Expression in systemic lupus erythematosus of an idiotype common to DNA-binding and nonbinding monoclonal antibodies produced by normal human lymphoid cells

Estrogen enhancement of anti-double-stranded DNA antibody and immunoglobulin G production in peripheral blood mononuclear cells from patients with systemic lupus erythematosus

OBJECTIVE

To study the in vitro effect of estrogen on IgG anti-double-stranded DNA (anti-dsDNA) antibody and total IgG production in peripheral blood mononuclear cells (PBMC) from patients with systemic lupus erythematosus (SLE), in order to elucidate its regulatory role in SLE.

METHODS

PBMC from SLE patients and normal donors were cultured with 17beta-estradiol (E2). IgG anti-dsDNA antibodies, total IgG, and cytokine activity in the culture supernatants were measured by enzyme-linked immunosorbent assay.

RESULTS

E2 enhanced production of IgG anti-dsDNA antibodies as well as total IgG in PBMC from SLE patients. Anti-dsDNA production in patients with inactive disease was less responsive to E2 than that in patients with active disease. E2 also enhanced total IgG, but not anti-dsDNA, production in the PBMC of normal donors. Antibody production was increased by E2 to a lesser extent in patients' B cells than in their PBMC. Anti-interleukin-10 (anti-IL-10) antibodies partially blocked the E2-induced increase in antibody production in patients' PBMC, but anti-IL-10 had no effect on B cells. E2 increased IL-10 production by patients' monocytes. Exogenous IL-10 acted additively with E2 in increasing antibody production in patients' B cells.

CONCLUSION

These results suggest that E2 may polyclonally increase the production of IgG, including IgG anti-dsDNA, in SLE patients' PBMC by enhancing B cell activity and by promoting IL-10 production in monocytes. These findings support the involvement of E2 in the pathogenesis of SLE.

Testosterone suppresses anti-DNA antibody production in peripheral blood mononuclear cells from patients with systemic lupus erythematosus

OBJECTIVE

To study the in vitro effect of testosterone on anti-DNA antibody production in peripheral blood mononuclear cells (PBMC) from patients with systemic lupus erythematosus (SLE) in order to elucidate its regulatory role in SLE.

METHODS

PBMC from SLE patients were cultured with testosterone. IgG anti-double-stranded DNA (anti-dsDNA) antibody, total IgG, and cytokine activity in the supernatants were measured by enzyme-linked immunosorbent assay.

RESULTS

Testosterone suppressed both IgG anti-dsDNA antibody and total IgG production in PBMC from SLE patients. Antibody production in B cells was also suppressed by testosterone, although the magnitude of its effect on B cells was lower than that on PBMC. Interleukin-6 (IL-6) partially restored the testosterone-induced decrease in antibody levels in PBMC. Testosterone reduced IL-6 production in monocytes.

CONCLUSION

These results suggest that testosterone may directly suppress anti-DNA antibody production in PBMC from SLE patients by inhibiting B cell hyperactivity and, indirectly, by down-regulating IL-6 production in monocytes. These results support the therapeutic effects of testosterone on SLE.

The role of the immunoglobulin heavy chain in human anti-DNA antibody binding specificity

OBJECTIVE

To investigate the structural basis for DNA binding of the natural human IgM lambda monoclonal antibody KIM4.6.

METHODS

An IgM lambda, non-DNA-reactive variant hybridoma was derived during in vitro subcloning of the anti-DNA antibody KIM4.6. The variable (V)-region heavy (H) and light (L) chain genes expressed by the variant hybridoma were amplified by polymerase chain reaction, cloned, sequenced, and compared with those of the KIM4.6 parent and other DNA-binding and non-DNA-binding antibodies.

RESULTS

The VL chain of the variant was identical to that of KIM4.6. In contrast, the VH chain was completely different from the VH chain of the parent but was similar or identical, except in the diversity (D) and joining regions, to the VH chain of the systemic lupus erythematosus (SLE) IgG anti-DNA antibody T14 and SLE IgM nephritogenic anti-DNA antibodies NE-1 and NE-13.

CONCLUSION

The expression of the KIM4.6 VL chain is not sufficient for DNA specificity. The VH chain and its D region play a key role in conferring DNA binding of the KIM4.6 anti-DNA antibody.

Isolated VH4 heavy chain variable regions bind DNA characterization of a recombinant antibody heavy chain library derived from patient(s) with active SLE

In many autoimmune diseases autoantibodies are intimately involved in disease manifestations. Molecular characterization of these autoantibodies should provide insights into the pathogenesis of these diseases, as well as suggest novel avenues for development of therapeutics. While some prior studies suggest that DNA binding may be a characteristic of individual heavy chain variable regions, the ability of these V regions to bind DNA in isolation has not been investigated. We have utilized a bacterial vector for cloning and expressing isolated antibody heavy chain variable regions. RNA was extracted from peripheral blood mononuclear cells of patients with active SLE, cDNA synthesized and heavy chain V regions amplified with VH specific oligonucleotide primers. The VH fragments were cloned into a bacterial expression plasmid including the pelB leader peptide to direct appropriate expression. Recombinant antibodies were screened for binding to 32P-labeled double-stranded plasmid DNA and later also characterized for binding to single-stranded DNA. Binding was confirmed by standard ELISA methodology. Sequence analysis of seven DNA binding VH fragments revealed that they utilized the VH gene family previously described to be associated with autoimmune responses, with a JH6 segment. On VH sequence analysis only one residue substitution in the consensus sequence is needed to form a VH4 germline gene. Potential contact residues with DNA were delineated by three-dimensional structure analysis. We concluded that the DNA binding characteristics of VH regions can be examined in the absence of light chain. DNA binding specificity appears to be a property of the germline VH4 gene. Analysis of such V regions can aid in the identification of hypervariable region contact residues important for DNA binding.

Autoantibodies-like antigen binding characteristics of induced antibodies against polylysine-polyglutamate complex

Rabbits immunized with polylysine-polyglutamate complex induced high titer antibodies. The immune IgG exhibited high degree of specificity towards the immunogen. In a competition assay, nDNA, heat denatured DNA and total buffalo thymus RNA were inhibitory. An appreciable binding with polyglutamate, poly(rG).poly(dC) poly(dG).poly(dC), cardiolipin, poly(dA-dU). Poly(dA-dU) and Z- or Z-like conformations demonstrates the polyspecificity of induced antibodies. The immunological specificity of induced antibodies was comparable to autoantibodies derived from SLE. The results might be of some help in understanding the etiology of autoimmune process.

Lupus-derived human monoclonal IgM anti-DNA antibody displays monospecificity, high affinity and private idiotype specificity

A human monoclonal IgM k anti-DNA antibody, designated 2F7, was prepared by somatic hybridization of peripheral blood lymphocytes from a lupus patient with a human-mouse heterohybridoma cell line, K6H6/B5. 2F7 was tested for its antigen binding and idiotypic specificity by direct binding and inhibition enzyme-linked immunosorbent assays. 2F7 had a high binding activity to single-stranded DNA (ssDNA) but not to double-stranded DNA. It cross-reacted with single-stranded homopolymers with pyrimidine bases and double-stranded polynucleotides containing those homopolymers, suggesting that 2F7 recognizes a conformational determinant made up of both deoxyribose-phosphate backbone and specific nucleotide base. 2F7 did not cross-react with eight structurally unrelated self-antigens. Dissociation constant (Kd) of 2F7 for sonicated ssDNA was approximately 4.5 x 10(-9) M, indicating its relatively high affinity. Idiotypic characterization with rabbit anti-idiotype raised against 2F7 suggested that 2F7 expressed an idiotype at or near its antigen-binding sites that was not detected in sera from 20 unrelated lupus patients, 10 lupus family members and 10 normal individuals. These results suggest that certain IgM class anti-DNA antibodies in human systemic lupus erythematosus may arise by antigen stimulation and not simply by polyclonal B-cell activation.

Molecular characterization of the human immunoglobulin V lambda I germline gene repertoire

To advance our understanding of the human immunoglobulin V lambda germline gene contribution to normal as well as autoimmune responses, we have isolated and sequenced six germline genes of the V lambda I subgroup. These genes can be divided into three sub-subgroups on the basis of greater than or equal to 93% nucleotide sequence homology and greater than or equal to 88% deduced amino acid sequence similarity. Examination of all cDNA and protein sequences available for expressed V lambda I genes supports the assignment of these three sub-subgroups. Sequence comparisons also suggest that germline gene members of two of these sub-subgroups, I-a and I-b, are preferentially utilized in the expressed V lambda I repertoire. This finding may be at least partially attributable to regulatory sequence abnormalities apparent in two of the other V lambda I germline genes (Humlv101 and Humlv104) which may interfere with their expression.

Evidence that a putative anti-idiotypic monoclonal antibody may actually be recognizing circulating immune complexes

Murine monoclonal antibodies (mAb) reacting with affinity-purified antihistone antibodies (AHA) from serum of a patient with systemic lupus erythematosus (SLE) were obtained. One of them, 8B3, was initially considered to recognize idiotypic (Id) determinants in AHA since (a) it reacted with AHA but not with control IgG; (b) this reactivity could be inhibited using affinity-purified AHA, but not with control IgG or whole serum; (c) affinity-isolated 8B3+ antibodies showed antihistone activity and not other activities tested so far; (d) antihistone activity due to 8B3+, but not that of 8B3- from the same serum, could be fully inhibited by the presence of 8B3 mAb in the antihistone assay and (e) serum levels of 8B3 reactivity were higher than normal in SLE patients with AHA (56%), in contrast with SLE patients without AHA (6%). From these results it was deduced that 8B3 defined a cross-reactive Id shared by a subset of AHA in SLE patients. However, the present results suggest that (a) 8B3 mAb did not recognize AHA or Ig, but did recognize a 55 kDa histone-binding protein; (b) this 55 kDa protein was present free at low concentration in all human sera, but also associated with IgG in 8B3+ SLE sera and (c) these complexes are responsible for the false positive results in the antihistone assay as shown for DNA/anti-DNA complexes. Thus, mAbs recognizing the non-Ig moiety of circulating immune complexes may resemble anti-Id antibodies with features of the so-called epibodies. These immune complexes may be responsible for false positive results and caution should be exercised in the interpretation of results.

Comparison of DNA antibody idiotypes in human sera: an international collaborative study of 19 idiotypes from 11 different laboratories

The distribution of and relationships between 18 anti-DNA antibody idiotypes and one anti-acetylcholine receptor antibody idiotype have been tested in an international collaborative study of human sera from 180 individuals. The main finding is that the serum levels of many of these idiotypes, whether of murine or human origin, show a high degree of statistical correlation. The studies in a wide range of autoimmune rheumatic diseases confirm that none of the idiotypes tested is disease specific, but 13 of 15 (87%) whose levels were recorded as OD units or cpm correlated strongly with anti-ssDNA antibody levels and 11 of 15 (73%) with total serum IgM. Expression of several idiotypes was found to fluctuate in parallel with disease activity in SLE; levels of others were also elevated in the healthy relatives of lupus patients whilst a few were also raised in the spouses of these patients. The data support the notion that there may be only a few groups of related DNA antibody idiotypes. The correlations between the idiotypes with regard to their quantities, association with disease activity, and wide distribution in different diseases and healthy individuals suggest at least two explanations. First, all of these idiotypes may be present in normal immunoglobulin repertoires and simply increase in response to poly- or oligoclonal B-cell activation in autoimmune diseases. Secondly, these idiotypes may be structurally linked to each other, so that their behaviour under conditions of specific antigenic stimulation is similar. Genetic and structural studies will be required to distinguish between these possibilities.

Comparative study of idiotypes on monoclonal antibodies derived from patients with lupus and leprosy and from normal individuals

A collaborative study was performed to compare the expression of a series of idiotypes defined on human anti-DNA and other autoantibodies. Three panels of human monoclonal antibodies were tested: eight derived from patients with systemic lupus erythematosus (SLE); 13 from an individual with lepromatous leprosy; and 38 from normal subjects. The following rabbit anti-idiotype sera were used: one (RId16/6) raised against the lupus-derived monoclonal anti-DNA antibody 16/6, four (RId8E7, RId4G7, RId4D5 and RIdTH9) against leprosy-derived monoclonal antibodies of various specificities, and one (anti-4.6.3) against a normal-derived anti-DNA monoclonal (KIM 4.6). In addition, two other anti-idiotypes were used--one a murine monoclonal (3I), the other a rabbit polyclonal (RIdD)--which had been raised against polyclonal anti-DNA antibodies from lupus serum. Further experiments were performed with immunoabsorbed fractions of RId8E7. Direct-binding and competition assays were used. All of the anti-idiotypes produced different patterns of positivity among the three panels of human monoclonal antibodies, with the exception of RId8E7 and RId4G7, which showed considerable concordance. There was a tendency towards anti-idiotypes being disease- or group-specific: thus anti-4.6.3 failed to bind to any of the lupus or leprosy-derived monoclonals, while RId16/6 and RId8E7 bound most strongly to the lupus- and leprosy-derived antibodies respectively. KIM 4.6 itself was bound only weakly by RId16/6, while 16/6 was not recognized by anti-4.6.3; 16/6 was, however, bound by 3I, while KIM 4.6 was not. 3I bound to several other monoclonals but RIdD, which has been shown to be specific for the anti-DNA fraction of lupus serum, did not bind to any of them. These results indicate that the majority of these anti-idiotype preparations recognize largely separate sets of determinants. The monoclonal antibodies which bind to DNA may be only partly representative of anti-DNA antibodies in the serum of lupus patients.

DNA antibody idiotypes: an analysis of their clinical connections and origins

Approximately thirty common DNA antibody idiotypes have been described on hybridoma derived or affinity purified DNA-binding antibodies. There are associations between some idiotypes and the clinical manifestations of systemic lupus erythematosus although none are sufficiently firm to be clinically useful in identifying subsets of SLE or in assessing disease activity in individual patients. The expression of these idiotypes is not confined to DNA antibodies in SLE. They may be found in the serum from patients with a range of autoimmune rheumatic disorders, infectious disease and blood dyscrasias. In most cases the antigen binding specificity of the antibody bearing the idiotype is unknown. The precise relationship between the various idiotypes is becoming better understood with increasing availability of genetic and structural data. DNA antibody idiotype manipulation may provide a potential new therapeutic modality in SLE.