Use of immunoglobulin variable-region genes by normal subjects and patients with systemic lupus erythematosus

Comparison of Two Strategies to Generate Antigen-Specific Human Monoclonal Antibodies: Which Method to Choose for Which Purpose?

Human monoclonal antibodies (mAbs) are valuable tools to link genetic information with functional features and to provide a platform for conformational epitope mapping. Additionally, combined data on genetic and functional features provide a valuable mosaic for systems immunology approaches. Strategies to generate human mAbs from peripheral blood have been described and used in several studies including single cell sequencing of antigen-binding B cells and the establishment of antigen-specific monoclonal Epstein-Barr Virus (EBV) immortalized lymphoblastoid cell lines (LCLs). However, direct comparisons of these two strategies are scarce. Hence, we sought to set up these two strategies in our laboratory using peanut 2S albumins (allergens) and the autoantigen anti-Rho guanosine diphosphate dissociation inhibitor 2 (RhoGDI2, alternatively 'ARHGDIB') as antigen targets to directly compare these strategies regarding costs, time expenditure, recovery, throughput and complexity. Regarding single cell sequencing, up to 50% of corresponding V(D)J gene transcripts were successfully amplified of which 54% were successfully cloned into expression vectors used for heterologous expression. Seventy-five percent of heterologously expressed mAbs showed specific binding to peanut 2S albumins resulting in an overall recovery of 20.3%, which may be increased to around 29% by ordering gene sequences commercially for antibody cloning. In comparison, the establishment of monoclonal EBV-LCLs showed a lower overall recovery of around 17.6%. Heterologous expression of a mAb carrying the same variable region as its native counterpart showed comparable concentration-dependent binding abilities. By directly comparing those two strategies, single cell sequencing allows a broad examination of antigen-binding mAbs in a moderate-throughput manner, while the establishment of monoclonal EBV-LCLs is a powerful tool to select a small number of highly reactive mAbs restricted to certain B cell subpopulations. Overall, both strategies, initially set-up for peanut 2S albumins, are suitable to obtain human mAbs and they are easily transferrable to other target antigens as shown for ARHGDIB.

Autoantibodies against C1q in systemic lupus erythematosus are antigen-driven

Autoantibodies against complement C1q (anti-C1q Abs) were shown to strongly correlate with the occurrence of severe nephritis in patients with systemic lupus erythematosus (SLE), suggesting a potential pathogenic role by interfering with the complement cascade. To analyze the humoral immune response against C1q at the molecular level, we screened a bone marrow-derived IgGkappa/IgGlambda Fab phage display library from a SLE patient with high anti-C1q Ab titer against purified human C1q. Six Fabs that exhibited strong binding to C1q in ELISA were isolated. The anti-C1q Fabs recognized neoepitopes that were only exposed on bound C1q and not present on soluble C1q mapping to different regions of the collagen-like region of C1q. Analysis of the genes encoding the variable H and L chains of the IgG-derived anti-C1q Fab revealed that all the variable H and L chain regions were highly mutated, with nucleotide and amino acid homologies to the closest germline in the range of 71-97% (average 85 +/- 4) and 72-92% (average 88 +/- 6), respectively. In addition, the variable region of the Fabs exhibited high replacement to silent ratios. The six anti-C1q Fabs were shown to be of high affinity, with a K(d) ranging from of 8.4 x 10(-8) M to 1.4 x 10(-7) M, comparable to an antiviral immune response. Our data underlines the notion that the development of anti-C1q Abs in SLE is the consequence of an Ag-driven, affinity-matured immune response. Those anti-C1q Fabs are unique tools to address how complement C1q is implicated in the pathogenesis of SLE.

V-gene amplification revisited - An optimised procedure for amplification of rearranged human antibody genes of different isotypes

For studying human antibody variable (V)-gene usage in any group of individuals or for the generation of recombinant human antibody libraries for phage display, quality and yield of the amplified V-gene repertoire is of utmost importance. Key parameters affecting the amplification of full antibody repertoires are V-gene specific primer design, complementary DNA (cDNA) synthesis from total RNA extracts of peripheral blood mononuclear cells (PBMCs) and ultimately the polymerase chain reaction (PCR). In this work we analysed all these factors; we performed a detailed bioinformatic analysis of V-gene specific primers based on VBASE2 and evaluated the influence of different commercially available reverse transcriptases on cDNA synthesis and polymerases on PCR efficiency. The primers presented cover near to 100% of all functional and putatively functional V-genes in VBASE2 and the final protocol presents an optimised combination of commercial enzymes and reaction additives for cDNA synthesis and PCR conditions for V-gene amplification. Finally, applying this protocol in combination with different immunoglobulin (Ig) chain specific reverse primers we were able to amplify rearranged antibody genes of different isotypes under investigation.

Potential of a unique antibody gene signature to predict conversion to clinically definite multiple sclerosis

We identified a unique antibody gene mutation pattern (i.e. "signature") in cerebrospinal fluid (CSF) B cells from multiple sclerosis (MS) patients not present in control populations. Prevalence of the signature in CSF B cells of patients at risk to develop MS predicted conversion to MS with 91% accuracy in a small cohort of clinically isolated syndrome patients. If confirmed, signature prevalence would be a novel genetic diagnostic tool candidate for patients with early demyelinating disease of the central nervous system.

Efficient generation of monoclonal antibodies from single human B cells by single cell RT-PCR and expression vector cloning

We have developed an efficient strategy that combines immunoglobulin (Ig) gene repertoire analysis and Ig reactivity profiling at the single cell level. Based on surface marker expression individual cells at different stages of human B cell development are isolated by fluorescence-activated cell sorting. For each cell Ig heavy and corresponding Ig light chain gene transcripts are amplified by nested RT-PCR and cloned into eukaryotic expression vectors to produce monoclonal human antibodies of the same specificity in vitro. All reactions are performed in 96-well plates and allow cloning of large numbers of Ig genes. The recombinant antibodies are tested for reactivity with diverse self- and non-self antigens and the reactivity profile can be directly linked to the complete Ig heavy and Ig light chain gene sequence information that is obtained as part of the cloning strategy. In summary, our method to clone and express human monoclonal antibodies is unbiased, highly efficient, requires only small cell numbers and the recombinant antibodies allow direct conclusions on the frequency of specific human B cells in a diverse repertoire.

Interleukin-6 is responsible for aberrant B-cell receptor-mediated regulation of RAG expression in systemic lupus erythematosus

Defective regulation of secondary immunoglobulin V(D)J gene rearrangement promotes the production of autoantibodies in systemic lupus erythematosus (SLE). It remains unclear, however, whether the regulation of the recombination-activating genes RAG1 and RAG2 is effective in SLE. RAG1 and RAG2 messenger RNA expression was analysed before and after in vitro activation of sorted CD19(+) CD5(-) B cells with anti-immunoglobulin M antibodies, in 20 SLE patients and 17 healthy controls. The expression of CDK2 and p27(Kip1) regulators of the RAG2 protein, were examined. The levels of interleukin-6 (IL-6) and its influence on RAG regulation were also evaluated in vitro. SLE patients had increased frequency of RAG-positive B cells. B-cell receptor (BCR) engagement induced a shift in the frequency of kappa- and lambda-positive cells, associated with a persistence of RAG messenger RNA and the maintenance of RAG2 protein within the nucleus. While expression of the RAG2-negative regulator CDK2 was normal, the positive regulator p27(Kip1) was up-regulated and enhanced by BCR engagement. This effect was the result of the aberrant production of IL-6 by SLE B cells. Furthermore, IL-6 receptor blockade led to a reduction in p27(Kip1) expression, and allowed the translocation of RAG2 from the nucleus to the cytoplasm. Our study indicates that aberrant production of IL-6 contributes to the inability of SLE B cells to terminate RAG protein production. Therefore, we hypothesize that because of constitutive IL-6 signalling in association with BCR engagement, SLE B cells would become prone to secondary immunoglobulin gene rearrangements and autoantibody production.

B cells in autoimmune diseases: insights from analyses of immunoglobulin variable (Ig V) gene usage

The role of B cells in autoimmune diseases has not been fully elucidated. It is also unclear whether breaking of B cell tolerance in patients with autoimmune diseases is due to underlying defects in the molecular mechanisms involved in the arrangement of antibody genes or deficiencies in the subsequent selective influences that shape the antibody repertoire. Analysis of immunoglobulin (Ig) variable (V) gene usage is beginning to provide answers to some of these questions. Such analyses have identified some differences in the basic Ig V gene repertoire of patients with autoimmune diseases compared to healthy controls, even though none of these differences can be considered major. Defects in positive and negative selection, mutational targeting and, in some cases, receptor editing have also been detected. In addition, analysis of Ig V gene usage in target organs and tissues of patients with autoimmune diseases has clearly demonstrated that there is a highly compartmentalized clonal expansion of B cells driven by a limited number of antigens in these tissues. Great progress has been made in the structural and functional characterization of disease-associated antibodies, largely because of the development of the combinatorial library technique. Use of antibodies generated by this technique offers great promise in identifying B cell epitopes on known target antigens and in gaining greater insights into the pathogenic role of B cells in both B and T cell mediated autoimmune diseases.

B-Cell Tolerance Checkpoints in Healthy Humans and Patients with Systemic Lupus Erythematosus

Antibodies are protective effector molecules in the body's immune defense against pathogens. However, if directed against the body's own tissues or organs, antibodies can also play a role in the pathogenesis of autoimmune disease. Here, we discuss our data on how autoreactive antibodies are regulated in healthy humans and how a failure to establish self-tolerance during early B-cell development in patients with systemic lupus erythematosus may predispose to the development of this autoimmune disease.

Defective B cell tolerance checkpoints in systemic lupus erythematosus

A cardinal feature of systemic lupus erythematosus (SLE) is the development of autoantibodies. The first autoantibodies described in patients with SLE were those specific for nuclei and DNA, but subsequent work has shown that individuals with this disease produce a panoply of different autoantibodies. Thus, one of the constant features of SLE is a profound breakdown in tolerance in the antibody system. The appearance of self-reactive antibodies in SLE precedes clinical disease, but where in the B cell pathway tolerance is first broken has not been defined. In healthy humans, autoantibodies are removed from the B cell repertoire in two discrete early checkpoints in B cell development. We found these checkpoints to be defective in three adolescent patients with SLE. 25–50% of the mature naive B cells in SLE patients produce self-reactive antibodies even before they participate in immune responses as compared with 5–20% in controls. We conclude that SLE is associated with abnormal early B cell tolerance.

Indications for peripheral light-chain revision and somatic hypermutation without a functional B-cell receptor in precursors of a composite diffuse large B-cell and Hodgkin's lymphoma

Composite lymphomas are rare combinations of Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma in the same patient, where clonal relatedness has been observed in most of the few cases analyzed. Here, we report a composite classical HL and diffuse large B-cell lymphoma (DLBCL) with interesting molecular features. Micromanipulation of single cells and analysis of V gene rearrangements revealed clonal relatedness with shared and distinct mutations, indicative of derivation from a common germinal center (GC) B-cell precursor and also of further development of both lymphomas in a GC. In the DLBCL, a very high mutation load, including inactivating mutations, and two copies of the same clonal rearrangement with different mutations in single cells were observed. Intriguingly, in the DLBCL precursor somatic hypermutation activity continued after acquisition of destructive V gene mutations, a feature previously found only in Epstein-Barr virus (EBV) infected B-cell expansions. Furthermore, we found evidence of light-chain receptor revision in the lymphoma precursor during a GC reaction. Re-expression of the V(D)J recombination machinery may enhance genomic instability in GC B cells and contribute to lymphomagenesis.

Semiquantitative and qualitative assessment of B-lymphocyte V H repertoire by a fluorescent multiplex PCR

We established a new tool to perform semiquantitative and qualitative screening for V(H) gene usage frequency during IgH rearrangements in human B-lymphocytes. In two separate multiplex PCRs, the rearranged VDJ regions were amplified with V(H) family-specific primers labeled with different fluorescent dyes (FAM, HEX, NED, or ROX). The relative amount of each of the particular V(H) family products and their ratios were determined by fragment analysis on a ABI PRISM 377 sequencer. We verified that the fluorescent multiplex PCR (FMPCR) shows high specificity and sensitivity, acceptable reproducibility and reliability. Data obtained were well in agreement with results revealed by sequencing following single-cell PCR. Ten healthy volunteers showed a comparable semiquantitative V(H) family distribution. The FMPCR also correctly detected a monoclonal peak in a CLL patient. Thus, labeling primers with various fluorescent dyes allows for an assessment of V(H) family usage and an immediate determination of the involved V(H) gene family if any clonal peaks are present. This method provides a quick, easy, and reliable tool for V(H) repertoire screening of larger populations of patients suffering from diseases with changes in the V(H) repertoire allowing for selection of cases worth a more detailed and cumbersome sequence analysis later on.

Antigen receptor selection by editing or downregulation of V(D)J recombination

Clonal selection is central to immune function, but it is complemented by "receptor selection", which regulates the immune repertoire not by cell death or proliferation but through the control of antigen receptor gene recombination. Inappropriate receptors, such as those that are autoreactive, underexpressed, or that fail to promote positive selection of thymocytes or B cells, stimulate secondary V-to-J recombinations that destroy and replace receptor genes. These processes play a central role in lymphocyte repertoire development. Recent work on the role of receptor selection in B and T cells has uncovered evidence for and against antigen-induced editing in thymocytes. Many studies suggest that editing plays a central role in B and T lymphocyte repertoire development. Important recent evidence has been uncovered addressing the role of tolerance-induced editing in thymocytes.

The VH gene repertoire of splenic B cells and somatic hypermutation in systemic lupus erythematosus

In systemic lupus erythematosus (SLE) it has been hypothesized that self-reactive B cells arise from virgin B cells that express low-affinity, nonpathogenic germline V genes that are cross-reactive for self and microbial antigens, which convert to high-affinity autoantibodies via somatic hypermutation. The aim of the present study was to determine whether the VH family repertoire and pattern of somatic hypermutation in germinal centre (GC) B cells deviates from normal in SLE. Rearranged immunoglobulin VH genes were cloned and sequenced from GCs of a SLE patient's spleen. From these data the GC V gene repertoire and the pattern of somatic mutation during the proliferation of B-cell clones were determined. The results highlighted a bias in VH5 gene family usage, previously unreported in SLE, and under-representation of the VH1 family, which is expressed in 20-30% of IgM+ B cells of healthy adults and confirmed a defect in negative selection. This is the first study of the splenic GC response in human SLE.

The cleavage efficiency of the human immunoglobulin heavy chain VH elements by the RAG complex: implications for the immune repertoire

The human immunoglobulin heavy chain locus contains 39 functional human V(H) elements. All 39 V(H) elements (with their adjacent heptamer/nonamer signal) were tested for site-specific cleavage with purified human core RAG1 and RAG2, and HMG1 proteins in a 12/23-coupled cleavage reaction. Both nicking and hairpin formation were measured. The individual V(H) cleavage efficiencies vary over nearly a 30-fold range. These measurements will be useful in considering the factors affecting the generation of the immunoglobulin and T-cell receptor repertoires in the adult humans. Interestingly, when these cleavage efficiencies are summed for each of the V(H) families, the six V(H) family efficiencies correspond closely to the observed profile of unselected V(H) family usage in the peripheral B cells of normal adult humans. This correspondence raises the possibility that the dominant factor determining V(H) element utilization within the 1-megabase human genomic V(H) array is simply the individual RAG cleavage efficiencies.

Clues to the etiology of autoimmune diseases through analysis of immunoglobulin genes

The role of autoantibodies in the etiology of autoimmune diseases remains unclear. However, an examination of the sequences of these autoantibodies can be informative. Antibody sequences that violate constraints normally imposed during ontogeny and during development point to a failure of regulation. The existence of clonally related sequences indicates that production of these antibodies may frequently be driven by self-antigen. A better understanding of the mechanisms that normally constrain the composition of the antibody repertoire and of the nature of the inciting and/or driving antigens may yield new insights into both the pathogenesis and potential treatment of these crippling diseases.

Antinuclear antibody- and extractable nuclear antigen-related diseases

In 1948, the observation of the LE cell phenomenon in a patient with systemic lupus erythematosus (SLE) began the discovery of a broad variety of autoantibodies directed to nuclear antigens called antinuclear antibodies (ANA). Nowadays, different ANA serve as important diagnostic parameters for differentiating most of the connective tissue diseases, such as SLE, neonatal lupus syndromes, Sjögren's syndrome, scleroderma, autoimmune myositis, mixed connective tissue disease and other overlaps. This overview summarizes the history of ANA and their detection methods, in part to introduce the subsequent papers dealing with special topics of ANA-related diseases in this issue. Furthermore, the pathogenic role of these autoantibodies in targeting non-organ-specific intracellular antigens as a functional important constituent of a subcellular particle or multimolecular complex is addressed. Notably, some of these autoantibodies have functioned as significant tools for cell biologists to elucidate the subcellular structures and functions of these autoantigens. In the future, we can expect further advances to answer such important questions as why these antigens are targets of autoantibodies, what is their pathogenic impact and what are the triggers of autoimmunity?