Objective. Double-stranded DNA (dsDNA) is a well-known target of autoantibodies in systemic lupus erythematosus (SLE). The majority of these autoanti-bodies are of the IgG isotype and show affinity matura-tion, both of which are known hallmarks of T cell help. T cell responses to autoantigens, including DNA, have been reported only incidentally in SLE patients. Nevertheless , in murine SLE, naked DNA and complexed DNA (nucleosomes) are known to be recognized by T cells. This study aimed to characterize the antinucleo-some response and its clinical impact on human SLE. Methods. Nucleosomes were prepared from chicken erythrocytes. Sera from SLE and control patients were investigated by enzyme-linked immunosor-bent assay (ELISA) for nucleosome-specific antibody responses. Peripheral blood mononuclear cells (PBMC) from SLE and control patients were analyzed by a kinetic T cell proliferation assay. PBMC were subsequently analyzed for nucleosome-specific T cell proliferation. Results. Of 136 SLE patients, 56% were seropos-itive for antinucleosome antibodies. In contrast, only 3% of 309 control patients (with rheumatoid arthritis, mixed connective tissue disease, undifferentiated connective tissue disease, Lyme borreliosis, scleroderma, Sjögren's syndrome, ulcerative colitis, hepatitis B virus infection, or human immunodeficiency virus infection) were seropositive. Thus, the antinucleosome ELISA had a sensitivity of 56%, a specificity of 97%, and a diagnostic confidence of 90% when applied to SLE. It was therefore superior to an anti-DNA ELISA that demonstrated a 69% diagnostic confidence in the same population. Antinucleosome reactivity in SLE patients correlated significantly with disease activity (P < 0.0001), nephritis (P < 0.002), and psychosis (P < 0.02). When proliferation assays were applied, 14 of 26 SLE patients (54%) were positive for nucleosome-specific T cells that proliferated in response to their cognate antigen. A suppressed response was elicited in 3 SLE patients (12%); in these patients, the PBMC response to nucleo-somes was lower than the proliferation of PBMC in the presence of culture medium only. PBMC from the remaining 9 SLE patients (35%) were nonresponsive to nucleosomes in either way. Responding, nonresponding, and suppressed populations differed from each other significantly (P < 0.0001). None of the PBMC from 7 healthy donors and 10 control patients could be stimulated with nucleosomal antigens. Conclusion. We present evidence that nucleo-somes are major autoantigens in human SLE and that antinucleosomal antibodies are highly specific for the disease. The antinucleosome ELISA has been shown to be superior to the anti-dsDNA ELISA and may thus be a significantly better tool for diagnosing SLE. Nucleosome-specific T cells in SLE patients may help B cells class switch to IgG and undergo affinity matura-tion.

A, Neidel J, Lehrach H, Thiesen HJ, Ruiz P, Bläß S. Molecular signatures and new candidates to target the pathogenesis of rheumatoid arthritis.

Objective The ubiquitously expressed intracellular protein formerly designated p68 has been identified as autoantigen at both the antibody and the T cell level in rheumatoid arthritis (RA). Methods We used 2 independent approaches, Edman degradation and matrix‐assisted laser desorption ionization–time‐of‐flight mass spectrometry, to characterize p68, and we compared its features with those of the endoplasmic reticulum stress protein BiP. Results In synovial sections from RA patients, BiP was highly overexpressed as compared with control sections. Under in vitro stress conditions, BiP was found to translocate to the nucleus and the cell surface. BiP‐specific autoantibodies were present in 63% of 400 RA patients, in 7% of 200 patients with other rheumatic diseases, and in none of the healthy subjects. Thus, BiP‐specific autoantibodies represent a new diagnostic marker in RA. Furthermore, we found that BiP‐specific T cell reactivity was altered in RA. In healthy individuals and patients with other rheumatic diseases, BiP‐reactive T cells were undetectable. In RA, overt T cell reactivity to BiP was observed or could be induced by specifically blocking antigen presentation to potentially regulatory T cells. Conclusion Since overexpression of BiP has been shown to decrease the sensitivity of cells to killing by cytotoxic T cells, BiP overexpression and BiP‐specific autoimmunity may be involved in the pathogenesis of RA.

Objective. The p205 autoantigen and interleukin-2 (IL-2) function synergistically to stimulate T lymphocytes from patients with rheumatoid arthritis (RA), and a p205-derived amino acid sequence is identical to an immunoglobulin sequence located within a domain that is reactive with rheumatoid factors (RF). This study was conducted to analyze in detail the T cell immune response against p205 and to investigate whether immunity to p205 may play a role in T cell-mediated immunopathology in active RA. Methods. Cibachron blue, protein A-Sepharose, and gel filtration on Sephacryl were used successively to enrich p205 from synovial fluid (SF). T lymphocytes from RA patients were isolated from the peripheral blood (PB), lymph nodes, and SF, and p205 and pep-tides derived from known sequences were assessed by T cell proliferation assays in the presence of IL-2. Results. P205-specific proliferation of T cells was observed in PB as well as in SF. When p205 was isolated from RA SF, proliferation of RA T cells peaked on day 3. With p205 purified from SF from trauma patients, there was a significant shift of the maximum T cell proliferation to day 8. T cells were of CD4 or CD8 phenotype, and B cells did not proliferate to a significant degree. The T cell response to p205 was always higher for SF mononuclear cells (SFMC) compared with PBMC (P < < < 0.001). In 1 RA patient who underwent repeated leukapheresis, this led to a reproducible decline in p205-specific T cell proliferation to control levels. PB T cells specifically proliferating in response to p205 were detected in 20 of 32 RA patients (63%). Of 26 patients with other inflammatory rheumatic diseases, only 1 showed a minor response to p205, while normal donors did not demonstrate a significant T cell proliferation. A synthetic p205-derived peptide, with an amino acid sequence identical to an immunoglobulin sequence located in the area where RF binds, was reactive with T cells from RA patients. Conclusion. P205 appears to be a major target of autoreactive T cells in RA. P205-specific T cells are primed and more abundant at the site of inflammation. As a T cell target in RA, p205 may well be an antigen involved in the initiation of RF production.