Article: Biochemical analysis of the epitope specificities of anti-C1q autoantibodies accompanying human lupus nephritis reveals them as a dynamic population in the course of the disease.[show abstract] [hide abstract]
ABSTRACT: We analyzed the epitope specificities of the polyclonal anti-C1q antibodies, present in human LN sera, searching to deduce the structural characteristics of C1q associated with its transition to an autoantigen. We screened 78 serum samples from LN patients distributed in three clinical groups - non-active, moderately active and severely active. We found three classes of C1q autoepitopes: (a) neo-epitopes, exposed upon immobilization due to conformational changes; (b) epitopes formed by sequences that are brought together by the conformation of the whole molecule; (c) cryptic epitopes that become exposed only after fragmentation of C1q. The latter suggest that the immunogen involved in the initiation of anti-C1q autoantibodies might be an extrinsic molecule that shares some degree of structural similarity to C1q. None of the tested epitope specificities was associated with active LN. We found a prevalence of anti-gC1q antibodies among the non-active LN patients suggesting that they might be the fraction of the polyclonal anti-C1q, preceding the initiation of autoimmunity to C1q, or alternatively, preceding LN flare.Immunology letters 09/2012; 148(1):69-76. · 2.91 Impact Factor
Vishnya Stoyanova, Svetla Petrova, Magdalena Tchorbadjieva, Boriana Deliyska, Vasil Vasilev, Ivanka Tsacheva[show abstract] [hide abstract]
ABSTRACT: C1q along with its physiological role in maintenance of homeostasis and normal function of the immune system is involved in pathological conditions associated with repetitive generation of anti-C1q autoantibodies. The time and events that cause their first appearance are still unknown. We addressed this issue by analyzing the immunogenicity of C1q in two target groups-one of non-diseased humans and the other of lupus nephritis (LN) patients whose autoimmune disorder is associated with high titers of anti-C1q autoantibodies. The non-diseased humans were represented by pregnant women because the sex hormones are thought to be involved in triggering autoimmune pathologies by their ability to tip the balance of female adaptive immune response to production of antibodies. We screened, using ELISA, 31 sera from healthy pregnant women for the presence of IgM and IgG classes of autoantibodies, recognizing epitopes within the native C1q molecule, its collagen-like region (CLR) and globular head fragment (gC1q). The latter was represented by recombinant analogs of the three globular fragments of A, B and C chains, comprising C1q-ghA, ghB and ghC. We did not find IgM antibodies for all test-antigens which suggest that the natural IgM antibodies are not involved in triggering autoimmunity to C1q. Still more, we did not detect anti-CLR antibodies which have been proved pathogenic in already manifested LN. We completed the analysis with comparative epitope mapping of gC1q and we found similar immunogenic behavior in both target groups-ghA and ghC contained the immunodominant epitopes. This implies that the initial immune response to C1q might occur when the molecule has interacted with its ligands via ghB as part of gC1q. The presence of anti-gC1q in both healthy and diseased humans also implies that these antibodies, unlike anti-CLR, may have a contribution to an onset of autoimmunity.Molecular Immunology 01/2011; 48(4):678-82. · 2.90 Impact Factor
Article: Detection of autoantibodies against the globular domain of human C1q in the sera of systemic lupus erythematosus patients.[show abstract] [hide abstract]
ABSTRACT: The anti-C1q antibodies present in systemic lupus erythematosus (SLE) patients' sera are associated with renal involvement and the titer of these autoantibodies correlates with the clinical activity of the disease. It has previously been shown that anti-C1q antibodies bind neo-epitopes within the collagen region of human C1q. Evidence that these polyclonal autoantibodies recognize epitopes within the globular domain (gC1q) of the molecule has not been documented. In this study, we screened, using ELISA, a number of sera from SLE patients for the presence of anti-gC1q autoantibodies using recombinant globular head regions of individual A (ghA), B (ghB) and C (ghC) chains of human C1q. The recombinant proteins were used as test antigens to determine the levels of autoantibodies directed against ghA, ghB and ghC. SLE sera, containing high levels of anti-C1q antibodies, showed differentially increased binding towards ghA and ghB, which suggested that the gC1q domain can also be target of anti-C1q antibodies generated in SLE patients. Such antibodies can have severe pathophysiological consequences since these are likely to further impair the ability of C1q to clear immune complexes.Molecular Immunology 04/2007; 44(8):2147-51. · 2.90 Impact Factor
Article: Lupus nephritis sera contain autoantibodies that recognize epitopes within the globular fragment of C1q.Boriana Deliyska, Ivanka Tsacheva, Maria Radanova, Vishnia Stoianova, Magdalena Tchorbadjieva, Nedialka Dobreva[show abstract] [hide abstract]
ABSTRACT: High levels of autoantibodies to some complement proteins are detected in the sera of SLE patients. Anti-C1q autoantibodies make a great part of them. Their presence is associated with renal involvement, in particular with lupus nephritis (LN) and the titre of these autoantibodies correlates with the clinical activity of the disease. We analysed by ELISA 18 SLE sera with biopsy-proved LN for the presence of autoantibodies against the globular fragment of C1q using recombinant globular head regions of A, B and C chains of human C1q (ghA, ghB and ghC, respectively). For reference we analysed the sera from 62 healthy volunteers. The recombinant proteins were used as test-antigens to evaluate the levels of autoantibodies specific for ghA, ghB and ghC. LN sera, containing high levels of anti-C1q antibodies, showed differential increased binding to ghA, ghB and ghC.Medicinski pregled 02/2007; 60 Suppl 2:25-7.
Article: Localization of ligand-binding sites on human C1q globular head region using recombinant globular head fragments and single-chain antibodiesMihaela S. Kojouharova, Ivanka G. Tsacheva, Magdalena I. Tchorbadjieva, Kenneth B.M. Reid, Uday Kishore[show abstract] [hide abstract]
ABSTRACT: As a charge pattern recognition molecule, human C1q can bind a range of immunoglobulin and non-immunoglobulin ligands via its carboxy-terminal globular domain and activate the classical complement pathway. Each globular domain has a heterotrimeric organization, composed of the carboxy-terminal halves of one A (ghA), one B (ghB), and one C (ghC) chain . Recently, we have found that the recombinant forms of individual ghA, ghB and ghC bind differentially to IgG, IgM, gp41 peptide 601–613 of human immunodeficiency virus-1 (HIV-1), gp21 peptide 400–429 of human T cell lymphotrophic virus-I (HTLV-I), β-amyloid peptide, and apoptotic cells, suggesting a modular organization of the globular domain. This paper examines the interaction of ghA, ghB and ghC with two known C1q ligands: Klebsiella pneumoniae porin OmpK36 and salivary agglutinin. In addition, we have used a panel of recombinant single-chain antibodies (scFv) specific for ghA, ghB and ghC in order to map sites on the heterotrimeric globular domain which are likely to interact with IgG1, IgG3, IgM, OmpK36, salivary agglutinin and gp41 loop peptide. The combined use of recombinant ghA, ghB, ghC and single-chain antibodies has revealed at least three ligand-binding sites on the globular domain of C1q: one is IgG- and OmpK36-specific, the second (IgM-binding site) is most likely overlapping with IgG/OmpK36 binding site, and the third (the gp41-binding site) seems to be located at the junction between the collagen and globular domains.Biochimica et Biophysica Acta (BBA) - Proteins & Proteomics.