Generation and analysis of clonal IgM- and IgG-producing human B cell lines expressing an anti-DNA-associated idiotype

A model for lupus brain disease

Systemic lupus erythematosus is an autoimmune disease characterized by antibodies that bind target autoantigens in multiple organs in the body. In peripheral organs, immune complexes engage the complement cascade, recruiting blood-borne inflammatory cells and initiating tissue inflammation. Immune complex-mediated activation of Fc receptors on infiltrating blood-borne cells and tissue resident cells amplifies an inflammatory cascade with resulting damage to tissue function, ultimately leading to tissue destruction. This pathophysiology appears to explain tissue injury throughout the body, except in the central nervous system. This review addresses a paradigm we have developed for autoantibody-mediated brain damage. This paradigm suggests that antibody-mediated brain disease does not depend on immune complex formation but rather on antibody-mediated alterations in neuronal activation and survival. Moreover, antibodies only access brain tissue when blood-brain barrier integrity is impaired, leading to a lack of concurrence of brain disease and tissue injury in other organs. We discuss the implications of this model for lupus and for identifying other antibodies that may contribute to brain disease.

Enhanced outgrowth of EBV-transformed chronic lymphocytic leukemia B cells mediated by coculture with macrophage feeder cells

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the clonal expansion of CD5-expressing B lymphocytes that produce mAbs often reactive with microbial or autoantigens. Long-term culture of B-CLL clones would permit the collection and characterization of B-CLL mAbs to study antigen specificity and of B-CLL DNA to investigate molecular mechanisms promoting the disease. However, the derivation of long-term cell lines (eg, by EBV), has not been efficient. We have improved the efficiency of EBV B-CLL transformation of CpG oligonucleotide-stimulated cells by incubating patient peripheral blood mononuclear cells in the presence of an irradiated mouse macrophage cell line, J774A.1. Using this approach, peripheral blood mononuclear cells isolated from 13 of 21 B-CLL patients were transformed as documented by IGHV-D-J sequencing. Four clones grew and retained CD5 expression in culture for 2 to 4 months. However, despite documentation of EBV infection by expression of EBNA2 and LMP1, B-CLL cells died after removal of macrophage feeder cells. Nevertheless, using electrofusion technology, we generated 6 stable hetero-hybridoma cell lines from EBV-transformed B-CLL cells, and these hetero-hybridomas produced immunoglobulin. Thus, we have established enhanced methods of B-CLL culture that will enable broader interrogation of B-CLL cells at the genetic and protein levels.

Monoclonal anti-endothelial cell antibodies from a patient with Takayasu arteritis activate endothelial cells from large vessels

OBJECTIVE

To create monoclonal anti-endothelial cell antibodies (mAECA) from a patient with Takayasu arteritis to evaluate their ability to activate human umbilical vein endothelial cells (HUVEC), and to characterize the mechanism of EC activation.

METHODS

A panel of mAECA was generated from peripheral blood lymphocytes of a patient with Takayasu arteritis, using Epstein-Barr virus transformation. Activity against macrovascular EC (HUVEC) and microvascular EC (human bone marrow EC immortalized by SV40) antigens was detected by enzyme-linked immunosorbent assay. Inhibition studies were used to select the monoclonal antibodies (mAECA) which share the same EC epitope binding specificity as the total IgG-AECA from the Takayasu arteritis patient. The binding of the mAECA to human aortic EC was studied by immunohistochemistry. The secretion levels of interleukin-6 (IL-6) and von Willebrand factor (vWF) were determined, to serve as markers for EC activation. The activated EC were examined for the adherence of a monocytic cell line (U937), as well as for expression of vascular cell adhesion molecule 1, intercellular adhesion molecule 1, and E-selectin. In addition, nuclear extracts of the mAECA-treated EC were analyzed for the induction of translocation of nuclear factor kappaB (NF-kappaB), using a specific NF-kappaB oligoprobe in an electrophoretic mobility shift assay.

RESULTS

Six mAECA were selected, the mixture of which produced 100% inhibition of binding of the original IgG (from the patient with Takayasu arteritis) to HUVEC. All mAECA possessed high activity against macrovascular EC, but none had significant antimicrovascular EC activity. The mAECA, but not normal human IgG, had anti-human aortic EC activity. Four of the 6 mAECA activated EC, manifested by increased IL-6 and vWF secretion. The 4 mAECA induced EC expression of adhesion molecules and increased adhesion of U937 monocytic cells to EC. In addition, these mAECA stimulated the nuclear translocation of the NF-kappaB transcription factor.

CONCLUSION

Our findings suggest that AECA may directly stimulate EC in Takayasu arteritis through elevation of adhesion molecule expression associated with NF-kappaB activation and adhesion of monocytes, and may therefore play a pathogenic role in the development of the vasculopathy in Takayasu arteritis.

Normal human cord blood B cells can produce high affinity IgG antibodies to dsDNA that are recognized by cord blood-derived anti-idiotypic antibodies

It is possible to identify, in Epstein-Barr virus-transformed normal human cord blood B cell populations, cells present at a low frequency that produce IgG antibodies specific for dsDNA. By cloning out these B cells as immortalized monoclonal cell lines, it could be shown that the antibodies were the products of CD5 positive B cells. Two monoclonal anti-dsDNA antibodies were derived from cell lines T52 and A7 and these were further characterized as anionic (pI approximately 6.4) IgG4 kappa antibodies that bound with affinities of 7.18 x 10(9) l/mol and 3.28 x 10(9) l/mol, respectively, to dsDNA but did not bind to ssDNA. These affinities were similar to those of polyclonal IgG anti-dsDNA antibodies from lupus patients, which ranged from 1 x 10(9) -8.9 x 10(10) l/mol. Both T52 and A7 monoclonal anti-dsDNA antibodies were recognized by cord blood-derived IgM antibodies. These IgM antibodies were not rheumatoid factors but bound to the F(ab')2 of A7 and T52 while failing to recognize T50, which is an autologous IgG4 kappa monoclonal antibody without specificity for dsDNA. A cloned B cell line A24 generated from the same cord blood sample as A7 produced an IgM monoclonal antibody that bound to the heavy chains of T52 and A7, but not T50 on Western blot and inhibited the binding of these antibodies to dsDNA. A7 and T52 competitively inhibited each other in their binding to the anti-idiotype A24, and A24 inhibited the binding to dsDNA of some polyclonal IgG anti-dsDNA antibodies purified from sera of lupus patients. The level of inhibition of binding of these antibodies to dsDNA was directly proportional to the levels of expression of the idiotype recognized by A24 on these antibodies. The normal human cord blood, therefore, may contain cells that form an idiotype/anti-idiotype network in which the idiotype is expressed on IgG antibodies with specificity for dsDNA and the anti-idiotype is an IgM antibody that binds to a heavy chain idiotope in such a way as to interfere with its interaction with dsDNA. The presence of a similar idiotype on some polyclonal anti-dsDNA antibodies in lupus that are similarly inhibitable by the cord blood-derived anti-idiotype raises the possibility that this network may persist in later life and perhaps become dysfunctional in systemic lupus erythematosus.

Analysis of human monoclonal antibodies elicited by vaccination with a Cryptococcus neoformans glucuronoxylomannan capsular polysaccharide vaccine

The Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan (GXM) has been conjugated to tetanus toxoid (GXM-TT) as an investigational vaccine. GXM-TT elicits antibodies that are protective in C. neoformans-infected mice. In an effort to characterize the fine specificity and molecular structure of human GXM-TT-elicited antibodies, we generated two GXM monoclonal antibodies (MAbs) from peripheral blood lymphocytes of a volunteer GXM-TT recipient and studied serum GXM antibody idiotype expression in 10 additional vaccinees. The MAbs, 2E9 and 3B6, are the immunoglobulin M(lambda) isotype and bind capsular polysaccharides of C. neoformans serotypes other than the serotype A that was used for immunization. Neither antibody competes with murine GXM MAbs for antigen binding, suggesting that the human MAbs recognize a different epitope. The B-cell superantigen staphylococcal protein A binds both MAbs, and human immunodeficiency virus gp120 binds 2E9. MAb nucleic acid sequence analysis revealed that both antibodies use an identical V lambda 1a-J lambda genetic element with different, somatically mutated, members of the VH3 gene family and different DH and JH gene elements. The gene elements used by both MAbs occur in fetal B-lymphocyte repertoires, autoantibodies, and other polysaccharide antibodies. Post-GXM-TT vaccination GXM antibodies from 10 additional vaccinees expressed a shared idiotype defined by rabbit antiserum raised against MAb 2E9. Our data suggest that the human GXM antibody response is restricted and raise questions regarding the importance of specific variable-region elements and superantigens in the generation of human antibody responses to encapsulated pathogens.

Analysis of the V kappa I family: germline genes from an SLE patient and expressed autoantibodies

Our studies of anti-DNA antibodies in systemic lupus erythematosus have demonstrated a preferential use of the V kappa I family to encode light chains of antibodies that express the anti-DNA associated 3I idiotype. This idiotype is present on a high percentage of anti-DNA antibodies in approximately 80% of SLE patients1,2. In this study, we employed PCR to obtain V kappa I germline genes from a lupus patient in order to address the following questions: Do the V kappa I germline genes of an individual with autoimmune disease differ from those of healthy individuals? What V kappa I genes are used to encode autoantibodies and are they used to encode protective antibodies also? Does the V kappa I gene family display peculiarities in V gene segment rearrangement or somatic mutation? Our analysis shows that the coding region sequences of germline genes of an autoimmune individual are highly homologous to those of non-autoimmune individuals. In addition, the same germline genes can be utilized to encode antibodies to both exogenous and self antigens. While rearranged V kappa genes are ordinarily derived from the J kappa proximal region of the V kappa locus, V kappa I genes encoding autoantibodies derive primarily from the J kappa distal region. It is not yet clear if this applies equally to V kappa I encoded antibodies directed to foreign antigen.

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

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

Serological and genetic characterization of a human monoclonal immunoglobulin G anti-DNA idiotype

This study analyzed the distribution of an idiotype, B3-Id, in patients with active SLE, classified according to organ involvement, normal controls, and other autoimmune rheumatic diseases. A polyclonal anti-idiotype was raised by immunizing a rabbit with a monoclonal IgG anti-double-stranded (ds) DNA antibody, B3, generated from a patient with SLE who had active arthritis. The idiotype is present on the lambda chain and is at or near the binding site for double-stranded DNA. The lambda chain, which was characterized by nucleotide sequencing, was 90% homologous to the V lambda 2.1 germline, which is known to be involved in coding for nephritogenic anti-DNA antibodies carrying the 8.12 idiotype. There were four changes to positively charged amino acids, known to be involved in DNA binding, in the complementarity determining regions of B3 lambda chain compared with a non-DNA binding, 8.12 positive antibody, PV11. Only one change to a positively charged amino acid occurs in the heavy chain of B3, which is 93.5% homologous to VH-26. The B3-Id was present on IgG antibodies in the serum of 20% of patients with SLE but was not found in the normal controls. Within the SLE group, there is a statistically significant association of B3-Id on IgG in the arthritis group (42%) compared to the other manifestations (9%) (P < 0.001). In four B3-Id-positive SLE patients tested serially, the level of B3-Id reflected the arthritis disease activity more closely than the overall disease activity (P < 0.05). The B3-Id was also present on IgM antibodies in one third of patients with rheumatoid arthritis. This idiotype is the first to be derived from a human monoclonal anti-DNA antibody of the IgG class, the isotype associated with active disease. Sequence analysis shows that positively charged amino acids on the lambda chain may contribute to DNA binding.

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

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

A potent, neutralizing human monoclonal antibody against a unique epitope overlapping the CD4-binding site of HIV-1 gp120 that is broadly conserved across North American and African virus isolates

A human monoclonal antibody (HuMAb), 5145A, against HIV-1 gp120 was isolated from an asymptomatic, seropositive hemophiliac. The epitope of this HuMAb was destroyed by reduction of gp120 disulfide bonds, but not by removal of N-linked carbohydrates. This epitope overlaps the CD4-binding site of gp120, because binding of 5145A to gp120 is inhibited by soluble CD4 and by 1125H, a previously described HuMAb directed toward the CD4-binding site. However, the 5145A epitope differs from those of 1125H and other anti-CD4-binding site HuMAbs previously described, as documented by the viral strain specificity of 5145A and its reactivity with a panel of gp120 mutants. Specifically, 5145A reacted with 14 of 15 HIV-1 isolates tested, including 9 isolates from the Central African Republic, 6 of which were not recognized by 1125H. Partial epitope mapping of 5145A, using a series of gp120 mutants, demonstrated its lack of sensitivity to mutations in residues 257 and 427, contrasting with a marked sensitivity to mutations in residues 368 and 370. This pattern of reactivity distinguishes its epitope from that of any HuMAb against the CD4-binding site region described to date. In addition, 5145A exhibited potent and essentially equivalent neutralization of the MN, SF-2, IIIB, and RF strains and possessed significant neutralizing activity against three of three African strains tested. Finally, 5145A synergistically neutralized the MN and SF-2 strains of HIV-1 when combined with 4117C, a HuMAb against the V3 loop. The broad strain specificity and potent neutralizing activity of 5145A, together with its ability to synergize with an anti-V3 loop HuMAb in neutralizing HIV-1, indicate that 5145A has excellent potential as a passive immunotherapeutic agent against HIV-1.

Variable region sequences of autoantibodies from mice with experimental systemic lupus erythematosus

We have sequenced nine monoclonal antibodies (mAb) derived from C3H.SW mice in which experimental systemic lupus erythematosus (SLE) was induced. The hybridomas were selected for binding to DNA or to HeLa nuclear extract (NE). Three mAb were found to bind DNA, and are shown to exhibit sequence characteristics of pathogenic anti-DNA antibodies. One, mAb 2C4C2, is shown to use a heavy chain V region gene (VH) identical to the VH of anti-DNA mAb isolated from other lupus-prone mice, namely (NZB x NZW)F1. The light chain V region gene (VL) of mAb 2C4C2 is 98% homologous to the VL of another anti-DNA mAb, also isolated from (NZB x NZW)F1 mice. The other two anti-DNA mAb, 5G12-4 and 5G12-6, share 93% of their VH sequences with that of mAb 2C4C2. Six mAb bound proteins of HeLa NE. Four of these six antibodies were found to use the VH124 VH and V-L7 VL. The nine mAb use a total of five VH and four VL germ-line genes, demonstrating that the autoantibodies induced in mice with experimental SLE do not originate from one B cell clone. Three of these nine VH and VL were identical in sequence to germ-line genes, while at least three others had somatic mutations. The latter suggests that the above autoantibodies arise in mice by both usage of existing (pre-immune) B cells, and through an antigen-driven process. Furthermore, it appears that autoantibodies found in mice with experimental SLE use genetic elements similar to those used by mAb that were isolated from mouse strains which develop lupus spontaneously.

Production and analysis of IgG monoclonal anti-DNA antibodies from systemic lupus erythematosus (SLE) patients

This study compares recently devised methods for producing IgG anti-DNA MoAbs from patients with SLE and analyses the antibodies generated from one patient at different phases of disease. Lymphocytes from SLE patients were transformed with Epstein-Barr virus(EBV) and/or fused with a heteromyeloma cell line, CB-F7. Direct fusion with CB-F7 resulted in the highest proportion of IgG-secreting lines, whereas EBV transformation resulted in a high percentage of IgM-secreting lines. Using direct fusion, five IgM anti-DNA antibody-secreting hybridomas were generated using lymphocytes from a patient with relatively inactive SLE. Six months later when the disease was active, only IgG anti-DNA antibodies were produced. The antigen-binding patterns of the MoAbs were analysed. Only one of the IgM anti-DNA antibodies reacted with dsDNA by ELISA and none by Crithidia immunofluorescence, whereas two of the IgG antibodies reacted with dsDNA by ELISA and Crithidia but did not bind to ssDNA. Only the two IgG high affinity anti-dsDNA antibodies bound to histones, and this was enhanced by added DNA, whereas three IgM antibodies bound to cardiolipin. This study supports the notion that MoAbs derived from a patient with SLE represent those found in the serum of SLE patients at different stages of disease activity. The binding to histones by the two IgG anti-dsDNA antibodies supports the recently expressed view that antibodies binding DNA/histone may be important in the pathogenesis of SLE.

Characterization of two human anti-DNA antibodies bearing the pathogenic idiotype 8.12

Antibodies against double stranded DNA (dsDNA) are characteristic of systemic lupus erythematosus (SLE) and have been implicated in disease pathogenesis. Up to one third of an SLE patient's anti-dsDNA antibodies can express the lambda L chain idiotype 8.12. Serum titers of this idiotype are elevated in 50% of SLE patients, and idiotypic antibodies are present in glomerular immune deposits associated with lupus nephritis. Two EBV transformed B cell lines, KS3 from a patient with SLE and SD6 from an individual without autoimmune disease, secrete 8.12+ IgG antibodies that bind dsDNA. The 8.12+ lambda L chains of these anti-DNA antibodies are encoded by members of the V lambda II gene family; the KS3 heavy chain is encoded by a VH4-DM1-DQ52-JH6b-C gamma 1 gene rearrangement and the SD6 heavy chain is encoded by a VH3-D21/9-JH6b-C gamma 1 rearrangement. Both of these monoclonal antibodies are somatically mutated: the KS3 antibody displays mutations in complementarity determining regions (CDRs) and the SD6 antibody in framework regions (FRs). The significance of these different patterns of mutation in two potentially pathogenic anti-DNA antibodies is discussed.

Molecular characteristics of antibodies bearing an anti-DNA-associated idiotype

Anti-double-stranded DNA antibodies are the hallmark of the disease systemic lupus erythematosus and are believed to contribute to pathogenesis. While a large number of anti-DNA antibodies from mice with lupus-like syndromes have been characterized and their variable region genes sequenced, few human anti-DNA antibodies have been reported. We describe here the variable region gene sequences of eight antibodies produced by Epstein-Barr virus (EBV)-transformed B cells that bear the 3I idiotype, an idiotype expressed on anti-DNA antibodies and present in high titer in patients with systemic lupus. The comparison of these antibodies to the light chains of 3I+ myeloma proteins and serum antibodies reveals that EBV transformation yields B cells producing antibodies representative of the expressed antibody repertoire. The analysis of nucleotide and amino acid sequences of these antibodies suggests the first complementarity determining region of the light chain may be important in DNA binding and that paradigms previously generated to account for DNA binding require modification. The understanding of the molecular genetics of the anti-DNA response requires a more complete description of the immunoglobulin germ line repertoire, but data reported here suggest that somatic diversification is a characteristic of the anti-DNA response.

Systemic lupus erythematosus

Systemic lupus erythematosus is a prototypic autoimmune disease characterized by antinuclear antibody production. In recent investigations, the contributions of various polymorphic immune response gene systems to disease pathogenesis have been analyzed. Unique cellular and molecular studies have also established the role of 'autoantigen drive' in autoantibody induction and its relationship to polyclonal B-cell activation.