从兔外周血直接克隆IgG重链可变区 

目的 从兔外周血总RNA中直接扩增出IgG重链可变区基因。方法 先从IMGT/GENE-DB数据库中获取编码大耳白兔免疫球蛋白（Ig）重链可变区（VH）的3个胚系基因片段VSUB>H/SUB>（IGHV）、D（IGHD）和JSUB>H/SUB>（IGHJ）,以及编码γ重链恒定区（CH）基因Cγ（IGHG）的cDNA序列,然后设计嵌套引物,以兔外周血总RNA为模板,进行RT-PCR和Nested-PCR扩增,产物经胶回收后克隆到T载体,随机挑选白色克隆测序,最后将序列用Bioedit软件的Local Blast功能比对出Cγ的基因型,同时提交到IMGT/V-QUEST分析出所属的VH、D和JH胚系基因。结果 获得25个克隆的插入子序列,每个克隆均为兔IgG重链可变区的编码基因,且包含了完整的VSUB>H/SUB>、D、JSUB>H/SUB>胚系基因片段,以及Cγ基因     

乙肝免疫球蛋白抗体的多样性

目的 基于重链可变区的编码基因序列对乙肝免疫球蛋白（HBIG）中的IgG抗体进行分类。方法 借用文献提供的引物,以HBsAb强阳性健康个体外周血中的总RNA为模板进行RT-PCR和Nested-PCR扩增,通过将产物克隆到T载体、随机挑选测序,分析并统计出插入子的V_H-J_H-C_γ组
合方式。结果 共获得56个有效克隆,全部为人V_H3-D-J_H-C_γ序列,可分成49种序列,其中5种序列有2或3个序列完全相同的克隆。4个Cγ功能基因也全部出现,其中IGHG2频率最高（28次）;23个V_H3功能基因有11个出现,其中频率最高的是IGHV3-23（29次）;23个D功能基因有16个出
现,其中频率最高的是IGHD1-26（8次）;6个J_H 功能基因则全部出现,其中频率最高的是IGHJ4（33次）。V_H3-D-J_H组合有33种,频率最高的是IGHV3-23/IGHD1-26/IGHJ4（8次）,其中5种与IGHG2拼接,但这5种V_H3-D-J_H-C_γ2序列仍有明显的差异。结论 成功地从HBsAb强阳性健康个体外周血中克隆到由VH3亚家族参与重排的IgG重链可变区序列;初步证实可变区序列不仅在V_H3-D-J_H-C_γ组合方式上具有极大的多样性,而且在序列上也具有明显的差异性;基于可变区测序对IgG抗体或B细胞进行分类是可行的,但需大大提高挑取克隆的数量或改用新一代大规模测序技术。     

Exonuclease activity and P nucleotide addition in the generation of the expressed immunoglobulin repertoire

Background

Immunoglobulin rearrangement involves random and imprecise processes that act to both create and constrain diversity. Two such processes are the loss of nucleotides through the action of unknown exonuclease(s) and the addition of P nucleotides. The study of such processes has been compromised by difficulties in reliably aligning immunoglobulin genes and in the partitioning of nucleotides between segment ends, and between N and P nucleotides.

Results

A dataset of 294 human IgM sequences was created and partitioned with the aid of a probabilistic model. Non-random removal of nucleotides is seen between the three IGH gene types with the IGHV gene averaging removals of 1.2 nucleotides compared to 4.7 for the other gene ends (p < 0.001). Individual IGHV, IGHD and IGHJ gene subgroups also display statistical differences in the level of nucleotide loss. For example, within the IGHJ group, IGHJ3 has average removals of 1.3 nucleotides compared to 6.4 nucleotides for IGHJ6 genes (p < 0.002). Analysis of putative P nucleotides within the IgM and pooled datasets revealed only a single putative P nucleotide motif (GTT at the 3' D-REGION end) to occur at a frequency significantly higher then would be expected from random N nucleotide addition.

Conclusions

The loss of nucleotides due to the action of exonucleases is not random, but is influenced by the nucleotide composition of the genes. P nucleotides do not make a significant contribution to diversity of immunoglobulin sequences. Although palindromic sequences are present in 10% of immunologlobulin rearrangements, most of the 'palindromic' nucleotides are likely to have been inserted into the junction during the process of N nucleotide addition. P nucleotides can only be stated with confidence to contribute to diversity of less than 1% of sequences. Any attempt to identify P nucleotides in immunoglobulins is therefore likely to introduce errors into the partitioning of such sequences.     

The human anti-bullous pemphigoid monoclonal autoantibody P22 is encoded by genes of the IGHV4 and IGLV4 families

We identified, cloned, and biochemically characterized the full-length cDNAs encoding the heavy and light chains of a human monoclonal antibody (mAb) from the Epstein-Barr virus (EBV)-cell line P22. The cell line P22, which originated from a patient with bullous pemphigoid (an autoimmune disease causing skin blistering) expressed immunoglobulin-G (IgG) with a lambda light chain. Although the variable heavy (IGHV) chain gene family could not be assigned by IGHV repertoire analysis, the determination of its nucleotide sequence demonstrated that the heavy chain of P22 belonged to the IGHV4 family. The limited IGHV4 gene usage by memory IgG, IGA and IgE-expressing cells supports the notion of the autoreactivity-associated IGHV4 genes and stresses the strong selection pressure within germinal centres towards IGHV4 family. Alignment of P22 IGHV4 cDNA sequence to germline sequences from gene databases, revealed a remarkable divergence, suggesting that the heavy chain of the P22 mAb encodes a distinct IGHV4 gene. The variable light chain (IGLV) encodes a IGLV4 gene and is 98% similar to a previously reported IGLV gene. Furthermore, fluorescent staining with the recombinant mAb showed the same reactivity to that of the native antibody. The data reported herein, (a) reveal an autoantibody encoding a distinct IGHV4 gene, (b) confirm the notion that autoantibodies preferentially use IGHV4 genes, and (c) hypothesize that somatic hypermutation within GC may be a mechanism by which autoreactive B lymphocytes escape negative selection.     

Natural human antibodies to pneumococcus have distinctive molecular characteristics and protect against pneumococcal disease

The molecular and functional characteristics of natural antibody from the preimmune repertoire have not been explored in detail in man. We describe seven human IgM monoclonal antibodies selected on the basis of pneumococcal polysaccharide binding that share both molecular and functional characteristics with natural antibody, suggesting a common B cell lineage origin. Unlike class-switched antibodies, which are serotype-specific, the antibodies were polyreactive and bound all pneumococcal polysaccharide capsular serotypes tested. Some bound endogenous antigens, including blood group antigens and intermediate filament proteins. All the antibodies used unmutated heavy chain V (IGHV) that are expressed at an increased frequency in the elderly and in the preimmune repertoire. The CDR3 was characterized by long length (mean aa 18.4 (+/-4.2) and selective use of IGHD6 (P < 0.001) and IGHJ6 (P < 0.01) family genes. The clones expressing IGHV1-69 and IGHV 3-21 provided significant passive protection against invasive pneumococcal disease in vivo.     

Isolation and characterization of human neutralizing antibodies to rabies virus derived from a recombinant immune antibody library

A human immune Fab library was constructed using RNAs from peripheral blood lymphocytes obtained from rabies virus hyperimmune volunteers on phagemid vector. The size of the constructed Fab library was 2 × 10⁷ Escherichia coli transformants. After four rounds of panning on whole inactivated rabies virus (PV-11), phage clones displaying rabies virus-specific human Fab were selected. The specificity of soluble Fab antibody fragments, derived from positive phage clones was verified by ELISA. Among 20 specific Fab clones, the genetic sequence of 6 of them (FabRV01, FabRV02, FabRV03, FabRV04, FabRV05, and FabRV06) was analyzed. The variable heavy (VH) and variable light (VL) domains were found to share 90% and 93% homology with sequences encoded by the corresponding human germline genes, respectively. The soluble Fab fragments, expressed in Escherichia coli were purified by a single step Nickel-NTA affinity chromatography via a hexa-histidine tag and their binding specificities to rabies virus were confirmed. Three of the Fab antibodies, FabRV01, FabRV02 and FabRV03, showed binding characteristics to rabies virus glycoprotein antigenic site III with affinities in the K_D range 7 × 10⁻⁹ to 5 × 10⁻⁸ M. The Fab fragments showed dose-dependent neutralization properties for the challenge virus standard (CVS-11).     

Clonal relationships between thyroid‐stimulating hormone receptor‐stimulating antibodies illustrate the effect of hypermutation on antibody function

Graves’ disease is characterized by production of agonist antibodies to the thyroid‐stimulating hormone receptor (TSHR), but knowledge of the genetic and somatic events leading to their aberrant production is limited. We describe the genetic analysis of two monoclonal antibodies (mAbs) with thyroid‐stimulating activity (TSAb) obtained from a single mouse with experimental Graves’ disease. The mAbs were class switched, but used the same rearrangement of immunoglobulin heavy chain, variable region (IGHV) and immunoglobulin light chain, variable region (IGLV) germline genes, implying a clonal relationship and derivation from a single precursor B‐cell clone. The IGHV‐region genes of the two mAbs underwent high degrees of somatic hypermutation by sharing numerous mutations before diverging, while the IGLV genes evolved separately. Interestingly, the mutations were present in both the complementarity‐determining regions (CDRs) and the framework regions. The cloned IGHV and IGLV genes were confirmed to have TSAb properties in experiments in which they were expressed as recombinant Fabs (rFabs). In other experiments, we swapped the IGLV genes with IGHV genes by constructing chimeric rFabs and showed that the chimeras retained TSAb activities, confirming the close functional relatedness of the V‐region genes. Importantly, the IGLV genes in chimeric rFabs had a dominant stimulatory effect at low concentrations, while the IGHV genes had a dominant effect at higher concentrations. Our findings demonstrate that, in experimentally immunized mice, multiple pathogenic antibodies to TSHR can arise from a single clone by a series of somatic mutations in the V‐region genes and may give an insight into how such antibodies develop spontaneously in autoimmune Graves’ disease.     

The human immunoglobulin heavy diversity (IGHD) and joining (IGHJ) segments.

The 'Human Immunoglobulin Heavy Diversity (IGHD) and Joining (IGHJ) segments', fifth report of the 'IMGT Locus on Focus' section, comprises six tables entitled: (1) 'Human germline IGHD segments at 14q32.33'; (2) 'Human IGHD alleles'; (3) 'Human germline IGHJ segments at 14q32.33'; (4) 'Human IGHJ alleles'; (5) 'Human germline IGHD orphons on chromosome 15 (15q11.2)'; (6) 'Correspondence between the different human IGHD nomenclatures', and two figures: (1) 'Protein display of human IGH D-REGIONs'; (2) 'Protein display of human IGH J-REGIONs'. These tables and figures are available at the IMGT Marie-Paule page from IMGT, the international ImMunoGeneTics database (http://imgt.cnusc.fr:8104) created by Marie-Paule Lefranc, Université Montpellier II, CNRS, France.     

Protein displays of the human immunoglobulin heavy, kappa and lambda variable and joining regions

'Protein displays of the Human Immunoglobulin Heavy, Kappa and Lambda Variable and Joining Regions', the 6th report of the 'IMGT Locus on Focus' section, comprises 4 figures: (1) 'Protein display of human IGH V-REGIONs'; (2) 'Protein display of human IGK V-REGIONs'; (3) 'Protein display of human IGL V-REGIONs and V-PREB REGION'; (4) 'Protein display of human IGH, IGK and IGL J-REGIONs', and 1 table entitled: 'FR-IMGT and CDR-IMGT length of the human IGHV, IGKV, IGLV and V-PREB genes'. These figures and table are available at the IMGT Marie-Paule page from IMGT, the international ImMunoGeneTics database (http://imgt.cnusc.fr: 8104) created by Marie-Paule Lefranc, Université Montpellier II, CNRS, France. Copyright Copyright 1999 S. Karger AG, Basel     

Rearrangement of only one human IGHV gene is sufficient to generate a wide repertoire of antigen specific antibody responses in transgenic mice

In recent years, mice carrying human IG transgenes are being generated for the production of human monoclonal antibodies as an alternative approach to the conventional use of mouse or chimeric-humanized antibodies. Theoretically, the size of the repertoire of human antibodies that these mice could produce would be critically dependent on the number of human V genes introduced in the transgene. This could be the case for BABkappa and BABkappa,lambda transgenic mice, which carry several genes from the human IGK (BABkappa), and IGK and IGL (BABkappa,lambda) loci, but only five human IGHV genes and the entire IGHD-IGHJ cluster linked to two human IGHC (IGHM-IGHD) genes. We analyzed the expressed human IG genes in 30 IgM-secreting hybridomas generated from transgenic mice immunized either with soluble proteins (human IgM coupled to KLH) or with cells (human PBMC, tumour cell lines or rat cells transfected with human CD69). The results show that all hybridoma cells analyzed rearranged exclusively the IGHV1-2 gene, in contrast with naive spleen B cells that used three out of the five IGHV genes present in the transgene. The configuration of the rearranged CDR3 region revealed a much higher heterogeneity in the heavy chains. A variety of IGHJ and IGHD genes were used in hybridomas, and somatic mutations were also seen in some hybrids. Regarding the rearranged light chains genes, it was a much higher variety in the use of V and J genes in both, kappa and lambda chains, than in the heavy chain, and also in the level of mutation. The results indicate that only one IGHV gene is sufficient to generate a wide repertoire of antigen specific antibody responses. Thus, efforts aimed at the generation of new transgenic mice should focus more on the integrity of the D/J region and on the DNA regions regulating somatic hypermutation, rather than on the number of V genes present in the transgene.     

The Teleostei immunoglobulin heavy IGH genes

'Teleostei Immunoglobulin Heavy IGH Genes', the eleventh report of the 'IMGT Locus in Focus' section, comprises four tables: (1) 'Teleostei IGHV genes'; (2) 'Teleostei germline IGHJ genes'; (3) 'Teleostei IGHC genes and alleles'; (4) 'FR-IMGT and CDR-IMGT length of the Teleostei IGHV genes'. These tables are available at the IMGT Marie-Paule page from IMGT, the international ImMunoGeneTics database (http://imgt.cines.fr: 8104) created in 1989 by Marie-Paule Lefranc, Université Montpellier II, CNRS, France.     

Analysis of the horse V(H) repertoire and comparison with the human IGHV germline genes, and sheep, cattle and pig V(H) sequences

We have constructed a chimeric antibody single-chain Fv (scFv) fragments phage-displayed library that combines an invariant human V(L) chain with the repertoire of V(H) domains amplified from a horse immunized against scorpion venom. To gain insight into the equine V(H) repertoire, the V(H) sequences of 46 unique clones randomly chosen from the library prior to antigenic selection were analyzed. Comparisons with previously reported equine V(H) sequences, as well as with the repertoire of human IGHV germline genes and known V(H) sequences of sheep, cattle and pig, suggest that the equine IGH locus harbors at least three IGHV gene families. Two families belong to clan II while the other was classified into clan I. The horse sequences were also found to encode a diverse repertoire of canonical structures. The most populated equine IGHV gene family, named IGHV1, and another family termed IGHV3, encode two out of the three canonical structures so far described for CDR1. The IGHV2 gene family has the third canonical structure at CDR1. In CDR2, nine loop lengths were found, with four of them matching the pattern of typical canonical structures. The remaining five CDR2 loop lengths are shorter or longer than those reported for human IGHV germline genes and known sequences of sheep, cattle and pig. The analysis of CDR3 loops indicates a length distribution broader than previous reports for horses; being similar to that of humans, sheep and pigs. Moreover, equine CDR3 loops were found to have a combination of lower content of cysteine and higher proportion of glycine not seen in the other species. This implies less constrained loops and therefore more apt for searching the conformational space of antigen-binding sites. Altogether, these findings reveal a more diverse perspective of the horse V(H) repertoire than previous estimations and lay foundations for future studies of the equine IGH locus.     

Autoreactivity of primary human immunoglobulins ancestral to hypermutated human antibodies that neutralize HCMV

The human antibody response to the AD-2S1 epitope of glycoprotein B (gB) of human cytomegalovirus (HCMV) is dominated by a family of closely related somatically mutated antibodies. These antibodies neutralize viral infectivity and the genes encoding them are derived from two commonly used germ-line variable (V) region genes, IGHV3-30 and IGKV3-11. Recombination of these V genes with the appropriate junctional diversity generates genes that encode primary immunoglobulins that bind to AD-2S1. To further understand the initial primary immunoglobulin response to AD-2S1 we synthesized the germ-line-based ancestor of one such family of antibodies and showed that it bound gB at the AD-2S1 epitope. Here we show that the germ-line ancestor of a second family of antibodies likewise binds to gB. We further show that one of the ancestral primary immunoglobulins, but not the other, also recognized autoantigens. In contrast, the hypermutated derivatives did not demonstrate autoreactivity and minor structural changes in the primary immunoglobulin were sufficient to generate or abolish autoreactivity or to change specificity. Thus, our demonstration that the ancestor of a highly mutated, non-autoreactive antiviral IgG antibody binds nuclear and cell-surface autoantigens indicates for the first time that self-reactivity is not necessarily a barrier to development into a follicular B lymphocyte that undergoes antigen-initiated affinity maturation.     

Genetic and epitopic analysis of thyroid peroxidase (TPO) autoantibodies: markers of the human thyroid autoimmune response

TPO autoantibodies, the hallmark of human autoimmune thyroid disease, are of IgG class and are associated with thyroid destruction and hypothyroidism. Using the immunoglobulin gene combinatorial library approach, a panel of human monoclonal TPO autoantibodies (expressed as Fab) has been generated from thyroid tissue-infiltrating B cells. TPO-specific Fab closely resemble patients' serum autoantibodies in terms of L chain type, IgG subclass, affinities for TPO as well as epitopes recognized by > 80% of TPO autoantibodies in an individual's serum. TPO autoantibody V region genes are not unique; H chain V genes are usually mutated, while L chain V genes are sometimes in germ-line conformation. The autoantibodies recognize an immunodominant region involving conformational, overlapping epitopes in domains A and B. Finally, TPO autoantibody epitopic fingerprints are distinctive for individual sera, are not associated with hypothyroidism, but are conserved over time (indicating a lack of B cell epitope spreading). Evidence for conservation as well as inheritance of the fingerprints in some families, together with V_H gene polymorphisms, may provide insight into the genetic basis of human autoimmune thyroid disease. Furthermore, monoclonal human TPO autoantibodies will be invaluable for B cell presentation of TPO to determine the T cell epitopes involved in TPO autoantibody production.     

Serum SmD autoantibody proteomes are clonally restricted and share variable-region peptides

Recent advances in mass spectrometry-based proteomic methods have allowed variable (V)-region peptide signatures to be derived from human autoantibodies present in complex serum mixtures. Here, we analysed the clonality and V-region composition of immunoglobulin (Ig) proteomes specific for the immunodominant SmD protein subunit of the lupus-specific Sm autoantigen. Precipitating SmD-specific IgGs were eluted from native SmD-coated ELISA plates preincubated with sera from six patients with systemic lupus erythematosus (SLE) positive for anti-Sm/RNP. Heavy (H)- and light (L)-chain clonality and V-region sequences were analysed by 2-dimensional gel electrophoresis and combined de novo database mass spectrometric sequencing. SmD autoantibody proteomes from all six patients with SLE expressed IgG1 kappa restricted clonotypes specified by IGHV3-7 and IGHV1-69 H-chains and IGKV3-20 and IGKV2-28 L-chains, with shared and individual V-region amino acid replacement mutations. Clonotypic sharing and restricted V-region diversity of systemic autoimmunity can now be extended from the Ro/La cluster to Sm autoantigen and implies a common pathway of anti-Sm autoantibody production in unrelated patients with SLE.     

以鼠源重链Fd片段为模板导向筛选人源性抗γ-精浆蛋白抗体轻链

目的:以鼠源抗γ-sm抗体重链Fd片段为模板,筛选人源性抗人γ-精浆蛋白抗体轻链。方法:利用RT-PCR从前列腺癌患者外周血淋巴细胞扩增出全套的人抗体轻链基因,克隆入含鼠源性抗γ-sm抗体重链Fd片段的噬粒载体pComb3X/mFd中,电转化大肠杆菌XL1-Blue后建立人-鼠杂合的Fab抗体库。通过稀释滴定、限制性酶切和随机测序,对所建杂合库的库容、重组率和多样性分别进行鉴定,以M13K07辅助噬菌体超感染,利用亲和纯化的γ-sm为抗原,对挽救展示的噬菌体抗体库进行3轮淘筛和克隆鉴定。最后对筛选出的杂合抗体进行初步的功能检测。结果:构建成功1.2×107CFU、重组率为90%、多样性好的杂合人-鼠噬菌体抗体库。利用纯化的γ-sm3轮亲和淘筛后,5个克隆成功诱导表达特异性的pIII融合抗体。ELISA进一步检测表明,5个克隆均呈特异性阳性反应,其中2个克隆亲和力较高,测序显示其所含轻链基因序列完全相同,可变区来源于IGKV4-101胚系基因家族。结论:利用鼠源Fd片段为模板,导向筛选杂合噬菌体库,成功筛选到人源性抗人γ-精浆蛋白抗体轻链。     

Non-germ-line encoded residues are critical for effective antibody recognition of a poorly immunogenic neutralization epitope on glycoprotein B of human cytomegalovirus

The capability of the antibody (Ab) repertoire to mount a response to appropriate epitopes on infectious agents will strongly affect the ability of the immune system to provide protection against disease. Certain epitopes may be poor inducers of immunity but are nevertheless able to promote biologically important protection when recognized by the immune repertoire. We have investigated the recognition by Ab of one such poorly immunogenic target, antigenic domain 2 (AD-2) on human cytomegalovirus glycoprotein B. To date, only two well-characterized human monoclonal Ab reactive with this epitope are known. To define parameters important for establishment of a human paratope recognizing this epitope, we created variants of the variable genes utilized by one of these Ab and used phage display technology to select Ab fragments with retained antigen specificity. We show here that residues in the first complementarity determining region of both the heavy and the light chain are involved in determining the AD-2 specificity and, in addition, that key mutations in the germ-line sequence are required for effective interaction with this epitope. Thus, the products of the human germ-line IGHV3-30 and IGKV3-11 genes, the only V genes that have been demonstrated to participate in an AD-2 specific Ab response, do not have the intrinsic features required for high-affinity recognition of this epitope. We propose that the inability of the human germ-line gene-encoded Ab repertoire to directly recognize this and possibly other antigenic determinants results in their poor immunogenicity in vivo. This may favor responses to other epitopes, which have a high-affinity imprint in the human germ-line Ab repertoire.