen/pharmacology , Immune Tolerance/immunology , Keratins/chemistry , Keratins/pharmacology , Male , Molecular Sequence Data , Peptide Fragments/chemistry , Rats , Rats, Inbred Lew , T-Lymphocytes/cytology , T-Lymphocytes/drug effects , Uveitis/chemically inducedABSTRACT
OBJECTIVE: The intracellular persistence of viable Chlamydia trachomatis (CT) within the joint is thought to initiate and maintain the inflammatory process in CT-induced arthritis. CT-induced arthritis is associated with HLA-B27. Recently it was shown that HLA-B27, besides being a T-cell restriction element, can directly influence the invasion and/or replication of enterobacteriae and alters salmonella-induced signal transduction. It was the aim of this study to analyze the effect of HLA-B27 on CT-invasion and replication in human host cells. METHODS: Human Hela cells and Hela cells transfected with either HLA-B27 cDNA or controls (HLA-A1 cDNA; HLA-B27 mutant = HLA-B27 without cytoplasmic tail; B27Q10 = HLA-B27 Exon 1-4 linked to Exon 5 of murine Q10) were infected with CT. By direct immunofluorescence chlamydial invasion was determined 4 hours post infection (p.i.), chlamydial replication 2 days and 4 days p.i. The number of infective CT in the different cell lines was determined by titration of the cell lysates on Hep-2 cells with subsequent immunoperoxidase staining. RESULTS: Invasion was not affected by HLA-B27. However, formation of chlamydial inclusion bodies and replication was suppressed by HLA-B27. Genetically engineered mutants of HLA-B27 (HLA-B27 mutant, B27Q10) lacking the cytoplasmic tail of HLA-B27 did not affect replication. CONCLUSION: The reduction of chlamydial replication by HLA-B27 depends on the cytoplasmic domain of HLA-B27, thus providing a new hypothesis for chlamydial persistence in HLA-B27 positive reactive arthritis.