Immortalisation of human antibody producing cells

Generation of acetylcholine receptor-specific human T cell lines using heterobifunctional antibody-targeted antigen presentation

Characterizing AChR-specific T lymphocyte clones is an important step towards the ability to induce antigen-specific tolerance in myasthenia gravis (MG). However, the limited supply of relatively inefficient autologous antigen presenting cells (APCs) makes establishing AChR-specific T lymphocyte lines difficult. In this study we targeted AChR to autologous surface IgM+ (sIgM+) APCs using heterobifunctional antibodies (bi-Ab) consisting of anti-sIgM linked to anti-AChR antibodies. FACScan analysis and whole cell-based radioimmunoassay (RIA) showed binding of bi-Ab/AChR conjugates to sIgM+ APCs. Using antigen targeting, AChR-presentation to a well-characterized AChR-specific T cell clone, and to T cell lines raised de novo from MG thymocytes, was improved. Thus, antigen targeting using bi-Ab improved the efficiency of presentation of the scarce autoantigen AChR, suggesting that this method might allow the use of relatively impure antigen preparations and normally inefficient non-antigen-specific APCs, including those which can be immortalized, to accelerate the characterization of the AChR epitopes recognized by pathogenic T helper lymphocytes.

Fetal calf serum in growth medium obscures the detection of early anticardiolipin antibody secreting clones

We have examined the effect of fetal calf serum (FCS) on the detection of early anticardiolipin antibody (ACL) secreting clones, using two well-established human IgG clones, LJ1 and AH2. By plating cells at 50/well and growing both clones simultaneously in standard growth (SG) medium containing 10% FCS, and in serum-free (SF) medium, we were able to measure by ELISA the total IgG and ACL levels in the supernatants. The mean OD values (x 1000) against cardiolipin for both LJ1 and AH2 were significantly higher for clones grown in SF than in SG medium: 331 OD units vs. 172, and 275 OD units vs. 166 respectively (p < 0.001). Importantly, the number of wells in which the OD value was > 0.25 units above background was: for LJ1 in SG only 3/36 vs. 30/36 in SF; similarly, for AH2 1/36 in SG vs. 22/36 in SF. In comparison, the total IgG assay using an OD value > 0.7 units above background, detected immunoglobulin secretion in all but one of the wells. We conclude that in ELISA procedures FCS in SG medium competes with solid phase cardiolipin for antibody binding. We suggest that these antibodies are binding to phospholipid from microvesicles found in FCS. We recommend that minimally 'positive' clones on testing should be re-tested and, if necessary, switched to SF medium in order to prevent such clones from being discarded prematurely.

Genetic and epitopic analysis of thyroid peroxidase (TPO) autoantibodies: markers of the human thyroid autoimmune response

TPO autoantibodies, the hallmark of human autoimmune thyroid disease, are of IgG class and are associated with thyroid destruction and hypothyroidism. Using the immunoglobulin gene combinatorial library approach, a panel of human monoclonal TPO autoantibodies (expressed as Fab) has been generated from thyroid tissue-infiltrating B cells. TPO-specific Fab closely resemble patients' serum autoantibodies in terms of L chain type, IgG subclass, affinities for TPO as well as epitopes recognized by > 80% of TPO autoantibodies in an individual's serum. TPO autoantibody V region genes are not unique; H chain V genes are usually mutated, while L chain V genes are sometimes in germ-line conformation. The autoantibodies recognize an immunodominant region involving conformational, overlapping epitopes in domains A and B. Finally, TPO autoantibody epitopic fingerprints are distinctive for individual sera, are not associated with hypothyroidism, but are conserved over time (indicating a lack of B cell epitope spreading). Evidence for conservation as well as inheritance of the fingerprints in some families, together with VH gene polymorphisms, may provide insight into the genetic basis of human autoimmune thyroid disease. Furthermore, monoclonal human TPO autoantibodies will be invaluable for B cell presentation of TPO to determine the T cell epitopes involved in TPO autoantibody production.

Human IgG monoclonal autoantibodies against muscle acetylcholine receptor: direct evidence for clonal heterogeneity of the antiself humoral response in myasthenia gravis

Human hybridomas were established from myasthenia gravis (MG) patients and screened using a fast and sensitive cell ELISA with the rhabdomyosarcoma cell line TE671. In a first series of 14 fusions using a standard protocol, 36 positive clones were detected and maintained for three passages. The number of clones in each fusion was correlated with in vivo titers of anti-acetylcholine receptor (AChR) autoantibodies. In a second series of four experiments, fusions were immediately followed by cell plating under limiting dilution conditions ('fusion cloning') providing eight stable hybridomas. These hybridomas produced monoclonal antibodies (mAbs) of IgG isotype reactive with TE671 cells, but not with AChR in solution using the radioimmunoprecipitation assay. Fine analysis of antigen specificity of these mAbs was performed using solid-phase ELISA against purified AChR from Torpedo (T-AChR) and immunoblot against recombinant chimaeric human AChR produced in bacteria. Five of the eight mAbs derived from the few patients whose antibodies showed cross-reactivity with T-AChR reacted against T-AChR. Of these five mAbs, two also reacted against chimaeric human AChR by immunoblotting. Furthermore, at least one of these two mAbs was capable of inducing antigenic modulation of labeled AChR with [125I]alpha-bungarotoxin from the surface of TE671 cells. These mAbs provide useful tools to explore the molecular basis of the structural and functional heterogeneity of the humoral anti-AChR response in myasthenia gravis.

Isolation and characterization of a monoclonal human thyroid peroxidase autoantibody of lambda light chain type

Thyroid peroxidase (TPO) autoantibodies, a hallmark of human autoimmune thyroid disease, may have kappa or lambda light chains. Monoclonal human TPO autoantibodies with kappa light chains have previously been developed by cloning and expressing "combinatorial" libraries of immunoglobulin genes in bacteria. In the present study, an IgG1/lambda combinatorial library was generated from thyroid cDNA of a Graves' patient whose serum contained lambda TPO antibodies. Screening the bacteriophage library with 125I-TPO yielded one clone, TR1.41. The oligonucleotide sequence of TR1.41 was determined and the nature of its interaction with TPO was investigated. The affinity of TR1.41 for TPO is high (Kd approximately 10(-9) M), comparable to that of monoclonal kappa TPO autoantibodies derived from the same patient. The genes encoding the heavy and light chains of TR1.41 differ in a number of respects from the closest available germline genes. Such differences are consistent with somatic mutation in a high-affinity antibody. An important characteristic of TR1.41 is its interaction with the immunodominant domain on TPO recognized by approximately 80% of serum TPO autoantibodies. The frequency of TPO-specific F(ab) generated from the thyroid gland of patient TR was much lower for F(ab) with lambda light chains (1:150,000) than for F(ab) with kappa light chains (1:13,000). Despite this low frequency, the high affinity of TR1.41 and its recognition of the immunodominant region on TPO indicate that lambda autoantibodies of this type may represent an important constituent of the TPO autoantibody response in man. In conclusion, this is the first report on the molecular cloning and characterization of a thyroid autoantibody of lambda L chain type by the combinatorial library approach.

Production and analysis of IgG monoclonal anti-DNA antibodies from systemic lupus erythematosus (SLE) patients

This study compares recently devised methods for producing IgG anti-DNA MoAbs from patients with SLE and analyses the antibodies generated from one patient at different phases of disease. Lymphocytes from SLE patients were transformed with Epstein-Barr virus(EBV) and/or fused with a heteromyeloma cell line, CB-F7. Direct fusion with CB-F7 resulted in the highest proportion of IgG-secreting lines, whereas EBV transformation resulted in a high percentage of IgM-secreting lines. Using direct fusion, five IgM anti-DNA antibody-secreting hybridomas were generated using lymphocytes from a patient with relatively inactive SLE. Six months later when the disease was active, only IgG anti-DNA antibodies were produced. The antigen-binding patterns of the MoAbs were analysed. Only one of the IgM anti-DNA antibodies reacted with dsDNA by ELISA and none by Crithidia immunofluorescence, whereas two of the IgG antibodies reacted with dsDNA by ELISA and Crithidia but did not bind to ssDNA. Only the two IgG high affinity anti-dsDNA antibodies bound to histones, and this was enhanced by added DNA, whereas three IgM antibodies bound to cardiolipin. This study supports the notion that MoAbs derived from a patient with SLE represent those found in the serum of SLE patients at different stages of disease activity. The binding to histones by the two IgG anti-dsDNA antibodies supports the recently expressed view that antibodies binding DNA/histone may be important in the pathogenesis of SLE.