Antigen-driven clonal proliferation of B cells within the target tissue of an autoimmune disease: the salivary glands of patients with Sjögren's syndrome

Structures resembling germinal centers are seen in the salivary glands of patients with Sjögren's syndrome, but it is not known whether the microenvironment of these cell clusters is sufficient for the induction of a germinal center response. Therefore, we cloned and sequenced rearranged Ig V genes expressed by B cells isolated from sections of labial salivary gland biopsies from two Sjögren's syndrome patients. Rearranged V genes from B cells within one cell cluster were polyclonal and most had few somatic mutations. Two adjacent clusters from another patient each contained one dominant B cell clone expressing hypermutated V genes. None of the rearranged V genes was found in both clusters, suggesting that cells are unable to migrate out into the surrounding tissue and seed new clusters. The ratios of replacement to silent mutations in the framework and complementarity determining regions suggest antigen selection of high-affinity mutants. These results show that an antigen-driven, germinal center-type B cell response is taking place within the salivary glands of Sjögren's syndrome patients. In view of the recent demonstration of a germinal center response within the rheumatoid synovial membrane and the existence of similar structures in the target tissues of other autoimmune. diseases, we propose that germinal center- type responses can be induced in the nonlymphoid target tissues of a variety of autoimmune diseases

Effect of dsDNA binding to SmD-derived peptides on clinical accuracy in the diagnosis of systemic lupus erythematosus

Systemic lupus erythematosus is characterized by antibodies to a variety of intracellular self-antigens, such as dsDNA and Sm, and these serve as hallmarks in the diagnosis of systemic autoimmune diseases. Several studies have shown that SmD1 and SmD3 synthetic peptides represent highly functional antigens for autoantibody detection and thus for diagnostic applications. The present study analysed the technical and clinical accuracy of an anti-SmD1 (amino acids 83–119) and an anti-SmD3 (amino acids 108–122) ELISA for the detection of anti-Sm antibodies. Depending on the cut-off value of the SmD1 ELISA, we found a high degree of concordance between the two tests. At an optimized cut-off value of 100 units for SmD1 we found the same clinical sensitivity (12.5%) and specificity (100%) in a group of systemic lupus erythematosus patients (n = 48) and in controls (n = 99). The concordance at this cut-off value was 100% (P < 0.0001; χ2 = 127.61). Using a second panel of sera (n = 65) preselected based on positive anti-Sm results, we confirmed the high degree of concordance between the two assays. Using dsDNA-coated ELISA plates and biotinylated peptides we confirmed the high dsDNA binding properties for SmD1, which were significantly higher than the SmD3-derived peptide. However, no cross-linking of anti-dsDNA antibodies to SmD1 was observed after adding increasing amounts of dsDNA to anti-dsDNA positive, anti-SmD1 negative serum. We therefore conclude that the reported difference in the sensitivity is related to the different cut-off levels and not to the detection of anti-dsDNA antibodies bridged via dsDNA to the SmD1 peptide. Moreover, we found that a subpopulation of anti-Sm antibodies cross-reacted with SmD1 and SmD3. Taken together, the data indicate that both SmD peptide ELISAs represent accurate assays and may be used as important standards for the detection of anti-Sm antibodies

Proteasome alpha-type subunit C9 is a primary target of autoantibodies in sera of patients with myositis and systemic lupus erythematosus

Autoantibodies occur in low frequencies among patients with myositis characterizing only distinct subsets of this disease. Most of these known antibodies are directed to enzymatically active complexes. The 20S proteasome represents an essential cytoplasmatic protein complex for intracellular nonlysosomal protein degradation, and is involved in major histocompatibility complex class I restricted antigen processing. In this study we investigated whether the 20S proteasome complex is an antibody target in myositis and in other autoimmune diseases. 34 sera of poly/dermatomyositis patients were assayed for antiproteasomal antibodies using enzyme-linked immunosorbent assay, immunoblot, and two-dimensional non-equilibrium pH gradient electrophoresis (NEPHGE). Sera was from patients with systemic lupus erythematosus (SLE), mixed connective tissue disease, and rheumatoid arthritis; healthy volunteers served as controls. In 62% (21/34) of the cases sera from patients with myositis and in 58% (30/52) of the cases sera from patients with SLE reacted with the 20S proteasome. These frequencies exceeded those of sera from patients with mixed connective tissue disease, rheumatoid arthritis, and healthy controls. The alpha-type subunit C9 of the 20S proteasome was determined to be the predominant target of the autoimmune sera in myositis and SLE. Lacking other frequent autoantibodies in myositis, the antiproteasome antibodies are the most common humoral immune response so far detected in this disease entity