Biomedical subjects

Tchavdar L Vassilev

Publications and source records attributed to Tchavdar L Vassilev.

5 recordsLinked to original sources

PubMed2006

Transition towards antigen-binding promiscuity of a monospecific antibody.

Polyspecificity is defined as the ability of a given antibody molecule to bind a large panel of structurally diverse antigens. A fraction of circulating IgG in all healthy individuals acquires promiscuous antigen-binding activity only after a transient exposure to certain protein destabilizing factors. The molecular mechanisms of this phenomenon are not well understood. Exposures to protein destabilizing agents are common steps in immunoglobulin isolation and purification processes. We performed kinetic and thermodynamic analyses using surface plasmon resonance-based technique in order to characterize the interactions of a single mouse monoclonal antibody to its cognate antigen before and after induction of promiscuous antigen-binding activity. The obtained results, suggest that enhanced antigen binding activity induced by exposure to mild denaturing condition resulted from an increase in the structural flexibility of the antigen-binding site. Further pH and ionic strength-dependence analyses of the antibody/antigen interactions demonstrated that the transition to promiscuous antigen-binding was accompanied by a change in the type of non-covalent forces involved in the complex formation. Moreover, from this study, it is evident that an antibody molecule could use two distinct thermodynamic pathways for binding to the same antigen while retaining the same value of the binding affinity. The obtained results may contribute to the understanding of the molecular mechanisms that lay behind natural antibody polyspecificity.

Animals↗

PubMed2005

Immunization with a DNA chimeric molecule encoding a hemagglutinin peptide and a scFv CD21-specific antibody fragment induces long-lasting IgM and CTL responses to influenza virus.

Killed viral vaccines are known to induce primarily antibody responses. By contrast DNA vaccination using naked DNA encoding viral antigens induces both humoral and cellular immune responses. Various approaches have been used to construct DNA vaccines with build-in adjuvanticity. We hypothesized that sequences encoding a common epitope of influenza A virus hemagglutinin jointed to sequences encoding a single-chain variable fragment (scFv) antibody fragment to a costimulatory B cell surface receptor would result in the in vivo expression of a chimeric viral peptide with increased immunogenicity. Such a hybrid DNA molecule was constructed by us, encoding a T and B cell epitope-containing influenza hemagglutinin peptide and a scFv antibody fragment binding to mouse complement receptors I and II (CR1 and CR2). A single immunization with a plasmid containing the described construct induced a strong anti-influenza cytotoxic response lasting for more than six months and a weak antibody response.

Adjuvants, Immunologic↗

PubMed2005

Ferrous ions and reactive oxygen species increase antigen-binding and anti-inflammatory activities of immunoglobulin G.

Polyspecific antibodies represent a first line of defense against infection and regulate inflammation, properties hypothesized to rely on their ability to interact with multiple antigens. We demonstrated that IgG exposure to pro-oxidative ferrous ions or to reactive oxygen species enhances paratope flexibility and hydrophobicity, leading to expansion of the spectrum of recognized antigens, regulation of cell proliferation, and protection in experimental sepsis. We propose that ferrous ions, released from transferrin and ferritin at sites of inflammation, synergize with reactive oxygen species to modify the immunoglobulins present in the surrounding microenvironment, thus quenching pro-inflammatory signals, while facilitating neutralization of pathogens.

Animals↗

PubMed2005

Serum IgM, IgG and IgA block by F(ab')-dependent mechanism the binding of natural IgG autoantibodies from therapeutic immunoglobulin preparations to self-antigens.

Natural polyreactive IgG autoantibodies are present in the plasma of healthy individuals and as a result in pooled therapeutic intravenous immunoglobulin (i.v.Ig) preparations. The spectrum of self-antigens to which these autoantibodies bind, their fate after intravenous infusion and their biological activity are not well understood. The identity of serum proteins that mask binding of natural autoantibodies to self-proteins is a matter of controversy. The spectrum of native serum proteins bound by i.v.Ig was analyzed by two-dimensional electrophoresis. The reactivity of i.v.Ig was directed mainly to circulating immunoglobulins. The binding of the IgG autoantibodies from i.v.Ig to native human liver antigens was blocked not only by a F(ab')2-dependent mechanism by circulating IgM and IgG (as has been previously suggested), but also by serum IgA. This control of anti-self reactivity may be inefficient in some autoimmune diseases.

Antigen-Antibody Reactions↗

PubMed2004

Optimization of casein-based semisynthetic medium for growing of toxigenic Corinebacterium diphtheriae in a fermenter.

Diphtheria toxin is produced by growing Corinebacterium diphtheriae either in a semisynthetic casein-based medium or in the Pope-Lingood meat extract based medium. The World Health Organization advises the use of the semisynthetic one, as it has important advantages. Data on the composition of casein-based media and their ability to support high toxin production are not freely available. Important factors affecting toxin production during C. diphtheriae cultivation are the pH of the culture medium and the concentration of casein hydrolysate and of Fe2+. We established that the optimal pH for toxin production is 7.2. The highest yield of toxin was obtained using a casein hydrolysate concentration of 35.0 g/L and a Fe2+ concentration of 0.05-0.41 microg/mL. Under these conditions, diphtheria toxin with higher purity and yield compared with the batches obtained using the meat-based medium of Pope-Lingood was produced.

Caseins↗