The human VK locus. Characterization of a duplicated region encoding 28 different immunoglobulin genes

Production and characterization of recombinant human anti-HBs Fab antibodies

Recombinant human Fab antibodies were generated with different reactivities against the hepatitis B virus surface (HBs) antigen. To isolate the antibodies, a method was used that combined transformation of human B cells by Epstein-Barr virus (EBV) infection with a primer-vector system developed for isolating DNA fragments of human Ig Fab portions. With this method, monoclonal and oligoclonal cell lines producing anti-HBs antibodies were established and three anti-HBs Fab antibodies were isolated from two of these cell lines. From analysis of affinity characteristics, immunohistochemical activity, and cytolysis activity, these three Fab antibodies were classified into three different groups. The first group had high affinity for HBs, the second had the ability to kill HBV-infected cells, and the third was applicable to immunohistochemical staining with HBV-infected cells. The combined effect of these antibodies was also investigated by complement-dependent cytotoxicity assay.

Characterization of molecular features, antigen-binding, and in vitro properties of IgG and IgM variants of 4E10, an anti-HIV type 1 neutralizing monoclonal antibody

The human monoclonal antibody 4E10 has been generated previously by immortalization of peripheral blood cells from an HIV-1-infected individual. This antibody binds to the linear epitope NWFDIT on gp41 and exhibits exceptional neutralizing activity against a broad spectrum of primary HIV-1 isolates. In the present study, molecular features, immunoreactivity, and functional activity of 4E10 were studied. The original hybridoma-derived 4E10 was of subtype IgG(3). Analysis of the variable segment of the heavy chain (VH) demonstrated extensive somatic mutations compared to the closest homologous germline gene VH1-69. Most amino acid substitutions occurred in the complementarity-determining region (CDR) 2, characteristic for an antigen-driven somatic maturation. The heavy chain of the CDR3 (H3) is of unusual length and cannot be attributed with certainty to any specific D(H) locus. To enable mass production and to prolong the in vivo half-life, 4E10 was subsequently cloned as IgG(1) in Chinese hamster ovary (CHO) cells. In additional studies, 4E10 was class switched to the IgM isotype. Binding to the linear epitope NWFDIT was not significantly changed after the cloning procedures. However, in vitro studies revealed dramatic differences in the neutralizing potential. The antiviral activity could be greatly enhanced by change of IgG(3) to IgG(1). In contrast, the IgM isotype almost completely lost its neutralizing potential.

Recombinant monoclonal thyrotropin-stimulation blocking antibody (TSBAb) established from peripheral lymphocytes of a hypothyroid patient with primary myxedema

Anti-TSH receptor antibodies (TRAbs) have been known to be involved in Graves' disease and primary hypothyroidism. We previously isolated and reconstituted immunoglobulin (Ig) genes of Epstein-Barr virus-transformed B cell clones producing monoclonal TRAbs obtained from Graves' patients. In the present study, we performed a similar experiment using a B cell clone, 32A-5, derived from a patient with primary hypothyroidism. The variable region genes of Ig heavy (H) and light (L) chains were isolated and sequenced from the 32A-5 clone. A significant number of somatic mutations were found in variable regions of H and L chain gene segments. Each pair of H and L chain cDNAs was ligated into an expression vector for IgG1 production and stably introduced into myeloma cells. The transfectants were injected ip into BALB/c mice to yield ample volume of the antibody for following applications. Interactions of recombinant 32A-5 with Graves' sera with varying thyroid-stimulating antibody (TSAb) activities were studied. The recombinant antibody tended to suppress TSAb activities in 10 of 15 Graves' sera, in which four were significantly inhibited. In summary, this is the first study to analyze human monoclonal TSH-stimulation blocking antibodies (TSBAb) at the molecular level. Use of human recombinant monoclonal TSBAb may be an analytical tool for molecular-basis etiology and an alternative therapeutic path for Graves' disease.

Evidence that the complement control protein-epidermal growth factor-like domain of thyroid peroxidase lies on the fringe of the immunodominant region recognized by autoantibodies

There is no consensus regarding the location of the immunodominant region (IDR) on thyroid peroxidase (TPO) recognized by the majority of autoantibodies. Strong evidence indicates that it lies upstream of amino acid 741. However, an epitope has been localized to downstream residues 742-848 encompassing a disulfide-rich complement control protein (CCP)-like and epidermal growth factor (EGF)-like domain. To determine whether these domains comprise part of the IDR, we used a recombinant CCP/EGF-like polypeptide to screen a thyroid B-cell-derived immunoglobulin gene phage display library. Two unusual TPO autoantibodies were isolated. Neither was among the 83 clones previously obtained by panning the same library on native or denatured TPO, or TPO with the IDR masked. Fab from these clones bound native TPO, one with high affinity (Kd 6 x 10(-10) M), and both recognized TPO expressed on the surface of mammalian cells. Phage-expressing multiple copies of the antibody (multivalent), but not monovalent Fab from these clones, bound to the CCP/EGF polypeptide. Most important, inhibition of TPO binding by autoantibodies to the IDR indicated that the epitopes of the two new autoantibodies overlap with this region. The value of these two rare clones lies in the insight they provide into the location of the TPO IDR. From their binding characteristics, we deduce that the CCP/EGF-like domain lies on the fringe of the TPO immunodominant region.

Molecular study of an IgG1kappa cryoglobulin yielding organized microtubular deposits and glomerulonephritis in the course of chronic lymphocytic leukaemia

Glomerulonephritis with organized microtubular monoclonal immunoglobulin deposits (GOMMID) and glomerulonephritis related to type I cryoglobulin are well-known but rare complications of B cell derived chronic lymphocytic leukaemia. In these disorders, monoclonal Ig have never been studied at the molecular level. We conducted a pathological and molecular analysis in a patient with chronic lymphocytic leukaemia, glomerulonephritis and a single circulating monoclonal Ig. Unusual IgG1kappa kidney deposits were observed. The heavy and light chain variable region sequences of that cryoprecipitating monoclonal Ig were characterized. Light microscopy revealed glomerulonephritis typical of cryoglobulinaemia, with neutrophil and macrophage infiltration, endocapillary hyperplasia and few protein thrombi. Electron microscopic study clearly evidenced numerous subepithelial mixed granular and organized deposits with a unique microtubular organization, reminiscent of the GOMMID. The Ig molecule sequence revealed alterations of charge and hydrophobicity potentially promoting a crystal-like aggregation and the aggregation of microtubules. This description suggests that common mechanisms are involved in various forms of precipitation and/or deposition of complete Ig molecules, with a variable extent of organization and with a possible overlap between pathological patterns of either glomerulonephritis with microtubular deposits or type I cryoglobulinic glomerulonephritis.

The kappa gene repertoire of human neonatal B cells

The kappa chain repertoire of individual IgD(+) human neonatal B cells was analyzed using a single cell PCR technique. A total of 104 productive and 90 non-productive VkappaJkappa rearrangements from three cord blood B cell samples were sequenced and compared to the adult IgM(+) peripheral B cell VkappaJkappa repertoire. All six Vkappa families were present in neonatal B cells, but the distribution was not random. In the non-productive repertoire Vkappa2 and Vkappa6 families were less frequent, Vkappa1 and Vkappa3 families were as frequent, and Vkappa4 and Vkappa5 families were more frequent than expected from random chance. Notably, the Vkappa2 family was negatively selected into the productive repertoire. In contrast, the Vkappa1 family was positively selected because of positive selection of three specific genes, O12/O2, L12a and L9. B3 (Vkappa4) and B2 (Vkappa5) were over-represented in the non-productive repertoire and then were expressed less frequently in the productive repertoire. In contrast, the Vkappa3 family gene, A27, was also over-represented in the non-productive repertoire but not further selected into the productive repertoire. Compared to the adult repertoire, junctional diversity was less marked because of a diminished influence of TdT activity, whereas the mean CDR3 length was comparable to that of normal adult B cells. Comparison of the distribution of Vkappa and Jkappa genes with those found in normal adult subjects suggested that there was less receptor editing in neonatal B cells. When neonatal CD5(+) B cells were compared with CD5(-) IgD(+) B cells, it was noted that the Vkappa gene A30 was used only in CD5(+) B cells in both the productive and non-productive repertoires. The results indicate that the usage of Vkappa genes by neonatal B cells is biased by both intrinsic molecular processes and selection. The evidence of selection indicates that the Vkappa repertoire is shaped by self antigens, since exposure to exogenous antigens is limited at the time of birth.

Primary cutaneous follicle center cell lymphomas and large B cell lymphomas of the leg descend from germinal center cells. A single cell polymerase chain reaction analysis

Primary cutaneous B cell lymphomas are defined as non-Hodgkin lymphomas that occur in the skin without extracutaneous involvement for 6 mo after diagnosis. They are characterized by a less aggressive course and better prognosis than their nodal counterparts. According to the European Organization for Research and Treatment of Cancer classification, the major subentities of primary cutaneous B cell lymphoma are follicle center cell lymphomas, immunocytomas, and large B cell lymphomas of the leg, which differ considerably regarding their clinical behavior, the former two being indolent, the latter being of intermediate malignancy. In this study, we applied a single cell polymerase chain reaction approach to analyze immunoglobulin V(H)/V(L) genes in 532 individual B lymphocytes from histologic sections of four follicle center cell lymphomas localized on the head and trunk, and four large B cell lymphomas on the leg. We found: (i) in six of eight patients a clonal heavy chain, and in seven of eight patients a clonal light chain rearrangement, all being potentially productive; (ii) no bias in VH gene usage, in four of seven light chain rearrangements the V kappa germline gene IGVK3-20*1 was used; (iii) no biallelic rearrangements; (iv) all V(H)/V(L) genes are extensively mutated (mutation rate 5.4-16.3%); (v) intraclonal diversity in six of eight cases (three of each group); and (vi) low replacement vs silent mutation ratios in framework regions indicating preservation of antigen-receptor structure, as in normal B cells selected for antibody expression. Our data indicate a germinal center cell origin of primary cutaneous follicle center cell lymphomas and large B cell lymphomas independent of those belonging to one of these subentities.

Human monoclonal autoantibodies to B-cell epitopes outside the thyroid peroxidase autoantibody immunodominant region

Human autoantibodies to thyroid peroxidase (TPO) interact with a restricted or immunodominant region (IDR) on intact TPO. However, a smaller proportion of polyclonal serum TPO autoantibodies bind outside this region. To isolate monoclonal nonimmunodominant region (non-IDR) TPO autoantibodies, we screened a thyroid-derived immunoglobulin gene phage display library while "epitope masking" the TPO IDR with four human TPO monoclonal autoantibodies that define the IDR. Among 31 non-IDR autoantibodies obtained (expressed as Fab), 8 representatives were analyzed further based on their restriction digestion profiles. All are encoded by almost identical H chains (VH3 family), with extremely long D regions, paired with three different types of light chains. In contrast, IDR TPO Fab from the same patient utilize seven different heavy chains (VH1 and VH5 families) paired nonpromiscuously with different light chains. Use of VH5 genes has not been reported previously for TPO autoantibodies. Both non-IDR and IDR Fab bind specifically to TPO and not to other proteins. The non-IDR Fab affinities for TPO are moderately high (Kd 1-2 x 10(-9) M), somewhat lower than those for most IDR Fab (Kd 1-4 x 10(-10) M). The epitopes of the three types of non-IDR Fab overlap with each other, indicating a major role for their heavy chain in TPO binding. Most importantly, the epitopes of non-IDR Fab are recognized by patients' serum autoantibodies. In summary, we provide the first insight into the immunoglobulin genes, affinities and epitopes of human monoclonal autoantibodies that bind outside the TPO-immunodominant region.

Clonal evolution in a primary cutaneous follicle center B cell lymphoma revealed by single cell analysis in sequential biopsies

B cell neoplasias descending from germinal center cells harbor the hallmark of intraclonal diversity resulting from ongoing mutation in the variable parts of their immunoglobulin-encoding genes. To characterize a primary cutaneous follicle center B cell lymphoma in more detail, we analyzed the respective VH and VL genes in single cells mobilized from four sequential biopsies, three taken from the skin and one obtained after internal dissemination from a retrobulbar infiltrate. The lymphoma cells were found to contain V5-51/D6-12/JH5b (heavy chain) and A27/Jkappa2 (light chain) gene rearrangements detected on both the genomic and the transcriptional level. To provide an accurate mutation analysis, the specific VH gene counterpart (V5-51UK) was cloned from the patient's germline. Analyzing 226 single cells, we found: (i) complete nucleotide identity when VH and VL genes of lymphoma cells from one particular biopsy were compared among each other; (ii) intraclonal diversity due to ongoing mutation comparing the sequences obtained from sequential biopsies; (iii) both VH and VL genes to be highly mutated. Deducing from the sequence data, we propose a scenario of the clonal evolution of the B cell tumor in this patient. From the molecular-biological point of view, this primary cutaneous follicle center B cell lymphoma shows the features of a germinal center cell lymphoma. To draw this conclusion from single cell PCR data, however, a sample of sequential biopsies had to be analyzed.

Somatic insertions and deletions shape the human antibody repertoire

We have sequenced the heavy and light chain genes from 365 IgG(+) B cells and found that 24 (6.5 %) contain somatically introduced insertions or deletions. These insertions and deletions are clustered at "hot-spots" in the antigen-binding site and frequently result in the creation of new combinations of canonical loop structures or entirely new loops that are not present in the human germline repertoire, but are similar to those seen in other species. Somatic insertion and deletion therefore provides a further mechanism for introducing structural diversity into antibodies in addition to somatic point mutation and receptor editing, which have small (single amino acid changes) and large (chain replacement) impacts on structural diversity, respectively.

Molecular mimicry between bacterial and self antigen in a patient with systemic lupus erythematosus

The importance of microbial infection as a trigger for the induction of systemic lupus erythematosus is frequently debated. Clinical observations indicate that anti-viral and antibacterial responses are often accompanied by self reactivity, and anti-pneumococcal antibodies elicited in non-autoimmune individuals by pneumococcal vaccine express lupus-associated anti-DNA idiotypes. To explore the relationship between protective and pathogenic antibodies in humans, we have used the phage display immunoglobulin expression system to generate a combinatorial library from spleen cells of a lupus patient immunized with a polyvalent pneumococcal polysaccharide vaccine prior to splenectomy. From this library, monovalent antigen-binding fragments expressing the 3I Vkappa1-associated idiotype were isolated. This idiotype is expressed on up to 90% of anti-DNA antibodies in the serum of lupus patients and on anti-pneumococcal antibodies in the serum of non-autoimmune individuals. Eight 3I+ monovalent antigen-binding fragments reacting with pneumococcal polysaccharide, DNA or both were analyzed. Four of these fragments were cross-reactive with both foreign and self antigen, demonstrating that a high percentage of anti-bacterial antibodies produced in a patient with lupus bind double-stranded DNA. These studies provide support at the molecular level for a potential role of molecular mimicry in the generation of anti-DNA antibodies. In addition, this is, to our knowledge, the first panel of fully sequenced human anti-pneumococcal antibodies.

Re-expression of RAG-1 and RAG-2 genes and evidence for secondary rearrangements in human germinal center B lymphocytes

V(D)J recombination occurs in immature B cells within primary lymphoid organs. However, recent evidence demonstrated that the recombination activating genes RAG-1 and RAG-2 can also be expressed in murine germinal centers (GC) where they can mediate secondary rearrangements. This finding raises a number of interesting questions, the most important of which is what is the physiological role, if any, of secondary immunoglobulin (Ig) gene rearrangements. In the present report, we provide evidence that human GC B cells that have lost surface immunoglobulin re-express RAG-1 and RAG-2, suggesting that they may be able to undergo Ig rearrangement. Furthermore, we describe two mature B cell clones in which secondary rearrangements have possibly occurred, resulting in light chain replacement. The two clones carry both kappa and lambda light chains productively rearranged, but fail to express the x chain on the cell surface due to a stop codon acquired by somatic mutation. Interestingly, the analysis of the extent of somatic mutations accumulated by the two light chains might suggest that the lambda chain could have been acquired through a secondary rearrangement. Taken together, these data suggest that secondary Ig gene rearrangements leading to replacement may occur in human GC and may contribute to the peripheral B cell repertoire.

Molecular characterization of five neutralizing anti-HIV type 1 antibodies: identification of nonconventional D segments in the human monoclonal antibodies 2G12 and 2F5

We have stabilized a panel of 33 hybridomas producing human monoclonal antibodies (MAbs) against HIV-1 gp160 and p24. Five of these antibodies were able to neutralize different HIV-1 isolates, and two of them (2F5 and 2G12) revealed remarkable potential to neutralize primary virus isolates of different clades in several in vitro tests. To determine whether a structural basis for neutralization could be identified, we analyzed the antibodies at the molecular level. This study reports the primary nucleotide and deduced amino acid sequences of the rearranged heavy and light chain V segments (VH, Vkappa) of the neutralizing MAbs (1B1, 1F7, 2F5, 2G12, and 3D5) and the nonneutralizing anti-gp41 MAb 3D6. Aligning the V segments with the nearest related germline genes illustrated the occurrence of somatic mutations. The neutralizing MAbs show mutational rates comparable to those of antibodies that appear in patients in whom the immune system is under constant antigenic pressure over a long period of time. In contrast, 3D6, which recognizes the immunodominant region on gp41, displays homologies as high as 97 and 98% compared with its VH and Vkappa germline genes. The diversity segments [D(H)] of 1B1, 1F7, 3D5, and 3D6 were assigned to single D(H) segments on the chromosomal D(H) locus. 2F5 presents a D(H) segment 52 nucleotides in length, which could be explained by fusion of two segments on the immunoglobulin heavy chain locus that have not yet been described as rearranged regions. 2G12 D(H) shows best homologies to a D(H) segment between D3-22 and D4-23. This D(H) segment could be the reason for the rare occurrence of antibodies competing with 2G12. Since this nearest related chromosomal region on the D(H) locus does not display recombination signals at the flanking regions, this segment is normally not taken into consideration as a site for immunoglobulin heavy chain rearrangement.

Can immunoglobulin C(H)1 constant region domain modulate antigen binding affinity of antibodies?

Although the switch process is frequently associated with affinity maturation, the constant region is not assumed to play a role in Ag-Ab binding. In the present work, we demonstrate that two clonally related human monoclonal Igs sharing identical V(H) and V(L) sequences, but expressing different isotypes (IgA1kappa(PER) and IgG1kappa(PER)), bind tubulin with significantly different affinities. This difference was mainly accounted for by a disparity in the association rate constants. These results suggest that affinity maturation of this clone could be achieved through class switching in the absence of further somatic mutations. Since the differences observed were found at the Fab level, they also suggest a role for the C(H)1 domain in structuring the Ag-binding site into a more kinetically competent form.

A human antibody specific for hepatitis C virus core protein: synthesis in a bacterial system and characterization

The cDNA coding for the Fab fragment of the human B12.F8 antibody (Ab), directed against the putative nucleocapsid component (core protein) of hepatitis C virus (HCV), was cloned in the prokaryotic phagemid vector, pHEN-1, to obtain its expression in Escherichia coli. The functionality and specificity of the recombinant Ab, called B12Fab, were examined by Western blot and ELISA using recombinant HCV core protein as antigen. The specificity of B12Fab was further confirmed by ELISA with the 33-mer peptide epitope recognized by the original whole B12.F8 Ab. By immunofluorescence, the recombinant B12Fab was shown to recognize HCV core protein produced in cells transfected with HCV cDNA, indicating that the recombinant B12Fab is suitable as a diagnostic tool for tissue localization of the virus. The B12Fab also functioned when displayed on phage particles, providing the basis for future experiments of in vitro affinity maturation and selection of mutants. The variable chain coding regions of the recombinant B12Fab clone were sequenced and the V-gene usage was determined by comparison with the V kappa and VH germline sequences. The B12Fab V kappa chain belongs to the subgroup II and shows the highest degree of homology with the A3 germline gene, whereas the sequence of the VH chain is strictly related to that of the Humhv3019b18 gene of the VH3 family. These results are, to our knowledge, the first report of molecular cloning and characterization of a functional human Ab specific for an HCV antigen.

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.

Somatic mutation and CDR3 lengths of immunoglobulin kappa light chains expressed in patients with rheumatoid arthritis and in normal individuals

Immunoglobulin secretion by plasma cells infiltrating synovial membranes is a prominent feature of RA. Previous analyses of a cDNA library generated from synovium of RA patient BC revealed immunoglobulin kappa light chain transcripts with extensive somatic mutation, frequent N region addition, and unexpected variation in the lengths of CDR3 regions which form the center of the antigen binding site. To determine if these characteristics are present in other individuals, we performed reverse transcription-polymerase chain reaction amplification and sequenced > or = 10 V kappa-containing amplicons from nine tissue samples: synovia of three individuals with long-standing RA (including patient BC), PBLs of two of these individuals, and PBLs or splenocytes of four normal individuals. Increased levels of somatic mutation in PBLs appeared to correlate with increased age, which may reflect accumulation of circulating memory cells and/or decreased bone marrow production of naive B lymphocytes. Two of three RA synovial samples and both RA PBL samples exhibited increased proportions of clones with unusual CDR3 lengths. Enrichment for these antibody binding sites could be due to abnormal regulation of the emerging repertoire or to selection for B lymphocytes bearing antibodies of unusual specificity, and may play a role in the pathogenesis of RA.

Anti-DNA and anti-platelet specificities of SLE-derived autoantibodies: evidence for CDR2H mutations and CDR3H motifs

Although polyreactivity appears to be a characteristic feature of natural autoantibodies, polyreactive anti-DNA autoantibodies can be derived both from patients with autoimmune disease and from normal individuals. It is unclear whether these autoantibodies differ depending on their origin, but previous studies from our laboratory have suggested that polyreactive systemic lupus erythematosus (SLE)-derived platelet-binding anti-DNA autoantibodies have more restricted antigen reactivity and greater functional activity than normal-derived polyreactive autoantibodies. The objective of the present study was to characterize the VH and VL region sequences of 10 human hybridoma anti-DNA autoantibodies derived from peripheral blood lymphocytes of different origins [SLE, rheumatoid arthritis (RA), or normal] to determine whether there are structural differences between these autoantibodies. We show that although some unmutated germline structures (VH and VL) are represented, these are not restricted to anti-DNA autoantibodies from normal individuals and that two normal-derived anti-DNA antibodies showed quite extensively mutated VH genes. However, these mutations, unlike those found in the CDR2H of several of the SLE-derived antibodies, did not appear to be antigen-selected. Three different amino acid motifs, putatively involved in antigen binding specificity, were observed in the CDR3H segments of some of the autoantibodies. One was the previously described YYGSG motif, which was found in a normal-derived anti-DNA autoantibody, while two new potential motifs were observed only in SLE-derived platelet-binding anti-DNA autoantibodies. These data suggest that antigenic and functional differences between SLE-derived and normal-derived platelet-binding anti-DNA autoantibodies may be due to antigen-selected mutations in the CDR2H and specific amino acid motifs in the CDR3H.

Predominant V-region gene configurations in the human antibody response to Haemophilus influenzae capsule polysaccharide

The antibody response to Haemophilus influenzae type b polysaccharide (Hib PS) is known to be encoded by a few V-region genes. We have obtained four human monoclonal Hib PS antibodies from four healthy adult subjects immunized with diphtheria toxin-conjugated Hib PS vaccine. The VH gene segments that encode for these antibodies belong to the VH3 gene family, of which two are related to the V3-23 gene and two to the VH3b subfamily. Both hybridomas that express a V3-23-related gene use short D-segments (3 bp), the JH6 gene segment and a V kappa gene derived from the A2 germline gene. The two hybridomas that express VH3b genes use D-segments of conventional length (24-33 bp), the JH4 gene segment and a non-A2 V kappa gene. Comparison of our sequences with those reported by others suggests that the above patterns of V-region gene segment association exemplify two V-region gene configurations that are predominant in the Hib PS antibody response. The first configuration is reminiscent of antibodies produced by B-1 B cells while the second is more characteristic of antibodies produced by conventional B cells. The possibility that these two configurations, in fact, represent the products of two different B cell lineages remains to be elucidated.

kappa+lambda+ dual receptor B cells are present in the human peripheral repertoire

It is a common notion that mature B lymphocytes express either kappa or lambda light (L) chains, although the mechanism that leads to such isotypic exclusion is still debated. We have investigated the extent of L chain isotypic exclusion in normal human peripheral blood B lymphocytes. By three-color staining with anti-CD19, anti-kappa, and anti-lambda antibodies we could estimate that 0.2-0.5% of peripheral blood B cells from healthy adults express both kappa and lambda on the cell surface. The kappa+lambda+ cells were sorted, immortalized by Epstein-Barr virus, and five independent clones were characterized in detail. All clones express both kappa and lambda on the cell surface and produce immunoglobulin M that contain both kappa and lambda chains in the same molecule, i.e., hybrid antibodies. Sequencing of the L chains revealed in three out of five clones evidence for somatic mutations. It is interesting to note that among a panel of single receptor B cell clones we identified two lambda+ clones that carried a productively rearranged kappa, which was inactivated by a stop codon generated by somatic mutation. These findings indicate that dual receptor B lymphocytes can be found among mature antigen-selected B cells and suggest that somatic mutation can contribute to increase the degree of isotypic exclusion by inactivating a passenger, nonselected L chain.

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.

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.

Immunoglobulin light chain class multiplicity and alternative organizational forms in early vertebrate phylogeny

The prototypic chondrichthyan immunoglobulin (Ig) light chain type (type I) isolated from Heterodontus francisci (horned shark) has a clustered organization in which variable (V), joining (J), and constant (C) elements are in relatively close linkage (V-J-C). Using a polymerase chain reaction-based approach on a light chain peptide sequence from the holocephalan, Hydrolagus colliei (spotted ratfish), it was possible to isolate members of a second light chain gene family. A probe to this light chain (type II) detects homologs in two orders of elasmobranchs, Heterodontus, a galeomorph and Raja erinacea (little skate), a batoid, suggesting that this light chain type may be present throughout the cartilaginous fishes. In all cases, V, J, and C regions of the type II gene are arranged in closely linked clusters typical of all known Ig genes in cartilaginous fishes. All representatives of this type II gene family are joined in the germline. A third (kappa-like) light chain type from Heterodontus is described. These findings establish that a degree of light chain class complexity comparable to that of the mammals is present in the most phylogenetically distant extant jawed vertebrates and that the phenomenon of germline-joined (pre-rearranged) genes, described originally in the heavy chain genes of cartilaginous fishes, extends to light chain genes.

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.

A directory of human germ-line V kappa segments reveals a strong bias in their usage

From the genomic DNA of a single individual, we have amplified, cloned and sequenced 37 human germ-line V kappa segments. Four of these segments were new. We then compiled a comprehensive directory of all germ-line V kappa segments and identified 50 different sequences with open reading frames. Comparison with 236 rearranged sequences revealed that no more than 24 of these germ-line sequences could be assigned rearranged counterparts, that some of these were rarely used, and that only about 11 sequences are used frequently. This suggests that the expressed V kappa repertoire is mainly derived from a limited number of segments. Most surprisingly, the J kappa-distal region of the locus appears to be rarely used: we could unambiguously assign 162 rearranged sequences to V kappa segments of the J kappa-proximal region, but only 5 to segments of the J kappa-distal region.

The human immunoglobulin kappa locus: pseudogenes, unique and repetitive sequences

The human kappa locus contains 25 pseudogenes. After seven of them were described earlier the structures of the remaining 18 are reported now, thus completing the description of all human V kappa genes and pseudogenes. Most of the pseudogenes carry several defects each. Alignments of the pseudogene sequences and comparison with the consensus sequences of the potentially functional V kappa genes indicate that, on PCR amplification of genomic DNA aimed at certain genes of the latter class, also some of the pseudogenes would be coamplified. Unique sequences, which qualify as sequence tagged sites (STS), were defined across the locus. The occurrence of 15 repetitive elements of the LINE1 type in the locus is described. The 15 sequenced Alu elements were assigned to the known Alu subfamilies of different evolutionary age. One of the Alu elements was found only in one of the copies of the kappa locus. It must, therefore, have been inserted after the duplication step which may have taken place about one million years ago. This element belongs to an Alu subfamily known to have been mobile until recently. Some aspects of the evolution of the V kappa pseudogenes and orphons (i.e. V kappa genes located outside the kappa locus) are also discussed.

An apparently common mechanism of generating antibody diversity: length variation of the VL-JL junction

The joining of various V, (D) and J gene segments during DNA rearrangement of the antigen receptor genes is one of the principle mechanisms responsible for the generation of antibody diversity. In the absence of N-segment variation, the structures of the coding joints formed during light chain rearrangement are thought to be less complex than their heavy chain counterparts. Consequently, the joining of the VL and JL gene segments during recombination account for all of the junctional diversity seen within the third complementarity determining region (CDR3). We generated kappa light chain transcripts from human fetal liver and peripheral blood lymphocytes and found that approximately one third exhibit a variation in the length of CDR3-independent of the JK gene segment utilized. Nucleotide sequence analysis reveals that many of the nucleotides at the VK-JK joint resulting in length variation of CDR3 are directly encoded by the germline VK and JK gene segments used in these transcripts. However, nearly 20% of the transcripts contain N-segment additions consistent with TdT-like activity. These observations suggest that TdT or an analogous enzyme must be active in a significant percentage of human B-lymphocytes during light chain rearrangement. Length variation in light chain CDR3 expands the potential repertoire and thus contributes an additional means of generating diversity in the antibody molecule.

Evidence of antigen receptor-influenced oligoclonal B lymphocyte expansion in the synovium of a patient with longstanding rheumatoid arthritis

Plasma cell infiltration of synovium is common in longstanding rheumatoid arthritis (RA). The mechanism(s) underlying synovial B cell proliferation remains unclear. One theory invokes nonspecific polyclonal stimuli; another implicates antigen as the driving force. Antigen-driven repertoires are characteristically enriched for related sets of V gene segments containing similar sequence in the antigen binding site (complementarity-determining regions; CDRs). To study the forces shaping B cell proliferation, we analyzed V kappa transcripts expressed in the synovium of an RA patient. We found Humkv325, a developmentally regulated V kappa III gene segment associated with autoantibody reactivity, in > 10% of randomly-chosen synovial C kappa cDNAs. Two sets of sequences contained identical charged amino acid residues at the V kappa-J kappa join, apparently due to N region addition. We generated "signature" oligonucleotides from these CDR3s and probed PCR amplified V kappa products from the synovium and PBLs of the same patient, and from PBLs and spleen of individuals without rheumatic disease. Significant expression of transcripts containing these unique CDR3 sequences occurred only in the patient's synovium. Thus, in this synovium there is expansion of a limited set of B cell clones expressing antigen receptors that bear evidence of antigen selection.

The V kappa genes of the L regions and the repertoire of V kappa gene sequences in the human germ line

Only 14 of the 25 V kappa genes and pseudogenes had been found before as parts of the L regions. The cloning and linking described in the accompanying report allowed us now to assign to Lp or Ld some V kappa genes which had been found before on scattered clones. In addition the sequences of several still unknown genes are reported here, thus completing the publication of the V kappa genes of the kappa locus as far as they are potentially functional or have only one or two 1-bp defects. Of the V kappa genes of the kappa locus, 32 are potentially functional, 16 have minor defects, 3 have both potentially functional and slightly defective alleles and 25 are pseudogenes which amounts to a repertoire of 76 V kappa-related gene sequences. The V kappa genes of the L regions are, within the subgroups, particularly similar to each other, which is in part due to common evolutionary origins and in part caused by gene conversion-like events. One donor-acceptor pair could be clearly identified, since converted and not-converted alleles of the acceptor gene were found. In other cases the duplicates of the converted genes served as non-converted controls.

Human antibody fragments specific for human blood group antigens from a phage display library

We have isolated human antibody fragments with binding specificities against the blood group antigens of the ABO and I blood group systems (B and HI), of the Rh system (D and E) and of the Kell system (Kpb), by selecting a phage-antibody library on human red cells. The fragments, expressed in bacteria, were antigen-specific and effective in assays including agglutination and immunohistochemistry. Selection of phage-antibody libraries using intact cells seems to offer a promising alternative to hybridoma technology for the production of antibodies against cell surface molecules.

cDNA clones encoding mink immunoglobulin lambda chains

Screening of a mink cDNA library with an antibody probe resulted in the isolation of clone pIGL-2 containing an Ig lambda chain coding sequence. The sequence comprised almost the entire V segment as well as J, C, and 3'-untranslated sequences. A second clone, pIGL-10, was isolated by rescreening the cDNA library with the use of pIGL-2 as a probe. pIGL-10 was found to contain a frameshift deletion of a single nucleotide in the C region. pIGL-2 and pIGL-10 were 81% homologous to each other in the FR3 of the V segment, and 95% of homology was found in their C regions. The J segments of the two clones differed in only one nucleotide position. Comparison of cloned lambda chain sequences with those of other mammals revealed that mink V lambda and C lambda genes have the highest homology with their human counterparts. The V lambda sequence of clone pIGL-2 appears to be a homologue of human subgroup III V lambda genes. Southern blot hybridization of mink DNA with the C lambda and V lambda probes derived from pIGL-2 revealed five or six hybridizing C lambda fragments and at least 11 hybridizing V lambda fragments. This suggested that the lambda genes in carnivores, like those in primates, have duplicated extensively during evolution.

Generation and molecular analyses of two rheumatoid synovial fluid-derived IgG rheumatoid factors

OBJECTIVE

To study the Ig genes that encode IgG rheumatoid factor (IgG-RF) from rheumatoid synovial fluid.

METHODS

We used rheumatoid synovial fluid B cells to generate IgG-RF-secreting hybridomas. We then characterized their binding properties and determined their nucleotide sequences.

RESULTS

Two monospecific IgG-RFs were obtained. Sequence analysis of the RFs revealed a new V lambda gene family (designated V lambda 9) and extensive somatic diversification, including a duplication-insertion of 18 nucleotides (6 amino acid residues) into a hypervariable region.

CONCLUSION

The data provide further support for an antigen-driven response in the sustained production of potentially pathogenic IgG-RFs in rheumatoid synovium.

Diversity of immunoglobulin kappa light chain gene rearrangements and evidence for somatic mutation in V kappa IV family gene segments in X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA) is a humoral immunodeficiency disease in man, characterized by an arrest in B lymphocyte differentiation at the precursor B cell stage. The structure of expressed immunoglobulin (Ig) kappa light (L) chain rearrangements of nine B lymphoblastoid cell lines from one XLA patient was investigated by amplification of cDNA by the polymerase chain reaction using 5' V kappa family-specific primers and a 3' kappa constant region primer. Members of all four V kappa gene families were found to be utilized in Ig kappa L chain rearrangements at frequencies that were consistent with random V kappa family usage. There was no preference for usage of any particular kappa joining segment. Additional diversity was generated by deletions and random nucleotide insertions at the site of juxtaposition. Particular V kappa members seemed to be overrepresented in the sample. The observed homology of the V kappa I, V kappa II and V kappa III region sequences, both to each other and to known germ-line V kappa sequence indicated the absence of somatic mutations in the majority of these expressed Ig genes. In contrast of the single-member V kappa IV family four different sequences were found to be expressed. That these sequences were mutated derivatives of a germ-line V kappa IV element was substantiated both by sequence analysis and oligonucleotide hybridization. This finding shows that the mutation process can occur in early stages of B cell development i.e. before H chain class switch has occurred. The presence of these mutations is probably independent of clonal expansion since XLA patients are unable to respond to antigen. We conclude that the differentiation arrest in XLA does not preclude early onset of somatic mutation events in V kappa gene segments.

V kappa gene segments rearranged in chronic lymphocytic leukemia are distributed over a large portion of the V kappa locus and do not show somatic mutation

The structure of the human V kappa locus has been thoroughly investigated, but how the germ-line V kappa gene segment repertoire is actually sampled in kappa chain gene rearrangements is not known. In order to begin to answer this question we have polymerase chain reaction (PCR) amplified the rearranged V kappa genes from 26 kappa-expressing cases of chronic lymphocytic leukemia (CLL), followed by cloning and sequencing of the PCR product. All four V kappa gene families were represented amongst rearranged genes. In 25 out of 32 cases, the sequence of the rearranged gene matches perfectly that of 1 of 11 different known germ-line V kappa genes, indicating that no somatic mutation has occurred. Of the remaining 7 rearranged V kappa genes, 4 differ from known germ-line genes by only one or two amino acid residues; and 3 differ from each other and from all known sequences by 5 or more residues, suggesting that somatic mutation has occurred in these 3 cases. We conclude that: (a) in at least three-quarters of cases the rearranged genes are unmutated; (b) there is preferential usage of individual V kappa genes but not of V kappa gene families; and (c) the V kappa genes used are widely dispersed in the V kappa locus.

A transgenic mouse that expresses a diversity of human sequence heavy and light chain immunoglobulins

We have generated transgenic mice that express a diverse repertoire of human sequence immunoglobulins. The expression of this repertoire is directed by light and heavy chain minilocus transgenes comprised of human protein coding sequences in an unrearranged, germ-line configuration. In this paper we describe the construction of these miniloci and the composition of the CDR3 repertoire generated by the transgenic mice. The largest transgene discussed is a heavy chain minilocus that includes human mu and gamma 1 coding sequences together with their respective switch regions. It consists of a single 61 kb DNA fragment propagated in a bacterial plasmid vector. Both human heavy chain classes are expressed in animals that carry the transgene. In light chain transgenic animals the unrearranged minilocus sequences recombine to form VJ joints that use all five human J kappa segments, resulting in a diversity of human-like CDR3 regions. Similarly, in heavy chain transgenics the inserted sequences undergo VDJ joining complete with N region addition to generate a human-like VH CDR3 repertoire. All six human JH segments and at least eight of the ten transgene encoded human D segments are expressed. The transgenic animals described in this paper represent a potential source of human sequence antibodies for in vivo therapeutic applications.

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.

Germline variable region gene segment derivation of human monoclonal anti-Rh(D) antibodies. Evidence for affinity maturation by somatic hypermutation and repertoire shift

To date, there has been no systematic study of the process of affinity maturation of human antibodies. We therefore sequenced the variable region genes (V genes) of 14 human monoclonal antibodies specific for the erythrocyte Rh(D) alloantigen and determined the germline gene segments of origin and extent of somatic hypermutation. These data were correlated with determinations of antibody affinity. The four IgM antibodies (low affinity) appear to be derived from two germline heavy chain variable region gene segments and one or two germline light chain variable region gene segments and were not extensively mutated. The 10 IgG antibodies (higher affinity) appear to be derived from somatic hypermutation of these V gene segments and by use of new V gene segments or V gene segment combinations (repertoire shift). Affinity generally increased with increasing somatic hypermutation; on average, there were 8.9 point mutations in the V gene segments of the four IgM antibodies (Ka = 1-4 x 10(7)/M-1) compared with 19 point mutations in the V gene segments of the 10 IgG antibodies. The four highest affinity antibodies (Ka = 0.9-3 x 10(9)/M-1) averaged 25.5 point mutations. The use of repertoire shift and somatic hypermutation in affinity maturation of human alloantibodies is similar to data obtained in inbred mice immunized with haptens.

Ongoing V kappa-J kappa recombination after formation of a productive V kappa-J kappa coding joint

V kappa genes of man can recombine with the J kappa gene segments either by an inversion or by a deletion mechanism. Back-to-back fusion products of the respective recombination signal sequences (signal joints) are retained on the chromosome after the formation of a V kappa-J kappa coding joint by an inversion. Our knowledge of the structure of the human kappa locus and the application of the polymerase chain reaction allowed us now to establish a direct relationship between different kappa recombination products in the lymphoid cell line JI. Two consecutive inversions fully explain the existence of two coding joints and two signal joints on the same chromosome of this cell line. Although the initially formed coding joint is productively rearranged and expressed, a second V kappa-J kappa rearrangement took place which leads to an aberrant joint. In this process a J kappa gene segment of the signal joint that had been created in the first V kappa-J kappa joining was used as the recombination target. The sequence of the two rearrangements is unequivocal since a product of the first (productive) reaction is a partner in the second (aberrant) one.

The human immunoglobulin kappa locus. Characterization of the duplicated A regions

The central regions of the kappa locus, the so-called A regions, have been fully characterized on cosmid and phage lambda clones. The regions, which are parts of the C kappa-proximal and -distal copies of the locus and are, therefore, called Ap and Ad regions, comprise about 140 kb each and contain together 30 V kappa genes and pseudogenes. The A regions have been linked on their 5' sides to the O regions and on their 3' sides to the L regions. Chromosomal walking has eliminated a previous gap in the Ap region. Detailed restriction maps of the Ap and Ad regions and the sequences of 9 V kappa genes are reported. Four events, which have occurred in evolution probably after the duplication of the A region, were identified: the insertion of an Alu element in Ad; the insertion of part of a LINE element in Ap; the deletion of a 17.5-kb fragment including one V kappa gene from Ap; the sequence divergence of duplicated V kappa gene regions which ranges among the five pairs studied here from 0 to 14 bp per kb and converted two genes to pseudogenes while their duplicates stayed functional. An analysis of the A regions of the lymphoid cell lines RPMI 6140 and GM607 confirmed the previous finding that the V kappa-J kappa rearrangement in these cell lines had occurred by deletion and inversion mechanisms, respectively. Thus, the structural data contribute to the understanding of the evolution and the functioning of the A regions of the kappa locus.

Of orphons and UHOs. Delimitation of the germline repertoire of human immunoglobulin kappa genes

Two problems in defining the germline repertoire of immunoglobulin kappa genes were investigated. One concerns putative transposed V kappa genes (orphons), the other one weak hybridization signals which may or may not turn out to be V kappa genes (UHOs). It was shown by sequencing that the three V kappa genes Z2, Z3 and Z4 are very closely related to the Z1 and V118 genes and to two other genes which had been localized on chromosomes 1 and 22, i.e. outside the kappa locus on chromosome 2. It is therefore likely that also the Z2-Z4 genes are orphons and not part of the kappa locus. Two UHOs turned out not to contain V kappa-like structures. This together with previous results makes it likely that we have detected all germline V kappa genes with the available hybridization probes.

Linkage of two pseudogenes from V kappa 1 and V kappa 9 murine immunoglobulin families

As an initial step towards the molecular analysis of the murine V kappa locus, a cosmid library from BALB/cJ mouse liver DNA was screened with probes representing 10 V kappa families. Of eight cosmids that were isolated from the initial screen, five contained a single restriction fragment that hybridized to the probes. Two cosmids contained two fragments that hybridized to the same probe, V kappa 4, indicating that some V kappa 4 gene segments are linked. One cosmid had two genes that belonged to different families, V kappa 1 and V kappa 9. The two gene segments were located within 12 kb of each other and lay in the same transcriptional orientation. Linkage of gene segments from the V kappa 1 and V kappa 9 families is consistent with a genetic map of the locus, and provides physical evidence for the first time that two genes from different families are closely linked in the murine kappa locus. Sequence analysis revealed that both genes are pseudogenes: the V kappa psi 1.7 gene segment has eight mutations, including termination codons, insertions, and deletions, and the V kappa psi 9B.8 gene segment has two mutations of an insertion and altered RNA splice site. Both genes have the potential to rearrange based on the sequence of their heptamer-nonamer motifs. The identification of pseudogenes raises the question of how many nonfunctional genes are present in the murine germline repertoire.

Genetic analysis of self-associating immunoglobulin G rheumatoid factors from two rheumatoid synovia implicates an antigen-driven response

Although much has been learned about the molecular basis of immunoglobulin M (IgM) rheumatoid factors (RFs) in healthy individuals and in patients with mixed cryoglobulinemia and rheumatoid arthritis, little is known about the genetic origins of the potentially pathogenic IgG RFs in the inflamed rheumatoid synovia of patients. Recently, we generated from unmanipulated synovium B cells several hybridomas that secreted self-associating IgG RFs. To delineate the genetic origins of such potentially pathogenic RFs, we adapted the anchored polymerase chain reaction to rapidly clone and characterize the expressed Ig V genes for the L1 and the D1 IgG RFs. Then, we identified the germline counterparts of the expressed L1 IgG RF V genes. The results showed that the L1 heavy chain was encoded by a Vh gene that is expressed preferentially during early ontogenic development, and that is probably located within 240 kb upstream of the Jh locus. The overlap between this RF Vh gene and the restricted fetal antibody repertoire is reminiscent of the natural antibody-associated Vh genes, and suggests that at least part of the "potential pathogenic" IgG RFs in rheumatoid synovium may derive from the "physiological" natural antibody repertoire in a normal immune system. Indeed, the corresponding germline Vh gene for L1 encodes the heavy chain of an IgM RF found in a 19-wk-old fetal spleen. Furthermore, the comparisons of the expressed RF V genes and their germline counterparts reveal that the L1 heavy and light chain variable regions had, respectively, 16 and 7 somatic mutations, which resulted in eight and four amino acid changes. Strikingly, all eight mutations in the complementarity determining regions of the V gene-encoded regions were replacement changes, while only 6 of 11 mutations in the framework regions caused amino acid changes. Combined with L1's high binding affinity toward the Fc fragment, these results suggest strongly that the L1 IgG RF must have been driven by the Fc antigen.

Immunoglobulin light chain variable region gene sequences for human antibodies to Haemophilus influenzae type b capsular polysaccharide are dominated by a limited number of V kappa and V lambda segments and VJ combinations

The immune repertoire to Haemophilus influenzae type b capsular polysaccharide (Hib PS) appears to be dominated by certain light chain variable region genes (IgVL). In order to examine the molecular basis underlying light chain bias, IgVL genes have been cloned from a panel of heterohybridomas secreting human anti-Hib PS (antibody) (anti-Hib PS Ab). One hybridoma, representative of the predominant serum clonotype of anti-Hib PS Ab in older children and adults following immunization or Hib infection, uses a V kappa II segment identical to the germline gene A2, and a JK3 segment. A second kappa hybridoma uses a member of the V kappa I family and a JK4 segment. Four lambda antibodies, all cross-reactive with the structurally related antigen Escherichia coli K100 PS, use V lambda VII segments which are 96-98% homologous to one another, and may originate from a single germline gene. Two additional lambda antibodies, not K100-cross-reactive, are encoded by members of the V lambda II family. All lambda antibodies use highly homologous J lambda 2 or J lambda 3 segments. The VJ joints of all lambda antibodies and the V kappa II-encoded antibody are notable for the presence of an arginine codon, suggesting an important role in antigen binding. Although more complex than heavy chain variable region gene usage, a significant portion of serum anti-Hib PS Ab is likely to be encoded by a limited number of V kappa and V lambda segments and VJ combinations, which may be selectively expressed during development, or following antigen exposure.