Immunoglobulin variable-region gene usage in systemic autoimmune diseases

Aberrant B Cell Signaling in Autoimmune Diseases

Aberrant B cell signaling plays a critical in role in various systemic and organ-specific autoimmune diseases. This is supported by genetic evidence by many functional studies in B cells from patients or specific animal models and by the observed efficacy of small-molecule inhibitors. In this review, we first discuss key signal transduction pathways downstream of the B cell receptor (BCR) that ensure that autoreactive B cells are removed from the repertoire or functionally silenced. We provide an overview of aberrant BCR signaling that is associated with inappropriate B cell repertoire selection and activation or survival of peripheral B cell populations and plasma cells, finally leading to autoantibody formation. Next to BCR signaling, abnormalities in other signal transduction pathways have been implicated in autoimmune disease. These include reduced activity of several phosphates that are downstream of co-inhibitory receptors on B cells and increased levels of BAFF and APRIL, which support survival of B cells and plasma cells. Importantly, pathogenic synergy of the BCR and Toll-like receptors (TLR), which can be activated by endogenous ligands, such as self-nucleic acids, has been shown to enhance autoimmunity. Finally, we will briefly discuss therapeutic strategies for autoimmune disease based on interfering with signal transduction in B cells.

Salivary free light chains and salivary immunoglobulins as potential non-invasive biomarkers in primary Sjögren's syndrome

BACKGROUND

B cells contribute significantly to the pathogenesis of primary Sjögren's syndrome (pSS). Free light chains (FLCs) are generated during the production of immunoglobulins (Igs) and are surrogates of B cell activity. We hypothesized that salivary FLCs and salivary Igs could represent salivary gland inflammation and therefore, serve as biomarkers in pSS.

METHODS

Patients >18 years old fulfilling the American College of Rheumatology / European League Against Rheumatism (EULAR) 2016 criteria for pSS and age-matched healthy and disease controls (sicca non-pSS, rheumatoid arthritis, systemic lupus erythematosus) were recruited for this cross-sectional study. FLCs in saliva and serum were measured by immunoturbidimetry. Serum and salivary Igs were measured by nephelometry and enzyme-linked immunosorbent assay, respectively. Area under the receiver operator characteristic curve was determined. The factors influencing the serum and salivary FLCs in pSS were determined using backward linear regression.

RESULTS

A total of 78 patients with pSS, 76 healthy controls and 62 disease controls were recruited. Median EULAR SS disease activity index (interquartile range) was 1 (3.75). Serum FLCκ and FLCλ, salivary FLCλ, serum and salivary IgG, salivary IgM was significantly higher in the pSS group compared to the controls. Areas under the curve for salivary FLCλ, serum FLCκ, serum and salivary IgG were 0.75, 0.72, 0.78 and 0.77, respectively. Regression analysis showed that salivary FLCκ, salivary FLCλ and salivary IgG were associated with positive salivary gland histopathology. Use of immunosuppressants and glucocorticoids was associated with lower values of salivary parameters.

CONCLUSION

Salivary FLCλ and salivary IgG were significantly different between pSS and control groups and could be potential non-invasive biomarkers in pSS. These findings should be confirmed in larger longitudinal studies.

Mosaicism in Human Health and Disease

Mosaicism refers to the occurrence of two or more genomes in an individual derived from a single zygote. Germline mosaicism is a mutation that is limited to the gonads and can be transmitted to offspring. Somatic mosaicism is a postzygotic mutation that occurs in the soma, and it may occur at any developmental stage or in adult tissues. Mosaic variation may be classified in six ways: (a) germline or somatic origin, (b) class of DNA mutation (ranging in scale from single base pairs to multiple chromosomes), (c) developmental context, (d) body location(s), (e) functional consequence (including deleterious, neutral, or advantageous), and (f) additional sources of mosaicism, including mitochondrial heteroplasmy, exogenous DNA sources such as vectors, and epigenetic changes such as imprinting and X-chromosome inactivation. Technological advances, including single-cell and other next-generation sequencing, have facilitated improved sensitivity and specificity to detect mosaicism in a variety of biological contexts.

Global Investigation of Immune Repertoire Suggests Kawasaki Disease Has Infectious Cause

BACKGROUND

Kawasaki disease (KD) severely threatens young children's health worldwide. The pathogenic mechanism of KD has not yet been solved, so there is still debate over whether KD is an infectious disease or an autoimmune disease.Methods and Results:To solve this problem, an immune repertoire analysis of KD was conducted. We collected blood cell RNA samples and prepared them into amplicons with iRepertoire kits. The amplicons were sequenced and analyzed with the iRepertoire pipeline. We first identified KD-specific VJ and VDJ forms that had the potential to serve as biomarkers of KD. In addition, the KD-specific VDJ forms were contributed mostly by immunoglobulin G. The D50 value analysis showed that B-cell diversity in KD is decreased, suggesting unique immunoglobulins are produced in KD. Moreover, V, D and J segment usage in IgA, IgG and IgM was consistent with previous KD studies. Further comparison showed no difference in CDR3 peptide length between KD and fever controls (subjects with fever but not diagnosed as KD), indicting KD had B-cell selection phenomenon that has a non-autoimmune pattern. The comparison of amino acid usage of the CDR3 region demonstrated a preference for hydrophilic amino acids in KD.

CONCLUSIONS

The results of D50 value, VDJ usage and CDR3 peptide length analyses suggested the characteristics of infectious disease for KD.

Antibodies to Cyclic Citrullinated Peptides in Patients With Juvenile Idiopathic Arthritis and Patients With Rheumatoid Arthritis: Shared Expression of the Inherently Autoreactive 9G4 Idiotype

OBJECTIVE

Antibodies to cyclic citrullinated peptides (anti-CCP) in rheumatoid arthritis (RA) can express the inherently autoreactive gene V_H 4-34, detected using the rat monoclonal antibody 9G4. Patients with the polyarticular subtype of juvenile idiopathic arthritis (JIA) share some but not all of the features of adult patients with RA. This study was undertaken to compare serologic findings for rheumatoid factor (RF), anti-CCP, and 9G4-expressing anti-CCP in a large JIA cohort with a cohort of adult RA patients.

METHODS

Serum from 88 patients with polyarticular JIA, 29 patients with enthesitis-related arthritis, 38 patients with extended oligoarthritis, 31 adolescent controls, 35 patients with RA, and 30 adult controls were tested for RF, for IgG, IgA, and IgM anti-CCP, and for 9G4-expressing anti-CCP by enzyme-linked immunosorbent assay. Total serum 9G4-positive IgM was also measured.

RESULTS

Of 65 patients with RF-negative polyarticular JIA, 4 (6.2%) were IgG anti-CCP positive. Sera from 20 of 23 patients with RF-positive polyarticular JIA (87.0%), 24 of 35 patients with RA (68.6%), and 1 patient with extended oligoarthritis contained IgG anti-CCP. IgA and IgM anti-CCP levels were lower in the adolescent group (P < 0.01). Levels of 9G4-expressing anti-CCP were higher in patients with RF-positive polyarticular JIA than in those with RF-negative polyarticular JIA (P < 0.0001). Median levels of 9G4-expressing anti-CCP in patients with RF-positive polyarticular JIA and those with RA did not differ. Expression of 9G4 on serum total IgM was greater in patients with RF-positive polyarticular JIA than other adolescent groups (P < 0.01), but similar to adult RF-positive RA.

CONCLUSION

In healthy individuals, 9G4-positive B cells comprise 5-10% of the peripheral blood pool but serum immunoglobulins utilizing V_H 4-34 are disproportionately low. The idiotope recognized by 9G4 was detected on anti-CCP antibodies in >80% of patients with RF-positive polyarticular JIA. V_H 4-34 usage by anti-CCP in both JIA and RA patients suggest elicitation of these autoantibodies through shared pathogenic B cell selection processes.

Aging affects B-cell antigen receptor repertoire diversity in primary and secondary lymphoid tissues

The elderly immune system is characterized by reduced responses to infections and vaccines, and an increase in the incidence of autoimmune diseases and cancer. Age-related deficits in the immune system may be caused by peripheral homeostatic pressures that limit bone marrow B-cell production or migration to the peripheral lymphoid tissues. Studies of peripheral blood B-cell receptor spectratypes have shown that those of the elderly are characterized by reduced diversity, which is correlated with poor health status. In the present study, we performed for the first time high-throughput sequencing of immunoglobulin genes from archived biopsy samples of primary and secondary lymphoid tissues in old (74 ± 7 years old, range 61-89) versus young (24 ± 5 years old, range 18-45) individuals, analyzed repertoire diversities and compared these to results in peripheral blood. We found reduced repertoire diversity in peripheral blood and lymph node repertoires from old people, while in the old spleen samples the diversity was larger than in the young. There were no differences in somatic hypermutation characteristics between age groups. These results support the hypothesis that age-related immune frailty stems from altered B-cell homeostasis leading to narrower memory B-cell repertoires, rather than changes in somatic hypermutation mechanisms.

Expression of the inherently autoreactive idiotope 9G4 on autoantibodies to citrullinated peptides and on rheumatoid factors in patients with early and established rheumatoid arthritis

BACKGROUND

The pre-symptomatic stage of Rheumatoid arthritis (RA) is associated with pro-inflammatory cytokines and autoantibodies. High levels and epitope spread by Rheumatoid factors (RhF) and autoantibodies to citrullinated proteins signify progression towards disease expression. In established RA, the persistence of high autoantibody levels reflects production by both long-lived plasma cells and short-lived plasmablasts. Neither the relative contributions to pathogenesis by autoantibodies from either source, nor the factors responsible for deciding the fate of autoantigen specific 'parent' B-cells, is understood. Phenotypic markers identifying subsets of autoreactive B-cells are therefore of interest in understanding the origin and perpetuation of the autoimmune response in RA. One such phenotypic marker is the rat monoclonal antibody, 9G4, which recognises an idiotope on immunoglobuins derived from the inherently autoreactive VH-gene, VH4-34. We therefore investigated whether the 9G4 idiotope was expressed on autoantibodies in patients with RA.

METHODOLOGY/PRINCIPAL FINDINGS

Sera from 19 patients with established RA and those with <1year history of untreated polyarthritis either resolving into RA (n = 42) or non-RA diagnosis (n = 31) were included. Autoantibodies to cyclic citrullinated peptides (CCP), RhF and co-expression of the 9G4 idiotope were measured by ELISA. 9G4 recognised a population of anti-CCP antibodies in the majority of sera from patients with established disease and also in samples from patients with early disaese. 9G4+RhF levels were generally lower and not associated with positivity for, or levels of 9G4+CCP.

CONCLUSIONS/SIGNIFICANCE

The persistence of 9G4+ immunoglobulins, of any isotype, in serum is rare. We describe here the novel finding of 9G4 expression on anti-CCP antibodies in patients from the earliest symptoms of RA through to established disease. Our results suggest that 9G4 expression on anti-CCP autoantibodies was not due to polyclonal expansion of VH4-34-encoded immunoglobulins. These studies may therefore provide a new focus for investigation into the evolution of the autoimmune response in RA patients.

Immunopathogenic mechanisms of systemic autoimmune disease

Systemic lupus erythematosus, Sjögren's syndrome, and dermatomyositis are systemic autoimmune diseases that develop after environmental triggering of genetically susceptible individuals. The precise cellular and molecular mechanisms leading to autoimmune disease, and what factors determine which organs are involved, remain poorly understood. Recent insights into genetic susceptibility now make obvious that environmental triggers often act via cellular pathways containing disease-associated polymorphisms. In the breaking of tolerance, the initiating tissue--including dendritic cells--provides a decisive microenvironment that affects immune-cell differentiation, leading to activation of adaptive immunity. Type 1 interferon produced by innate immune cells has a central role in systemic autoimmunity and activates B cells and T cells. In turn, B-cell-derived autoantibodies stimulate dendritic cells to produce type 1 interferon; thus, a positive feedforward loop is formed that includes both the innate and adaptive systems. New treatments could simultaneously and specifically target several such vital pathways in autoimmunity.

Mechanisms of B cell autoimmunity in SLE

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that is known to be associated with polyclonal B-cell hyperreactivity. The underlying causes of the diffuse B-cell over-reactivity are unclear, but potential candidates include (a) intrinsic hyper-reactivity leading to polyclonal B-cell activation with disturbed activation thresholds and ineffective negative selection; (b) lack of immunoregulatory functions; (c) secondary effects of an overactive inflammatory environment, such as overactive germinal center and ectopic follicular activity; and/or (d) disturbed cytokine production by non-B immune cells. These mechanisms are not mutually exclusive and may operate to varying extents and at varying times in SLE. Phenotypic and molecular studies as well as the results of recent clinical trials have begun to provide new insights to address these possibilities. Of importance, new information has made it possible to distinguish between the contribution played by abnormalities in central checkpoints that could lead to a pre-immune repertoire enriched in autoreactive B cells, on the one hand, and the possibility that autoimmunity arises in the periphery from somatic hypermutation and abnormal selection during T cell-dependent B-cell responses on the other. There is an intriguing possibility that apoptotic material bound to the surface of follicular dendritic cells positively selects autoreactive B cells that arise from non-autoreactive B-cell precursors as a result of somatic hypermutation and thereby promotes the peripheral emergence of autoimmunity.

Abnormalities of B cell subsets in patients with systemic lupus erythematosus

The prototypic autoimmune disease, SLE, is known to be associated with polyclonal B cell hyperreactivity. Developing an understanding of the complex nature of human B cell differentiation, largely through the application of multiparameter flow cytometry to an analysis of circulating B cells has permitted an assessment of whether specific stages of B cell maturation are affected by the tendency for polyclonal B cell activation. Moreover, the analysis of perturbations of the specific stages of B cell maturation has generated new information on whether abnormalities in B cell differentiation are primarily involved in autoimmune disease immunopathology or, rather, are secondary to the inflammatory environment characteristic of subjects with this autoimmune disease. Multivariant analysis has begun to document abnormalities in B cell maturation that are primarily associated with lupus, or, alternatively related to disease duration, disease activity and concomitant medication. Together, these analyses have provided new insights on the role of B cell over-reactivity in SLE.

Individual variation in the germline Ig gene repertoire inferred from variable region gene rearrangements

Individual variation in the Ig germline gene repertoire leads to individual differences in the combinatorial diversity of the Ab repertoire, but the study of such variation has been problematic. The application of high-throughput DNA sequencing to the study of rearranged Ig genes now makes this possible. The sequencing of thousands of VDJ rearrangements from an individual, either from genomic DNA or expressed mRNA, should allow their germline IGHV, IGHD, and IGHJ repertoires to be inferred. In addition, where previously mere glimpses of diversity could be gained from sequencing studies, new large data sets should allow the rearrangement frequency of different genes and alleles to be seen with clarity. We analyzed the DNA of 108,210 human IgH chain rearrangements from 12 individuals and determined their individual IGH genotypes. The number of reportedly functional IGHV genes and allelic variants ranged from 45 to 60, principally because of variable levels of gene heterozygosity, and included 14 previously unreported IGHV polymorphisms. New polymorphisms of the IGHD3-16 and IGHJ6 genes were also seen. At heterozygous loci, remarkably different rearrangement frequencies were seen for the various IGHV alleles, and these frequencies were consistent between individuals. The specific alleles that make up an individual's Ig genotype may therefore be critical in shaping the combinatorial repertoire. The extent of genotypic variation between individuals is highlighted by an individual with aplastic anemia who appears to lack six contiguous IGHD genes on both chromosomes. These deletions significantly alter the potential expressed IGH repertoire, and possibly immune function, in this individual.

Overcoming self-tolerance to tumour cells

Over the past decade, immunotherapy has emerged as a promising alternative form of cancer treatment with the potential to eradicate tumour metastasis. However, its curative potential is in general limited by peripheral tolerance mechanisms and the elimination of self-reactive T cells via thymic negative selection. Unlike infectious challenges, tumour cells arise endogenously, and therefore the majority of tumour antigens are recognized as self. Under appropriate conditions, however, tumour reacting T cells can be activated through a mechanism of molecular mimicry, which involves the recognition of cross reactive foreign antigens mimicking tumour antigens. Moreover, dendritic cells can be reprogrammed by RNA interference to present self-antigens and activate anti-tumour T cells. This review highlights some of the strategies used to break self-tolerance against solid and blood tumour cells. Also, the possibility of reprogramming DC and/or lymphocyte functions using small interfering RNAi (siRNA) is discussed.

Autoantibodies against C1q in systemic lupus erythematosus are antigen-driven

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

Transmembrane BAFF from rheumatoid synoviocytes requires interleukin-6 to induce the expression of recombination-activating gene in B lymphocytes

OBJECTIVE

B cells that accumulate in the synovial tissue of rheumatoid arthritis (RA) patients revise their receptors due to coordinate expression of recombination-activating gene 1 (RAG-1) and RAG-2 genes. The aim of this study was to determine the mechanisms that control this re-expression.

METHODS

B cells from healthy control subjects were cocultured with fibroblast-like synoviocytes (FLS) from patients with RA and osteoarthritis (OA). Re-expression of RAG messenger RNA (mRNA) and proteins was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and indirect immunofluorescence. Activity of RAG enzymes was evaluated by flow cytometry to measure variations in immunoglobulin kappa and lambda light chain expression and by ligation-mediated-PCR to assess specific DNA breaks. Blocking antibodies, short hairpin RNA, and recombinant cytokine were used to identify the molecules involved in RAG re-expression.

RESULTS

RA FLS, but not OA FLS, induced B cells to re-express RAG mRNA and proteins. Enzymes were functional, since the kappa-to-lambda ratios decreased and specific DNA breaks were detectable after coculture with RA FLS. Transmembrane BAFF provided the first signal of RAG re-expression, since its down-regulation in RA FLS prevented RAG gene transcription in B cells. The failure of transmembrane BAFF from OA FLS to induce RAG suggests that a second signal was provided by RA FLS. Interleukin-6 (IL-6) is a candidate, since blockade of its receptors precluded transcription of RAG genes by RA FLS. Unless supplemented with IL-6, OA FLS were unable to induce RAG gene expression in normal B cells.

CONCLUSION

Two independent signals are required for the induction of RAG gene expression in B cells that infiltrate the synovium of patients with RA.

Modulation of molecular imprints in the antigen-experienced B cell repertoire by rituximab

OBJECTIVE

Transient B cell depletion by rituximab has recently gained more importance in the treatment of rheumatic disorders. Nevertheless, little is known about the reemerging B cells. We analyzed dynamic changes in the repopulating B cells, particularly the postswitch B cells, and studied the mutational patterns of Ig genes in antigen-experienced B cells.

METHODS

Five patients with active rheumatoid arthritis (RA) were treated with rituximab. In 3 patients, B cell receptor (BCR) gene analysis was performed before treatment and during B cell recovery using genomic DNA. In 2 patients, B cell subsets were studied during the early recovery phase using single-cell technology. For comparison, immunophenotyping of B cell subsets was performed.

RESULTS

Early B cell recovery was marked by a relatively expanded population of highly mutated B cells, which were correlated with B cells with a plasmablast phenotype on comparative immunophenotyping. Analysis of the mutational pattern in these cells revealed increased RGYW/WRCY (where R = A/G, Y = C/T, and W = A/T) hotspot targeting (44% before rituximab versus 59% after) and elevated ratios of replacement to silent mutations within the complementarity-determining regions in Ig genes (1.87 before rituximab versus 2.67 after; P < or = 0.0025).

CONCLUSION

Our findings show that rituximab leads to qualitative changes in the imprints of highly mutated, antigen-experienced BCRs, representing the result of selection, whereas molecular processes such as Ig V rearrangements are not affected by this treatment.

Autoreactive IgG memory antibodies in patients with systemic lupus erythematosus arise from nonreactive and polyreactive precursors

Persistent autoantibody production in patients with systemic lupus erythematosus (SLE) suggests the existence of autoreactive humoral memory, but the frequency of self-reactive memory B cells in SLE has not been determined. Here, we report on the reactivity of 200 monoclonal antibodies from single IgG+ memory B cells of four SLE patients. The overall frequency of polyreactive and HEp-2 self-reactive antibodies in this compartment was similar to controls. We found 15% of IgG memory B cell antibodies highly reactive and specific for SLE-associated extractable nuclear antigens (ENA) Ro52 and La in one patient with serum autoantibody titers of the same specificity but not in the other three patients or healthy individuals. The germ-line forms of the ENA antibodies were non-self-reactive or polyreactive with low binding to Ro52, supporting the idea that somatic mutations contributed to autoantibody specificity and reactivity. Heterogeneity in the frequency of memory B cells expressing SLE-associated autoantibodies suggests that this variable may be important in the outcome of therapies that ablate this compartment.

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

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

iHMMune-align: hidden Markov model-based alignment and identification of germline genes in rearranged immunoglobulin gene sequences

MOTIVATION

Immunoglobulin heavy chain (IGH) genes in mature B lymphocytes are the result of recombination of IGHV, IGHD and IGHJ germline genes, followed by somatic mutation. The correct identification of the germline genes that make up a variable VH domain is essential to our understanding of the process of antibody diversity generation as well as to clinical investigations of some leukaemias and lymphomas.

RESULTS

We have developed iHMMune-align, an alignment program that uses a hidden Markov model (HMM) to model the processes involved in human IGH gene rearrangement and maturation. The performance of iHMMune-align was compared to that of other immunoglobulin gene alignment utilities using both clonally related and randomly selected IGH sequences. This evaluation suggests that iHMMune-align provides a more accurate identification of component germline genes than other currently available IGH gene characterization programs.

AVAILABILITY

iHMMune-align cross-platform Java executable and web interface are freely available to academic users and can be accessed at http://www.emi.unsw.edu.au/~ihmmune/.

Focused antibody response in plasma cell-infiltrated non-medullary (NOS) breast cancers

Breast tumors with prominent plasma cell (PC) infiltrates often have a more favorable natural course that may plausibly be mediated by anti-tumor activity of the elicited antibodies. These breast tumor-associated PCs are typically IgG dominant in contrast to normal breast PCs, which are mainly IgA. It is our hypothesis that this PC infiltration represents a host immune response that is driven by one or more tumor antigens. Previously, we and others showed that medullary carcinoma (MC) had a focused repertoire and features suggestive of a protein antigen driven response. Infrequently, non-MC, not otherwise specified (NOS) breast tumors may exhibit heavy PC infiltrations, also of IgG isotype. In this first characterization of this favorable prognosis NOS subgroup, IgG heavy chain (Hc) and light chain (Lc) variable (V) regions from three PC-infiltrated NOS tumors were randomly cloned and sequenced. We found biased (V) gene usage by the infiltrating PCs and somatic hypermutation in the rearranged Ig Hc and Lc V regions that were compatible with antigenic selection of the progenitor B cells. The antibody response of NOS infiltrated breast cancer is repertoire-focused, with 13-68% of isolates being clonally reiterated in the samples. Each NOS patient used distinct Hc V-D-J and Lc V-J rearrangements, with her own immune response "footprint," but the overall pattern of gene usage followed that typical of exogenous antigen-induced immune responses. The data are consistent with the hypothesis that PC infiltrates infrequently arising in NOS tumors, as previously inferred for MC, are in response to one or more breast cancer-associated protein tumor antigens.

Pathophysiology of Sjögren's syndrome

The term Sjögren's syndrome refers to keratoconjunctivitis sicca and xerostomia due to lymphocytic infiltrates of lachrymal and salivary glands. The current used criteria for diagnosis of primary Sjögren's syndrome is the American-European consensus. Primary Sjögren's syndrome is an autoimmune disorder characterized by lymphocytic infiltrates and destruction of the salivary and lachrymal glands and systemic production of autoantibodies to the ribonucleoprotein particles SS-A/Ro and SS-B/La. The infiltrating cells (T- and B-cells, dendritic cells) interfere with glandular function at several points: destruction of glandular elements by cell-mediated mechanisms; secretion of cytokines that activate pathways bearing the signature of type 1 and 2 interferons; production of autoantibodies that interfere with muscarinic receptors; and secretion of metalloproteinases (MMPs) that interfere with the interaction of the glandular cell with its extracellular matrix, which is necessary for efficient glandular function. As the process progresses, the mucosal surfaces become sites of chronic inflammation and the start of a vicious circle. Despite extensive study of the underlying cause of Sjögren's syndrome, the pathogenesis remains obscure. In broad terms, pathogenesis is multifactorial; environmental factors are thought to trigger inflammation in individuals with a genetic predisposition to the disorder.

Persistent expression of autoantibodies in SLE patients in remission

A majority of the antibodies expressed by nascent B cells in healthy humans are self-reactive, but most of these antibodies are removed from the repertoire during B cell development. In contrast, untreated systemic lupus erythematosus (SLE) patients fail to remove many of the self-reactive and polyreactive antibodies from the naive repertoire. Here, we report that SLE patients in clinical remission continue to produce elevated numbers of self-reactive and polyreactive antibodies in the mature naive B cell compartment, but the number of B cells expressing these antibodies is lower than in patients with active disease. Our finding that abnormal levels of self-reactive mature naive B cells persist in the majority of patients in clinical remission suggests that early checkpoint abnormalities are an integral feature of SLE.

Reconsidering the human immunoglobulin heavy-chain locus:

We have used a bioinformatics approach to evaluate the completeness and functionality of the reported human immunoglobulin heavy-chain IGHD gene repertoire. Using the hidden Markov-model-based iHMMune-align program, 1,080 relatively unmutated heavy-chain sequences were aligned against the reported repertoire. These alignments were compared with alignments to 1,639 more highly mutated sequences. Comparisons of the frequencies of gene utilization in the two databases, and analysis of features of aligned IGHD gene segments, including their length, the frequency with which they appear to mutate, and the frequency with which specific mutations were seen, were used to determine the reliability of alignments to the less commonly seen IGHD genes. Analysis demonstrates that IGHD4-23 and IGHD5-24, which have been reported to be open reading frames of uncertain functionality, are represented in the expressed gene repertoire; however, the functionality of IGHD6-25 must be questioned. Sequence similarities make the unequivocal identification of members of the IGHD1 gene family problematic, although all genes except IGHD1-14*01 appear to be functional. On the other hand, reported allelic variants of IGHD2-2 and of the IGHD3 gene family appear to be nonfunctional, very rare, or nonexistent. Analysis also suggests that the reported repertoire is relatively complete, although one new putative polymorphism (IGHD3-10*p03) was identified. This study therefore confirms a surprising lack of diversity in the available IGHD gene repertoire, and restriction of the germline sequence databases to the functional set described here will substantially improve the accuracy of IGHD gene alignments and therefore the accuracy of analysis of the V-D-J junction.

Rituximab anti-B-cell therapy in systemic lupus erythematosus: pointing to the future

PURPOSE OF REVIEW

To discuss the clinical effects and the immunologic consequences of transient B-cell depletion using the anti-CD20 monoclonal antibody rituximab in systemic lupus erythematosus.

RECENT FINDINGS

A total of 100 rituximab-treated patients with severe disease, refractory to major immunosuppressive treatment, have been reported so far. Within a median follow-up period of 12 months rituximab was well tolerated, which is compatible with the experience accumulated from its use in more than 500 000 lymphoma patients. About 80% of patients achieved marked and rapid reductions in global disease activity. Because of the clinical heterogeneity, dosing differences, and concomitant treatments, including cyclophosphamide in 35% of patients, a proper evaluation of the clinical efficacy or rituximab is difficult. Variable degrees of clinical benefit have been reported for all clinical systemic lupus erythematosus manifestations, including active proliferative nephritis. Whereas 4-weekly infusions of 375 mg/m of rituximab result in complete B-cell depletion lasting most often from 3 to 8 months, a prolonged depletion does not always correlate with a more favorable clinical response. Total immunoglobulin levels and protective antibodies are preserved, but anti-dsDNA antibody titers decrease, often independently of the clinical response.

SUMMARY

The findings reviewed point to a growing optimism for targeting B cells in the treatment of systemic lupus erythematosus; therefore double-blind studies comparing rituximab with existing immunosuppressive therapies are needed. Moreover, careful assessments of the effects of transient B-cell depletion on distinct autoimmune pathogenetic processes will enable optimization of therapeutic single or combined therapeutic schemes.

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

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

Remission of proliferative lupus nephritis following B cell depletion therapy is preceded by down-regulation of the T cell costimulatory molecule CD40 ligand: an open-label trial

OBJECTIVE

Autoreactive B cells play a key role in tissue injury in systemic autoimmune disease, and therefore a treatment resulting in B cell depletion could have benefit. This open-label study was undertaken to evaluate the efficacy of the anti-CD20 monoclonal antibody rituximab in the treatment of lupus nephritis.

METHODS

Lupus patients with active proliferative nephritis (4 with focal disease and 6 with diffuse disease) received rituximab (4 weekly infusions of 375 mg/m(2)) combined with oral prednisolone. Clinical, laboratory, and immunologic responses, including peripheral lymphocyte subsets measured by flow cytometry, were prospectively assessed at monthly intervals for 12 months. Complete remission of nephritis was defined as normal serum creatinine and albumin levels, inactive urine sediment, and 24-hour urinary protein <500 mg. Partial remission was defined as >50% improvement in all renal parameters that were abnormal at baseline.

RESULTS

B cell depletion lasted from 1 month to 7 months and was well tolerated. Partial remission was achieved in 8 of 10 patients within a median of 2 months (range 1-4 months); in 5 of them, complete remission was subsequently established (at a median of 3 months from baseline), and it was sustained at 12 months in 4. As early as 1 month from baseline, the expression of the costimulatory molecule CD40 ligand on CD4+ T cells was decreased by 4-fold, and it was almost blocked when partial remission was clinically evident. The expression of T cell activation markers CD69 and HLA-DR was significantly decreased at time points when partial remission was observed, and was further decreased during complete remission. In contrast, in patients who did not exhibit a response or when relapse was detected in patients in whom an initial remission had been achieved, such decreases were not prominent. Serum concentrations of double-stranded DNA autoantibodies were decreased in all patients, regardless of clinical outcome.

CONCLUSION

Following B cell depletion, clinical remission of lupus nephritis is associated with a decrease in T helper cell activation, suggesting an additional role for B cells, independent of autoantibody production, in promoting disease. A controlled trial to confirm these promising clinical results is warranted.

Defective B cell tolerance checkpoints in systemic lupus erythematosus

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

Recombination activating genes (RAG) induce secondary Ig gene rearrangement in and subsequent apoptosis of human peripheral blood circulating B lymphocytes

Recombination activating gene (RAG) re-expression and secondary Ig gene rearrangement in mature B lymphocytes have been reported. Here, we have studied RAG expression of peripheral blood B lymphocytes in humans. Normal B cells did not express RAG1 and RAG2 spontaneously. More than a half of circulating B cells expressed RAG proteins, when activated with Staphylococcus aureus Cowan I (SAC) + IL-2. DNA binding activity of the RAG complex has been verified by a gel shift assay employing the recombination signal sequence (RSS). Secondary Ig light chain rearrangement in the RAG-expressing B cells was confirmed by linker-mediated (LM)-PCR. Highly purified surface kappa+ B cells activated by SAC + IL-2 became RAG+, and thereafter they started to express lambda chain mRNA. 2 colour immunofluorescence analysis disclosed that a part of the RAG+ cells derived from the purified kappa+ B cells activated by SAC + IL-2 turned to lambda+ phenotype in vitro. Similarly, apoptosis induction was observed in a part of the RAG+ B cells. Our study suggests that a majority of peripheral blood B cells re-expresses RAG and the RAG+ B lymphocytes could be eliminated from the B cell repertoire either by changing Ag receptor specificity due to secondary rearrangement or by apoptosis induction. Thus, RAG expression of mature B cells in peripheral blood would contribute to not only receptor revision for further diversification of B cell repertoire but in some cases (or in some B cell subsets) to prevention or induction of autoAb responses at this differentiation stage in humans.

Recent advances in understanding molecular mechanisms in the pathogenesis and antibody profile of Sjögren's syndrome

Sjögren's syndrome is a chronic autoimmune and rheumatic disorder of the mucous membranes caused by a lack of proper exocrine secretions, with prominent sicca complaints. The molecular mechanisms of the pathogenesis are virtually unknown, although progress has been made with regard to chemokines, B cell activating factor, and apoptosis. A large number of autoantibodies have been reported in Sjögren's syndrome, some of which relate to impairment of glandular function. Sjögren's syndrome is a female-dominant disease with a late age of onset; most patients contract the disease at the age of 40 to 50 years. Lately, attention has been drawn to the effects of adrenopause in Sjögren's syndrome and on dehydroepiandrosterone and its intracrine metabolism in target tissues. This can influence the maintenance and remodeling of exocrine glands and may explain, in part, another important disease symptom--fatigue.

Abnormal germinal center reactions in systemic lupus erythematosus demonstrated by blockade of CD154-CD40 interactions

To determine the role of CD154-CD40 interactions in the B cell overactivity exhibited by patients with active systemic lupus erythematosus (SLE), CD19+ peripheral B cells were examined before and after treatment with humanized anti-CD154 mAb (BG9588, 5c8). Before treatment, SLE patients manifested activated B cells that expressed CD154, CD69, CD38, CD5, and CD27. Cells expressing CD38, CD5, or CD27 disappeared from the periphery during treatment with anti-CD154 mAb, and cells expressing CD69 and CD154 disappeared from the periphery during the post-treatment period. Before treatment, active-SLE patients had circulating CD38 (bright) Ig-secreting cells that were not found in normal individuals. Disappearance of this plasma cell subset during treatment was associated with decreases in anti-double-stranded DNA (anti-dsDNA) Ab levels, proteinuria, and SLE disease activity index. Consistent with this finding, peripheral B cells cultured in vitro spontaneously proliferated and secreted Ig in a manner that was inhibited by anti-CD154 mAb. Finally, the CD38(+/++)IgD(+), CD38(+++), and CD38(+)IgD(-) B cell subsets present in the peripheral blood also disappeared following treatment with humanized anti-CD154. Together, these results indicate that patients with active lupus nephritis exhibit abnormalities in the peripheral B cell compartment that are consistent with intensive germinal center activity, are driven via CD154-CD40 interactions, and may reflect or contribute to the propensity of these patients to produce autoantibodies.

B cell abnormalities in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic, multisystem autoimmune disease characterized by the differentiation of short- and long-lived immunoglobulin secreting plasma cells that secrete pathogenic autoantibodies. Ectopic germinal centers and plasma cells secreting autoantibodies have been observed in lupus nephritis kidneys. Candidate genetic susceptibility loci for SLE include genes that affect differentiation and survival of plasma cells, such as those that influence activation, proliferation, cytokine and chemokine secretion/responsiveness, and apoptosis of the T and B cells that are involved in humoral immunity generated in germinal centers, as well as genes that are involved in presentation and clearance of apoptotic material and autoantigens by antigen presenting cells and other phagocytes. Emerging data have demonstrated that B lymphocytes are active participants in humoral immune responses that lead to T-dependent and T-independent differentiation of immunoglobulin-secreting plasma cells by homotypic CD154–CD40 interactions as well as continued stimulation by B cell activating factor through B cell maturation antigen, B cell activating factor receptor and transmembrane activater.

Immunoglobulin gene rearrangement, repertoire diversity, and the allergic response

The immunoglobulin repertoire arises as a consequence of combinatorial diversity, junctional diversity, and the process of somatic point mutation. Each of these processes involves biases that limit and shape the available immunoglobulin repertoire. The expressed repertoire is further shaped by selection, to the extent that biased gene usage can become apparent in many disease states. The study of rearranged immunoglobulin genes therefore may not only provide insights into the molecular processes involved in the generation of antibody diversity but also inform us of pathogenic processes and perhaps identify particular lymphocyte clones as therapeutic targets. Partly as a consequence of the low numbers of circulating IgE-committed B-cells, studies of rearranged IgE genes in allergic individuals have commenced relatively recently. In this review, recent advances in our understanding of the processes of immunoglobulin gene rearrangement and somatic point mutation are described, and biases inherent to these processes are discussed. The evidence that some diseases may be associated with particular gene rearrangements is then considered, with a particular focus on allergic disease. Reviewed data suggest that an important contribution to the IgE response may come from cells that use relatively rare heavy chain V (V(H)) segment genes, which display little somatic point mutation. Some IgE antibodies also seem to display polyreactive binding. In other contexts, these 3 characteristics have been associated with antibodies of the B-1 B-cell subset, and the possibility that B-1 B-cells contribute to the allergic response is therefore considered.

Systematic analysis of sequences of anti-DNA antibodies--relevance to theories of origin and pathogenicity

Sequence analysis of anti-DNA antibodies is important in determining the molecular features which distinguish potentially pathogenic antibodies from those which are less likely to be pathogenic. Previous analysis of murine anti-DNA antibody sequences suggested that particular murine immunoglobulin genes are used preferentially to encode such antibodies and that somatic mutations to arginine, asparagine and lysine may be important in the creation of DNA binding sites. In this paper, a systematic analysis of published human anti-DNA sequences shows no strong evidence for preferential usage of particular human V(H) or V(L) genes in anti-DNA antibodies. Somatic mutations in IgG and IgA antibodies are clustered in the complementarity determining regions (CDRs) due to the effect of antigen drive. This process contributes to an excess of arginine, asparagine and lysine residues in these CDRs, some of which are likely to play an important role in binding to DNA. Computer modeling and in-vitro expression experiments are likely to help define the roles played by these residues in antigen binding and pathogenicity more clearly.

Abnormalities of B cell phenotype, immunoglobulin gene expression and the emergence of autoimmunity in Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is an autoimmune disorder characterized by specific pathologic features and the production of typical autoantibodies. In addition, characteristic changes in the distribution of peripheral B cell subsets and differences in use of immunoglobulin variable-region genes are also features of pSS. Comparison of B cells from the blood and parotid gland of patients with pSS with those of normal donors suggests that there is a depletion of memory B cells from the peripheral blood and an accumulation or retention of these antigen-experienced B cells in the parotids. Because disordered selection leads to considerable differences in the B cell repertoire in these patients, the delineation of its nature should provide important further clues to the pathogenesis of this autoimmune inflammatory disorder.