Analysis of immunoglobulin gamma heavy chain expression in synovial tissue of a patient with rheumatoid arthritis

Accumulation of VH Replacement Products in IgH Genes Derived from Autoimmune Diseases and Anti-Viral Responses in Human

V_H replacement refers to RAG-mediated secondary recombination of the IgH genes, which renews almost the entire V_H gene coding region but retains a short stretch of nucleotides as a V_H replacement footprint at the newly generated V_H–D_H junction. To explore the biological significance of V_H replacement to the antibody repertoire, we developed a Java-based V_H replacement footprint analyzer program and analyzed the distribution of V_H replacement products in 61,851 human IgH gene sequences downloaded from the NCBI database. The initial assignment of the V_H, D_H, and J_H gene segments provided a comprehensive view of the human IgH repertoire. To our interest, the overall frequency of V_H replacement products is 12.1%; the frequencies of V_H replacement products in IgH genes using different V_H germline genes vary significantly. Importantly, the frequencies of V_H replacement products are significantly elevated in IgH genes derived from different autoimmune diseases, including rheumatoid arthritis, systemic lupus erythematosus, and allergic rhinitis, and in IgH genes encoding various autoantibodies or anti-viral antibodies. The identified V_H replacement footprints preferentially encoded charged amino acids to elongate IgH CDR3 regions, which may contribute to their autoreactivities or anti-viral functions. Analyses of the mutation status of the identified V_H replacement products suggested that they had been actively involved in immune responses. These results provide a global view of the distribution of V_H replacement products in human IgH genes, especially in IgH genes derived from autoimmune diseases and anti-viral immune responses.

Monoclonal IgG antibodies generated from joint-derived B cells of RA patients have a strong bias toward citrullinated autoantigen recognition

Synovial IgG-expressing B cells from patients with rheumatoid arthritis show specificity for citrullinated autoantigens.

Antibodies targeting citrullinated proteins (ACPAs [anticitrullinated protein antibodies]) are commonly found in patients with rheumatoid arthritis (RA), strongly associate with distinct HLA-DR alleles, and predict a more aggressive disease course as compared with seronegative patients. Still, many features of these antibodies, including their site of production and the extent of MHC class II–driven T cell help, remain unclarified. To address these questions, we have used a single B cell–based cloning technology to isolate and express immunoglobulin (Ig) genes from joint-derived B cells of active RA patients. We found ∼25% of synovial IgG-expressing B cells to be specific for citrullinated autoantigens in the investigated ACPA⁺ RA patients, whereas such antibodies were not found in ACPA⁻ patients. The citrulline-reactive monoclonal antibodies did not react with the unmodified arginine peptides, yet several reacted with more than one citrullinated antigen. A role for active antigen selection of the citrulline-reactive synovial B cells was supported by the strong bias toward amino acid replacement mutations in ACPA⁺ antibodies and by their loss of reactivity to citrullinated autoantigens when somatic mutations were reverted to the corresponding germline sequences.

V-region gene analysis of locally defined synovial B and plasma cells reveals selected B cell expansion and accumulation of plasma cell clones in rheumatoid arthritis

OBJECTIVE

To elucidate the development of synovial tissue-specific B cell immune responses, the clonality of individual naive B cells, memory B cells, and plasma cells and their organization and histologic localization in the inflamed tissue were investigated in patients with rheumatoid arthritis (RA).

METHODS

B and plasma cells were isolated by laser capture microdissection (LCM) from the synovial tissue of patients with RA. In addition, single naive B cells, memory B cells, and plasma cells were sorted from synovial tissue cell suspensions. RNA was extracted from the cells, and Ig VH genes were amplified, cloned, and sequenced.

RESULTS

Both LCM and single cell sorting analyses showed that naive and memory B cells infiltrated the RA synovial tissue. Comparison of the V-gene repertoire of B and plasma cells suggested that synovial plasma cells were generated, by and large, from locally activated B cells, indicating that a selected population of memory B cells differentiates into large plasma cell clones that then accumulate in the inflamed tissue. Clonally related plasma cells were isolated from separate and distinct localized areas of the tissue, suggesting that the newly generated plasma cells have a high migratory capacity.

CONCLUSION

These results support the idea of a continuous activation of selected B cell clones, and hence a massive accumulation of plasma cells, in RA synovial tissue. As B cells and their secreted antibodies are an important factor in controlling inflammatory processes, patients with RA displaying intensive synovial tissue lymphocytic infiltrations might benefit from B cell depletion therapy. Early treatment will prevent accumulation of pathogenic plasma cells.

B‐Cell Self‐Tolerance in Humans

Two mechanisms account for generation of the human antibody repertoire; V(D)J recombination during the early stages of B-cell development in the bone marrow and somatic mutation of immunoglobulin genes in mature B cells responding to antigen in the periphery. V(D)J recombination produces diversity by random joining of gene segments and somatic mutation by introducing random point mutations. Both are required to attain the degree of antigen receptor diversification that is necessary for immune protection: defects in either mechanism are associated with increased susceptibility to infection. However, the downside of producing enormous random diversity in the antibody repertoire is the generation of autoantibodies. To prevent autoimmunity B cells expressing autoantibodies are regulated by strict mechanisms that either modify the specificity of autoantibodies or the fate of cells expressing such antibodies. Abnormalities in B-cell self-tolerance are associated with a large number of autoimmune diseases, but the precise nature of the defects is less well defined. Here we summarize recent data on the self-reactive B-cell repertoire in healthy humans and in patients with autoimmunity.

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

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

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.

Normal B cells express 51p1-encoded Ig heavy chains that are distinct from those expressed by chronic lymphocytic leukemia B cells

51p1 is an allele of V(H)1-69 that frequently is expressed by chronic lymphocytic leukemia (CLL) B cells with little or no somatic mutation. The rearranged 51p1 genes expressed by CLL B cells have a distinctive use of D segments D3-3/DXP4 and D3-10/DXP'1, a favored use of J(H)6, and a longer third complementarity-determining region than the rearranged Ig genes used by CLL B cells that express V(H)1 genes other than V(H)1-69. We examined the 51p1-encoded Ig expressed by blood B cells of healthy donors. In contrast to the infrequent use of J(H)4 by 51p1-expressing CLL (e.g., 4%), 36% of the rearranged 51p1 sequences from normal blood B cells used J(H)4. Furthermore, the D segment use of the rearranged 51p1 sequences from normal blood B cells was not restricted, but reflected the D segment use of nonselected IgH of normal B cells. Finally, the mean length of the third complementarity-determining region for the 51p1 genes of normal blood B cells was 14.6 +/- 4.3 (SD) codons. This is significantly shorter than that noted for 51p1-expressing CLL B cells (18.8 +/- 3.2; p < 0.0001, n = 51). This study demonstrates that the 51p1-encoded IgH expressed in CLL are not representative of the 51p1-encoded IgH expressed by normal blood B cells, indicating that CLL B cells express IgH that are distinctive from those found in the normal adult blood B cell repertoire.

Immunoglobulin heavy chain variable region gene replacement As a mechanism for receptor revision in rheumatoid arthritis synovial tissue B lymphocytes

Mature B cells can alter their antibody repertoires by several mechanisms, including immunoglobulin heavy chain variable region (V(H)) replacement. This process changes the antigen combining site by replacing a portion of the original V(H)/diversity/heavy chain joining region (V(H)DJ(H)) rearrangement with a corresponding portion of a new V(H) segment. This exchange can involve cryptic heptamer-like sequences embedded in the coding regions of V(H) genes. While studying the B lymphocytes that expand in the synovial tissues of patients with rheumatoid arthritis (RA), clones with V(H)DJ(H) variants that were apparently generated by V(H) replacement were identified with surprising frequency (approximately 8%). Examples of multiple independent V(H) replacement events occurring in distinct progeny clones were also identified. These secondary V(H) rearrangements were documented at both the cDNA and genomic DNA levels and involved several heptamer-like sequences at four distinct locations within V(H) (three sites in framework region 3 and one in complementarity determining region 2). The identification of blunt-ended double-stranded DNA breaks at the embedded heptamers and the demonstration of recombinase activating gene (RAG) expression suggested that these rearrangements could occur in the synovial tissues, presumably in pseudo-germinal centers, and that they could be mediated by RAG in a recognition signal sequence-specific manner. The presence of V(H) mutations in the clones that had undergone replacement indicated that these B cells were immunocompetent and could receive and respond to diversification signals. A relationship between these secondary V(H) gene rearrangements and the autoimmunity characteristic of RA should be considered.

In situ hybridization analysis of immunoglobulin heavy chain variable gene expression with family specific oligonucleotide probes

We have developed an improved in situ hybridization (ISH) technique for the analysis of human immunoglobulin heavy chain variable (V(H)) gene family expression in suspensions of human B lymphocytes. Oligonucleotide probes specific for framework region (FR) consensus germline sequences for each of the seven human V(H) gene families were designed and hybridization conditions were developed to accommodate the greatest degree of V(H) gene variation, maximize the sensitivity of transcript detection, and assure the specificity of the technique. The hybridization parameters were rigorously characterized by Southern hybridization to a panel of 30 V(H) cDNA clones and by ISH to 17 B cell lines expressing characterized V(H) genes. Results obtained with ISH using V(H) gene family and isotype-specific gene probes correlated well with histochemical measures of Ig gene product expression. Profiles of cellular V(H) gene expression were generated for mitogen stimulated peripheral blood B lymphocytes from six normal subjects. When compared with estimates of frequency of V(H) genes in the human germline, the results were consistent with a random pattern of V(H) family utilization.

Similar characteristics of the CDR3 of V(H)1-69/DP-10 rearrangements in normal human peripheral blood and chronic lymphocytic leukaemia B cells

The variable heavy chain (V(H)) gene segment V(H)1-69/DP-10 has been shown to be over-represented in B-cell chronic lymphocytic leukaemia (CLL). Because of certain similar characteristics of their complementarity determining region 3 (CDR3), including preferential utilization of J(H)6 elements and an extended length, it has been suggested that antigenic stimulation might be involved in leukaemogenesis. Utilizing single-cell PCR to amplify and sequence genomic DNA from individual normal human peripheral blood B cells, we have obtained 7/421 productively and 1/69 nonproductively rearranged V(H) genes that used V(H)1-69/DP-10. All productive rearrangements were unmutated, used J(H)6 and had an average CDR3 length similar to that previously found in V(H)1-69/DP-10-expressing CLL cells. These results suggest that CLL may arise from B cells commonly found in the peripheral B-cell repertoire and do not represent expansion of a unique subset of specific antigen-reactive B cells.

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

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