Complete protein sequences of the variable regions of the cloned heavy and light chains of a human anti-cytomegalovirus antibody reveal a striking similarity to human monoclonal rheumatoid factors of the Wa idiotypic family

Chimeric Antigen Receptors Targeting Human Cytomegalovirus

Human cytomegalovirus (CMV) is a ubiquitous pathogen that causes significant morbidity in some vulnerable populations. Individualized adoptive transfer of ex vivo expanded CMV-specific CD8+ T cells has provided proof-of-concept that immunotherapy can be highly effective, but a chimeric antigen receptor (CAR) approach would provide a feasible method for broad application. We created 8 novel CARs using anti-CMV neutralizing antibody sequences, which were transduced via lentiviral vector into primary CD8+ T cells. All CARs were expressed. Activity against CMV-infected target cells was assessed by release of cytokines (interferon-γ and tumor necrosis factor-α), upregulation of surface CD107a, proliferation, cytolysis of infected cells, and suppression of viral replication. While some CARs showed varying functional activity across these assays, 1 CAR based on antibody 21E9 was consistently superior in all measures. These results support development of a CMV-specific CAR for therapeutic use against CMV and potentially other applications harnessing CMV-driven immunotherapies.

Recombinant antibodies encoded by IGHV1-69 react with pUL32, a phosphoprotein of cytomegalovirus and B-cell superantigen

Leukemia cells from patients with chronic lymphocytic leukemia (CLL) express a highly restricted immunoglobulin heavy variable chain (IGHV) repertoire, suggesting that a limited set of antigens reacts with leukemic cells. Here, we evaluated the reactivity of a panel of different CLL recombinant antibodies (rAbs) encoded by the most commonly expressed IGHV genes with a panel of selected viral and bacterial pathogens. Six different CLL rAbs encoded by IGHV1-69 or IGHV3-21, but not a CLL rAb encoded by IGHV4-39 genes, reacted with a single protein of human cytomegalovirus (CMV). The CMV protein was identified as the large structural phosphoprotein pUL32. In contrast, none of the CLL rAbs bound to any other structure of CMV, adenovirus serotype 2, Salmonella enterica serovar Typhimurium, or of cells used for propagation of these microorganisms. Monoclonal antibodies or humanized rAbs of irrelevant specificity to pUL32 did not react with any of the proteins present in the different lysates. Still, rAbs encoded by a germ line IGHV1-69 51p1 allele from CMV-seropositive and -negative adults also reacted with pUL32. The observed reactivity of multiple different CLL rAbs and natural antibodies from CMV-seronegative adults with pUL32 is consistent with the properties of a superantigen.

Detailed analysis of the E2-IgM complex in hepatitis C-related type II mixed cryoglobulinaemia

Hepatitis C virus (HCV) plays a major role in the induction of type II mixed cryoglobulinaemia (MCII). The role of HCV proteins and virus-host interaction in the pathogenesis of MC remains to be defined. To address this issue, we have characterized, in detail, the monoclonal IgM and the viral component of circulating immune complexes in eight patients with HCV-associated MCII. The proportion of HCV-RNA compartmentalized in the cryoprecipitate (CP) varied greatly (10-80% of total HCV-RNA). The complementary determining region (CDR)3 sequences of monoclonal immunoglobulin M (IgM) VH and VK genes were highly homologous to rheumatoid factor and to antibodies against HCV-E2. Furthermore, the CDR3 sequences in some of our MCII patients were highly similar to those described in HCV-positive patients with non-Hodgkin's lymphoma (NHL). From these results, it appears that, as in the case of NHL, the IgM-rheumatoid factor (RF) production in MCII patients is antigen driven, namely by E2. However, the limited number of mutations in VH and VK genes with respect to the germline and their distribution showed that the B-cell response in these cases was prevented from undergoing affinity maturation. Furthermore, in patients with monoclonal IgM and definite compartmentalization of HCV in either CP or supernatant, a highly homogeneous E2-hypervariable region (HVR)1 sequence distribution was found (90-100% identical clones), a feature of the quasispecies frequently associated with an impaired humoral immune response to HCV. These findings suggest that in patients with HCV-associated MCII, maturation of monoclonal B lymphocytes may be blocked in a primitive stage preventing serious damaging effects because of the auto-reactivity of their secreted immunoglobulins.

Acquisition of potential N-glycosylation sites in the immunoglobulin variable region by somatic mutation is a distinctive feature of follicular lymphoma

Most patients with follicular lymphoma (FL) have somatically mutated V genes with intraclonal variation, consistent with location in the germinal center site. Using our own and published sequences, we have investigated the frequency of potential N-glycosylation sites introduced into functional V(H) genes as a consequence of somatic mutation. FL cells were compared with normal memory B cells or plasma cells matched for similar levels of mutation. Strikingly, novel sites were detected in 55 of 70 (79%) patients with FL, compared to 7 of 75 (9%) in the normal B-cell population (P <.001). Diffuse large B-cell lymphoma (DLCL) showed an intermediate frequency (13 of 32 [41%] patients). Myeloma and the mutated subset of chronic lymphocytic leukemia showed frequencies similar to those of normal cells in 5 of 64 (8%) patients and 5 of 40 (13%) patients, respectively. In 3 of 3 random patients with FL, immunoglobulin was expressed as recombinant single-chain Fv in Pichia pastoris, and glycosylation was demonstrated. These findings indicate that N-glycosylation of the variable region may be common in FL and in a subset of DLCL. Most novel sites are located in the complementarity-determining regions. V(H) sequences of nonfunctional V(H) genes contained few sites, arguing for positive selection in FL. One possibility is that the added carbohydrate in the variable region contributes to interaction with elements in the germinal center environment. This common feature of FL may be critical for tumor behavior.

Lack of autoantibody production associated with cytomegalovirus infection

To confirm an association between cytomegalovirus (CMV) infection and the presence of antibodies to Smith (Sm), to ribonucleoprotein (RNP), and to a component of the U1 ribonucleoproteins (U1-70 kD), we measured antibodies to these protein antigens using an enzyme immunoassay and an immunoblot. The antibodies were measured in the sera of 80 healthy subjects, one-half of whom were naturally CMV seropositive and one-half were CMV seronegative, and in eight subjects immunized with a live attenuated strain of CMV. None of the vaccinees developed antibodies to Sm, to RNP, or to U1-70 kD at either 4 or 12 months after immunization. Additionally, there was no statistically significant association between levels of antibodies to Sm or to RNP and between sera obtained from vaccinees, natural CMV seropositive individuals, and CMV seronegative individuals. One CMV seropositive serum and one CMV seronegative serum tested positive for antibodies to U1-70 kD. These data indicate that neither wild-type infection nor the live-attenuated Towne vaccine frequently induce autoantibody production.

Clonal Analysis of a Human Antibody Response. III. Nucleotide Sequences of Monoclonal IgM, IgG, and IgA to Rabies Virus Reveal Restricted Vκ Gene Utilization, Junctional VκJκ and VλJλ Diversity, and Somatic Hypermutation

In previous work, we generated four IgM, five IgG1, and one IgA1 mAbs to rabies virus using B cells from four subjects vaccinated with inactivated rabies virus, a thymus-dependent (TD) mosaic Ag, and sequenced the mAb VHDJH genes. Here, we have cloned the VκJκ and VλJλ genes to complete the primary structure of the Ag-binding site of these mAbs. While the anti-rabies virus mAb selection of Vλ genes (2e.2.2 twice, DPL11, and DPL23) reflected the representation of the Vλ genes in the human haploid genome (stochastic utilization), that of Vκ genes (O2/O12 twice, O8/O18, A3/A19, A27, and L2) did not (p = 0.0018) (nonstochastic utilization). Furthermore, the selection of both Vκ and Vλ genes by the anti-rabies virus mAbs vastly overlapped with that of 557 assorted VκJκ rearrangements, that of 253 VλJλ rearrangements in λ-type gammopathies, and that of other Abs to thymus-dependent Ags, including 23 anti-HIV mAbs and 51 rheumatoid factors, but differed from that of 43 Abs to Haemophilus influenzae type b polysaccharide, a prototypic thymus-independent (TI) Ag. The anti-rabies virus mAb VκJκ and VλJλ segments displayed variable numbers of somatic mutations, which, in mAb58 and the virus-neutralizing mAb57, entailed a significant concentration of amino acid replacements in the complementarity-determining regions (p = 0.0028 and p = 0.0023, respectively), suggesting a selection by Ag. This Ag-dependent somatic selection process was superimposed on a somatic diversification process that occurred at the stage of B cell receptor for Ag rearrangement, and that entailed V gene 3′ truncation and N nucleotide additions to yield heterogeneous CDR3s.

Nucleotide sequence analysis of a human monoclonal antibody 22-13 reactive with lung tumor-associated antigen

A human monoclonal antibody (HuMAb) 22-13 (IgG1, kappa) recognizes a cytoplasmic antigen associated primarily with human lung tumors. This study reports the primary nucleotide and deduced amino acid sequences of the rearranged heavy and light chains of the HuMAb 22-13. This HuMAb uses a VH gene member of the V(H)Ia gene family, 51P1 and is productively rearranged with a D-D fusion product of the D(LR)2 and D(XP)2 germ line DH genes and the germ line JH3 gene. HuMAb 22-13 Vkappa belongs to the kappa light chain variable subgroup IIIb family and appears to be derived from the Humkv325 germ line gene and is rearranged with a germ line Jkappa5 gene. The results reveal that production of a HuMAb 22-13 is achieved by rearrangement of the 51P1/Humkv325 germ line variable region gene combination, associated with the autoimmune repertoire and that HuMAb 22-13 has a striking sequence homology to rheumatoid factors (RFs) of the Wa idiotypic family. HuMAb 22-13 and Wa RFs have in common V(H)Ia and VkappaIIIb gene segments, but use different DH, JH and Jkappa gene segments. However, in spite of this structural similarity, HuMAb 22-13 does not display rheumatoid factor activity. Taken together with the reported findings, these data indicate the representation of the shared usage of highly homologous variable region genes in entirely different humoral immune responses in the human system.

Lupus-specific antibodies reveal an altered pattern of somatic mutation

The F4 idiotype is a heavy chain determinant expressed almost exclusively on IgG immunoglobulins and is highly associated with specificity for double-stranded DNA. Since high-titered F4 expression is present predominantly in sera of patients with systemic lupus erythematosus (SLE), we thought F4+ IgG antibodies might constitute a useful subset of immunoglobulins in which to investigate lupus-specific alterations in variable (V) region gene expression or in the process of somatic mutation. This molecular analysis of F4+ B cell lines generated from lupus patients demonstrates that despite the strong association of F4 reactivity with specificity for native DNA, there is no apparent VH gene restriction. Furthermore, VH gene segments encoding these antibodies are also used in protective immune responses. An examination of the process of somatic mutation in F4+ antibodies showed no abnormality in frequency of somatic mutation nor in the distribution of mutations in complementarity-determining regions or framework regions. However, there was a decrease in targeting of mutations to putative mutational hot spots. This subtle difference in mutations present in these antibodies may reflect an intrinsic defect in mutational machinery or, more likely, altered state of B cell activation that affects the mutational process and perhaps also negative selection.

Characteristics of human antibody repertoires following active immune responses in vivo

Possibilities to develop human monoclonal antibody specificities have recently been much facilitated by improvements of human hybridoma technology but even more so by the emerging phage-display technique. However, until recently very little has been known about the characteristics at the molecular level of the induced, T cell-dependent human antibody response, frequently targeted by these techniques. Rather, the major part of available sequence information has been related to tumor-derived or autoreactive antibodies. We have now investigated high affinity, monospecific, human antibody repertoires as developed by hybridoma technology. The VH region gene usage among such in vivo-induced repertoires is in only some respects similar to that found in the total B cell population. A limited number of heavy-chain variable segment loci account for the majority of all induced antibodies. A particular VH gene locus (4-34) frequently employed by peripheral B cells and associated with autoreactive antibodies was rarely used by the induced repertoire. Furthermore, in particular antigen systems, V region usage differs from the total available repertoire, and heavy-chain CDR3 is generally longer among antibodies induced against foreign protein antigens than in the average B cell population. Light-chain gene usage is often restricted to just a few dominant genes frequently found among B cells in general. In comparison, variable regions derived by phage-display technology in some antigen systems display even longer heavy-chain CDR3 than hybridoma-derived antibodies. This technique also appears to select a different set of germline genes preferentially (both with respect to VH and JH) as compared to hybridoma technology. In summary, the T cell-dependent antibody response against foreign antigens appears to differ from the average circulating B cell in several ways, and thus does not seem to represent a random selection of the available repertoire.

The human antibody repertoire: heavy and light chain variable region gene usage in six alloantibodies specific for human HLA class I and class II alloantigens

Peripheral blood B lymphocytes have been isolated from healthy individuals who were immunized with lymphocytes from HLA-incompatible donors and transformed with Epstein-Barr virus to produce human monoclonal cell lines specific for human HLA molecules. The cell lines have been previously characterized and are known to bind to various class I and class II alloantigens. In this report we describe the molecular characterization of the heavy and light chain variable region gene segments that are utilized by these monoclonal antibodies. Using the polymerase chain reaction and primer pairs specific for the respective constant region and VH or VL family, rearranged variable region gene segments were amplified from cDNA from individual cell lines. Products were then subcloned, sequenced and analysed for gene usage and apparent somatic mutation. The results show that the VH3 gene family predominates in a group of six heavy chains (four out of six) with one VH1 and one VH4 gene segment. The light chain variable region gene family usage is more diverse with 2 V kappa 3, 1 V kappa 1, 2 V lambda 2 and 1 V lambda 3. The extent of apparent somatic mutation is minimal, relative to our previous observations in a group of high affinity human monoclonal antibodies specific for pathogenic organisms.

B-cell superantigens: implications for selection of the human antibody repertoire

For several decades, B-cell interactions with antigens were thought to occur only through a clonal activation mechanism, in which the hypervariable regions of the immunoglobulin receptor are exclusively involved in ligand binding. However, an additional mode of interaction can occur, whereby molecules, termed B-cell superantigens, can bind human B cells bearing immunoglobulin receptors of a given variable (V)-gene family. This mechanism requires contributions from regions outside the conventional hypervariable loops and results in a B-cell response of increased magnitude. Here, Moncef Zouali reviews recent in vitro and in vivo observations on human B-cell superantigens in the context of the current consensus of B-cell development, and discusses the implications of these novel concepts with respect to pathogenesis.

A human anti-insulin IgG autoantibody apparently arises through clonal selection from an insulin-specific "germ-line" natural antibody template. Analysis by V gene segment reassortment and site-directed mutagenesis

We analyzed the structural correlates underlying the insulin-dependent selection of the specific anti-insulin IgG1 kappa mAb13-producing cell clone, derived from a patient with insulin-dependent diabetes mellitus treated with recombinant human insulin. First, we cloned the germ-line genes that putatively gave rise to the expressed VH and V kappa segments and used them to generate the full (unmutated) "germ-line revertant" of the "wild-type" (somatically mutated) mAb13, using recombinant PCR methods and an in vitro human C gamma 1 and C kappa expression system. The full "germ-line revertant" bound insulin specifically and in a dose-saturable fashion, but with a relative avidity (AVrel) more than three-fold lower than that of its wild-type counterpart (Avrel, 1.69 x 10(-8) vs 4.91 x 10(-9) g/microliters). Second, we established, by reassorting wild-type and germ-line revertant forms of the mAb13 VH and V kappa segments, that the increased Avrel for insulin of mAb13 when compared with its full "germ-line revertant" counterpart was entirely dependent on the mutations in the VH not those in the V kappa chain. Third, we determined, by site-directed mutagenesis experiments, that of the three mutations in the mAb13 VH segment (Ser-->Gly, Ser-->Thr, and Ser-->Arg at positions 31, 56, and 58, respectively), only Arg58 was crucial in increasing the mAb13 Avrel (from 1.44 x 10(-8) to 5.14 x 10(-9) g/microliters) and affinity (Kd, from 189 to 59 nM) for insulin. The affinity enhancement mediated by the VH segment Arg58 residue reflected about a threefold decrease in dissociation rate constant (Koff, from 4.92 x 10(-3) to 1.54 x 10(-3) s-1) but not an increase in association rate constant (Kon, from 2.60 x 10(4) to 2.61 x 10(4) M-1 s-1), and it contrasted with the complete loss of insulin binding resulting from the substitution of the VH segment Asn52 by Lys. The present findings suggest that human insulin, a self Ag, has the potential to recruit a natural autoantibody-producing cell precursor expressing a specific surface receptor for Ag in unmutated configuration, and drive it through affinity maturation. They also show that binding of insulin by such a receptor can be enhanced or completely abrogated by a single amino acid change.

Restricted variable region gene usage and possible rheumatoid factor relationship among human monoclonal antibodies specific for the AD-1 epitope on cytomegalovirus glycoprotein B

The nucleotide sequences of the variable region genes encoding five different human, high affinity antibodies, specific for the major neutralization determinant (AD-1) expressed by human cytomegalovirus glycoprotein B (gp58/116), have been determined. Three of the five heavy chain variable regions belonged to the small VHV-family, although they combined with a diverse set of light chains (V kappa IIIb, V lambda II and V lambda III). The other two antibodies belonged to VH-families III and IV. One of the VHV-family genes most likely originated from a previously unreported germline gene or allele, since it carries a nine nucleotide insert in framework 1. In addition, V lambda-genes showed variable homology (77-95%) to known germline sequences, while V kappa-genes showed high homology (approximately 98%) with their proposed germline origin. Despite the close homology of the V kappa IIIb-gene used to express one of the antibodies with its corresponding germline gene, the protein did not strongly express some idiotypes associated with this light chain family. There is, thus, no direct relation between the expression of these crossreactive idiotypes and the use of even modestly mutated light chains belonging to this V kappa-family, which has been implicated in the development of anti-idiotypic networks possibly inducing autoantibodies, such as rheumatoid factors.

Variable region sequences of a protective human monoclonal antibody specific for the Haemophilus influenzae type b capsular polysaccharide

A hybridoma secreting a human immunoglobulin G2 kappa monoclonal antibody (MAb) specific for the capsular polysaccharide of Haemophilus influenzae type b (Hib) was isolated. This MAb, designated CA4, was bactericidal to Hib in vitro and protected infant rats from Hib bacteremia. Nucleotide sequence analysis of CA4 variable (V) region cDNA showed that the heavy (H)-chain V region was of subgroup III and was 96% identical to the VH germ line gene segment DP77 (V3-21). The light (L)-chain V region was of the kappa subgroup III and was 94% identical to the A27 (Humkv325) germ line gene, which is commonly used by rheumatoid factors and other autoantibodies. MAb CA4 did not have rheumatoid factor activity and did not react with histones, DNA, or chromatin. These findings identify an additional VHIII gene segment which can contribute to the anti-Hib capsular polysaccharide repertoire and demonstrate that a VL gene commonly encoding autoantibodies can be utilized for protective immunity.

A human rheumatoid factor C304 shares VH and VL gene usage with antibodies specific for ubiquitous human viral pathogens

Analysis of the variable region gene sequences of a human hybridoma rheumatoid factor (RF), derived from a patient with rheumatoid arthritis (RA), revealed the expression of genes from the V lambda I and VH3 families. Specifically, the C304 RF had rearranged the DPL8/Humlv1042 and VH26 germline VL and VH genes, respectively. This gene usage has been observed in the rearrangement of human anti-viral antibodies specific for the herpes group of viruses. This overlap between the autoimmune and anti-viral antibody gene repertoires suggests a possible structural relationship between the immune response directed against ubiquitous pathogens and the induction of RF production.

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.

Evidence that the V kappa III gene usage is nonstochastic in both adult and newborn peripheral B cells and that peripheral CD5+ adult B cells are oligoclonal

There is evidence that in certain situations the expressed antibody repertoire is dominated by small subsets of V gene segments. They include fetal, CD5+, and autoantibody-forming B cells as well as low grade B cell malignancies. For instance, inside the V kappa III family of approximately 10 members, only 3 (humkv325, 328, and Vg) are used recurrently for autoantibody production. However, the significance of this recurrence is difficult to interpret without a clear vision of the actual repertoire in normal subjects. To address this, we have sequenced and compared two sets of rearranged V kappa III genes generated by cDNA PCR amplification from a normal newborn, a normal adult, and from CD5+ B cells of the same adult donor. The results show that: (a) only four V kappa III gene segments are used by neonatal and total adult B cells (humkv325, humkv328, Vg, and kv305), humkv325 being overexpressed in both repertoires; (b) there is no significant difference in terms of V kappa III gene usage between the adult and newborn repertoires; (c) regarding the junction regions, there is a favored use of the most 5' JK gene segments (Jk1-Jk2); approximately 20% of the newborn and adult junction sequences was characterized by one or two additional codons, most probably resulting from a nontemplate addition of nucleotides; (d) adult clones, in contrast to most newborn clones, show sequence divergences from prototype sequences with patterns which suggest antigen-driven diversity; (e) regarding the adult CD5+ B cell library, it is most probable that the 78 clones analyzed derived from no more than nine different VK-JK rearrangements. Humkv325 is used by at least six of them, and most of the expressed V genes were in exact or very near germline configuration. Collectively these results suggest that the expressed antibody V kappa III repertoire in the adult represents only a fraction of the potential genetic information and that it resembles the preimmune repertoire of the neonate. The data, which also suggest that the adult peripheral blood CD5+ B cell population may be dominated by a small number of B cell clones, are discussed with regards to the V kappa III usage in pathological situations.

Cloning and characterisation of TPO autoantibodies using combinatorial phage display libraries

Thyroid lymphocyte RNA from a Hashimoto patient with high serum levels of autoantibodies to thyroid peroxidase (TPO) was used to construct a phage display antibody library in the phagemid vector pComb3. The library (100,000cfu) encoded IgG1 heavy chains together with kappa light chains. Selection of the phages displaying TPO antibody on TPO-coated ELISA plates yielded a phage population enriched for surface expression of TPO antibody Fabs. 3 different Fabs specific for TPO were subsequently isolated with affinities in the region of 10(9) molar-1. 2 of the Fabs recognised the same, or closely related, epitopes on TPO whereas the third Fab recognised a different epitope. These 2 epitopes were recognised by TPO autoantibodies in the serum of the lymphocyte donor and a series of 10 patient sera. Available sequence data showed that several non-self antibodies and non-thyroid autoantibodies use the same V kappa and VH germline genes as TPO autoantibodies. There appeared to be no clear relationship between gene sequence or gene family usage by TPO autoantibodies of the same or similar epitope specificity.

IgG3 reactive rheumatoid factor in rheumatoid arthritis: etiologic and pathogenic considerations

Rheumatoid factor (RF) is a polyclonal autoantibody directed against the Fc portion of IgG. Although the role of RF in patients with rheumatoid arthritis (RA) is unclear, immune complexes that form between RF and IgG can activate the classical complement (C) pathway, leading to pathogenic outcomes involving inflammatory events and tissue damage. The specificity of serum RF and RF produced by rheumatoid synovial cells (RSC) is different. Serum RF has specificity for rabbit IgG and human IgG subclasses IgG1, 2, and 4, but binds poorly to IgG3. The affinity of serum RF for IgG Fc is low, having an association constant of 10(4)-10(5) M-1. RSC RF, however, has specificity for human IgG and high avidity for IgG3. Because of this greater specificity and avidity for IgG3, and because RSC RF may be pathogenically more important than serum RF, an important role for IgG3-reactive RF in RA may exist. Binding of RF to IgG may be dependent on the allotype and glycosylation of IgG. Infectious agents present in RA patients may directly or indirectly induce the production of certain RF. In this communication, we review and expand on several observations examining the role of IgG3-reactive RF in RA including: 1) binding differences between RF derived from RSC and serum; 2) glycosylation characteristics of IgG and its interaction with RF; 3) apparent allotype dependent binding of IgG3-reactive RF; and 4) possible relationship between infectious agents and the production of IgG3-reactive RF. Taken together, these observations suggest an important role for IgG3-reactive RF in better understanding the etiology and pathogenesis of RA.

Molecular characterization of human antibodies to bacterial antigens: utilization of the less frequently expressed VH2 and VH6 heavy chain variable region gene families

Structural analysis of the human immunoglobulin repertoire holds promise for determining the basis of variable region gene usage in response to a variety of auto and exogenous antigens. Here we report the nucleotide sequences of the heavy and light chain variable regions expressed by three human monoclonal antibodies specific for two clinically relevant bacterial pathogens, Bordetella pertussis and Haemophilus influenzae type b. The cell lines were derived by in vitro stimulation of lymphocytes from spleen or tonsillar tissue, respectively, and bind to different antigens from the two organisms. The single B. pertussis antibody is of the IgM lambda isotype and utilizes the single VH6 gene segment in combination with a V lambda 2 gene and demonstrates limited somatic mutation, yet is highly indicative of an antigen-driven immune response. One H. influenzae antibody is of the IgG2 lambda isotype and expresses a VH3 gene segment with a V lambda 1 gene, while the second cell line produces an IgG3 lambda antibody expressing a combination of VH2/V lambda 3. Both molecules show evidence of somatic mutation. The D gene segments of the heavy chains vary in length and display limited sequence homology with known germline D segments. As demonstrated previously, JH4 predominates (two JH4 and one JH3) and all three utilize the J lambda 3 gene segment. In addition, we have isolated and sequenced a number of germline VH2 gene segments in an attempt to better understand the nature of the VH2 germline repertoire. In addition to contributing to the understanding of the human antibody repertoire, such clinically relevant molecules may prove to be a source of passive immunotherapy for those at risk to developing disease.

Human rheumatoid B-1a (CD5+ B) cells make somatically hypermutated high affinity IgM rheumatoid factors

To analyze the structure and formally ascertain the B-1a cellular origin of IgM rheumatoid factor (RF) autoantibodies, we generated 4 IgM RF mAb-producing cell lines using sorted (surface CD5+) B-1a cells from a patient with active rheumatoid arthritis. The RF mAb111, mAb112, mAb113, and mAb114 were monoreactive and displayed a relatively high affinity for human IgG Fc fragment (Kd, 3.1 x 10(-7) to 6.8 x 10(-7) M). The B-1a origin of the lymphocytes that gave rise to the IgM RF was confirmed by the expression of surface CD5 and specific CD5 mRNA by all mAb-producing cell lines. Analysis of the genes encoding the RF mAb VH and VL regions revealed that members of the VHI and VHIII families were utilized in conjunction with V kappa IIIa, V kappa IIIb, or V lambda I genes. JH3 and JH4 genes were each utilized twice. The H chain CDR3 sequences were divergent and variable in length. The RF mAb VH genes were identical or closely related to those expressed in the "restricted" fetal B cell repertoire and/or were JH-proximal. For instance, mAb111 VH gene likely constituted a mutated variant of the expressed fetal 20P3 which is the second most JH-proximal gene (125 kb from JH). In addition, the expressed VH and VL genes were among those that have been found to encode other RF, different autoantibodies, high affinity antibodies induced by exogenous Ag, and natural autoantibodies in the adult and neonatal B cell repertoires. When compared with those of known germline genes, the expressed V gene sequences displayed a number of differences. By cloning and sequencing DNA from PMN of the same patient whose B lymphocytes were used for the mAb generation, we showed that such differences resulted from somatic hypermutation in the RF mAb112 VH gene. The germline gene (112GL) that presumably gave rise to the RF mAb112 VH segment was identical to the expressed fetal 51P1 gene. The distribution and the high replacement to silent mutation ratio of the nucleotide mutations in RF mAb112 VH segment were highly consistent with their selection by Ag. RF mAb113 was clonally related to RF mAb112, as shown by the utilization of the same sets of VHI-D-JH4 and V kappa IIIb-J kappa 4 genes, displaying identical junctional sequences, and the presence of two identical replacement and one silent mutations.(ABSTRACT TRUNCATED AT 400 WORDS)

Restricted immunoglobulin VH usage and VDJ combinations in the human response to Haemophilus influenzae type b capsular polysaccharide. Nucleotide sequences of monospecific anti-Haemophilus antibodies and polyspecific antibodies cross-reacting with self antigens

To examine the human antibody repertoire generated against a biologically significant antigen we have obtained sequences of heavy chain variable region genes (IgVH) from 15 monoclonal antibodies specific for the capsular polysaccharide of Haemophilus influenzae type b (Hib PS). All VH segments are members of the VH3 family and 9 of 15 are members of the smaller VH3b subfamily. Restriction is evident by the shared use of certain VDJ joints in independent hybridomas from different subjects. Two hybridomas generated from the same subject demonstrate identical heavy chain variable region gene sequences but differ in isotype and rearrange alternative light chain variable region genes (IgVL), suggesting that in a normal immune response, a single pre-B cell clone may use different light chain rearrangements and give rise to progeny capable of reacting with antigen. Using a polymerase chain reaction assay optimized to detect base pair differences among VH genes we demonstrate that at least a portion of expressed anti-Hib PS VH genes have undergone somatic mutation. Anti-Hib PS heavy chain genes are homologous to VH segments encoding autoantibodies and two hybridomas secrete anti-Hib PS antibody that cross-reacts with self antigens (double-stranded DNA and single-stranded DNA). Comparison of VH regions of self-reactive and monospecific anti-Hib PS Ab demonstrates no consistent structural feature correlating with fine antigen specificity. These data demonstrate significant restriction in VH usage and VDJ recombination in the anti-Hib PS response and confirm that autoantibodies may be elicited during normal immune responses.

Correlative studies of rheumatoid factors and anti-viral antibodies in patients with rheumatoid arthritis

An analysis of the relationship between the immune response to ubiquitous herpes family viruses, namely Epstein-Barr virus (EBV), cytomegalovirus (CMV), and varicella-zoster virus (VZV) and the presence of rheumatoid factors (RF), which are autoantibodies characteristic of patients with rheumatoid arthritis (RA), was conducted. Antibody profiles (RF, anti-viral antibodies) were monitored in the serum of the RA patients, and in normal individuals. No patient was found to have circulating RF in the absence of anti-viral antibodies. When the patients and normal controls were subdivided according to the presence of serum RF, it was found that when RF were present, the frequency of anti-CMV antibodies, but not anti-EBV or anti-VZV antibodies, was significantly higher (P = 0.02) when compared with RF-negative individuals. The titres of anti-CMV but not anti-VZV antibodies were found to increase in the RA patients with disease duration. To see if these viruses could stimulate RF production in vitro, peripheral blood mononuclear cells (PBMC) isolated from the patients and normal controls were stimulated with viral antigens. PBMC from normal controls, but not from RA patients, appeared to be responsive to viral antigen stimulation and produced RF. These data suggest that the immune response to CMV, to a greater extent than to EBV or VZV, correlates with the presence of RF.

Characterization of two highly homologous autoantibody-related VH1 genes in humans

Previously, we showed that the Humha 1lr rearranged gene was almost identical to the consensus amino acid sequence of several G6 idiotype-positive rheumatoid factor (RF) heavy chains, and to the VH gene-encoded region of the fetally expressed 51P1 cDNA. The finding led us to suggest that the ha 1lr-corresponding germline gene encodes the heavy chains of many human IgM RFs. We now report the isolation of the proposed germline gene, designated Humhv1051; it is identical to the consensus sequence of the G6 heavy chain V regions. During this experiment, we also isolated unexpectedly an additional VH1 gene, termed Humhv1051K; it differs from hv1051 by one amino acid residue. Importantly, hv1051K is identical to Humha113, the rearranged VH1 gene of a natural anti-cardiolipin antibody.

Sequence analyses of three immunoglobulin G anti-virus antibodies reveal their utilization of autoantibody-related immunoglobulin Vh genes, but not V lambda genes

Accumulated sequence analyses of the antibody repertoire have revealed that most autoantibodies and developmentally regulated antibodies share a small set of germline Ig-variable region (V) genes. The findings have prompted speculation that certain autoantibodies are of developmental importance and may be instrumental in maintaining homeostasis of the adult antibody repertoire. In order to evaluate this hypothesis critically, it is first necessary to determine the V gene usage in human antibodies against foreign substances. Unfortunately, only a few such antibodies have had their heavy and light chains characterized. To rectify the situation, we adapted the anchored polymerase chain reaction to clone and analyze rapidly the expressed V genes for three anti-virus IgG antibodies. The results show that all three heavy chain V (Vh) genes are highly homologous to the known autoantibody-related Vh genes. In contrast, two light chain V (VL) genes of the V lambda 1 subgroup are similar to a non-autoantibody-related germline V lambda 1 gene. Taken together with the reported Vh and VL sequences of several antibodies against viruses and bacteria, the data show that many antipathogen antibodies may use the same small set of Vh genes that encode autoantibodies, but diverse VL genes that are distinct from autoantibody-related VL genes. Thus, only a small portion of the potentially functional germline Vh genes are used recurrently to generate most antibodies in a normal antibody repertoire, regardless of their reactivities with either self or non-self.

A statistical examination of hypervariability in complementarity-determining regions of immunoglobulins

To determine the relative importance of gene conversion followed by natural selection and of natural selection for point mutation in generating variability in immunoglobulins, the numbers of synonymous and nonsynonymous substitutions in immunoglobulin sequences of various subgroups were estimated for complementarity-determining regions (CDRs) and for framework regions (FRs). Both the number of synonymous substitutions and the number of nonsynonymous substitutions in the CDR were found to exceed the corresponding numbers in the FR. Therefore, gene conversion is likely to be an important mechanism for providing variability in the CDR of immunoglobulins. The correlation coefficients between the number of synonymous substitutions and the number of nonsynonymous substitutions and between the substitution number in the CDR and that in the FR were found to be very low. Again, gene conversion is thought to be responsible for this finding.

The repertoire of human germline VH sequences reveals about fifty groups of VH segments with different hypervariable loops

We have used the polymerase chain reaction and VH family-based primers to clone and sequence 74 human germline VH segments from a single individual and built a directory to include all known germline sequences. The directory contains 122 VH segments with different nucleotide sequences, 83 of which have open reading frames. The directory indicates that the structural diversity of the germline repertoire for antigen binding is fixed by about 50 groups of VH segments: each group encodes identical hypervariable loops. The directory should help in mapping the VH locus, in estimating somatic mutation and VH segment usage and in designing and constructing synthetic antibody libraries.

Characterization of the cDNA of a broadly reactive neutralizing human anti-gp120 monoclonal antibody

The F105 mAb, identified in an HIV-1-infected individual, binds to a discontinuous epitope on the HIV-1 gp120 envelope glycoprotein, blocks the binding of gp120 to the CD4 viral receptor, and neutralizes a broad range of HIV-1 isolates. This study reports the primary nucleotide and deduced amino acid sequences of the rearranged heavy and light chains of the mAb F105. This IgG1k mAb uses a VH gene member of the VH4 gene family (V71-4) and is productively rearranged with a D-D fusion product of the dlr4 and da4 germline DH genes and the JH5 gene. This rearranged heavy chain gene expresses the VH4-HV2a idiotope, which is seen in human monoclonal IgM cold agglutinins. The F105 Vk appears to be derived from the Humvk325 germline gene and is rearranged with a Jk2 gene. For both chains, the mutational pattern in the rearranged VH and VL genes is indicative of an antigen-driven process. These studies show that production of a broadly neutralizing anti-HIV-1 antibody that recognizes determinants within the CD4 recognition site of the envelope glycoprotein is achieved by rearrangement of the V71-4 and Humvk325 germline variable region genes along with selected individual point mutations in the rearranged genes.

Recognition by recombinant autoimmune thyroid disease-derived Fab fragments of a dominant conformational epitope on human thyroid peroxidase

To characterize the nature of thyroid peroxidase (TPO) autoantibodies present in the sera of patients with autoimmune thyroid disease, we cloned three IgG1/kappa Fab fragments which bind 125I-TPO. This was accomplished by the molecular cloning and expression in bacteria of IgG gene fragments from B cells infiltrating the thyroid of a patient with Graves' disease. The three Fab fragments (SP2, SP4, and SP5) are coded for by a common heavy chain (VH1, D, JH3) and three related, but different, light chains (VK1, JK2). The SP Fab fragments bind specifically to TPO with high affinities (6 x 10(-11)-2 x 10(-10) M) comparable to those of serum TPO autoantibodies. TPO autoantibodies represented by the SP Fab fragments are present in all 11 patients studied, constitute a high proportion (36-72%) of serum TPO autoantibodies in individual patients and interact with a conformational epitope on TPO.

A continuous sequence of more than 70 amino acids is essential for antibody binding to the dominant antigenic site of glycoprotein gp58 of human cytomegalovirus

Antigenic domain 1 (AD-1) on glycoprotein gp58 of human cytomegalovirus was characterized in detail, using mouse and human monoclonal antibodies as well as human convalescent sera. Series of procaryotically expressed fusion proteins and synthetic peptides of various lengths were used as sources of antigen. Binding of antibodies was found to depend on a continuous sequence of more than 70 amino acids between residues 552 and 635 of gp58. The fine specificities for sequences involved in antibody binding were (i) amino acids 557 to 635 for neutralizing as well as nonneutralizing mouse monoclonal antibodies, (ii) amino acids 552 to 630 for a neutralizing human monoclonal antibody, and (iii) amino acids 557 to 630 for antibodies present in human sera. Experiments involving fragments of AD-1, presented either as procaryotically expressed fusion protein or as synthetic peptides, indicated that the intact structure was required for recognition of AD-1 by antibodies.

Molecular analysis of the V kappa III-J kappa junctional diversity of polyclonal rheumatoid factors during rheumatoid arthritis frequently reveals N addition

Much interest was stirred in recent years by the evidence that rheumatoid factors (RF) variable regions are encoded by a restricted set of V genes, with little or no somatic mutations, that are often overexpressed in the fetal repertoire. This is reminiscent of what has been observed for natural autoantibodies. However, these data come from studies of monoclonal RF (mRF) isolated from patients with lymphoproliferative disorders who usually do not present autoimmune symptoms. The molecular characterization of RF during autoimmune diseases such as rheumatoid arthritis (RA) has been hampered for some time because of their polyclonality; recently using the polymerase chain reaction method, we have demonstrated that RF kappa variable regions from a patient with RA were encoded by V kappa III genes known to code for mRF but that these genes had undergone somatic mutations with a pattern suggesting an antigen-driven maturation. Because an important role of the light chain third complementarity-determining region (CDR3) in anti-IgG reactivity and idiotype expression has already been suspected for RF, we now report the molecular characterization of the junction regions of these rearranged V kappa gens. Surprisingly, our data show that in 55% of the cases there is addition of a proline and/or glycine amino acid residue at the recombination site between V kappa and J kappa. The sequence analysis of our patients' germ-line Vg and J kappa 4 genes segments and their flanking regions demonstrates that the additional codons are not readily explicable by recombination between germ-line sequences and probably result from an N addition process. Since we could not find such an additional codon in 15 previously published mRF kappa chains we suggest that "pathogenic" RF during RA and mRF derive from different, although overlapping, B cell subsets. Moreover, since additional codons at the recombination site of V kappa and J kappa seem exceptional in expressed human kappa chains and because the resulting amino acid residue is a proline in most cases, we think that RF kappa chain CDR3 is under a very strong selective pressure during RA.

Complete amino acid sequence of the variable regions of two highly related heavy and light chains of human IgG (SFL) and IgM (RIV) rheumatoid factors

The complete amino acid structure of the variable regions of two monoclonal human rheumatoid factors (RF), antibodies that bind to the Fc portion of IgG, is presented. Although these RFs are of different isotypes, IgG (SFL) and IgM (RIV), they are highly related. They probably derive from the same KIII light chain variable region used, but the heavy chains are derived from genes of the VHIII family that are probably evolutionarily related. An analysis of the level of somatic mutation reveals that antigen selection was probably involved in the maturation of these clones. These antibodies, although highly related, are not merely IgM to IgG switch variants which occurred independently in different individuals. Little is currently known about the structure of IgG RFs and this study indicates that the level of somatic mutation of SFL is similar to other autoantibodies or antiviral antibodies of the IgG isotype.

Human combinatorial antibody libraries to hepatitis B surface antigen

Human antibody Fab fragments that bind to hepatitis B surface antigen (HBsAg) were generated by using a recombinant phage surface-display expression system. Characterization of HBsAg-specific Fab fragments isolated from two vaccinated individuals reveals diversity in specificity of antigen binding and in the sequences of the complementarity-determining region. The sequence results show examples of human light-chain promiscuity that result in fine specificity changes and a strong relationship to a human germ-line gene. This application illustrates further that this technique is a powerful tool to isolate distinct human antibodies against immunogenic viral targets.

CD5 negative IGM rheumatoid factor B cells in B-chronic lymphocytic leukemia and benign mixed cryoglobulinemia

IgM-RF B cell precursors are abnormally overrepresented in "well differentiated" lymphoid monoclonal proliferations while data on less mature lymphoid malignancies are still awaited. This nevertheless suggests that RF activity plays a role in the transforming process perhaps by inducing constant stimulation of the precursor B cells. Despite the preferential use of similar VH and VL genes with little or no somatic hypermutations in both malignant B-cell CLL and nonmalignant mixed cryoglobulinemia, these proliferations do differ in CD5 membrane expression and in their clinical evolution. One possibility could be that CD5 glycoprotein is lost during maturation of the lymphocyte into a secreting cell as suggested by data on Waldenström's disease and the LES-CLL and by in vitro studies. Alternatively, CD5 expression could play an additional direct role in malignant transformation as suggested by recent data on the CD5 receptor ligand. Further data on the proliferating cells in both situations as well as on the genetic control of CD5 expression in B cells and its physiology should shed additional light on the mechanisms of B-cell malignancy.

Hidden rheumatoid factor and Wa idiotype expression in juvenile rheumatoid arthritis

The major rheumatoid factor cross-reactive idiotype, which was defined by prototypic monoclonal IgM rheumatoid factors from Waldenstrom's macroglobulinaemia patient Wa, is present on 60% of all monoclonal IgM RF paraproteins. One-third of patients with juvenile rheumatoid arthritis (JRA), who are seronegative for classic IgM rheumatoid factor (RF), express the Wa idiotype in high titre in their sera. To determine if the Wa idiotype is present on hidden rheumatoid factors in JRA patient sera, we studied hidden RF expression by both ELISA and haemolytic assay techniques. The majority of JRA sera with increased concentrations of the Wa idiotype did not have increased RF activity nor hidden RF activity. In some JRA patients, the Wa idiotype may be expressed on a parallel set of immunoglobulin molecules, related to RFs, but lacking the ability to bind to IgG.

Molecular characterization of five human anti-human immunodeficiency virus type 1 antibody heavy chains reveals extensive somatic mutation typical of an antigen-driven immune response

We report the heavy chain variable region sequences from the cDNAs of five previously described monoclonal cell lines producing human antibodies specific for the human immunodeficiency virus type 1 and detail the molecular characteristics, germ-line origins, and extent of somatic mutation among these antibodies. Three of the five heavy chain variable regions derive from the VHIV gene family, but each has arisen from a different heavy chain variable region (VH) gene segment within the VHIV family. In addition, one is derived from a VHI gene segment, and one is derived from a VHV gene segment. Since four of the five antibodies arise from known germ-line VH elements, a precise determination of the extent of somatic variation is possible. The amount of variation from the closest germ-line sequence ranges from 4.5% to 14.8% among these antibodies, most of which is concentrated in the complementarity-determining regions. In general, the diversity (D) segments are long, characteristic of D-D fusions and/or extensive terminal deoxynucleotidyltransferase activity; however, definitive homologies cannot be found with the known germ-line D segments. Joining (JH) gene segment utilization appears random. The use of five different germ-line VH gene segments and extensive somatic mutation provides evidence that a polyclonal, antigen-driven immune response occurs during the natural infection with human immunodeficiency virus.

Expression of the major rheumatoid factor cross-reactive idiotype in pediatric patients with systemic lupus erythematosus

Rheumatoid factor cross-reactive idiotype (RF-CRI) is expressed in high concentrations in the sera of some patients with rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA). To determine if RF-CRI is specifically expressed in rheumatic disease or if it is secondary to polyclonal B-cell activation, we examined sera of 23 children with SLE, 16 adolescents with infectious mononucleosis (IM), and age-matched pediatric controls for RF-CRI expression. Concentrations of RF-CRI in serum, determined by an inhibition ELISA, were 24 +/- 17 micrograms/ml (mean +/- SD) in 25 normal children, 31 +/- 17 in 16 young adults with IM, and were significantly increased, 70 +/- 80 micrograms/ml, in the 23 children with SLE (p less than 0.036). Eleven of 23 SLE patients had serum RF-CRI greater than the mean +/- 2 SD for normal children. Ten of 23 SLE sera contained IgM rheumatoid factor (RF) activity. One patient with IM had a borderline elevated RF-CRI level, and 5 IM patients had RF in their sera. The serum IgM concentrations in sera were: SLE (192 +/- 93 mg/dl) and IM (234 +/- 77 mg/dl) sera. These levels were significantly elevated compared to controls (132 +/- 44 mg/dl), p less than 0.031 for SLE and p less than 0.001 for IM, suggesting that polyclonal activation of B cells was present in SLE and IM patient groups. Increased expression of RF-CRI in the SLE patients correlated directly with high titer anti-DNA antibody values (r = 0.3965, p less than 0.05) and RF activity when human IgG (r = 0.5026, p less than 0.05) was used as the RF binding substrate and inversely with serum C3 levels (r = 0.3925, p less than 0.05). RF-CRI expression did not correlate with RF that bound rabbit (r = 0.3123, p greater than 0.05). Increased serum RF-CRI expression is not a result of polyclonal B-cell activation. RF-CRI may be selectively up-regulated in patients with SLE.

Framework peptides from kappa IIIb rheumatoid factor light chains with binding activity for aggregated IgG

Most monoclonal human rheumatoid factors (RF) and some RF from rheumatoid patient's synovia are restricted in their light chains, using predominantly the kappa IIIb subfamily. Very few sequence differences are found between these light chains. Light chains with similar variable region framework sequences are also found in some mouse monoclonal RF derived from mice stimulated with lipopolysaccharide or secondarily immunized with protein antigens. There are two likely explanations for this restriction in framework sequences between the two species: (a) the sequences are important for the immunoregulation of RF production or (b) the sequences are concerned with the antibody binding specificity of the RF. We have examined overlapping octapeptides from the kappa IIIb light chain variable region and show that some framework peptides have the ability to bind aggregated IgG. Replacement of amino acids within the peak binding peptide have indicated the critical amino acids necessary for binding.

Relationship of the CD5 B cell to human tonsillar lymphocytes that express autoantibody-associated cross-reactive idiotypes

We examined human tonsillar B cells for expression of autoantibody heavy-chain or kappa light-chain cross-reactive idiotypes (CRIs), respectively defined by murine MAbs G6 or 17.109. We find 17.109 or G6 each specifically binds a subpopulation of B cells, respectively reacting with 3.8 +/- 3% (mean +/- SD) or 2.0 +/- 1.2% of all tonsillar lymphocytes. Cells reactive with both 17.109 and G6 comprise only 0.4 +/- 0.3% of tonsillar lymphocytes. Although each tested specimen had 17.109-positive cells, 2 of 19 tonsils (11%) did not have any G6-reactive cells. We find that CRI-positive cells and CD5 B cells both co-express slgD but fail to bind peanut agglutinin or MAbs specific for CD10, indicating that both cell types reside in the mantle zones of secondary B cell follicles. However, less than half of the B cells bearing one or both of these CRIs express detectable levels of CD5. Nevertheless, we find that G6-reactive lymphocytes constitute a multiclonal population of cells that express homologous heavy chain variable region genes, each rearranged to one of several distinct and apparently nonmutated D and JH gene segments. Collectively, these studies indicate that expression of nondiversified autoantibody-encoding variable region genes may not be an exclusive property of B cells that bear detectable levels of the CD5 surface antigen.

Restricted diversity of the variable region nucleotide sequences of the heavy and light chains of a human rheumatoid factor

The complete nucleotide sequences of the variable region genes of the heavy and light polypeptide chains of a human monoclonal rheumatoid factor (RF) produced from a human-mouse heterohybridoma were determined. The antibody, designated YES8c, contained V kappa III, J kappa 2, VH1, JH4, and a D gene segment of 9 amino acids. The nucleotide sequences and the deduced amino acid sequences of the light chain variable region were remarkably homologous (97-98%) to previously described RF of the Wa idiotypic family (PAY, GLO, CUR, FLO, and GAR) and to that of a V kappa III germline gene (Humkv325). The YES8c heavy chain variable region gene was most closely related to the VH1 gene of the restricted human fetal repertoire, designated 51p1, and also to 3 rearranged VH1 genes that were recently isolated from patients with chronic lymphocytic leukemia. These results suggest that variable region genes of RFs are highly conserved and that YES8c VH, as well as V kappa, may be identical to heavy and light chains expressed during early B cell development.

Evolutionary relationship between human and mouse immunoglobulin kappa light chain variable region genes

Similar to the Igh-V multigene family, the human or mouse Igk-V repertoire is a distorted continuum of homologous genes that may be grouped into families displaying greater than 80% nucleic acid sequence similarity among their members. Systematic interspecies sequence comparisons reveal that most human Igk-V gene families exhibit clear homology to mouse Igk-V families (sequence similarity generally greater than 74%). A hypothetical phylogenetic tree of Igk-V genes predicts that a minimum of seven Igk-V genes/families predate mammalian radiation. In two cases, several interrelated mouse Igk-V families exhibit phylogenetic equidistance with just one human Igk-V family, implying a more pronounced divergence for the elevated number of Igk-V gene families in the mouse. Mouse-human Igk-V comparisons, moreover, illustrate how expansion, contraction, and perhaps deletion of Igk-V gene families shape the Igk-V repertoire during mammalian evolution.

Structural characterization of the second major cross-reactive idiotype group of human rheumatoid factors. Association with the VH4 gene family

Rheumatoid factors (RF) are the most common type of functional antibodies among naturally occurring human monoclonal IgM proteins. A large subset of these autoantibodies use structurally homologous light chains of the kappa III subgroup, which bear the 6B6.6 cross-reactive idiotype (CRI). Although antibody binding activity requires both heavy and light chains, information about the heavy chains used by these autoantibodies is limited. To investigate these proteins, the murine monoclonal antibodies, 5-14 and 6-10, were generated by immunization with the heavy chains of the 6B6.6 CRI-positive RF, COR and LEW. These antiidiotypic antibodies reacted with 8 of 11 autoantibodies that coexpressed the 6B6.6 CRI. All 8 RF had heavy chains from the VH4 gene family, as assessed by reactivity with a VH4-specific primary sequence-dependent antibody. The same RF were also identified by the previously described murine monoclonal antiidiotype, LC1. Further experiments revealed that the LC1 antibody delineates a subfamily of VH4 heavy chains that is preferentially used in kappa III-6B6.6 CRI-positive IgM-RF. The cumulative data suggest that 13-22% of RF express both the kappa III-6B6.6 and VH4-LC1 CRI. These findings document that RF autoantibody activity requires specific VL-VH pairing, and that a subset of idiotypically related VH4 heavy chains is commonly expressed in disease-associated monoclonal IgM-RF.

Structural characterization of human monoclonal cold agglutinins: evidence for a distinct primary sequence-defined VH4 idiotype

Cold agglutinins that bind the developmentally regulated I red cell determinant occur naturally among human monoclonal IgM proteins. These autoantibodies are known to use light chains that derive mainly from the minor kappa III (kappa III) variable region subgroup. The kappa III subgroup is also highly expressed in monoclonal rheumatoid factors. However, while most monoclonal rheumatoid factors use structurally homologous heavy chains that derive from the VH1 family, information regarding the structure of the cold agglutinin heavy chains remains fragmentary. We demonstrate here that the kappa III cold agglutinin autoantibodies exclusively use heavy chains that derive from the VH4 family. Furthermore, these autoantibody heavy chains all express the same primary sequence-defined idiotype, corresponding to the second hypervariable region. These data indicate that cold agglutinins use a remarkably homogeneous subset of heavy chain variable regions. Moreover, unique patterns of preferential VH and VL pairing clearly distinguish the anti-I cold agglutinins from all other known monoreactive autoantibodies.

The biologic significance of human natural autoimmune responses: relationship to the germline, early immune and malignant B cell variable gene repertoire

The potential for autoreactivity that has been well documented in normal individuals implies that natural autoimmune responses must serve some physiologic function. To investigate the genetic mechanisms involved in the emergence of such responses, we have determined the sequences of heavy (VH) and light (VL) chain variable region genes for several human monoclonal autoantibodies and compared these with corresponding sequences reported for other antibodies and autoantibodies. Our data reveal that natural autoantibodies can be encoded by nonmutated germline VH and VL genes which are essentially identical to V genes expressed in early B cell ontogeny as well as in some B-lineage tumors. Taken together with other structural data on human autoantibodies, these findings suggest that natural autoimmune responses originate early in ontogeny and that such antibodies may play a regulatory role in development of the normal immune repertoire and possibly in suppressing pathogenic autoimmune or malignant responses.

A human anti-cardiolipin autoantibody is encoded by developementally restricted heavy and light chain variable region genes

Based on recent structural analyses of monoclonal autoantibodies, it appears that a number of these antibodies express germ-line immunoglobulin variable region (V) genes with little or no somatic mutation. In addition, our group and others have noted the identity or near identity of some autoantibody-associated V genes to V genes apparently expressed preferentially in the fetal pre-B cell repertoire. To extend these data, we now report that the heavy and light chain V genes of an anti-cardiolipin antibody derived from a healthy individual display 99% nucleotide sequence homology with V genes expressed in early B cell ontogeny. Sequence comparisons indicate the likely use of fetal-restricted V genes by this autoantibody. Taken together with other data on autoantibody V gene usage, these findings provide further evidence for overlap between the autoantibody-associated and early ontogeny expressed V gene repertoires and suggest that natural autoreactivity may be instrumental in the development and maintenance of the normal immune repertoire.