The immunoglobulin kappa light chain repertoire expressed in the synovium of a patient with rheumatoid arthritis

Identifying Key Genes and Functionally Enriched Pathways in Osteoporotic Patients by Weighted Gene Co-Expression Network Analysis

Osteoporosis is a systemic bone disease characterized by low bone mineral density and bone microstructure damage, resulting in increased bone fragility and fracture risk. The present study aimed to identify key genes and functionally enriched pathways in osteoporotic patients. Weighted Gene Co-expression Network Analysis (WGCNA) was applied to microarray datasets of blood samples of osteoporotic patients from the Sao Paulo Ageing & Health [SPAH] study (26 osteoporotic samples and 31 normal samples) to construct co-expression networks and identify hub gene. The results showed that HDGF, AP2M1, DNAJC6, TMEM183B, MFSD2B, IGKV1-5, IGKV1-8, IGKV3-7, IGKV3D-11, and IGKV1D-42 are genes which were associated with the disease status of osteoporosis. Differentially expressed genes are enriched in proteasomal protein catabolic process, ubiquitin ligase complex, and ubiquitin-like protein transferase activity. Functional enrichment analysis demonstrated that genes in the tan module were enriched in immune-related functions, indicating that the immune system plays a critical role in osteoporosis. Validation assay demonstrated that the HDGF, AP2M1, TMEM183B, and MFSD2B levels were decreased in osteoporosis samples compared with healthy controls, while the levels of IGKV1-5, IGKV1-8, and IGKV1D-42 were increased in osteoporosis samples compared with healthy controls. In conclusion, our data identified and validated the association of HDGF, AP2M1, TMEM183B, MFSD2B, IGKV1-5, IGKV1-8, and IGKV1D-42 with osteoporosis in elderly women. These results suggest that these transcripts have potential clinical significance and may help to explain the molecular mechanisms and biological functions of osteoporosis.

Antibody repertoire analysis in polygenic autoimmune diseases

High-throughput sequencing of the DNA/RNA encoding antibody heavy- and light-chains is rapidly transforming the field of adaptive immunity. It can address key questions, including: (i) how the B-cell repertoire differs in health and disease; and (ii) if it does differ, the point(s) in B-cell development at which this occurs. The advent of technologies, such as whole-genome sequencing, offers the chance to link abnormalities in the B-cell antibody repertoire to specific genomic variants and polymorphisms. Here, we discuss the current research using B-cell antibody repertoire sequencing in three polygenic autoimmune diseases where there is good evidence for a pathological role for B-cells, namely systemic lupus erythematosus, multiple sclerosis and rheumatoid arthritis. These autoimmune diseases exhibit significantly skewed B-cell receptor repertoires compared with healthy controls. Interestingly, some common repertoire defects are shared between diseases, such as elevated IGHV4-34 gene usage. B-cell clones have effectively been characterized and tracked between different tissues and blood in autoimmune disease. It has been hypothesized that these differences may signify differences in B-cell tolerance; however, the mechanisms and implications of these defects are not clear.

In situ B cell-mediated immune responses and tubulointerstitial inflammation in human lupus nephritis

The most prevalent severe manifestation of systemic lupus erythematosus is nephritis, which is characterized by immune complex deposition, inflammation, and scarring in glomeruli and the tubulointerstitium. Numerous studies indicated that glomerulonephritis results from a systemic break in B cell tolerance, resulting in the local deposition of immune complexes containing Abs reactive with ubiquitous self-Ags. However, the pathogenesis of systemic lupus erythematosus tubulointerstitial disease is not known. In this article, we demonstrate that in more than half of a cohort of 68 lupus nephritis biopsies, the tubulointerstitial infiltrate was organized into well-circumscribed T:B cell aggregates or germinal centers (GCs) containing follicular dendritic cells. Sampling of the in situ-expressed Ig repertoire revealed that both histological patterns were associated with intrarenal B cell clonal expansion and ongoing somatic hypermutation. However, in the GC histology, the proliferating cells were CD138(-)CD20(+) centroblasts, whereas they were CD138(+)CD20(low/-) plasmablasts in T:B aggregates. The presence of GCs or T:B aggregates was strongly associated with tubular basement membrane immune complexes. These data implicate tertiary lymphoid neogenesis in the pathogenesis of lupus tubulointerstitial inflammation.

Structure and function of immunoglobulins

Immunoglobulins are heterodimeric proteins composed of 2 heavy and 2 light chains. They can be separated functionally into variable domains that bind antigens and constant domains that specify effector functions, such as activation of complement or binding to Fc receptors. The variable domains are created by means of a complex series of gene rearrangement events and can then be subjected to somatic hypermutation after exposure to antigen to allow affinity maturation. Each variable domain can be split into 3 regions of sequence variability termed the complementarity-determining regions (CDRs) and 4 regions of relatively constant sequence termed the framework regions. The 3 CDRs of the heavy chain are paired with the 3 CDRs of the light chain to form the antigen-binding site, as classically defined. The constant domains of the heavy chain can be switched to allow altered effector function while maintaining antigen specificity. There are 5 main classes of heavy chain constant domains. Each class defines the IgM, IgG, IgA, IgD, and IgE isotypes. IgG can be split into 4 subclasses, IgG1, IgG2, IgG3, and IgG4, each with its own biologic properties, and IgA can similarly be split into IgA1 and IgA2.

Chemokine receptor expression and functional effects of chemokines on B cells: implication in the pathogenesis of rheumatoid arthritis

Introduction

Accumulation of B cells in the rheumatoid arthritis (RA) synovium has been reported, and it has been thought that these cells might contribute to the pathogenesis of RA by antigen presentation, autoantibody production, and/or inflammatory cytokine production. Chemokines could enhance the accumulation of B cells in the synovium. The aims of this study were to determine chemokine receptor expression by B cells both in the peripheral blood of normal donors and subjects with RA, and at the inflammatory site in RA, and the effects of chemokines on B cell activation.

Methods

Cell surface molecule expression was analyzed by flow cytometry. Cellular migration was assessed using chemotaxis chambers. Cellular proliferation was examined by ³H-thymidine incorporation. Tumor necrosis factor (TNF) production was assayed by enzyme-linked immunosorbent assay.

Results

Significant numbers of peripheral blood B cells of healthy donors and subjects with RA expressed CC chemokine receptor (CCR)5 and CXCR3, and most B cells expressed CCR6, CCR7, CXCR4 and CXCR5. CCR5 expression was more frequent on CD27⁺ than CD27^- peripheral blood B cells of healthy donors and RA. Synovial B cells more frequently expressed CCR5, but less often expressed CCR6, CCR7 and CXCR5 compared to peripheral blood in RA. Further functional analyses were performed on peripheral blood B cells from healthy donors. Migration of peripheral blood B cells, especially CD27⁺ B cells, was enhanced by CC chemokine ligand (CCL)20, CCL19, CCL21 and CXCL12. All four chemokines alone induced B cell proliferation; with CCL21 being the most effective. CCL21 also enhanced the proliferation of anti-immunoglobulin (Ig)M-stimulated B cells and blockade of CCR7 inhibited this effect. CCL20, CCL21 and CXCL12 enhanced TNF production by anti-IgM mAb-stimulated B cells. Finally, stimulation with CXCL12, but not CCL20, CCL19 and CCL21, enhanced inducible costimulator-ligand (ICOSL) expression by peripheral blood B cells of healthy donors and RA, but did not increase B cell-activating factor receptor or transmembrane activator and CAML-interactor.

Conclusions

The data suggest that CCR5, CCR6, CCR7, CXCR3, CXCR4 and CXCR5 may be important for the B cell migration into the synovium of RA patients, and also their local proliferation, cytokine production and ICOSL expression in the synovium.

Differential expression of immunoglobulin kappa chain constant region in human abdominal aortic aneurysm

BACKGROUND

A number of the research into the pathogenesis of the abdominal aortic aneurysm (AAA) have focused on the alteration of gene expression. The current technique for elucidating alterations of gene expression has a setback in that many artifact complementary DNA (cDNA) products present abnormal polymerase chain reaction (PCR) amplification. Our study was designed to identify differentially expressed genes in AAA using the annealing control primer (ACP) system, which was recently developed to identify only authentic genes.

MATERIALS AND METHODS

The tissues of the human abdominal aorta were obtained from the patients of AAA and aortic occlusive disease (AOD), and normal abdominal aorta (NA) from brain death donors. Total RNAs were isolated from three groups of human abdominal aorta (10 AAA, five NA, three AOD) and then reverse transcribed into complementary DNA (cDNA). The ACP method was done to screen the difference in the expression pattern of the mRNA (mRNA).

RESULTS

One differentially expressed cDNA band was detected in AAA but not in NA and AOD. This cDNA was sequenced and computer searching against the GenBank revealed that the cDNA had more than 90% identity with the immunoglobulin kappa chain constant region (Ig kappa-C).

DISCUSSION

Our finding suggests that differentially expressed Ig kappa-C gene only in AAA is a candidate gene that may play a pivotal role in the pathogenesis of AAA formation. The correlation of mRNA level and protein level is, however, not clear. Thus, to directly identify the role of Ig light chains in the pathogenic event of AAA, the further study comparing the level and kinds of expressed protein with the corresponding Ig kappa-C gene will be required.

Human IgG Fc-binding phage antibodies constructed from synovial fluid CD38+ B cells of patients with rheumatoid arthritis show the imprints of an antigen-dependent process of somatic hypermutation and clonal selection

The persistent presence of rheumatoid factors (RFs) in the circulation is a characteristic phenomenon in patients with rheumatoid arthritis (RA). Recent data indicate that RFs associated with seropositive RA are derived from terminally differentiated CD20-, CD38+ plasma cells (PCs) present in synovial fluids of the inflamed joints. These cells were shown to secrete RFs actively and are thought to originate from germinal centre (GC)-like structures present in the inflamed synovium. To obtain a representative image of the structural properties of IgM and IgG RFs associated with RA, phage antibody display libraries were constructed from CD38+ PCs isolated from the inflamed joints of RF-seropositive patients with RA. Subsequently, human IgG Fc-binding monoclonal phage antibodies were selected and analysed. The data suggest that RA-associated RFs are encoded by a diverse set of VL and a more restricted set of VH regions. VH gene family usage of PC-derived IgM- and IgG-RFs was found to be restricted to the VH1 and 3 gene families, with a preference for VH3, and many different VL genes were shown to contribute to RF specificity. Clonally related VH as well as VL sequences were identified, based on the presence of identical CDR3 regions and shared somatic mutations. In this B cell selection process base-pair substitutions as well as deletions of triplets in CDR regions, leaving the transcripts in frame, were involved. Together, these data provide further evidence for an Ag-driven immune response in the terminal differentiation into RF-producing PCs in patients with RA, including expansion of clonally related B cells, selection and isotype switching, all hallmarks of a GC reaction.

Slow, programmed maturation of the immunoglobulin HCDR3 repertoire during the third trimester of fetal life

The mean distribution of lengths in the third complementarity-determining region of the heavy chain (HCDR3) serves as a measure of the development of the antibody repertoire during ontogeny. To determine the timing and pattern of HCDR3 length maturation during the third trimester of pregnancy, the mean distribution of HCDR3 lengths among variable-diversity-joining-constant-mu (VDJC(mu)) transcripts from the cord blood was analyzed from 138 infants of 23 to 40 weeks' gestation, including 3 sets of twins, 2 of which were of dizygotic origin. HCDR3 maturation begins at the start of the third trimester; follows a slow, continuous expansion over a 5-month period; and is unaffected by race or sex. The range and mean distribution of lengths may vary in dizygotic twins, indicating individual rates of development. The mean HCDR3 length distribution in 10 premature infants with documented bacterial sepsis was then followed for 2 to 12 weeks after their first positive blood culture. HCDR3 spectrotype analysis demonstrated oligoclonal B-cell activation and expansion after sepsis, but maturation of the repertoire was not accelerated even by the systemic exposure to external antigen represented by bacteremia. Antibody repertoire development appears to be endogenously controlled and adheres to an individualized developmental progression that probably contributes to the relative immaturity of the neonatal immune response.

Expression of recombination-activating genes and terminal deoxynucleotidyl transferase and secondary rearrangement of immunoglobulin kappa light chains in rheumatoid arthritis synovial tissue

OBJECTIVE

Lymphocytic infiltrates in rheumatoid arthritis (RA) synovium often resemble lymphoid follicles and contain clonally related Ig transcripts, suggesting in situ antigen-dependent B cell selection. Recent reports have shown expression of recombination-activating genes (RAGs) and concurrent secondary rearrangement of Ig genes in normal peripheral lymphoid organs (receptor revision). We sought to determine if RAG-mediated receptor revision of Ig kappa light chains occurs in B cells within the RA synovium. Because we previously reported enhanced N-region addition at V(L)-J(L) joins in clonally expanded light-chain transcripts from RA synovium, we also sought expression of terminal deoxynucleotidyl transferase (TdT), which is normally expressed only in B cell precursors or immature B cells.

METHODS

Reverse transcription-polymerase chain reaction (PCR) was used to detect RAG and TdT transcripts from unselected and B cell-enriched synovial and peripheral blood mononuclear cells obtained from 12 RA patients. Activity of RAG protein was sought using ligation-mediated PCR to detect recombination intermediates, and immunohistochemistry was performed to identify RAG+ cells within synovia.

RESULTS

We found evidence of RAG-mediated secondary Ig kappa light chain rearrangements in about one-third of RA synovia. TdT expression was found in several samples, but did not correlate with RAG expression.

CONCLUSION

RAG-mediated secondary Ig rearrangements of kappa light chains may contribute to the local production of antibodies to autoantigens (e.g., rheumatoid factor) or exogenous antigens, or it may represent a failed attempt at immune tolerance. TdT expression suggests the presence of immature B cells in RA synovia. These findings have important implications for the local generation of antibodies in RA and other chronic inflammatory diseases.

Pathogenesis of rheumatoid arthritis. Role of B lymphocytes

Despite many years of investigation, there remain many unanswered fundamental questions on the role of B cells in RA. Why is RF found in the sera of 80% of patients with RA and often in other chronic inflammatory diseases? What signals lead B lymphocytes to migrate into the subsynovial lining of joints? Does receptor revision in synovium play a role in the generation of autoantibodies in RA? What is the relative contribution of B-cell inhibition on the salutary effect of medications for RA? Can targeting autoreactive B cells, in conjunction with other therapies, provide therapeutic benefit in RA? We are hopeful that through continued basic, clinical, and translational research, these questions can be answered.

Analysis of Ig kappa light chain gene variable regions expressed in the rheumatoid synovial B cells

Sequence analysis of antibody variable (V) regions can provide an insight regarding whether B cells have gone through an antigen-driven process of affinity maturation. In this study, we analyzed 16 V-regions of immunoglobulin (Ig) kappa light chain genes obtained from a cDNA library of a rheumatoid arthritis (RA) synovial tissue. A salient feature of our results is the high frequency utilization of germline V kappa I family genes, especially the O2/O12 gene (38%). All kappa V-regions showed extensive somatic hypermutation with 5.4% of an average mutation rate. Replacement to silent mutation (R/S) ratio in the complementarity determining region (CDR) was > 2.9 in 12 out of 16 clones, indicating that the majority of the RA synovial B cells had undergone affinity maturation. However, the four other clones showed R/S ratios of < 2.9 in the CDR despite a high mutation rate. In contrast to the previous reports, long CDR3 was not a characteristic feature of these clones. In summary, these data show the high frequency utilization of the germline O2/O12 gene and a high rate of mutation with an evidence of antigen selection in most of the Ig kappa genes expressed in the RA synovium.

Production and characterization of monoclonal IgM autoantibodies specific for the T-cell receptor

Natural autoantibodies to the T-cell receptor (Tcr) have been identified in all human sera. However, titer, epitope specificity, and isotype vary with physiological conditions, autoimmune diseases, and retroviral infections. The levels of anti-Tcr autoantibodies in rheumatoid arthritis (RA) patients are significantly higher than in normal individuals, and the autoantibodies are typically IgM. To obtain detailed information on these autoantibodies, we generated B-cell heterohybridomas secreting monoclonal IgM autoantibodies (mAAbs) from the synovial tissue and peripheral blood of RA patients. We selected clones secreting mAAbs that bound a major Vbeta epitope defined by a synthetic peptide that contains the CDR1 region of the Vbeta 8.1 gene product. From these we isolated a subset of seven mAAbs that bound a recombinant single-chain Valpha/Vbeta construct containing the peptide epitope and, also to JURKAT cells which express Vbeta 8.1. The mAAbs produced by these clones were distinct from each other in their V-region sequences. However, all the V regions were essentially identical to germline sequences in both the heavy and light chains. Heavy-chain CDR3 segments ranged in length from 17 to 26 residues, did not correspond to any known autoantibodies, and showed extensive N-region diversity in the V(D)J junctions. Five monoclonal autoantibodies use VH 3 genes, while the remaining two utilized VH 4 sequences. Light-chain variable regions used were Vkappa3 (two), Vlambda3 (four), and one Vlambda2. These autoantibodies derived their unique features from their CDR3 segments that could not be aligned with any known sequences.

Differential use of immunoglobulin light chain genes and B lymphocyte expansion at sites of disease in rheumatoid arthritis (RA) compared with circulating B lymphocytes

The presence of germinal centre-like structures and clonotypic expansion of lymphocytes in RA synovia may indicate a site-specific immune response to local antigens, rather than passively entrapped immune cells, that sustains synovial inflammation. In this study we compare the nature of immunoglobulin light chain variable region gene use in the synovium of RA patients with peripheral B cells to determine the nature of the synovial immune response. Using Vlambda and Vkappa gene fingerprinting, which relies on differences in CDR3 length, we demonstrate differences in the pattern of Vlambda and Vkappa use and clonotypic expansion of B cells between the synovium and peripheral blood of RA patients. Further, we show that some synovial rearrangements with long CDR3 are selectively expanded. These longer than usual CDR3 were generated by a number of mechanisms including N-additions. However, the observed differences were not uniform in different patients. These observations suggest that local synovial antigens drive significant numbers of T and B lymphocytes selected from an existing repertoire shaped by genetic and environmental factors. Further, the data argue against passive retention of most B cells in the synovium of RA patients.

Evidence for selection of 11 amino acid CDR3 domains in V kappa III-derived immunoglobulin light chains in Kawasaki disease

Kawasaki disease (KD) is a rheumatic disease that occurs during childhood. Although T cells have been implicated as having an important role in the pathogenesis of KD, the role of B cells is unclear. To detect preferential expression of 11 amino acid complementarity determining region (CDR)3 domains, we used two-stage PCR (polymerase chain reaction) to analyze the CDR3 lengths of VkIII-derived immunoglobulin kappa light chains expressed in peripheral blood B cells during the acute, subacute, and convalescent phase of this disease. As controls, the peripheral blood B cells of age-matched normal and children with acute febrile diseases other than KD were tested. In 5 of 7 KD patients, expression of kappa light chains containing 11 amino acid codon CDR3 intervals was increased during the acute and subacute phase of KD but decreased during the convalescent phase. Two of the 7 KD patients showed the same pattern during the subacute and convalescent phase, but not during the acute phase. Two of the 5 patients with acute febrile diseases other than KD showed increased expression of kappa chains with 11 amino acid codon CDR3 intervals, but it was not a major fraction. Three of the 5 patients with acute febrile diseases other than KD and all normal control subjects showed only 9 and 10 amino acid CDR3 domains. These results strongly suggest that B cells expressing kappa light chains with the 11 amino acid CDR3 domains might be involved in the pathogenesis of KD.

Molecular single-cell analysis reveals that CD5-positive peripheral blood B cells in healthy humans are characterized by rearranged Vkappa genes lacking somatic mutation

B cells expressing the CD5 cell surface antigen are involved in certain B cell malignancies and autoimmune diseases. From studies in the mouse, it emerged that CD5+ B cells represent a separate lineage of B lymphocytes that, in contrast to conventional (CD5-) B cells, are not driven into T cell-dependent immune responses in which rearranged variable (V) region genes are diversified by somatic hypermutation. Against this background it came as a surprise that human disease-involved CD5-positive autoreactive B cells as well as B cell chronic lymphocytic leukemias can harbor somatically mutated V region genes. Recent V gene analyses on CD5+ B cells in healthy adults did not give rise to a clear picture about the fraction of somatically mutated among all CD5+ B cells. In this work we used a molecular single-cell analysis to determine reliably the frequency of mutated CD5+ B cells in healthy humans: single, kappa light chain-expressing CD5+ peripheral blood B cells were isolated by flow cytometry, and rearranged Vkappa genes were amplified by PCR. From one donor, CD5+CD19+ B cells were analyzed. Since CD5+ B cells were found among IgM+IgD+ and IgM+IgD- cells (but almost not among class-switched cells) from two other donors, individual cells corresponding to these IgM-expressing subsets were investigated separately. The sequence analysis of rearranged Vkappa genes revealed that most if not all CD5+ B cells in healthy humans carry unmutated V region genes. From one of the donors, a novel polymorphic Jkappa2 gene segment was identified. To explain the discrepancy between the frequent occurrence of disease-associated somatically mutated CD5+ B cells and the low incidence or absence of somatic mutation in normal CD5+ B cells, we speculate that CD5+ B cells usually do not participate in germinal center reactions, but if they occasionally do so, they may be at an increased risk to become involved in autoimmune diseases or B cell malignancies.

Increased responsiveness of rheumatoid factor-producing B cells in seronegative and seropositive rheumatoid arthritis

OBJECTIVE

To compare the frequencies and responsiveness of rheumatoid factor (RF)-producing B cells in the peripheral blood of patients with seronegative and seropositive rheumatoid arthritis (RA).

METHODS

Frequencies of IgM+, IgG+, and RF+ B cells were determined by limiting-dilution analysis of purified peripheral blood B cells from 6 patients with seropositive RA, 8 patients with seronegative RA, and 7 normal controls. B cell help was provided by cloned T helper cells, which were stimulated by either anti-CD3 or the bacterial superantigen staphylococcal enterotoxin D (SED). IgM and IgG antibodies and RF in culture supernatants were detected by enzyme-linked immunosorbent assay.

RESULTS

In the presence of anti-CD3-stimulated T helper cells, 2-10% of B cells from normal individuals secreted IgM and IgG antibodies. The frequency of RF+ B cells was low and ranged from 1:182 to 1:885 (RF+: IgM+) B cells. In patients with seropositive RA, the numbers of Ig-producing B cells were reduced by a factor of 2, while the fraction of RF+ B cell precursors was expanded by more than 50-fold (7-20% of IgM+ B cells; P = 0.004). Patients with seronegative RA had higher frequencies of RF-producing B cells (1.5-6% of IgM+ B cells) than normal individuals (P = 0.002), but not to the same extent as seropositive patients (P = 0.002). Stimulation of B cells using SED preferentially induced RF+ B cells in normal controls and in patients with seronegative and seropositive RA.

CONCLUSION

B cell precursors with the potential to secrete RF were detectable in high frequencies in normal individuals and in patients with seropositive and seronegative RA. In all donors, these B cells could be stimulated with the bacterial superantigen SED. In normal individuals, RF+ B cells remained nonresponsive to help provided by anti-CD3-activated T cells, but were responsive in RA patients. Seronegative and seropositive RA form a continuous spectrum of disease, with a higher number of RF-secreting B cells in the seropositive patients.

The B lymphocyte in rheumatoid arthritis: analysis of rearranged V kappa genes from B cells infiltrating the synovial membrane

The participation of the humoral immune system in rheumatoid arthritis (RA) is characterized by the production of rheumatoid factors (RF). RF are autoantibodies against the Fc part of IgG which are encoded by diverse germ-line genes. Most of the RF-encoding genes are unmutated, but in RA, a substantial quantity is encoded by somatically mutated genes. In addition, the synovial membranes (SM) of the diseased joints of RA patients are infiltrated by B lymphocytes which form germinal center-like aggregates. To analyze the local immune response, B cell foci from two RA SM were isolated by micromanipulation. From DNA of these foci, the rearranged kappa light chain variable region (V kappa) genes were amplified by polymerase chain reaction (PCR), cloned and sequenced. The amplification of different V kappa-J kappa combinations of different foci suggested oligoclonal expansion of B lymphocytes, which was confirmed by sequence analysis: each PCR product contained members of a single B cell clone. The sequence analysis of 29 different clones revealed rearrangements of diverse V kappa genes. Both frequent representatives of the V kappa 3 and the V kappa 1 family, as well as rarely used genes such as the L10 and B2 genes of the V kappa 2 and V kappa 5 families were found. Of the eleven potentially functional gene rearrangements, eight were significantly mutated, indicating their derivation from antigen-selected B cells. Intraclonal diversity in one of these clones may suggest ongoing mutation in the diseased synovial membrane of patients with RA.

Somatic mutation and CDR3 lengths of immunoglobulin kappa light chains expressed in patients with rheumatoid arthritis and in normal individuals

Immunoglobulin secretion by plasma cells infiltrating synovial membranes is a prominent feature of RA. Previous analyses of a cDNA library generated from synovium of RA patient BC revealed immunoglobulin kappa light chain transcripts with extensive somatic mutation, frequent N region addition, and unexpected variation in the lengths of CDR3 regions which form the center of the antigen binding site. To determine if these characteristics are present in other individuals, we performed reverse transcription-polymerase chain reaction amplification and sequenced > or = 10 V kappa-containing amplicons from nine tissue samples: synovia of three individuals with long-standing RA (including patient BC), PBLs of two of these individuals, and PBLs or splenocytes of four normal individuals. Increased levels of somatic mutation in PBLs appeared to correlate with increased age, which may reflect accumulation of circulating memory cells and/or decreased bone marrow production of naive B lymphocytes. Two of three RA synovial samples and both RA PBL samples exhibited increased proportions of clones with unusual CDR3 lengths. Enrichment for these antibody binding sites could be due to abnormal regulation of the emerging repertoire or to selection for B lymphocytes bearing antibodies of unusual specificity, and may play a role in the pathogenesis of RA.

Somatic diversification and selection of immunoglobulin heavy and light chain variable region genes in IgG+ CD5+ chronic lymphocytic leukemia B cells

Chronic lymphocytic leukemia (CLL) is characterized by the clonal expansion of CD5-expressing B lymphocytes. Most studies have found that these leukemic CD5+ B cells, like their normal counterparts, use immunoglobulin (Ig) variable (V) region genes that exhibit minimal, if any, somatic diversity. These and other observations have suggested that CD5+ B cells may be incapable of generating Ig V gene diversity, and therefore may not be able to develop higher affinity binding sites that could be selected by antigen. However, most of the studies of CLL and normal CD5+ B cells have focused on IgM-producing cells. Since somatic mutations are most often seen in B cells that have undergone an isotype class switch, we analyzed the Ig heavy (H) and light (L) chain variable region genes of seven IgG+CD5+ CLL B cells to determine if somatic diversification and antigen selection had occurred. The data derived provide evidence for skewed use, somatic diversification, and antigenic selection of the Ig V region genes. Nonrandom use of both H and L chain V region genes was manifested by an overrepresentation of VH4 and VKI family genes and the underrepresentation of the JH4 gene segment. Furthermore, VH4 gene use was restricted to only two family members (4.21 and 4.18). In four of the seven cases, the VH and VL genes displayed > or = 5% difference from the most homologous known germline counterparts. Polymerase chain reaction and Southern blot analyses performed in two of these patients demonstrated that their unique VH CDR2 and adjacent sequences were not present in their germline DNA. In addition, a significant level of diversity was seen in the rearranged DJH segments and at the VL-JL junctions of every patient that occurred both at the time of recombination and subsequently. The localization of replacement changes to complementarity determining regions of some patients suggested that antigen selection had occurred. Furthermore, the mutations identified in the VH and VL genes of each individual patient were strikingly similar, both in number and location. Collectively, the data indicate that a subset of CD5+ CLL B cells can display Ig V region gene mutations. In addition, they are consistent with the notions that in some cases antigen selection of these mutations may have occurred, and that antigen stimulation may be a promoting factor in the evolution of certain CLL clones.

IgH and L chain variable region gene sequence analyses of twelve synovial tissue-derived B cell lines producing IgA, IgG, and IgM rheumatoid factors structure/function comparisons of antigenic specificity, V gene sequence, and Ig isotype

In the present study, the complete sequences of the Ig H and L chain variable region genes of twelve RF+ B cell lines from two patients with RA were analyzed. Seven of the RF-producing B cells used VH3 family genes, four used VH4 genes, and one a VH1 gene. All but two of the cell lines expressing VH3 genes utilized different family members; among the VH4-expressing cells, a more restricted pattern was noted. V kappa gene use was restricted to the V kappa I and III families; V lambda gene use was more diverse, involving five different families. Computer comparisons of the expressed VH genes with their presumed germline progenitors indicated significant differences in every instance; eight of the corresponding VL genes also were significantly different. In many cases, assignment of the germline D segment(s) incorporated into the rearranged VH genes was impossible. These differences from the germline gene segments indicated the extensive changes induced by rearrangement, enzymatic activities, and somatic mutation. In hopes of defining a structural reason for the disparate antigen specificities of these cells, the CDR3 amino acid sequences of the multi- vs. the mono-reactive RF-producers were compared. Although CDR3 length was not appreciably different between these two sets of mAb, a greater than two-fold increase in charged amino acids was found in the H chain CDR3 of the multireactive RF. This relationship did not exist for the L chain CDR3. Thus, these sequence data indicate the use of a broad base of Ig V gene segments that have undergone extensive diversification. Based on the localization of R substitutions in the CDR of most of the V genes studied, the diversification appears to be antigen driven and selected. The significance of these findings for the evolution of these B cell clones into isotype-switched producers that are heterogeneous for antigen specificity (mono- vs. multi-reactivity) is discussed.

Molecular characterization of monoclonal IgM derived from human B cell lines expressing the 4C9 rheumatoid factor associated idiotype

Ten human monoclonal B cell lines that express the RF associated Id 4C9 were analyzed using an immunogenetic approach. Five of eight tested lines were also strongly positive for the 6B6.6 Id. We found that all the 4C9/6B6.6 positive lines expressed VkIIIa light chain genes. In contrast, 4C9 reactivity was also found on a cell line expressing a VkIIIb light chain gene and on a line expressing a V light chain gene. The two anti-Ids recognized a linear light chain determinant on Humkv328 encoded light chains but also a conformational determinant on Vg encoded light chains that appeared to be dependent on the presence of a heavy chain. Idiotypic reactivity occurred on both RF positive and RF negative antibodies. Within this idiotypic system, the basis for idiotypic reactivity and RF reactivity is complex, subject to both heavy and light chain gene usage and sensitive to small numbers of somatic mutations.

Immunoglobulin gene expression in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by inflammation of synovium, in which immunoglobulin-secreting plasma cells are generally present. The forces driving immunoglobulin expression in RA synovium are unknown. Sequences of VH and VK transcripts from an RA synovial cDNA library demonstrate patterns of somatic mutation typical of an antigen-driven response. Moreover, 5% of the kappa repertoire appears to derive from the same B cell progenitor, suggesting an oligoclonal response. Immunoglobulin expression in this synovium thus appears to result from antigen stimulation. In addition, this patient's synovium is enriched for unusually long VK-JK joins (CDR3s), suggesting abnormal selection or regulation of the B cell response in RA.

Profile of lambda light chain variable region genes in Graves' orbital tissue

Graves' ophthalmopathy, a human autoimmune disease of unknown etiology, is strongly associated with autoimmune hyperthyroidism. A major controversy is whether retro-ocular muscle or orbital fat/connective tissue is the target of the immune response. Previously, we observed preferential PCR amplification of lambda (relative to kappa) light chain DNA from cDNA of Graves' orbital tissue-infiltrating B cells/plasma cells. There is little information on V lambda gene usage in man and none in diseased tissue. To characterize the orbital lambda light chains, we constructed cDNA libraries using PCR-amplified DNA from three tissues and sequenced the variable region genes from randomly selected clones. Analysis of 27 clones from orbital fat/connective tissue libraries from two patients with acute inflammatory eye disease, and 15 clones from orbital muscle of one of these patients, revealed a diverse spectrum of lambda V region genes. The nucleotide sequences of these 42 clones were most homologous to 12 different germline genes: four family I (subfamilies I-a, -b and -c), three family II, two family III and one family VII germline genes. Each orbital tissue had a distinct profile of V lambda sequences. However, all clones used J lambda 2/3 and all three orbital tissues contained clones related to family II genes. Although some clones had V region sequences in near germline conformation, the majority differed from the closest germline gene in both framework and complementarity determining regions. Whether or not these differences result from multiple germline gene usage or somatic mutation of a smaller number of germline genes cannot be determined until information on the V lambda repertoire and its polymorphisms is complete. However, the V lambda gene diversity we observed in both orbital muscle and orbital fat/connective tissue suggests a role for lambda autoantibodies in the pathogenesis of Graves' ophthalmopathy.

Biased utilization of immunoglobulin variable region heavy- and light-chain genes by the malignant CD5- B lymphocytes from patients with Burkitt's lymphoma

Twenty-six established Burkitt's lymphoma (BL) cell lines from endemic or sporadic groups of patients were examined for the expression of cross-reactive idiotypes (CRI) associated with VHI, VHIII, VHIV, VHVI, VKIIIa and VKIIIb heavy- and light-chain gene products, using a panel of anti-CRI and anti-subgroup monoclonal antibodies (MAbs). Membrane, cytoplasmic and secreted immunoglobulins (Ig) were analysed by immunofluorescence, immunoperoxidase and ELISA respectively. While 35% of the lines expressed either of the VHIV-associated CRI, recognised by the MAbs 9G4 or LCI, none expressed the other VH-associated CRI included in our study. Of the kappa light chain expressing BL lines 54% and 46% belonged to the VKIII subgroup and VKIIIb sub-subgroups respectively. None, however, was found to express the VKIIIa or VKIIIb-associated CRI, recognised by the 6B6.6 and 17-109 MAbs. A significant association has been observed between the expression of the VHIV-associated CRI and the VKIII subgroup within the BL lines derived from the sporadic group of patients as compared with their endemic counterparts. Our results suggest that the expressed repertoire of Ig variable region genes within the malignant B lymphocytes of BL is not random and that a highly selective mechanism(s) may operate on this subset of B lymphocytes, as evidenced by the expression of the VH and VK gene products.

Rheumatoid factors from the peripheral blood of two patients with rheumatoid arthritis are genetically heterogeneous and somatically mutated

We report the DNA sequences of the heavy and light chain immunoglobulin genes of 11 monoclonal rheumatoid factor (RF)-secreting lines derived from the peripheral blood of two patients with rheumatoid arthritis (RA). It is evident from immunogenetic analysis of these lines that RA-associated RF activity can arise from a wide variety of heavy and light chain genes and gene combinations. Although the RF response from our two patients shows a bias in gene usage toward those genes used to encode monoclonal RF, particularly VkIII, relatively few of these RFs are reactive with the monoclonal antiidiotypes 6B6.6 and 17.109 that define VkIII germline-encoded light chains and the loss of this idiotypic reactivity is clearly related to somatic mutation. Finally, RFs derived from peripheral blood of RA patients show a similar heterogeneity of epitope binding to Fc as that seen for synovium-derived RF and some are clearly different in binding specificity from the restricted RF population found in patients with B cell malignancies. Somatic mutations as well as different VH/VL combinations contribute to the heterogeneity in the binding patterns of these RA-derived RF.

An apparently common mechanism of generating antibody diversity: length variation of the VL-JL junction

The joining of various V, (D) and J gene segments during DNA rearrangement of the antigen receptor genes is one of the principle mechanisms responsible for the generation of antibody diversity. In the absence of N-segment variation, the structures of the coding joints formed during light chain rearrangement are thought to be less complex than their heavy chain counterparts. Consequently, the joining of the VL and JL gene segments during recombination account for all of the junctional diversity seen within the third complementarity determining region (CDR3). We generated kappa light chain transcripts from human fetal liver and peripheral blood lymphocytes and found that approximately one third exhibit a variation in the length of CDR3-independent of the JK gene segment utilized. Nucleotide sequence analysis reveals that many of the nucleotides at the VK-JK joint resulting in length variation of CDR3 are directly encoded by the germline VK and JK gene segments used in these transcripts. However, nearly 20% of the transcripts contain N-segment additions consistent with TdT-like activity. These observations suggest that TdT or an analogous enzyme must be active in a significant percentage of human B-lymphocytes during light chain rearrangement. Length variation in light chain CDR3 expands the potential repertoire and thus contributes an additional means of generating diversity in the antibody molecule.

Evidence of antigen receptor-influenced oligoclonal B lymphocyte expansion in the synovium of a patient with longstanding rheumatoid arthritis

Plasma cell infiltration of synovium is common in longstanding rheumatoid arthritis (RA). The mechanism(s) underlying synovial B cell proliferation remains unclear. One theory invokes nonspecific polyclonal stimuli; another implicates antigen as the driving force. Antigen-driven repertoires are characteristically enriched for related sets of V gene segments containing similar sequence in the antigen binding site (complementarity-determining regions; CDRs). To study the forces shaping B cell proliferation, we analyzed V kappa transcripts expressed in the synovium of an RA patient. We found Humkv325, a developmentally regulated V kappa III gene segment associated with autoantibody reactivity, in > 10% of randomly-chosen synovial C kappa cDNAs. Two sets of sequences contained identical charged amino acid residues at the V kappa-J kappa join, apparently due to N region addition. We generated "signature" oligonucleotides from these CDR3s and probed PCR amplified V kappa products from the synovium and PBLs of the same patient, and from PBLs and spleen of individuals without rheumatic disease. Significant expression of transcripts containing these unique CDR3 sequences occurred only in the patient's synovium. Thus, in this synovium there is expansion of a limited set of B cell clones expressing antigen receptors that bear evidence of antigen selection.

Human rheumatoid factor cross-idiotypes. IV. Studies on WA XId-positive IgM without rheumatoid factor activity provide evidence that the WA XId is not unique to rheumatoid factors and is distinct from the 17.109 and G6 XIds

The WA cross-idiotype (XId) is the major XId among human monoclonal rheumatoid factors (mRF) and is almost always associated with the light (L) chain XId, 17.109, and the heavy (H) chain XId, G6. A cell line, 35G6, was cloned that bears the WA XId, but shows no reactivity with immunoglobulin G (IgG) and is negative for the 17.109 and G6 XIds. The 35G6 L chain appears to be derived from the same VKIII-JKI genes as most WA mRFs L chains. In contrast to the WA mRFs H chains in which VH1 genes are used, the 35G6 IgM expresses a VH3 gene. Sequence comparisons with other WA XId-positive mRF suggested several common structural features that may be related to the WA XId and differences that may relate to lack of IgG reactivity. Cells similar to 35G6 have previously been described in pokeweed mitogen-stimulated cell lines of peripheral blood lymphocytes from normal individuals and patients with rheumatoid arthritis and type II mixed cryoglobulinemia. These observations were confirmed, and in addition, it was shown that the majority of WA XId-positive cells in these cultures were negative for the 17.109 and G6 XIds. The presence of the WA XId in the absence of IgG reactivity suggests that the WA XId is more directly associated with an antigen specificity other than IgG, and its association with RF activity may be incidental. It is postulated that these WA XId-positive RF-negative antibodies may serve a physiologic role as natural antibodies to a pervasive pathogen, and that IgG reactivity is a consequence of somatic diversification accompanying proliferation of the WA XId-positive RF-negative cell.

Human IgM+IgD+ B cells, the major B cell subset in the peripheral blood, express V kappa genes with no or little somatic mutation throughout life

Peripheral blood B cells of a 67-year-old person were separated into IgM+IgD+, IgM+IgD-, and IgM-IgD- subsets, and nucleotide sequences of expressed immunoglobulin light chain variable (V) regions encoded by V kappa 3 and V kappa 4 gene family members were determined from amplified cDNA. V region sequences from IgM+IgD+ cells (the major B cell population in the blood) showed no or little somatic mutation (0.3%), in contrast to V kappa sequences from IgM+IgD- and IgM-IgD- B cells (2.0% and 3.9%, respectively). This suggests that in the human like in the mouse, and independently of age, somatically mutated memory B cells accumulate in the compartment of IgM-IgD- cells, whereas the IgM+IgD+ subpopulation consists of cells whose antibody repertoire is mainly determined by V region gene rearrangements and N-region insertion, at the molecular level. The somatically mutated IgM+IgD- cells may represent early descendants of IgM+IgD+ cells recruited into the memory cell compartment.

Analysis of the V kappa III variable regions of polyclonal rheumatoid factors arising during Epstein Barr virus induced infectious mononucleosis

The mechanisms that govern autoantibody production are still under debate. In particular, auto-antibodies can appear as a consequence of a polyclonal activation of B cells or as a consequence of an antigen driven B cell expansion. The molecular analysis of the variable regions of auto-antibodies arising during different clinical situations can help to understand the origin of auto-antibodies. We recently described the main light chain variable regions of polyclonal rheumatoid factors occurring during rheumatoid arthritis and suggested that the mutation pattern of these regions could reflect an antigen driven process. Using the same approach, we now report the molecular analysis of the same light chain variable region containing a VKIII segment of rheumatoid factors originating from a polyclonal activation of B cells during an in vivo Epstein-Barr virus infection, infectious mononucleosis. The cDNA derived from rheumatoid factor synthetizing cells were amplified by two sets of polymerase chain reaction. The amplified products were cloned in M13mp19 phages and sequenced. The nucleotide analysis of the VKIII containing VK regions shows that: 1) the rheumatoid factor activity is associated with the 3 VKIII genes (Kv 325, Kv 328 and Vg) already known to encode for monoclonal and polyclonal rheumatoid factors, 2) there is a preferential use of Kv 328 and Vg, each one of these genes being poorly mutated, 3) the CDR mutation rates of these genes is no higher than the framework mutation rates, 4) there is a restriction of the JK usage; Kv 328 derived gene segments rearrange exclusively with JK1, Vg preferentially rearranges with JK1 and JK4. These results mainly suggest that naturally occurring polyclonal activation of autoreactive B cells produces poorly mutated autoantibodies.

A rheumatoid factor from a normal individual encoded by VH2 and V kappa II gene segments

OBJECTIVE

To gain insight into the immunoglobulin variable-region repertoire of anti-IgG antibodies (rheumatoid factors [RF]), we characterized the VH and V kappa gene segments utilized in an IgM-RF-secreting lymphoblastoid cell line (SSH23) isolated from a normal individual.

METHODS

The cell line SSH23 was established by Epstein-Barr virus transformation of peripheral blood non-T mononuclear cells. First-strand complementary DNA (cDNA) was generated and used for polymerase chain reaction amplification of the heavy and light chain variable domains. The amplified variable domains were sequenced and compared with an extensive database of germline and cDNA V gene segments.

RESULTS

The VH sequence was found to be identical to a previously described fetal VH2 incomplete cDNA and to differ by only 3 nucleotides from a JH proximal germline VH2 gene segment. To our knowledge, this is the first example of a VH2 rheumatoid factor. The V kappa 2-J kappa 4 light chain contains an uncommon 10-amino acid third complementarity-determining region (CDR 3).

CONCLUSION

Utilization of preimmune fetal VH gene segments and unusual light chain junctional diversity appear to be features shared by many physiologic and pathologic rheumatoid factors.