Autoantibodies against C1q in systemic lupus erythematosus are antigen-driven. 2009

Monica Schaller, and Cornelia Bigler, and Doris Danner, and Henrik J Ditzel, and Marten Trendelenburg
Department Biomedicine, Laboratory of Clinical Immunology, University Hospital Basel, Basel, Switzerland. monica.schaller@unibas.ch

Autoantibodies against complement C1q (anti-C1q Abs) were shown to strongly correlate with the occurrence of severe nephritis in patients with systemic lupus erythematosus (SLE), suggesting a potential pathogenic role by interfering with the complement cascade. To analyze the humoral immune response against C1q at the molecular level, we screened a bone marrow-derived IgGkappa/IgGlambda Fab phage display library from a SLE patient with high anti-C1q Ab titer against purified human C1q. Six Fabs that exhibited strong binding to C1q in ELISA were isolated. The anti-C1q Fabs recognized neoepitopes that were only exposed on bound C1q and not present on soluble C1q mapping to different regions of the collagen-like region of C1q. Analysis of the genes encoding the variable H and L chains of the IgG-derived anti-C1q Fab revealed that all the variable H and L chain regions were highly mutated, with nucleotide and amino acid homologies to the closest germline in the range of 71-97% (average 85 +/- 4) and 72-92% (average 88 +/- 6), respectively. In addition, the variable region of the Fabs exhibited high replacement to silent ratios. The six anti-C1q Fabs were shown to be of high affinity, with a K(d) ranging from of 8.4 x 10(-8) M to 1.4 x 10(-7) M, comparable to an antiviral immune response. Our data underlines the notion that the development of anti-C1q Abs in SLE is the consequence of an Ag-driven, affinity-matured immune response. Those anti-C1q Fabs are unique tools to address how complement C1q is implicated in the pathogenesis of SLE.

UI MeSH Term Description Entries
D007140 Immunoglobulin Fab Fragments Univalent antigen-binding fragments composed of one entire IMMUNOGLOBULIN LIGHT CHAIN and the amino terminal end of one of the IMMUNOGLOBULIN HEAVY CHAINS from the hinge region, linked to each other by disulfide bonds. Fab contains the IMMUNOGLOBULIN VARIABLE REGIONS, which are part of the antigen-binding site, and the first IMMUNOGLOBULIN CONSTANT REGIONS. This fragment can be obtained by digestion of immunoglobulins with the proteolytic enzyme PAPAIN. Fab Fragment,Fab Fragments,Ig Fab Fragments,Immunoglobulins, Fab Fragment,Fab Immunoglobulin Fragments,Immunoglobulin Fab Fragment,Immunoglobulins, Fab,Fab Fragment Immunoglobulins,Fab Fragment, Immunoglobulin,Fab Fragments, Immunoglobulin,Fragment Immunoglobulins, Fab,Fragment, Fab,Immunoglobulin Fragments, Fab
D008180 Lupus Erythematosus, Systemic A chronic, relapsing, inflammatory, and often febrile multisystemic disorder of connective tissue, characterized principally by involvement of the skin, joints, kidneys, and serosal membranes. It is of unknown etiology, but is thought to represent a failure of the regulatory mechanisms of the autoimmune system. The disease is marked by a wide range of system dysfunctions, an elevated erythrocyte sedimentation rate, and the formation of LE cells in the blood or bone marrow. Libman-Sacks Disease,Lupus Erythematosus Disseminatus,Systemic Lupus Erythematosus,Disease, Libman-Sacks,Libman Sacks Disease
D008969 Molecular Sequence Data Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories. Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000595 Amino Acid Sequence The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION. Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein
D000911 Antibodies, Monoclonal Antibodies produced by a single clone of cells. Monoclonal Antibodies,Monoclonal Antibody,Antibody, Monoclonal
D000915 Antibody Affinity A measure of the binding strength between antibody and a simple hapten or antigen determinant. It depends on the closeness of stereochemical fit between antibody combining sites and antigen determinants, on the size of the area of contact between them, and on the distribution of charged and hydrophobic groups. It includes the concept of "avidity," which refers to the strength of the antigen-antibody bond after formation of reversible complexes. Affinity, Antibody,Antibody Avidity,Avidity, Antibody,Affinities, Antibody,Antibody Affinities,Antibody Avidities,Avidities, Antibody
D000918 Antibody Specificity The property of antibodies which enables them to react with some ANTIGENIC DETERMINANTS and not with others. Specificity is dependent on chemical composition, physical forces, and molecular structure at the binding site. Antibody Specificities,Specificities, Antibody,Specificity, Antibody
D001323 Autoantibodies Antibodies that react with self-antigens (AUTOANTIGENS) of the organism that produced them. Autoantibody
D001324 Autoantigens Endogenous tissue constituents with the ability to interact with AUTOANTIBODIES and cause an immune response. Autoantigen,Autologous Antigen,Autologous Antigens,Self-Antigen,Self-Antigens,Antigen, Autologous,Antigens, Autologous,Self Antigen,Self Antigens

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