The antibody repertoire of early human B cells. III. Expression of cross-reactive idiotopes characteristic of certain rheumatoid factors and identifying V kappa III, VHI, and VHIII gene family products

Human B-cell ontogeny in humanized NOD/SCID γc(null) mice generates a diverse yet auto/poly- and HIV-1-reactive antibody repertoire

Characterization of the human antibody (Ab) repertoire in mouse models of the human immune system is essential to establish their relevance in translational studies. Single human B-cells were sorted from bone marrow and periphery of humanized NOD/SCID γc^null mice at 8–10 months post-engraftment with human cord blood-derived CD34⁺ stem cells. Human immunoglobulin variable heavy (V_H) and kappa (V_κ) genes were amplified, cognate V_H-V_κ gene-pairs assembled as single-chain variable fragment-Fc antibodies (scFvFcs) and functional studies performed. Although overall distribution of V_H genes approximated the normal human Ab repertoire, analysis of the V_H-third complementarity determining regions (H-CDR3) in the mature B-cell subset demonstrated an increase in length and positive charges suggesting autoimmune characteristics. Additionally, >70% of V_κ sequences utilized V_κ4-1, a germline gene associated with autoimmunity. The mature B-cell subset-derived scFvFcs displayed the highest frequency of autoreactivity and polyspecificity, suggesting defects in checkpoint control mechanisms. Furthermore, these scFvFcs demonstrated binding to recombinant HIV envelope corroborating previous observations of poly/autoreactivity in anti-HIVgp140 antibodies. These data lend support to the hypothesis that anti-HIV BnAbs may be derived from auto/polyspecific Abs that escaped immune elimination and that the hNSG mouse could provide a new experimental platform for studying the origin of anti-HIV neutralizing Ab responses.

Monozygotic rheumatoid arthritis twin pairs express similar levels of conserved immunoglobulin V gene in polyclonal rheumatoid factors irrespective of disease status

The degree of polyclonal RF heterogeneity was assessed in diseased and non-diseased twins with rheumatoid arthritis (RA). The distribution of variable region determinants encoded by a set of immunoglobulin germline, or minimally mutated germline, genes within IgM RF, IgG RF and IgA RF isotypes was determined by ELISA using specific mouse monoclonal antibodies (MoAb) in fractionated plasma from 12 members of six monozygotic twin pairs with RA. The results reveal that at least 40% (range approximately 18-87%) of IgM RF are encoded by a small set of approximately 10 genes from the VH1, 3 and 4 families. Furthermore, a significant proportion of IgG RF and IgA RF (approximately 30%) are also encoded by these same genes. Comparison with RF-negative fractions of immunoglobulins showed that the examined variable region determinants were overrepresented in the RF fractions. The level of expression of the variable region determinants in RF were generally similar within twins but different between unrelated twin pairs irrespective of disease status. The variability of VH gene usage between unrelated individuals suggests that the level of expression and regulation of the variable region determinants may be genetically regulated or influenced by common environmental factors.

Structural characteristics of four human hybridoma antibodies specific for the pp65 protein of the human cytomegalovirus and their relationship to human rheumatoid factors

Four human hybridoma antibodies directed against the human cytomegalovirus (CMV) were characterized with respect to their immunoglobulin gene usage and expression of rheumatoid factor (RF) associated idiotypes and variable region epitopes. The aims of these experiments were: (1) to characterize the immunoglobulin gene usage of four antibodies directed against a single protein of a human pathogen; and (2) to examine how this humoral response may be linked to the production of RFs, autoantibodies found in the majority of patients with rheumatoid arthritis (RA). All four anti-CMV antibodies were of the gamma heavy chain isotype and were specific for the immunodominant 65 kDa viral matrix phosphoprotein (pp65). The four anti-pp65 antibodies expressed different light (L) and heavy (H) chain variable region gene combinations. These were: VkIII/VH3, V lambda 1/VH3, V lambda 1/VH4 and V lambda 3/VH3, respectively for the HCV-2, HCV-3, HCV-63 and HCV-65 hybridoma cell lines. Although none had RF activity, each of these antibodies expressed a unique set of RF-associated determinants, implying different three-dimensional configurations of the variable regions of these antibodies. The HCV-2 antibody, however, had the most extensive similarities to human RFs since it not only expressed the greatest number of RF-associated determinants but also had a protein sequence that was very homologous to RFs of the "Po" idiotypic family. Furthermore, predicted germline gene usage by anti-CMV antibodies and RFs suggest that some are encoded by identical or similar genes and that the different specificities are achieved by somatic mutations in the L and H chain complementarity determining regions (CDRs) and genetic diversity in the H chain CDR3.

Heavy-chain directed B-cell maturation: continuous clonal selection beginning at the pre-B cell stage

A number of laboratories have demonstrated a biased representation of certain V-region segments in the primary B-cell repertoire. This may reflect clonal selection at the pre-B cell stage of differentiation. Here, Robert Schwartz and David Stollar suggest that pre-B cells undergo positive selection directed by the presence of surface heavy chain with low affinity to autoantigen. This mechanism would account for the anti-self property of the pre-immune B-cell repertoire.

Immunoglobulin VH3 gene products: natural ligands for HIV gp120

Infection with human immunodeficiency virus-type 1 (HIV-1) depletes T cells expressing CD4 and B cells expressing immunoglobulin (Ig) VH3 gene products. A subpopulation of normal B cells from non-HIV-infected individuals was shown to bind to HIV gp120 by means of membrane Ig; most of these B cells expressed VH3 family Ig. Serum VH3 IgM from uninfected individuals also avidly bound gp120. Finally, gp120 selectively induced Ig secretion by VH3 B cells, indicating that the binding of gp120 functionally activated these cells. These results indicate that naturally occurring VH3 Ig is a second ligand for gp120 and a candidate superantigen for VH3 B cells.

Restricted immunoglobulin variable region gene usage by hybridoma rheumatoid factors from patients with systemic lupus erythematosus and rheumatoid arthritis

Rheumatoid factors (RFs) are autoantibodies that are produced by approximately 75% of patients with rheumatoid arthritis (RA). Their role in pathogenesis is not well understood. In this study of 81 human hybridoma IgM antibodies derived from unstimulated peripheral blood B-cells of patients with RA and systemic lupus erythematosus (SLE), we have demonstrated that idiotypes associated with RFs derived from patients with mixed cryoglobulinemia were expressed by approximately 60% of RFs and 6% of IgM antibodies lacking RF activity. The specificity of the RFs for the Fc portion of IgG only (monospecificity) or for Fc and additional self antigens (polyreactivity) was found to correlate with the expression of specific heavy chain associated idiotypes. The VH3 associated RF idiotypes, D12 and B6, were expressed by 0/16 (0%) of monospecific RFs compared with 6/22 (27%) of polyreactive RFs. The predominant use of VH3 was verified by analysis of the expressed Ig with VH family specific anti-peptide antibodies. The light chains expressed by both populations of IgM RFs were found to be predominantly VKIII, both by detection of specific epitopes/idiotypes and V family analysis. This non-random gene usage of both the heavy and light chains suggests that there is a selective expression of V regions in the RF producing B-cells in patients with RA and SLE. We suggest that different antigen-driven, clonal selection events may occur which result in either monospecific RFs or polyreactive RFs.

Autoimmunity-prone B-1 (CD5 B) cells, natural antibodies and self recognition

The delineation of distinct subsets committed to the production of antibodies with different antigen-binding activities supports the view of a compartmentalization and specialization of function in the B cell repertoire and is consistent with the hypothesis of a developmentally layered immune system; as originally proposed by Herzenberg and Herzenberg. On the basis of the data by Solvason and Kearney in the human fetus and our data in the adult, and in agreement with the findings of Herzenberg et al. and Hardy et al. in the mouse, we propose that the human B cell repertoire includes at least three distinct B cell subsets: B-1a cells, which develop from progenitors in the fetal splanchnic district, namely the omentum, and are maintained in adult life by virtue of their self-replenishing nature; B-1b cells, progenitors of which can be found in the splanchnic district and, perhaps, adult bone marrow; and, finally, B-2 cells, which arise in the fetal liver and are continuously replenished in adult life by progenitors in the bone marrow (Figure 5). The different B cells types are distinguished by their differential expression of surface CD5 and, perhaps, CD11b and CD14, their differential expression of CD5 mRNA, and the different classes and specificities of the Ig they produce (Figure 5). B-1 lymphocytes play a major role in autoimmunity and constitute the physiological equivalent of the neoplastic forms in various lymphoproliferative disorders, such as CLL and SLL, which are often associated with the production of monoclonal antibodies to self antigens. Human B-1a (CD5+ B) and B-1b (CD5- CD45RAlo B) cells are responsible for the production of natural (polyreactive and monoreactive) antibodies in the fetus, neonate, and adult, and can give rise to the autoantibody-producing cells characteristic of several autoimmune disease states. Our recent findings suggest that while in healthy subjects the majority of natural polyreactive antibodies is encoded in V genes in germline configuration, some polyreactive antibodies are encoded in somatically mutated V genes, in a fashion consistent with an antigen-driven process of selection of such mutations. The nature of the antigen(s) involved in these selection processes remains to be determined. Under possibly different circumstances, the application of an antigen-driven process of clonal selection to B-1a and/or B-1b cells, previously committed to natural antibody production, can result in the generation of monoreactive high affinity and possibly pathogenic autoantibodies (Figures 5A and 5B).(ABSTRACT TRUNCATED AT 400 WORDS)

Repertoire of CD5+ and CD5- cord blood B cells: specificity and expression of VH I and VH III associated idiotopes

Epstein-Barr (EBV)-immortalized B cell clones were established from CD5+ and CD5- cord blood B cells separated by flow cytometry. We have previously shown that IgM from many of the clones was polyreactive, exhibiting reactivity with a number of autoantigens. In this study, IgM produced by the clones was analysed by MoAb for the expression of cross-reactive idiotypes (CRI) associated with rheumatoid factor paraproteins and from defined VH and V kappa subgroups of immunoglobulin heavy and light chains. IgM produced by clones established from CD5+ and CD5- B cells expressed the VH I associated idiotope G8. Furthermore, IgM produced by both sets of clones exhibited a similar frequency of VH III heavy chain subgroup expression, as determined by reactivity with staphylococcal protein A (SpA) and VH III-associated CRI expression (B6 and/or D12). In contrast, expression of the V kappa III-associated 17.109 CRI was significantly higher in IgM antibodies produced by clones established from CD5+ compared with the CD5- clones (32 versus 5%: P less than 0.05). Analysis of the VH and VL subgroup expression by IgM produced by the CD5+ and CD5- cord blood clones, and their autoantigen reactivity profile did not reveal restriction or selection within CD5+ and CD5- populations. However, our data suggest that differences may exist in the expression of certain germ-line genes between CD5+ and CD5- cord blood B cells and might indicate an expansion of CD5+ B cells within the fetal environment.

A human monoclonal autoantibody to a nucleolar structure

Peripheral blood lymphocytes from a scleroderma patient (CDC) were isolated, transformed with Epstein-Barr virus and fused to the heteromyeloma SHM-D33. Supernatants from cultures were screened for autoantibody production against nucleoprotamine by ELISA. Positive wells were cloned by limiting dilution. After cloning, supernatants from two wells were positive for the nucleoprotamine assay. One named CDC-1 has been studied in our laboratory. CDC-1 recognized a nucleolar antigen by indirect immunofluorescence. By using an ELISA with purified recombinant antigens, CDC-1 reacted against Ro/SS-A, U1 (RNP) and Sm. By immunoblotting using a lysate of MOLT-4 cell line, CDC-1 was able to react against a structure of 60 kD. When the antigen recognized by CDC-1 was purified, SDS-PAGE under reducing conditions with purified antigen and subsequent silver staining of the gel allowed us to detect three bands at 60, 55 and 39 kD, respectively. A screening by ELISA with previously characterized antisera against our purified antigen demonstrated reactivity of the CDC-1 antigen with those antisera able to recognize Ro/SS-A.

Restricted use of fetal VH3 immunoglobulin genes by unselected B cells in the adult. Predominance of 56p1-like VH genes in common variable immunodeficiency

The large VH3 family of human immunoglobulin genes is commonly used throughout B cell ontogeny. However, B cells of the fetus and certain autoantibody-producing clones are restricted to a recurrent subset of VH3 genes, and VH3 B cells are deficient in certain immunodeficiency diseases. In this study, we have sequenced a set of rearranged VH3 genes generated by genomic polymerase chain reaction (PCR) from normal adults and those with common variable immunodeficiency (CVI). In both groups, all cones were readily identifiable with the fetal VH3 subset, and were further distinguished by limited DH motifs and exclusive use of JH4. In CVI, the residual population of VH3 B cells were notable for predominant use of 56p1-like VH genes. All clones displayed sequence divergence (including somatic mutation) with evidence of strong selection against complementarity-determining region (CDR) coding change. A survey of other V gene families indicates that human V gene diversity may be restricted in general by germline mechanisms. These findings suggest that the expressed antibody repertoire in the human adult may be much smaller than anticipated, and selected by processes in part distinct from the paradigm of maximal antigen-binding diversity.

The human VH repertoire: a restricted set of VH genes may be the target of immune regulation

During the development of the immune system, a restricted set of VH gene segments provides the bulk of the immunoglobulin heavy chain repertoire. Most of these VH genes have been found later in life encoding autospecificities either in normals or in patients with autoimmune diseases. Additionally, there is considerable evidence that the fetal/neonatal B-cell repertoire is autoreactive and idiotypically connected. In the course of sequencing the heavy chain of a panel of human autoantibodies mainly derived from patients with autoimmune diseases, we found that one of the VH families, and more specifically one single VH gene contributes to a large extent to the adult autoimmune repertoire in restricted as well as unrestricted responses. This VH gene segment is not particularly overexpressed in the fetus. Since the only common element to these autoreactive responses is the region encoded by the VH gene itself, these observations may provide an important insight into B-cell regulation.

The antibody repertoire of early human B cells. II: Expression of anti-DNA-related idiotypes

Cord blood B cells were immortalized in vitro with Epstein-Barr virus (EBV). Supernatants containing greater than 500 ng/ml IgM from clones/lines were tested for expression of anti-DNA-associated 16/6 and PR4 idiotypes (id) by ELISA. Four of 70 lines, but no clones, were positive for 16/6 id and none expressed the PR4 id. The presence of 16/6 id on four cell lines was associated with specificity for ssDNA, cardiolipin and Fc of IgG. No association was seen with binding to the K30 polysaccharide of Klebsiella. One clone binding this antigen also had anti-ssDNA, anti-Fc and anti-cardiolipin activity but did not express 16/6 id. Our data support the germ-line nature of the 16/6 id and are consistent with the notion that IgM autoantibody-producing B cells use VH genes which are part of the normal B cell repertoire.