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

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.

The role of Antibody Vκ Framework 3 region towards Antigen binding: Effects on recombinant production and Protein L binding

Antibody research has traditionally focused on heavy chains, often neglecting the important complementary role of light chains in antibody formation and secretion. In the light chain, the complementarity-determining region 3 (VL-CDR3) is specifically implicated in disease states. By modulating VL-CDR3 exposure on the scaffold through deletions in the framework region 3 (VL-FWR3), we further investigated the effects on secretion in recombinant production and antigen binding kinetics. Our random deletions of two residues in the VL-FWR3 of a Trastuzumab model showed that the single deletions could impact recombinant production without significant effect on Her2 binding. When both the selected residues were deleted, antibody secretion was additively decreased, and so was Her2 binding kinetics. Interestingly, we also found allosteric effects on the Protein L binding site at VL-FWR1 elicited by these deletions in VL- FWR3. Together, these findings demonstrate the importance of light chain FWR3 in antigen binding, recombinant production, and antibody purification using Protein L.

Antibody repertoire development in fetal and neonatal piglets. XXII. λ Rearrangement precedes κ rearrangement during B-cell lymphogenesis in swine

VDJ and VJ rearrangements, expression of RAG-1, Tdt and VpreB, and the presence of signal joint circles (SJC) were used to identify sites of B-cell lymphogenesis. VDJ, VλJλ but not VκJκ rearrangements or SJC were recovered from yolk sac (YS) at 20 days of gestation (DG) along with strong expression of VpreB and RAG-1 but weak Tdt expression. VλJλ rearrangements but not VκJκ rearrangements were recovered from fetal liver at 30-50 DG. SJC were pronounced in bone marrow at 95 DG where VκJκ rearrangements were first recovered. The VλJλ rearrangements recovered at 20-50 DG used some of the same Vλ and Jλ segments seen in older fetuses and adult animals. Hence the textbook paradigm for the order of light-chain rearrangement does not apply to swine. Consistent with weak Tdt expression in early sites of lymphogenesis, N-region additions in VDJ rearrangements were more frequent at 95 DG. Junctional diversity in VλJλ rearrangement was limited at all stages of development. There was little evidence for B-cell lymphogenesis in the ileal Peyer's patches. The widespread recovery of VpreB transcripts in whole, non-lymphoid tissue was unexpected as was its recovery from bone marrow and peripheral blood monocytes. Based on recovery of SJC, B-cell lymphogenesis continues for at least 5 weeks postpartum.

The porcine antibody repertoire: variations on the textbook theme

The genes encoding the heavy and light chains of swine antibodies are organized in the same manner as in other eutherian mammals. There are ∼30 VH genes, two functional DH genes and one functional JH gene, 14-60 Vκ genes, 5 Jκ segments, 12-13 functional Vλ genes, and two functional Jλ genes. The heavy chain constant regions encode the same repertoire of isotypes common to other eutherian mammals. The piglet models offers advantage over rodent models since the fetal repertoire develops without maternal influences and the precocial nature of their multiple offspring allows the experimenter to control the influences of environmental and maternal factors on repertoire development postnatally. B cell lymphogenesis in swine begins in the fetal yolk sac at 20 days of gestation (DG), moves to the fetal liver at 30 DG and eventually to the bone marrow which dominates until birth (114 DG) and to at least 5 weeks postpartum. There is no evidence that the ileal Peyers patches are a site of B cell lymphogenesis or are required for B cell maintenance. Unlike rodents and humans, light chain rearrangement begins first in the lambda locus; kappa rearrangements are not seen until late gestation. Dissimilar to lab rodents and more in the direction of the rabbit, swine utilize a small number of VH genes to form >90% of their pre-immune repertoire. Diversification in response to environmental antigen does not alter this pattern and is achieved by somatic hypermutation (SHM) of the same small number of VH genes. The situation for light chains is less well studied, but certain Vκ and Jκ and Vλ and Jλ are dominant in transcripts and in contrast to rearranged heavy chains, there is little junctional diversity, less SHM, and mutations are not concentrated in CDR regions. The transcribed and secreted pre-immune antibodies of the fetus include mainly IgM, IgA, and IgG3; this last isotype may provide a type of first responder mucosal immunity. Development of functional adaptive immunity is dependent on bacterial MAMPs or MAMPs provided by viral infections, indicating the importance of innate immunity for development of adaptive immunity. The structural analysis of Ig genes of this species indicate that especially the VH and Cγ gene are the result of tandem gene duplication in the context of genomic gene conversion. Since only a few of these duplicated VH genes substantially contribute to the antibody repertoire, polygeny may be a vestige from a time before somatic processes became prominently evolved to generate the antibody repertoire. In swine we believe such duplications within the genome have very limited functional significance and their occurrence is therefore overrated.

Mechanism and prevention of acute kidney injury from cast nephropathy in a rodent model

A common renal complication of multiple myeloma is "myeloma kidney," a condition also known as cast nephropathy. The renal lesions (casts) are directly related to the production of monoclonal immunoglobulin free light chains (FLCs), which coprecipitate with Tamm-Horsfall glycoprotein (THP) in the lumen of the distal nephron, obstructing tubular fluid flow. Here, we report that analysis of the binding interaction between FLCs and THP demonstrates that the secondary structure and key amino acid residues on the complementarity-determining region 3 (CDR3) of FLCs are critically important determinants of the molecular interaction with THP. The findings permitted development of a cyclized competitor peptide that demonstrated strong inhibitory capability in the binding of FLCs to THP in vitro. When used in a rodent model of cast nephropathy, this cyclized peptide construct served as an effective inhibitor of intraluminal cast formation and prevented the functional manifestations of acute kidney injury in vivo. These experiments provide proof of concept that intraluminal cast formation is integrally involved in the pathogenesis of acute kidney injury from cast nephropathy. Further, the data support a clinically relevant approach to the management of renal failure in the setting of multiple myeloma.

Somatic hypermutation and antigen-driven selection of B cells are altered in autoimmune diseases

B cells have been found to play a critical role in the pathogenesis of several autoimmune (AI) diseases. A common feature amongst many AI diseases is the formation of ectopic germinal centers (GC) within the afflicted tissue or organ, in which activated B cells expand and undergo somatic hypermutation (SHM) and antigen-driven selection on their immunoglobulin variable region (IgV) genes. However, it is not yet clear whether these processes occurring in ectopic GCs are identical to those in normal GCs. The analysis of IgV mutations has aided in revealing many aspects concerning B cell expansion, mutation and selection in GC reactions. We have applied several mutation analysis methods, based on lineage tree construction, to a large set of data, containing IgV productive and non-productive heavy and light chain sequences from several different tissues, to examine three of the most profoundly studied AI diseases - Rheumatoid Arthritis (RA), Multiple Sclerosis (MS) and Sjögren's Syndrome (SS). We have found that RA and MS sequences exhibited normal mutation spectra and targeting motifs, but a stricter selection compared to normal controls, which was more apparent in RA. SS sequence analysis results deviated from normal controls in both mutation spectra and indications of selection, also showing differences between light and heavy chain IgV and between different tissues. The differences revealed between AI diseases and normal control mutation patterns may result from the different microenvironmental influences to which ectopic GCs are exposed, relative to those in normal secondary lymphoid tissues.

RAG-mediated secondary rearrangements of B-cell antigen receptors in rheumatoid synovial tissue

Rheumatoid arthritis (RA) induces major changes in synovial tissue (ST) and cartilage and bone destruction. Still, its pathogenesis is poorly understood. Accumulating evidence points to an important role for B lymphocytes. Rheumatoid-ST is characterized by activation of the synoviocytes and infiltrated by various inflammatory cells such as B and T lymphocytes. The infiltrate is diffuse or organized as germinal centers (GCs). These accommodate the immune response and favor self-tolerance breakdown. Receptor revision in B cells results from re-expression of the recombination activating genes (RAGs) which reinitiate immunoglobulin gene recombination, and modify the B-cell antigen receptor accordingly. In rheumatoid ST, secondary VDJ rearrangements occur and RAG proteins are detected. The mechanism that triggers and controls this revision remains elusive. We favor the hypothesis that such an uncontrolled process leads to autoimmunity.

Abnormal kappa:lambda light chain ratio in circulating immune complexes as a marker for B cell activity in juvenile idiopathic arthritis

Patients with juvenile idiopathic arthritis (JIA) have been shown to have elevated levels of circulating immune complexes (CICs) which correlated with disease activity. Our aim was to assess B cell activity by measuring the amount of and the kappa:lambda chain immunoglobulin light (L) chain ratio in CICs from JIA patients and to determine potential evidence for either an antigen-driven response or B-cell receptor editing. We used an enzyme-linked immunosorbent assay to measure kappa and lambda chains present in the CICs from the sera of patients with JIA. Statistical analysis was performed using Pearson's correlation, one-way ANOVA and Bonferroni post hoc analysis. Sera from 44 JIA patients were examined for the concentration of L chains in CICs. Healthy controls had a kappa:lambda chain ratio of 1.2:1, whereas this ratio was reversed among JIA subgroups with RF-positive polyarthritis (1:1.2), RF-negative polyarthritis (1:1.3), oligoarthritis (1:2.3) and systemic-onset arthritis (1:2.5). In addition, overall lambda chain selection was not significantly associated with a particular immunoglobulin heavy (H) chain and occurred with all immunoglobulin isotypes. We showed preferential selection of lambda chains contributing to the formation of potentially pathogenic CICs from JIA patients, of all onset types compared to healthy controls, in an H chain-independent manner. The reversal of kappa:lambda chain ratio within the JIA CICs and association with all immunoglobulin isotypes demonstrated the potential for L chain editing. Furthermore, we conclude that a reversal of the normal kappa:lambda chain ratio in JIA CICs may be used as a marker for increased B-cell activity.

The role of B cells and autoantibodies in rheumatoid arthritis

In this article, we will review B lymphocyte development and function, then discuss the role of B cells in RA, including immune complex formation; the K/BxN mouse model of RA; toll-like receptors; B cells as antigen presenting cells; germinal center-like structures in RA synovium; and influence on T cell activation, leukocyte infiltration, and angiogenesis. With regard to autoantibody production, we will focus on rheumatoid factor (RF) and anti-CCP antibodies, particularly mechanisms of their production; sensitivity and specificity in RA; and their roles as prognostic factors. Other autoantibodies will be discussed, as will treatment implications and future areas of investigation related to B cells and autoantibodies in RA.

Limited VH gene usage in B-cell clones established with nurse-like cells from patients with rheumatoid arthritis

OBJECTIVES

Nurse-like stromal cells (NLC) in synovia and bone marrow of patients with rheumatoid arthritis (RA) can support pseudoemperipolesis, protect from apoptosis and enhance immunoglobulin production of peripheral blood B cells isolated from healthy individuals, suggesting the profound contribution of hyperactivation of B cells in RA. In the course of establishing RA-NLC from RA patients, we observed the growth of B cells in the presence of RA-NLC.

METHODS

We cloned B cells from the synovium or bone marrow of RA patients using the limiting dilution technique. For established clones, nucleotide sequences of immunoglobulin and surface antigens were investigated. To investigate the dependence of these clones on NLC, differences in the proliferation and the amount of immunoglobulin produced in the presence or absence of NLC were compared. Immunocytochemical staining of various cells was performed using the antibody these clones produced.

RESULTS

Nine B-cell clones established from RA patients showed RA-NLC-dependent growth. These B-cell clones expressed CD19, CD20, CD38, CD39 and CD40, suggesting that the cloned cells were mature and activated. All clones secreted immunoglobulins in culture media, which were specific for intracellular components of various cell lines, including RA-NLC. Interestingly, we found limited usage of immunoglobulin heavy-chain variable regions (VH) among B-cell clones from RA patients. These repertoires were reported to be detected preferentially in fetal livers.

CONCLUSION

The present study provides a novel insight into the involvement of RA-NLC in the immunopathogenesis of RA via an autoreactive B cell development and/or activation mechanism.

Impaired early B cell tolerance in patients with rheumatoid arthritis

Autoantibody production is a characteristic of most autoimmune diseases including rheumatoid arthritis (RA). The role of these autoantibodies in the pathogenesis of RA remains elusive, but they appear in the serum many years before the onset of clinical disease suggesting an early break in B cell tolerance. The stage of B cell development at which B cell tolerance is broken in RA remains unknown. We previously established in healthy donors that most polyreactive developing B cells are silenced in the bone marrow, and additional autoreactive B cells are removed in the periphery. B cell tolerance in untreated active RA patients was analyzed by testing the specificity of recombinant antibodies cloned from single B cells. We find that autoreactive B cells fail to be removed in all six RA patients and represent 35-52% of the mature naive B cell compartment compared with 20% in healthy donors. In some patients, RA B cells express an increased proportion of polyreactive antibodies that can recognize immunoglobulins and cyclic citrullinated peptides, suggesting early defects in central B cell tolerance. Thus, RA patients exhibit defective B cell tolerance checkpoints that may favor the development of autoimmunity.

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.

Management of paraproteinemic renal disease

PURPOSE OF REVIEW

Paraproteinemic renal diseases comprise a group of renal disorders that are difficult to manage, in part because of subtleties in the clinical presentation and confusion regarding diagnosis and appropriate therapy. Often, nephrologists make the diagnosis of the underlying plasma cell dyscrasia following renal biopsy. This review seeks to provide a greater understanding of the mechanism of disease and recent approaches to the management of patients who have AL-amyloidosis, monoclonal light-chain and light and heavy-chain deposition disease [termed ML(H)CDD], and cast nephropathy. All three renal lesions are caused by deposition of immunoglobulin light chains. This review seeks to provide a greater understanding of the mechanism of disease and recent approaches to the management of these patients.

RECENT FINDINGS

The immunoglobulin light chain takes the center stage in the pathogenesis of AL-amyloidosis, ML(H)CDD and cast nephropathy. Modifications in the variable domain are responsible for the affinity of the light chain for a given segment of the nephron and the subsequent toxic manifestations. Therapy aimed at eradicating the offending clone of plasma cells that secrete the monoclonal light chain should be beneficial, but this hypothesis lacks confirmation. Four nonrandomized studies have now demonstrated clinical benefit, including return of renal function, of high-dose chemotherapy with autologous stem cell transplantation (HDT/SCT) in the treatment of patients who have AL-amyloidosis or ML(H)CDD.

SUMMARY

While randomized trials are lacking, the data support the clinical efficacy of more aggressive treatments designed to reduce the plasma cell clone responsible for these renal disorders.

Selection of Ig mu heavy chains by complementarity-determining region 3 length and amino acid composition

Although it is generally accepted that Ig heavy chains (HC) are selected at the pre-B cell receptor (pre-BCR) checkpoint, the characteristics of a functional HC and the role of pre-BCR assembly in their selection have remained elusive. We determined the characteristics of HCs that successfully passed the pre-BCR checkpoint by examining transcripts harboring V(H)81X and J(H)4 gene segments from J(H)(+/-) and lambda5(-/-)mice. V(H)81X-J(H)4-HC transcripts isolated from cells before or in the absence of pre-BCR assembly had no distinguishing complementarity-determining region 3 traits. In contrast, transcripts isolated subsequent to passage through the pre-BCR checkpoint had distinctive complementarity-determining regions 3 of nine amino acids in length (49%) and a histidine at position 1 (73%). Hence, our data define specific structural requirements for a functional HC, which is instrumental in shaping the diverse B cell repertoire.

Age-related accumulation of Ig V(H) gene somatic mutations in peripheral B cells from aged humans

To investigate age-related alterations in human humoral immunity, we analysed Ig heavy chain variable region genes expressed by peripheral B cells from young and aged individuals. Three hundred and twenty-seven cDNA sequences, 163 micro and 164 gamma transcripts with VH5 family genes, were analysed for somatic hypermutation and VHDJH recombinational features. Unmutated and mutated micro transcripts were interpreted as being from naive and memory IgM B cells, respectively. In young and aged individuals, the percentages of naive IgM among total micro transcripts were 39% and 42%, respectively. D and JH segment usage in naive IgM from aged individuals was similar to that from young individuals. The mutational frequencies of memory IgM were similar in young and aged individuals. gamma transcripts, which are regarded as being from memory IgG B cells, showed a significantly higher mutational frequency (7.6%) in aged than in young individuals (5.8%) (P < 0.01). These findings suggest that VHDJH recombinational diversity was preserved, but that the accumulation of somatic mutations in the IgG VH region was increased in aged humans. The accumulation of somatic mutations in IgG B cells during ageing may imply that an age-related alteration exists in the selection and/or maintenance of peripheral memory B cells.

B lymphocytopenia in rheumatoid arthritis is associated with the DRB1 shared epitope and increased acute phase response

The influence of HLA DRB1 alleles on B-cell homeostasis was analyzed in 164 patients with rheumatoid arthritis (RA). The percentages of CD19+ B lymphocytes determined in the peripheral circulation of 94 retrospectively recruited RA patients followed a bimodal distribution. Two frequency peaks (B-cell(low) patients and B-cell(high) patients) were separated by the population median of a B-cell frequency of 8.5% of all lymphocytes. Human leucocyte antigen genotyping revealed that the B-cell(low) patients were more frequently positive for the RA-associated HLA DRB1 shared epitope (SE) than were B-cell(high) patients. Accordingly, SE-positive patients had lower CD19 percentages in the rank-sum analysis when compared with SE-negative patients, and were markedly B lymphocytopenic when compared with a healthy control group. To confirm the differential frequencies of CD19+ B cells, absolute numbers in peripheral blood were determined prospectively in a cohort of 70 RA patients with recent onset disease. SE-positive patients were found to have lower absolute numbers of circulating CD19+ B cells. B-cell counts below the mean of the study population were associated with higher acute phase response and with increased levels of rheumatoid factor IgA. No correlation between absolute numbers of circulating B cells and radiographic progression of joint destruction was seen. The influence of immunogenetic parameters on B-cell homeostasis in RA reported here has not been described previously. The clinical relevance of B lymphocytopenia in SE-positive RA will be further investigated in longitudinal studies.

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.

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.

Terminal deoxynucleotidyl transferase deficiency decreases autoimmune disease in MRL-Fas(lpr) mice

The neonatal Ab and TCR repertoires are much less diverse, and also very different from, the adult repertoires due to the delayed onset of terminal deoxynucleotidyl transferase (TdT) expression in ontogeny. TdT adds nontemplated N nucleotides to the junctions of Igs and TCRs, and thus its absence removes one of the major components of junctional diversity in complementarity-determining region 3 (CDR3). We have generated TdT-deficient MRL/lpr, Fas-deficient (MRL-Fas(lpr)) mice, and show that they have an increased lifespan, decreased incidence of skin lesions, and much lower serum levels of anti-dsDNA, anti-chromatin, and IgM rheumatoid factors. The generalized hypergammaglobulinemia characteristic of MRL-Fas(lpr) mice is also greatly reduced, as is the percentage of CD4(-)CD8(-)B220(+) (double-negative) T cells. IgG deposits in the kidney are significantly reduced, although evidence of renal disease is present in many mice at 6 mo. CDR3 regions of both IgH and TCR from peripheral lymphocytes of MRL-Fas(lpr) mice are shorter in the absence of TdT, and there is a paucity of arginines in the IgH CDR3 regions of the MRL-Fas(lpr) TdT(-/-) mice. Because the amelioration of symptoms is so widespread, it is likely that the absence of N regions has more of an affect than merely decreasing the precursor frequency of anti-dsDNA B cells. Hence, either the T or B cell repertoires, or more likely both, require N region diversity to produce the full spectrum of autoimmune lupus disease.

Circulating human B cells that express surrogate light chains display a unique antibody repertoire

Circulating human B cells that coexpress V-preB and conventional L chains (V-preB+L+ B cells) are a recently described subset of B cells that express Abs with features of self-reactivity. Initial analysis of V-preB+L+ B cells was limited to Ig-kappa and to the small, underused VH5 family. To determine whether Abs commonly expressed by V-preB+L+ B cells show similar features, we analyzed Ig H chains from three highly expressed VH families, VH1, VH3, and VH4, and Ig-lambda. We find that VH1 and VH3 Abs expressed by V-preB+L+ B cells resemble VH5 in that they display increased JH6 use, long CDR3s, and an increased frequency of D-D fusions. Abs in all three of these VH families also show skewed D reading frame use resulting in predominance of hydrophobic amino acids, which are counterselected in conventional B cells. Like Ig-kappa genes, the Ig-lambda genes in V-preB+L+ B cells show long CDR3s, but they differ from Ig-kappa genes in that they display no evidence of receptor editing. We conclude that a large number of H and L chain Abs expressed by V-preB+L+ B cells display features associated with self-reactive Abs.

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.

Mutational analysis of immunoglobulin germline derived Vlambda4B light chains in rheumatoid arthritis

OBJECTIVE

We investigated the somatic mutational pattern of a specific Vlambda light chain variable region (V) gene in rheumatoid arthritis (RA) patients. The Vlambda4B light chain was chosen because of its location on the lambda locus and because of its previously observed use in IgM rheumatoid factors.

METHODS

We sequenced 13 different mRNA transcripts of Vlambda4B from the synovium of three different RA patients. These were compared to 31 identifiable Vlambda4B sequences from GenBank, which were obtained from the PBL of patients without RA.

RESULTS

A subset of Vlambda4B had a high rate of mutation, especially in the framework regions within the RA synovium. Furthermore, a set of codons within the first complementary determining region of Vlambda4B displayed frequent replacement mutations but did not possess any silent mutations.

CONCLUSION

The hypermutation of RA synovial-derived Vlambda4B sequences, especially in the framework areas, may contribute to or may be the result of altered mutational mechanisms and/or prolonged B cell life.

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.

Mapping the binding domain of immunoglobulin light chains for Tamm-Horsfall protein

Cast nephropathy, or myeloma kidney, is a potentially reversible cause of chronic renal failure. In this condition, filtered light chains bind to a common site on Tamm-Horsfall protein (THP), which is produced by cells of the thick ascending limb of the loop of HENLE: Subsequent aggregation of these proteins produces casts that obstruct tubule fluid flow and results in renal failure. In the present study, we used the yeast two-hybrid system to determine the site of interaction of light chains with THP. The third complementarity-determining region (CDR3) of both kappa and lambda light chains interacted with THP. These findings were confirmed in a series of competition studies using a synthetic peptide that corresponded to the CDR3 region and purified THP and light chains. Variations in the CDR3 sequence of the light chain affected binding. Thus, the current studies increase our understanding of the process of cast formation and provide an opportunity to develop strategies that may inhibit this interaction and prevent the clinical manifestations of myeloma kidney.

Mutational analysis of immunoglobulin germline derived Vlambda4A light chains in rheumatoid arthritis

In order to better characterize the expression of a family of light chains previously expressed in IgM rheumatoid factors, we studied the usage and somatic mutational pattern of the Vlambda4A light chain gene in rheumatoid arthritis (RA) patients. We sequenced 11 different transcripts of Vlambda4A from the synovial tissue of three different RA patients. For comparison, we found 8 rearranged transcripts of Vlambda4A from 4 normal peripheral blood lymphocyte libraries and 1 rearranged transcript from a non-RA con-A-resistant hybridoma in GenBank. A previously undescribed polymorphism of Vlambda4A was noted. Furthermore, conserved replacement mutations in the complementary determining regions, common silent mutations around these replacement mutations, and two subsets of mutated sequences were detected in multiple RA patients. These mutation patterns also correlated with observed consistencies in the rearrangements of the Vlambda4A/Jlambda junction. These data suggest that there is clonal expansion of Vlambda4A light chains in the RA synovium in response to a RA-specific antigen or as the result of an idiotypic response in RA.

Impact of age on hypermutation of immunoglobulin variable genes in humans

Chronological aging is associated with an accumulation of DNA mutations that results in cancer formation. The effect of aging on spontaneous mutations in humans is difficult to study because mutations are infrequent in the overall genome and tumors are relatively rare. In contrast, somatic mutations in immunoglobulin variable genes are abundant and can be studied in peripheral blood lymphocytes. To determine if aging alters the frequency and pattern of hypermutation, we sequenced 331 cDNA clones with rearranged V(H)6 genes and compared 452 mutations from young humans to 570 mutations from old humans. There were more mutated clones in the young population compared to the old population. Among the mutated clones, the frequency, location, and types of substitutions were similar between the young and the old groups. However, the ratio of replacement-to-silent mutations was much higher in the complementarity-determining regions of heavy chains from old people, which indicates that their B cells had been selected by antigen. Among individuals, there was variability in the frequency of tandem mutations, which we have observed in mice defective for the PMS2 mismatch repair protein. Microsatellite variability in DNA, which is caused by impaired mismatch repair, was then measured, and there was a strong correlation between the frequency of tandem mutations and microsatellite alterations. The data suggest that individuals vary in their mismatch repair capacity, which can affect the mutational spectra in their antibodies.

The long isoform of terminal deoxynucleotidyl transferase enters the nucleus and, rather than catalyzing nontemplated nucleotide addition, modulates the catalytic activity of the short isoform

During variable/diversity/joining (V[D]J) recombination, the enzyme terminal deoxynucleotidyl transferase (Tdt) adds random nucleotides at the junctions of the rearranging gene segments, increasing diversity of the antibody (Ab) and T cell receptor repertoires. Two splice variants of Tdt have been described, but only one (short isoform of Tdt [TdtS]) has been convincingly demonstrated to catalyze nontemplated (N) addition in vitro. We have expressed each splice variant of Tdt in transgenic (Tg) mice and found that the TdtS transgene catalyzes N addition on the endogenous Tdt(-/)- background and in fetal liver, but that the long isoform of Tdt (TdtL) transgene does neither. In contrast to previous in vitro results, both TdtS and TdtL are translocated to the nucleus in our model. Furthermore, TdtL/TdtS double Tg mice exhibit less N addition in fetal liver than do TdtS Tg mice. Whereas the TdtS transgene was shown to have functional consequences on the antiphosphorylcholine (PC) B cell repertoire, TdtL Tg mice exhibit a normal PC response, and Tdt(-/)- mice actually exhibit an increase in the PC response and in TEPC 15 idiotype(+) Ab production. We conclude that TdtL localizes to the nucleus in vivo where it serves to modulate TdtS function.

Circulating human B cells that express surrogate light chains and edited receptors

Immunoglobulin gene recombination can result in the assembly of self-reactive antibodies. Deletion, anergy or receptor editing normally silence B cells that produce these autoantibodies. Receptor editing is highly efficient in mouse B cells that carry pre-recombined autoantibody transgenes or gene "knock-ins". However, it has been difficult to identify cells that have edited receptors in unmanipulated mice and humans. To try to identify such cells we isolated and characterized B cells that coexpress surrogate and conventional light chains (V-preB+L+) from the blood of normal human donors. V-preB+L+ B cells express RAG mRNA, display an unusual heavy and light chain antibody repertoire consistent with antiself reactivity, and show evidence of receptor editing. These cells accumulate in the joints of patients with rheumatoid arthritis, consistent with a role for V-preB+L+ B cells and receptor editing in autoimmune disease.

IgVH genes from different anatomical regions, with different histopathological patterns, of a rheumatoid arthritis patient suggest cyclic re-entry of mature synovial B-cells in the hypermutation process

In the present study 55 IgVH genes amplified from three different anatomical regions of a rheumatoid arthritis (RA) patient were analyzed, adding further information on synovial B-cell maturation and recirculation in RA. This analysis demonstrated somatically mutated IgVh genes in all regions studied, with amino acid deletions and mixed IgVh molecules, suggesting the existence of a novel pathway to generate (auto) antibody specificities. Comparison of amino acid sequences of amplified genes that belong to the VH1 family (with predominantly the same germline counterpart) exhibited strong homology, indicating an apparently conserved mutational pattern. This suggests that the number of antigens that activate B cells in different locations is restricted. The most striking result was the finding of clonally related sequences in different anatomical regions, indicating a recirculation of activated B cells between the different affected joints.

Effect of a genetic deficiency of terminal deoxynucleotidyl transferase on autoantibody production by C57BL6 Fas(lpr) mice

Terminal deoxynucleotidyl transferase (TdT) adds nontemplate coded nucleotides (N additions) between the recombining ends of immunoglobulin and T cell receptor genes. These nucleotides add significant diversity to the Ig and TCR repertoires. Amino acids coded for by these nucleotides play a key role in the binding of self antigens by autoantibodies and autoreactive T cells. To determine the effect of a lack of N additions on autoantibody production, we bred the TdT knockout genotype onto the autoimmune C57BL/6-Fas(lpr) background. TdT-deficient mice had significantly lower sera anti-DNA and rheumatoid factor activity than their TdT-producing littermates. C57BL/6-Fas(lpr) TdT-deficient mice had shorter VH CDR3 regions and fewer VH CDR3 arginines [0.6% versus 4. 7%] than their TdT-producing littermates. These data indicate that the absence of TdT limited the production of anti-DNA antibodies and rheumatoid factors in C57BL/6-Fas(lpr) mice, likely due to constraints on Ig diversity secondary to the lack of TdT-derived N additions.

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.

Junctional diversity in Xenopus immunoglobulin light chains

Xenopus cDNA sequences encoding the homolog of mammalian kappa (kappa) light (L) chains were isolated from isogenic tadpole and adult individuals to investigate whether there existed stage-specific immunoglobulin L chain expression and somatic diversification. In the course of these studies rearrangements to a sixth J(L) gene segment and a pseudogene (J(L)psi) were found, and it is suggested that the order of these gene segments with respect to the L chain constant (C) region exon is: J(L)6-J(L)1-J(L)2-J(L)3-J(L)4-J(L)5-J(L)psi-C(L). The cDNA junctional diversity was analyzed; few N and P regions were found and almost all the CDR3 were 9 codons in length. There were restricted patterns of recombination site resolution, and this is attributed to some constraint in JL coding end processing.

Dominance of intrinsic genetic factors in shaping the human immunoglobulin Vlambda repertoire

The expressed human immunoglobulin Vlambda repertoire demonstrates a strong bias in the use of individual Vlambda segments. Mechanisms that underlie such biases can be divided into two categories: intrinsic genetic processes that lead to the preferential rearrangement and/or expression of certain segments; and selection following light chain expression. Here, we have used two approaches to investigate the factors that shape the human Vlambda repertoire. Firstly, we characterised 136 Vlambda rearrangements (59 productive and 77 non-productive) amplified from the human genomic DNA of peripheral blood cells. Secondly, we analysed Vlambda segment use in a library of 2000 cDNA clones from a transgenic mouse containing a 380 kb region (including 15 functional Vlambda segments) from the human immunoglobulin lambda locus. By hybridisation and sequencing we found that the patterns of use of human Vlambda segments in the transgenic mouse were similar to those found in the expressed human peripheral blood repertoire and in productive and non-productive genomic DNA rearrangements. These data indicate the importance of intrinsic genetic factors in shaping the human Vlambda repertoire and highlight the remarkable conservation of the molecular mechanisms involved in the production of the antibody repertoire in mouse and man. Therefore, transgenic mice represent a good model for analysis of the human antibody repertoire and for the production of human antibodies.

Light chain variable (VL) sequences of rheumatoid factors (RF) in patients with primary Sjögren's syndrome (pSS): moderate contribution of somatic hypermutation

We have characterized and sequenced the variable (V) region genes of the light (L) chains of 10 immunoglobulin (IgM) rheumatoid factor (RF) monoclonal antibodies (MoAb) derived by the hybridoma/Epstein-Barr virus (EBV) technique from the peripheral blood of patients with primary Sjögren's syndrome (pSS). Six out of 10 RFs used lambda (lambda) L chains, while four RFs used kappa (kappa) L chains. Five out of the six lambda RFs were encoded by Vlambda3 gene segments, the sixth one was encoded by a Vlambda1 gene segment. This preferential utilization of the Vlambda3 family genes suggests selective expansion of the B cell in pSS. Three of the kappa RFs used Vkappa3 gene segments, while the fourth used a Vkappa2 gene segment. Half of the RFs were found as unmutated copies of their closest germline (GL) gene. Interestingly these RFs were previously shown to use heavy (H) chains in GL gene configuration. Three RFs have very few mutations (2-3) and only two RFs have substantial numbers of mutations (6 and 11). This also correlated with the number of mutations in the respective H chains. In contrast to RFs in normal and RA these results further suggest the somatic mutation to be of moderate importance in the generation of RF from the peripheral blood of pSS patients.

Detection of immunoglobulin kappa light chain rearrangements by polymerase chain reaction. An improved method for detecting clonal B-cell lymphoproliferative disorders

The clonal determination of B-cell lymphoproliferative disorders by immunoglobulin heavy chain (IgH) rearrangement by polymerase chain reaction (PCR) is widely used. However, few attempts have been made to detect immunoglobulin kappa light chain (Igkappa) gene rearrangement using PCR. We studied 145 cases of B-cell neoplasms, along with 58 atypical and 18 reactive lymphoproliferative disorders, using newly designed degenerate oligoprimers recognizing the framework 3 (FR3kappa) and the joint (Jkappa) regions of the Igkappa gene. PCR products were analyzed on nondenaturing polyacrylamide gel (ndPAGE). Clonal B-cell determination was further investigated using IgH rearrangement and t(11:14) or t(14:18). By combining these methods, we detected either clonality or translocation in 117 of 137 cases (85%) in mature B-cell neoplasms. The additional analysis of Igkappa rearrangement improved sensitivity from 66% to 85%. To investigate whether the Ig gene configuration could be characterized using Igkappa PCR in B-cell neoplasms showing severe breakdown of genomic DNA, 18 selected cases were analyzed. Successful amplification was detected in 72% of the cases using either FR3/2-JH and/or FR3Jkappa oligoprimers. Finally, clonality was detected in 21 of 58 atypical B-cell proliferations, and among them, the atypical marginal cell (54%) and atypical large cell (50%) proliferations showed the highest frequency of clonal immunoglobulin gene products. We concluded that PCR/ndPAGE analysis of Igkappa is a sensitive, rapid, and efficient method for assessing clonality in conjunction with IgH and specific translocation analysis. This approach is particularly useful in the characterization of B-cell lymphoproliferative disorders in archival material with poor preservation of the genomic DNA.

Age-related alterations of somatic hypermutation and CDR3 lengths in human Vkappa4-expressing B lymphocytes

The lower avidity and/or affinity of antibodies generated by an aged immune system could be attributed to two major changes in the antibody repertoire: a shift in germline gene usage and a decrease in the rate of immunoglobulin hypermutation. In an attempt to identify the mechanisms involved in the observed humoral immune deficiency in the elderly, we studied whether differences in the somatic diversity of a particular Vkappa region occurred with ageing. By using the polymerase chain reaction and sequencing, we analysed and compared Vkappa4-Jkappa rearrangements isolated from young (mean age 21 years) and aged (mean age 83 years) healthy adults. Mutations in the Vkappa4 gene compared with the germline sequence were determined as well as the length and structure of the CDR3 sequence. We analysed in detail various mechanisms contributing to CDR3 and Vkappa variability in rearrangements involving the Vkappa4 gene. Our data revealed that, despite strong individual variations, significantly lower levels of somatic mutation were found in the aged group, both for complementarity-determining regions (CDRs) and framework regions (FRs) encoding Vkappa4 sequences. This decrease mostly affected mutations responsible for replacements and thus resulted in a lowered somatic diversification of the encoded Vkappa4 proteins in aged individuals. Moreover, comparison of the CDR3 regions of the Vkappa4-Ckappa cDNA revealed changes in light-chain junctional diversity that correlated with age. Altogether these data suggest an impaired light-chain somatic diversity in connection with human senescence.

A human immunoglobulin lambda locus is similarly well expressed in mice and humans

Transgenic mice carrying a 380-kb region of the human immunoglobulin (Ig) lambda light (L) chain locus in germline configuration were created. The introduced translocus on a yeast artificial chromosome (YAC) accommodates the most proximal Iglambda variable region (V) gene cluster, including 15 Vlambda genes that contribute to >60% of lambda L chains in humans, all Jlambda-Clambda segments, and the 3' enhancer. HuIglambdaYAC mice were bred with animals in which mouse Igkappa production was silenced by gene targeting. In the kappa-/- background, human Iglambda was expressed by approximately 84% of splenic B cells. A striking result was that human Iglambda was also produced at high levels in mice with normal kappa locus. Analysis of bone marrow cells showed that human Iglambda and mouse Igkappa were expressed at similar levels throughout B cell development, suggesting that the Iglambda translocus and the endogenous kappa locus rearrange independently and with equal efficiency at the same developmental stage. This is further supported by the finding that in hybridomas expressing human Iglambda the endogenous L chain loci were in germline configuration. The presence of somatic hypermutation in the human Vlambda genes indicated that the Iglambda-expressing cells function normally. The finding that human lambda genes can be utilized with similar efficiency in mice and humans implies that L chain expression is critically dependent on the configuration of the locus.

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.

Frequent N addition and clonal relatedness among immunoglobulin lambda light chains expressed in rheumatoid arthritis synovia and PBL, and the influence of V lambda gene segment utilization on CDR3 length

BACKGROUND

In rheumatoid arthritis (RA), B-lineage cells in the synovial membrane secrete large amounts of immunoglobulin that contribute to tissue destruction. The CDR3 of an immunoglobulin light chain is formed by rearrangements of VL and JL gene segments. Addition of non-germline-encoded (N) nucleotides at V(D)J joins by the enzyme terminal deoxynucleotidyl transferase (TdT) enhances antibody diversity. TdT was previously thought to be active in B cells only during heavy chain rearrangement, but we and others reported unexpectedly high levels of N addition in kappa light chains. We also found clonally related kappa chains bearing unusually long CDR3 intervals in RA synovium, suggesting oligoclonal expansion of a set of atypical B lymphocytes. In this study, we analyzed lambda light chain expression to determine if N addition occurs throughout immunoglobulin gene rearrangement and to compare CDR3 lengths of lambda and kappa light chains in RA patients and normal individuals.

MATERIALS AND METHODS

Reverse transcription-polymerase chain reaction (RT-PCR) amplification of V lambda III transcripts was performed on RA synovia and peripheral blood lymphocytes (PBL) and normal PBL for which kappa repertoires were previously analyzed. Representative lambda + PCR products were cloned and sequenced.

RESULTS

Analysis of 161 cDNA clones revealed that N addition occurs in lambda light chains of RA patients and normal controls. The lambda light chain repertoires in RA were enriched for long CDR3 intervals. In both RA and controls, CDR3 lengths were strongly influenced by which V lambda gene segment was present in the rearrangement. Five sets of clonally related sequences were found in RA synovia and PBL; one set was found in normal PBL.

CONCLUSIONS

In humans, unlike mice, N addition enhances antibody diversity at all stages of immunoglobulin assembly, and the structural diversity of lambda CDR3 intervals is greater than that of kappa light chains. Clonally related V lambda gene segments in RA support an antigen-driven B-cell response.

VH usage and somatic hypermutation in peripheral blood B cells of patients with rheumatoid arthritis (RA)

The human antibody repertoire has been demonstrated to have a marked V-gene-dependent bias that is conserved between individuals. In RA patients, certain heavy chain V genes (VH) have been found to be preferentially used for encoding autoantibodies. To determine if such preferential use of VH genes in autoantibodies is associated with a general distortion of the V gene repertoire in RA patients, the VH composition of peripheral blood B cells was analysed among four RA patients and four age- and sex-matched healthy controls. Usage of individual VH genes (eight VH3 and three VH4 genes tested by hybridization with a set of gene-specific oligonucleotide probes) was highly biased among RA patients, but no evidence of a distortion in the bias was observed compared with healthy controls. However, the occurrence of somatic mutations in these VH genes (estimated by differential hybridization with motif-specific oligonucleotide probes targeted to CDR and FR of the tested genes, and by DNA sequence analysis) was strikingly different between patients and healthy subjects. The number of VH3 rearrangements that had accumulated somatic mutations and the number of mutations per rearrangement were significantly elevated in three of the four RA patients. A slight but not significant elevation in mutations among rearranged VH4 genes was also observed in these patients. These data suggest that although usage of individual VH genes among peripheral blood B cells is not affected by the disease, the autoimmune process may involve a significant fraction of the B cell compartment.

Sequence of the spacer in the recombination signal sequence affects V(D)J rearrangement frequency and correlates with nonrandom Vkappa usage in vivo

Functional variable (V), diversity (D), and joining (J) gene segments contribute unequally to the primary repertoire. One factor contributing to this nonrandom usage is the relative frequency with which the different gene segments rearrange. Variation from the consensus sequence in the heptamer and nonamer of the recombination signal sequence (RSS) is therefore considered a major factor affecting the relative representation of gene segments in the primary repertoire. In this study, we show that the sequence of the spacer is also a determinant factor contributing to the frequency of rearrangement. Moreover, the effect of the spacer on recombination rates of various human Vkappa gene segments in vitro correlates with their frequency of rearrangement in vivo in pre-B cells and with their representation in the peripheral repertoire.

Myosin-reactive autoantibodies in rheumatic carditis and normal fetus

EBV-transformed B cells from a 20-week human fetal spleen and from blood of patients with poststreptococcal rheumatic carditis were studied. Most antibodies from nine fetal and six patient myosin-reactive B cell clones were multireactive (reacting with cardiac myosin, Streptococcus pyogenes, and rat cardiac myocytes) which supports a role for molecular mimicry in stimulation of these autoantibodies. Sequence analysis revealed that fetal and patient anti-myosin repertoires were composed of unrelated clones with diverse V gene usages. Fetal and patient antibodies had reduced VH CDR3 length on average and reduced light chain N region addition with a low rate of somatic mutation in the variable region genes, characteristics generally associated with fetal B cells but also with some adult B cells. Five of six myosin-reactive patient clones used VH3, whereas only two of nine fetal clones used VH3, suggesting skewing from the average 50-60% VH3 gene usage found in randomly selected adult and fetal antibodies.

Somatic hypermutation in normal and transformed human B cells

In the human, most IgM+IgD+ as well as CD5+ peripheral blood B cells express unmutated V genes and thus can be assigned to a pre-germinal centre (GC) stage of development. The memory B-cell compartment generated in the GC reaction and characterized by cells bearing somatically mutated V-region genes consists not only of class-switched cells, but also of IgM-only B cells and perhaps a subset of IgM+IgD+B cells expressing the CD27 antigen. Comparison of the rearranged V-region genes of human B-cell lymphomas with those of the normal B-cell subsets allows the identification of the progenitor cells of these tumours in terms of their stage of maturation. On this basis, most B-cell non-Hodgkin lymphomas, and in addition Hodgkin and Reed-Sternberg (HRS) cells in Hodgkin's disease (HD), are derived from B cells at a GC or post-GC stage of development. The mutation pattern indicates that the precursors of the tumour clones have been stringently selected for expression of a functional antigen receptor with one notable exception: HRS cells in classical (but not lymphocyte-predominant) HD appear to be derived from "crippled" GC B cells. Sequence analysis of rearranged V genes amplified from single tonsillar GC B cells revealed that the somatic hypermutation process introduces deletions and/or insertions into V-region genes more frequently than indicated by previous investigations. Presumably, this feature of the hypermutation mechanism is often responsible for the generation of heavy chain disease, and also several types of chromosomal translocations of oncogenes into immunoglobulin loci in human B-cell lymphomas.

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.

Analysis of the molecular basis of synovial rheumatoid factors in rheumatoid arthritis

The objective of this study was to better understand the molecular basis of IgM rheumatoid factor in rheumatoid arthritis (RA). We recently generated 10 different monoclonal IgM RF (mRF) molecules isolated from the synovium of a single patient with RA. The heavy (H) and light chain (L) variable region (V) genes of these 10 mRFs were cloned and sequenced. Six mRFs used kappa light chains and 4 mRFs used lambda light chains. Of particular interest, 8 of 10 heavy chains used the JH4 joining region gene, and all five VH4 heavy chains used the DK4 diversity region gene with the JH4. Four of the VH4 clones used the same germline gene, likely representing a novel but closely related germline gene to VH4.18, and may be clonally related because of the extensive homology in their heavy chain sequence. Two VH4 clones shared the same light chain gene, VkappaIIIb kv325 (99% homology) and the same JK4 joining region gene, while three VH4 clones used two different light chain genes, an uncommon Vkappa4 and a Vlambda4 gene, respectively. In this RA patient, there was recurrent utilization of VH4-DK4-21/10-JH4 genes and a recurring association with gene elements Vkappa3 and Vlambda4. Recurring usage of Vkappa3 (kv325) and Vlambda4 (lv418) gene elements may result from a light chain editing process whereby immature autoreactive B cells encountering self-antigen attempt, and often succeed, in altering their specificities through secondary Ig light chain gene rearrangement. Moreover, the oligoclonality of these RFs suggest clonal relatedness secondary to an antigen-driven response.