Comparison of a monoclonal and polyclonal anti-idiotype against a human IgG anti-DNA antibody

Molecular expression systems for anti-DNA antibodies--2

Antibodies to double-stranded DNA are the best-known serological markers of systemic lupus erythematosus, and are closely associated with its renal pathogenesis. How these antibodies recognize DNA is not fully understood. An understanding of the relationship between the functional attributes of an antibody with the three-dimensional structure of its antigen-combining site would allow an insight into the rules that dictate auto-antibody-nucleic acid interaction and consequent pathogenicity of the autoantibody. Data from such studies could assist the development of novel drugs as an approach to specific therapies that can inhibit or disrupt protein-nucleic acid interactions. A full understanding of the binding specificities can be achieved only by experimental determination of detailed three-dimensional structure of these antibodies alone, and of their complexes with specific DNA antigens. A prerequisite of such a study is the ability to produce multimilligram quantities of the antibody protein. However, these antibodies are particularly difficult to express, probably due to their DNA-binding activity. This review attempts to focus on the recent developments on the over-expression of anti-DNA antibody fragments in heterologous cell expression systems and their purification to homogeneity that would in turn allow their structural studies via crystallization.

Anti-idiotypic antibodies to anti-PDC-E2 in primary biliary cirrhosis and normal subjects

Anti-idiotypic antibodies may regulate the immune system and influence pathogenic autoimmunity. We investigated idiotype-anti-idiotype interactions in sera of patients with primary biliary cirrhosis (PBC), normal subjects and animals immunized with pyruvate dehydrogenase complex (PDC) or its derivatives. IgG autoantibody to the E2 subunit of PDC (PDC-E2) was derived by affinity-purification from sera of 12 patients with PBC, and F(ab)2 was prepared (anti-PDC-E2-F[ab]2). This was used as a reactant by enzyme-linked immunosorbent assay (ELISA) with sera from patients with PBC, normal subjects, or immunized animals. Results were that IgG antibody to anti-PDC-E2-F(ab)2 was detectable at low concentration in 12 PBC sera (mean optical density [OD] +/- SD: 1.02 +/- 0.26), and also in 19 normal sera (mean OD +/- SD: 0.97 +/- 0. 35) using a serum dilution of 1:20; background OD was 0.09 to 0.10, whereas antisera from animals immunized with PDC or PDC-E2 were nonreactive. There was a significant inverse correlation (r = -.59, P =.04) between the levels of anti-PDC-E2 in PBC sera (but not normal sera), and anti-idiotypic antibody reactive with anti-PDC-E2-F(ab)2. Anti-idiotypic antibody existed as a complex with anti-PDC-E2, because the removal of anti-PDC-E2 from serum resulted in decreased reactivity to anti-PDC-E2-F(ab)2. Reactivity between PDC-E2 and anti-PDC-E2 from PBC serum was not inhibited by normal sera, indicating that anti-idiotypic antibody from normal sera with anti-PDC-E2 reacts with the framework of F(ab) rather than the paratope. The conclusions are that PBC and normal sera contain IgG class anti-idiotypic antibodies to anti-PDC-E2, the characteristic autoantibody in PBC. Anti-PDC-E2 in immunized animals does not contain an idiotype cross-reactive with human anti-PDC-E2. Anti-idiotypic antibody in PBC is complexed with anti-PDC-E2 and in part accounts for immune complexes demonstrable in PBC. Anti-idiotypic antibody in PBC may regulate levels of anti-PDC-E2.

Cross-reacting idiotypes on anti-insulin autoantibodies in autoimmune diseases, identified by monoclonal antibodies

Investigations on the specific idiotypes of autoantibodies are supposed to help with the understanding of the control mechanisms participating in the pathogenesis of autoimmune diseases. This study describes three monoclonal antibodies (Mabs) that recognize distinct idiotypic determinants on anti-insulin autoantibodies. The preabsorption by IAA-positive sera of insulin inhibits their subsequent binding to the anti-Id, thus suggesting that the Mabs recognize epitopes located at or near the binding site of insulin autoantibodies (IAA). These idiotypes are detected in sera from patients with insulin-dependent diabetes mellitus (IDDM), which are IAA-negative, also. It is possible that the expression of the idiotypes recognized might generally be associated with induction of autoantibodies, since they were found in sera from patients with rheumatoid arthritis (RA), autoimmune thyroid disease (AITD), and cataract (K). It can be assumed that the corresponding idiotypes of these Mabs, or similar structures (sequential or conformational), are expressed on autoantibodies with various antigen-binding specificities. These data suggest that some autoimmune diseases are preceded by the secretion of autoantibodies which express a common or similar pathological idiotype.