ABSTRACT
OBJECTIVE: The study of autoantibody isotypes in autoimmune diseases is useful for identifying clinically relevant endotypes. This study was undertaken to study the prevalence and clinical significance of different isotypes and IgG subclasses of anti-peptidylarginine deiminase 4 (anti-PAD4) autoantibodies in individuals with rheumatoid arthritis (RA). METHODS: In 196 RA subjects and 64 healthy controls, anti-PAD4 antibody types were determined using enzyme-linked immunosorbent assay. We investigated associations between anti-PAD4 antibodies and clinical outcomes, and relevant features were confirmed in an independent RA cohort. RESULTS: Anti-PAD4 IgG1, anti-PAD4 IgG2, anti-PAD4 IgG3, anti-PAD4 IgG4, anti-PAD4 IgA, and anti-PAD4 IgE antibodies were more frequent in RA patients than healthy controls (P < 0.001). Anti-PAD4 IgG1, anti-PAD4 IgG3, and anti-PAD4 IgE were associated with distinct clinical features. Anti-PAD4 IgG1 was predictive of progressive radiographic joint damage (odds ratio [OR] 4.88, P = 0.005), especially in RA patients without baseline joint damage (40% versus 0%, P = 0.003) or in those negative for anti-cyclic citrullinated peptide and/or rheumatoid factor (OR 32; P = 0.009). IgG1 was also associated with higher levels of C-reactive protein (P = 0.006) and interleukin-6 (P = 0.021). RA patients with anti-PAD4 IgG3 had higher baseline joint damage scores (median Sharp/van der Heijde score 13 versus 7, P = 0.046), while those with anti-PAD4 IgE had higher Disease Activity Score in 28 joints (median 4.0 versus 3.5, P = 0.025), more frequent rheumatoid nodules (31% versus 16%, P = 0.025), and more frequent interstitial lung disease (ground-glass opacification) (24% versus 9%, P = 0.014). Anti-PAD4 IgG1 antibody associations with joint damage were corroborated in an independent RA cohort. CONCLUSION: Anti-PAD4 IgG1, anti-PAD4 IgG3, and anti-PAD4 IgE antibodies identify discrete disease subsets in RA, suggesting that heavy chain usage drives distinct effector mechanisms of anti-PAD4 antibodies in RA.
Subject(s)
Arthritis, Rheumatoid , Humans , Protein-Arginine Deiminases , Protein-Arginine Deiminase Type 4 , Autoantibodies , Biomarkers , Immunoglobulin G , Immunoglobulin EABSTRACT
We have studied responses in thymoma patients to interferon-alpha and to the acetylcholine receptor (AChR) in early-onset myasthenia gravis (EOMG), seeking clues to autoimmunizing mechanisms. Our new evidence implicates a two-step process: (step 1) professional antigen-presenting cells and thymic epithelial cells prime AChR-specific T cells; then (step 2) thymic myoid cells subsequently provoke germinal center formation in EOMG. Our unifying hypothesis proposes that AChR epitopes expressed by neoplastic or hyperplastic thymic epithelial cells aberrantly prime helper T cells, whether generated locally or infiltrating from the circulation. These helper T cells then induce antibody responses against linear epitopes that cross-react with whole AChR and attack myoid cells in the EOMG thymus. The resulting antigen-antibody complexes and the recruitment of professional antigen-presenting cells increase the exposure of thymic cells to the infiltrates and provoke local germinal center formation and determinant spreading. Both these and the consequently enhanced heterogeneity and pathogenicity of the autoantibodies should be minimized by early thymectomy.
Subject(s)
Autoimmunity , B-Lymphocytes/immunology , Myasthenia Gravis/immunology , T-Lymphocytes/immunology , Age of Onset , Animals , Autoantibodies , Bungarotoxins/metabolism , Enzyme-Linked Immunosorbent Assay , Epithelial Cells/physiology , Epitopes/immunology , Fluorescent Antibody Technique , Germinal Center , Histocompatibility Antigens Class II/metabolism , Humans , Insulin/metabolism , Interferon-alpha/immunology , Interleukin-2/immunology , Keratins/metabolism , Models, Immunological , Mutation , Myasthenia Gravis/metabolism , Receptors, Cholinergic/immunology , Stromal Cells , T-Lymphocytes/classification , Thymoma/immunology , Thymus Gland/cytology , Thymus Gland/physiology , Thymus Neoplasms , Troponin I/metabolismABSTRACT
The muscle weakness in myasthenia gravis (MG) is mediated by autoantibodies against the nicotinic acetylcholine receptor (AChR) at the neuromuscular junction. Production of these pathogenic autoantibodies is believed to be associated with germinal centers (GC) and anti-AChR-secreting plasma cells in the hyperplastic thymus of patients with early onset MG (EOMG). Here, we describe the repertoire of rearranged heavy chain V genes and their clonal origins in GC from a typical EOMG patient. Three hundred fifteen rearranged Ig V(H) genes were amplified, cloned, and sequenced from sections of four thymic GC containing AChR-specific B cells. We found that thymic GC contain a remarkably heterogeneous population of B cells. Both naive and circulating memory B cells undergo Ag-driven clonal proliferation, somatic hypermutation, and selection. Numerous B cell clones were present, with no individual clone dominating the response. Comparisons of B cell clonal sequences from different GC and known anti-AChR Abs from other patients showed convergent mutations in the complementarity determining regions. These results are consistent with AChR driving an ongoing GC response in the thymus of EOMG patients. This is the first detailed analysis of B cell clones in human GC responding to a defined protein Ag, and the response we observed may reflect the effects of chronic stimulation by autoantigen.
Subject(s)
B-Lymphocyte Subsets/metabolism , Gene Rearrangement, B-Lymphocyte, Heavy Chain/genetics , Germinal Center/metabolism , Mutation , Myasthenia Gravis/genetics , Myasthenia Gravis/immunology , Receptors, Cholinergic/immunology , Thymus Gland/metabolism , Adult , Amino Acid Sequence , B-Lymphocyte Subsets/immunology , B-Lymphocyte Subsets/pathology , Bungarotoxins/metabolism , Clone Cells , Complementarity Determining Regions/biosynthesis , Complementarity Determining Regions/genetics , Female , Gene Amplification , Germinal Center/cytology , Germinal Center/immunology , Germinal Center/pathology , Humans , Immunoglobulin Heavy Chains/biosynthesis , Immunoglobulin Heavy Chains/genetics , Immunoglobulin Variable Region/biosynthesis , Immunoglobulin Variable Region/genetics , Immunologic Memory/genetics , Interphase/genetics , Interphase/immunology , Iodine Radioisotopes/metabolism , Lymphocyte Activation/genetics , Lymphoid Tissue/cytology , Molecular Sequence Data , Multigene Family/immunology , Receptors, Cholinergic/metabolism , Thymus Gland/cytology , Thymus Gland/immunology , Thymus Gland/pathology , Tumor Cells, CulturedSubject(s)
B-Lymphocytes/pathology , Immunoglobulin Fragments/immunology , Immunoglobulin Variable Region/immunology , Peptide Library , Salivary Glands/pathology , Sjogren's Syndrome/pathology , Autoantibodies/analysis , B-Lymphocytes/physiology , Cell Division , Cellular Senescence , Clone Cells/pathology , Genes, Immunoglobulin , Humans , Immunoglobulin Heavy Chains/genetics , Immunoglobulin lambda-Chains/genetics , Mutation , Recombinant Fusion Proteins , Salivary Glands/physiopathology , Sjogren's Syndrome/physiopathologyABSTRACT
The primary and secondary structure of the small-subunit ribosomal RNA (ssrRNA) gene from the naked, marine amoeba, Vannella anglica (subclass Gymnamoebia), was determined. The ssrRNA is 1962 nucleotides in length, with a low G+C content of 37.1%. The ssrRNA is composed of several uncommon secondary structure features including helix E8-1, which may be a useful target for rRNA probes for the direct identification of isolates in mixed culture. Phylogenetic analysis of sequence data showed that V. anglica branched prior to the rapid diversification of the eukaryotes. It did not associate with the other naked, lobose amoebae represented by Acanthamoeba and Hartmannella, indicating that Vannella represents a separate amoeboid lineage and the subclass Gymnamoebia is polyphyletic.