Complete analysis of the B-cell response to a protein antigen, from in vivo germinal centre formation to 3-D modelling of affinity maturation

Somatic hypermutation of immunoglobulin variable region genes occurs within germinal centres (GCs) and is the process responsible for affinity maturation of antibodies during an immune response. Previous studies have focused almost exclusively on the immune response to haptens, which may be unrepresentative of epitopes on protein antigens. In this study, we have exploited a model system that uses transgenic B and CD4+ T cells specific for hen egg lysozyme (HEL) and a chicken ovalbumin peptide, respectively, to investigate a tightly synchronized immune response to protein antigens of widely differing affinities, thus allowing us to track many facets of the development of an antibody response at the antigen-specific B cell level in an integrated system in vivo. Somatic hypermutation of immunoglobulin variable genes was analysed in clones of transgenic B cells proliferating in individual GCs in response to HEL or the cross-reactive low-affinity antigen, duck egg lysozyme (DEL). Molecular modelling of the antibody-antigen interface demonstrates that recurring mutations in the antigen-binding site, selected in GCs, enhance interactions of the antibody with DEL. The effects of these mutations on affinity maturation are demonstrated by a shift of transgenic serum antibodies towards higher affinity for DEL in DEL-cOVA immunized mice. The results show that B cells with high affinity antigen receptors can revise their specificity by somatic hypermutation and antigen selection in response to a low-affinity, cross-reactive antigen. These observations shed further light on the nature of the immune response to pathogens and autoimmunity and demonstrate the utility of this novel model for studies of the mechanisms of somatic hypermutation.

Long-term kinetics of adult human antibody repertoires

In healthy humans, antibody repertoires change during ontogeny and senescence. The dynamics of antibody repertoires among adults over a longer period of time in one and the same individual has, however, not been extensively studied. In this study we analysed peripheral blood samples from five healthy adults, taken over a period of 10 weeks and once 9 years later. A competitive, quantitative polymerase chain reaction (PCR) was developed to investigate short and long-term variations in VH gene family repertoires. Serum antibody levels to common self and non-self antigens were determined in samples taken at the same time-points as the cell samples to analyse possible correlations between molecular and serological expression profiles. We found a high degree of stability in the VH gene family repertoire over time as well as between individuals with a Caucasian background. A specific change in the usage of primarily the VH3 and VH5 gene families was observed in one individual at one time-point. The deviating pattern resembled the VH gene family utilization pattern observed in naturally activated B lymphocytes. The fluctuations in VH3 and VH5 gene family expression correlated with the presence of rheumatoid factor in serum. We discuss the possible influence of polyclonal, transient stimulation of B cells on VH gene repertoires, as measured in circulating B cells.

Two classes of germline genes both derived from the V(H)1 family direct the formation of human antibodies that recognize distinct antigenic sites in the C2 domain of factor VIII

Most plasmas from patients with inhibitors contain antibodies that are reactive with the C2 domain of factor VIII. Previously, we have shown that the variable heavy chain (V(H)) regions of antibodies to the C2 domain are encoded by the closely related germline gene segments DP-10, DP-14, and DP-88, which all belong to the V(H)1 gene family. Here, we report on the isolation and characterization of additional anti-C2 antibodies that are derived from V(H) gene segments DP-88 and DP-5. Competition experiments using murine monoclonal antibodies CLB-CAg 117 and ESH4 demonstrated that antibodies derived from DP-5 and DP-88 bound to different sites within the C2 domain. Epitope mapping studies using a series of factor VIII/factor V hybrids revealed that residues 2223 to 2332 of factor VIII are required for binding of the DP-10-, DP-14-, and DP-88-encoded antibodies. In contrast, binding of the DP-5-encoded antibodies required residues in both the amino- and carboxy-terminus of the C2 domain. Inspection of the reactivity of the antibodies with a series of human/porcine hybrids yielded similar data. Binding of antibodies derived from germline gene segments DP-10, DP-14, and DP-88 was unaffected by replacement of residues 2181 to 2243 of human factor VIII for the porcine sequence, whereas binding of the DP-5-encoded antibodies was abrogated by this replacement. Together these data indicate that antibodies assembled from V(H) gene segments DP-5 and the closely related germline gene segments DP-10, DP-14, and DP-88 target 2 distinct antigenic sites in the C2 domain of factor VIII.

Platelet alphaIIbbeta3 recombinant autoantibodies from the B-cell repertoire of a post-transfusion purpura patient

The biallelic human platelet alloantigen (HPA) 1 system encodes a leucine to proline substitution at position 33 in the beta3 integrin. Homozygous individuals can be immunized by the non-self allele-encoded protein following transfusion or during pregnancy. In post-transfusion purpura (PTP), a subsequent recall alloantibody response against the non-self form of beta3 is paralleled by the destruction of autologous platelets, leading to profound thrombocytopenia. Although serological evidence suggests platelet autoantibodies are responsible, such autoantibodies are poorly defined. We used variable gene phage display to isolate alphaIIbbeta3 autoantibodies formed in the acute phase of PTP and determined the epitopes recognized. An immunoglobulin G (IgG)-encoded variable heavy-chain domain (VH) gene repertoire containing 4.7 x 10(7) single-chain Fv fragments was cloned and three alphaIIbbeta3 antibodies were isolated (clones 2F2, E3 and B12). All three used different VH genes with a low level of somatic mutation for genes derived from gamma-encoding mRNA. Two (2F2 and E3) recognized an overlapping epitope and their binding was inhibited by sera from patients with PTP; all three recognized Ca2+-dependent compound epitopes on alphaIIbbeta3. Our results support the theory that a transient loss of tolerance for alphaIIbbeta3 with autoantibody formation occurs in PTP.

Somatic diversity of the immunoglobulin repertoire is controlled in an isotype-specific manner

We have studied two aspects of the IgE immune response. First, we have compared the kinetics of the IgE response to the T cell-dependent antigen ph-Ox coupled to ovalbumin with that of the IgG1 response and we have assessed the quality of the IgE response. Second, we have studied the generation of somatic diversity, understood as the combined effect of somatic mutation and the selection of D(iversity) and J(oining) elements, in germinal center B cells at the molecular level, using the germ-line sequence of the prototype anti-ph-Ox heavy chain variable element V(H)Ox1 as reference. We evaluated sequences derived from mu-, gamma 1- and epsilon-variable elements and showed that somatic diversification was different for all isotypes studied. We further compared the IgE responses of wild-type mice with those of mice expressing a truncated cytoplasmic IgE tail (IgE(KVK Delta tail)). IgE(KVK Delta tail) mice showed a more diverse sequence pattern. We corroborated previous results suggesting that short CDR3 regions are indicative for high-affinity antibodies by measuring relative affinities of phage-expressed Fab fragments with prototype long and short CDR3 regions. Therefore, the composition of the antigen-receptor is responsible for the selection process and the expansion of antigen-specific cells, leading to an isotype-specific antibody repertoire.

Characterization of monoclonal antibodies against carcinoembryonic antigen (CEA) and expression in E. coli

Eight monoclonal antibodies (MAbs) against carcinoembryonic antigen (CEA) were characterized. Five clones are IgG(1), two clones are IgM and one clone is IgG(2b); all have kappa light chain. The affinities are in the range of 1.1 x 10(-7) approximately 2.4 x 10(-9) M; the affinities of two IgM clones could not be estimated because of their low enzyme-linked immunoadsorbent assay (ELISA) signal. Each clone was constructed as single-chain Fv (scFv) and expression was performed in E. coli. Four clones out of 8 could express scFv soluble to culture media and the expression was confirmed further by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. The nucleotide and amino acid sequences of V(H) and V(L) of four scFvs were deduced and their family and subgroup were analyzed. We found that the clones that do not express the scFv have aberrant kappa chain (incorrect V/J recombination or stop codon); in contrast, their heavy chain sequences proved correct. The E. coli-expressed scFvs showed 1.5 x 3.4-fold lower affinities (2.8 x 10(-8) approximately 3.6 x 10(-9) M) than those of hybridoma-derived parental antibodies except the one clone (C5), which exhibited approximately 10(-6) M of affinity.

Immunoglobulin genes and antibody responses in the spotted wolffish (Anarhichas minor Olafsen)

The spotted wolffish Anarhichas minor Olafsen is a promising new species in aquaculture in the cold waters of northern Norway. In this paper, some basic immunological studies of this marine species are reported. Of comparative interest are the cDNA sequences of the immunoglobulin transcript and the antibody responses to model antigens. Of more practical importance are the humoral immune responses and antibody specificities to potentially pathogenic bacteria. Full length cDNA clones encoding the immunoglobulin heavy and light chains in the spotted wolffish were sequenced demonstrating variable degrees of similarity to other teleost fish species. Also in the spotted wolffish the CH4 domain was deleted in the transmembrane form of the immunoglobulin heavy chain (IgH) as a receptor on B cells, with the transmembrane exon spliced directly to the CH3 domain. The antibody responses to various antigens like hapten-carrier molecules, protein antigens and bacterial pathogens were relatively high, but with some interesting exceptions. Anti-hapten responses to NIP and FITC were high while anti-DNS responses were low, but more surprisingly, there was hardly any B-cell response to the carrier molecule LPH. On the other hand, protein antigens like CGG and BSA were highly immunogenic in the spotted wolffish as were the bacterial antigens Vibrio anguillarum, V. salmonicida and Aeromonas salmonicida.

Immunoglobulin VH-gene usage of autoantibodies in mercuric chloride-induced membranous glomerulopathy in the rat

Brown-Norway (BN) and Dorus Zadel Black (DZB) rats develop a T-cell-dependent membranous glomerulopathy (MGP) with high proteinuria and antiglomerular basement membrane (GBM) autoreactive antibodies (Abs), upon exposure to mercuric chloride (HgCl2). Laminin is an important autoantigenic target of the anti-GBM Abs, absorbing approximately 30% of the anti-GBM reactivity. Although many anti-GBM Abs have undergone isotype switching, it is currently unclear whether affinity maturation occurs during the HgCl2-induced autoimmune response. To address this question we analysed the rearranged immunoglobulin heavy chain variable-region genes (VHDJH regions) of 15 mAbs that were previously obtained from HgCl2-treated rats. Seven of these mAbs exhibit reactivity towards laminin. Our study showed that the VH-gene usage of antilaminin mAbs is largely restricted to the PC7183 VH-gene family (six out of seven). In addition, we demonstrated that at least three out of six laminin reactive and five out of six non-laminin-binding mAbs are encoded by germline VH genes (a total of eight out of 12 mAbs). Of the eight mAbs that are encoded by germline VH genes, seven are of a non-immunoglobulin M (IgM) isotype, indicating that isotype switching has occurred in these mAbs in the absence of somatic mutations. The mutations observed in the VH genes of the four remaining mAbs do not provide strong evidence for antigenic selection. The data support the notion that B cells in this model of MGP are not subjected to affinity maturation and probably result from polyclonal B-cell activation.

Third complementarity-determining region of mutated VH immunoglobulin genes contains shorter V, D, J, P, and N components than non-mutated genes

The third complementarity-determining region (CDR3) of immunoglobulin variable genes for the heavy chain (VH) has been shown to be shorter in length in hypermutated antibodies than in non-hypermutated antibodies. To determine which components of CDR3 contribute to the shorter length, and if there is an effect of age on the length, we analysed 235 cDNA clones from human peripheral blood of VH6 genes rearranged to immunoglobulin M (IgM) constant genes. There was similar use of diversity (D) and joining (JH) gene segments between clones from young and old donors, and there was similar use of D segments among the mutated and non-mutated heavy chains. However, in the mutated heavy chains, there was increased use of shorter JH4 segments and decreased use of longer JH6 segments compared to the non-mutated proteins. The overall length of CDR3 did not change with age within the mutated and non-mutated categories, but was significantly shorter by three amino acids in the mutated clones compared to the non-mutated clones. Analyses of the individual components that comprise CDR3 indicated that they were all shorter in the mutated clones. Thus, there were more nucleotides deleted from the ends of VH, D, and JH gene segments, and fewer P and N nucleotides added. The results suggest that B cells bearing immunoglobulin receptors with shorter CDR3s have been selected for binding to antigen. A smaller CDR3 may allow room in the antibody binding pocket for antigen to interact with CDRs 1 and 2 as well, so that as the VDJ gene undergoes hypermutation, substitutions in all three CDRs can further contribute to the binding energy.

Notch signaling suppresses IgH gene expression in chicken B cells: implication in spatially restricted expression of Serrate2/Notch1 in the bursa of Fabricius

The bursa of Fabricius is a central organ for chicken B cell development and provides an essential microenvironment for expansion of the B cell pool and for generation of a diversified B cell repertoire. We report here that genes encoding the Notch family of transmembrane proteins, key regulators of cell fate determination in development, are differentially expressed in the bursa of Fabricius: Notch1 is expressed in medullary B cells located close to the basement membrane-associated epithelium (BMAE). In contrast, a Notch ligand, Serrate2, is expressed exclusively in the BMAE, which surrounds bursal medulla. A basic helix-loop-helix-type transcription factor, Hairy1, a downstream target of Notch signaling, is expressed in the bursa coordinately with Notch1 and Serrate2 and an immature B cell line, TLT1, which expresses both Notch1 and Serrate2. Furthermore, stable expression of a constitutively active form of chicken Notch1 or Notch2 in a B cell line results in a down-regulation of surface IgM expression, which is accompanied by the reduction of IgH gene transcripts. Transient reporter assay with the human IgH gene intronic enhancer reveals that an active form of Notch1 inhibits the IgH enhancer activity in chicken B cells, suggesting that Notch-mediated signals suppress the IgH gene expression via influencing the IgH intronic enhancer. These findings raise the possibility that the local activation of Notch1 in a subset of B cells by Serrate2 expressed in BMAE may influence the cell fate decision that is involved in B cell differentiation and selection inside the bursa.

Rearrangement of the human heavy chain variable region gene V3-23 in transgenic mice generates antibodies reactive with a range of antigens on the basis of VHCDR3 and residues intrinsic to the heavy chain variable region

To formulate a 'logic' for how a single immunoglobulin variable region gene generates antibodies with different antigen specificity and polyreactivity, we analysed chimeric antibodies produced in transgenic mice carrying the germ-line human V3-23 gene, multiple diversity (D) and joining (J) gene segments. Hybridomas producing antibodies encoded by the V3-23 gene in combination with different mouse Vkappa genes were obtained by fusion of splenocytes from transgenic mice. All antibodies had human mu-chains and mouse light chains, were multimeric in structure and expressed the human V3-23 gene. Nucleotide sequence analyses of genes encoding the heavy and light chains of 12 antibodies in relation to antigen specificity highlighted the importance of heavy chain variable region CDR3 in determining reactivity with different antigens. However, the results also suggest that non-CDR3 sequences intrinsic to the V3-23 gene itself may be involved in, or determine, the binding of the chimeric antibodies to some of the antigens tested in the current study.

Chronic lymphocytic leukemia complicated by plasmacytoma originating from different clones

In a woman with chronic lymphocytic leukemia (CLL), a plasmacytoma developed on the back region after four years. CLL cases complicated with plasmacytoma are rare. In the present case, the plasmacytoma showed kappa cytoplasmic immunoglobulin (Ig), and the CLL showed gamma lambda surface Ig. To reveal the clonal origin of CLL and plasmacytoma, we analyzed Ig gene rearrangements in the patient's peripheral blood and plasmacytoma. Ig gene DNA analysis confirmed the presence of different rearrangements in the heavy and light chain genes of CLL and plasmacytoma. These findings suggest that in this patient, the two B cell malignancies arose from expansion of two phenotypically and genotypically distinct clones.

Transcripts of immunoglobulin germline mu: an amplified myeloid and B-lymphoid common gene program in various leukemias

To investigate the clinical implications of germline C mu transcription, the splice region between the 3' end of the enhancer and the first exon of immunoglobulin germline mu; was analyzed by RT-PCR in 63 samples from 59 patients with leukemia. Immunophenotypes of 33 samples from patients with acute leukemia were analyzed using a panel of these monoclonal antibodies: anti-immature/stem cell (HLA-DR, CD34); anti-mature myeloid (CD33, CD15); anti-T lymphoid (CD2, CD3, CD5, CD7, CD8), and anti-B lymphoid (CD10, CD19, CD20). Of the 63 samples, 33 (52%) contained germline C mu transcripts: 2/2 patients with chronic lymphocytic leukemia; 17/26 (65.4%) patients with acute myeloblastic leukemia; all 4 patients with chronic myelogenous leukemia in blast crisis and 1 in accelerated phase; 9/12 patients with acute lymphocytic leukemia. A clear correlation between germline transcripts and HLA-DR expression was observed among germline-positive cases (p < 0. 01). C mu expression and response to therapy clearly indicated that germline-mu-positive leukemia patients responded poorly to chemotherapy and had a worse clinical prognosis compared with C mu-negative patients (p < 0.01). After two courses of chemotherapy, 7/9 C mu-negative patients achieved complete remission compared to only 7/29 C mu-positive patients (p < 0.01). We conclude that the gene-regulating immunoglobulin germline C mu may be amplified in myeloid and B-lymphoid cells during leukemogenesis. Such genetic changes may be correlated with cellular terminal differentiation injury, resistance to chemotherapy and uncontrolled malignant cell proliferation.

Genes coding evolutionary novel anti-carbohydrate antibodies: studies on anti-Gal production in alpha 1,3galactosyltransferase knock out mice

This study analyzes the gene repertoire coding for antibodies to an evolutionary novel immunogenic carbohydrate antigen in mice. The alpha-gal epitope (Gal alpha 1-3Gal beta 1-4GlcNAc-R) is an autoantigen, abundantly expressed in wild type mice, but absent in alpha 1,3galactosyltransferase knock-out (KO) mice, where it can induce the production of the anti-Gal antibody. Hybridoma clones secreting anti-Gal were isolated from different mice and their immunoglobulin genes were analyzed. All anti-Gal clones were found to be encoded by the heavy chain gene VH22.1 and light chain gene VK5.1. Moreover, one 'forbidden' anti-Gal clone, produced in a wild type mouse, was also encoded by VH 22.1 and VK 5.1. The genes coding for the different anti-Gal clones were found to contain somatic mutations and different CDR3 domains. These data imply that a highly restricted gene usage combined with junctional diversity and somatic mutations can generate new antibodies that have not been produced in the course of the evolution of a species.

Structure and diversification of the bovine immunoglobulin repertoire

Our understanding of the basis to immunoglobulin formation in cattle has benefited substantially from the application of molecular biology over the past decade. It is now established that both the lambda light chain and heavy chain repertoires are founded upon the frequent expression of single gene families and subgroups of segments which are of conserved sequence. It is likely that a functional kappa locus exists in the bovine genome but this isotype comprises as few as 5% of bovine light chains. Similarly, alternative but non-expressed V(H) gene families are present posing intriguing but unresolved questions about the regulation of immunoglobulin synthesis. The heavy chain frequently bears a third complementarity-determining region which is atypically long but the processes which expand this region of the reading frame and its contribution to the interaction with antigen remain matters of speculation. Opportunities exist to map the major immunoglobulin loci and to define the membership and sequence diversity of the gene families which dominate each repertoire. However, it is already evident that cattle cannot generate significant diversity from rearrangement and junctional imprecision alone. Elucidation of the mechanism(s), dynamics and tissue distribution of immunoglobulin diversification in cattle, thus, remain key challenges in this branch of veterinary immunology.

Avian B cell development: lessons from transgenic models

The bursa of Fabricius is critical for the development of B lymphocytes in avian species. Despite considerable advances in our understanding of the molecular mechanisms by which avian antibody diversity is generated, many stages of B-cell development in the bursa and the means by which they are regulated remain unclear. Here we discuss the use of productive chicken retroviral vectors which allow gene transfer in vitro or in vivo as tools to probe the requirements for bursal B-cell development. Expression of a truncated form of bursal cell surface IgM, lacking variable region encoded determinants, is sufficient to promote the initial colonization and clonal expansion of B-cells within the bursa. Expression of this truncated IgM does not, however, protect developing bursal cells against the apoptosis that occurs within the bursa after hatch. Conversely, over-expression of the proto-oncogene bcl-2, following retroviral gene transfer, protects cells against apoptotic cell death but is not sufficient to allow B lineage progression in the absence of sIgM expression. Finally we discuss the use of regulated promoters within the retroviral gene transfer system to show that while bursal cells are susceptible to transformation by the v-rel oncogene in vitro, this oncogene preferentially targets mature peripheral cells in vivo.

Gene-conversion in rabbit B-cell ontogeny and during immune responses in splenic germinal centers

Combinatorial diversity is limited in rabbits because only a few V(H) genes rearrange. Most diversification of the primary repertoire is generated by somatic hypermutation and gene conversion-like changes of rearranged V(H) in B cells that migrate to appendix and other gut associated lymphoid tissues (GALT) of young rabbits. The changes are referred to as gene conversion-like because the non-reciprocal nature of the alterations introduced has not yet been demonstrated. There are many similarities between rabbits and chickens in how their B cells develop and diversify their repertoires. However, although the majority of rabbit B cells may have rearranged and diversified their V genes early in life, some B cells in adult rabbits have rearranged VH sequences that are identical or nearly identical to germline sequences. We found these cells in splenic germinal centers (GC) on days 7 and 10 after immunization of normal adult rabbits with DNP-BGG. By day 15, all rearranged V(H) sequences were diversified. We find an overall pattern of splenic precursor cells whose germline or near germline sequences change both by gene conversion and point mutations during early divisions and mainly by point mutations during later divisions. These events, in parallel with diversification of light chain sequences, may produce the diverse combining sites that serve as substrates for further affinity maturation by selection either within GC or later among emigrant cells in sites such as bone marrow. Some of the sequences altered by gene conversion in splenic germinal centers may also produce new members of the B-cell repertoire in adult rabbits comparable to those produced in GALT of neonatal rabbits.

A single chain Fv specific against Western equine encephalitis virus

A recombinant single chain Fv (scFv) specific against Western equine encephalitis virus (WEE) was developed and characterized. The scFv was generated from 11D2 hybridoma producing anti-WEE antibody reactive to E1 component of viral envelope glycoprotein. V(L) and V(H) gene segments of 11D2 scFv were generated and joined together with a (gly4ser)3 linker by polymerase chain reaction (PCR). The resulting scFv was successfully expressed in P. pastoris expression system. Fifteen individual plasmids were tested and six of them were shown to drive scFv expression. DNA sequence analysis from three productive plasmids showed that they all carried the same VL and V(H) gene segments with a few base differences. Comparison of 11D2 scFv DNA sequence to the Kabat database showed that VH of 11D2 antibody belonged to subgroup IIID and subfamily XIV, while VL domain did not belong to any known subgroup or subfamily. Western blot analysis of 11D2 scFv using anti-c-myc antibody for detection showed different band pattern among clones derived from different plasmids. This was thought to be due to the different glycosylation where amino acid substitution occurred. Successful purification of 11D2 scFv could be done by immobilized metal affinity chromatography with an unoptimized yield of 700 microg/L. Functional studies showed that 11D2 scFv could bind to its respective WEE antigen as demonstrated by Western blot analysis and enzyme-linked immunosorbent assay (ELISA). The binding affinity of 11D2 scFv is reasonably good compared to the parental 11D2 bivalent monoclonal antibody (MAb). Thus, 11D2 scFv and its derivatives have a potential use as immunotherapeutic and immunodiagnostic agents of WEE infections.

Genetic control of the humoral responses to xenografts. III. Identification of the immunoglobulin V(H) genes responsible for encoding rat immunoglobin G xenoantibodies to hamster heart grafts

BACKGROUND

We have previously reported that the early phases of the immune response of rats to hamster xenografts are characterized by the production of IgM xenoantibodies encoded by a restricted group of Ig germline V(H) genes (V(H)HAR family). In the later phases of the reaction, an IgM to IgG isotype switch occurs and our study examines the structure of the rearranged V(H)HAR genes used to encode IgG antibodies after this isotype switch.

METHODS

A quantitative polymerase chain reaction was used to investigate the changes in the levels of V(H)HAR+ IgG mRNA seen after xenotransplantation. cDNA libraries specific for V(H)HAR+ Iggamma chain were established from total RNA extracted from splenocytes of naive rats and xenograft recipients of hamster hearts at days 4, 8, 21, and 28 posttransplantation. Colony filter hybridization was used to estimate the relative frequency of the use of individual V(H)HAR+ IgG subclasses. Selected IgG clones from day 21 cDNA libraries were sequenced and analyzed for VH-D-J(H) gene usage and antibody combining site structure.

RESULTS

The level of mRNA for V(H)HAR+ IgG increased 6-fold in xenograft recipients at day 21 post-transplantation when compared with naive animals. The relative frequency of isotype usage for V(H)HAR+ IgG1 antibodies alone increased from 22.3% at day 0 to 37.4% at day 21 PTx. Ten IgG clones from the day 21 cDNA libraries have been sequenced for the rearranged V(H)-D-J(H) genes. Thirty percent (3/10) of these IgG clones used V(H)HAR genes for the coding of heavy chain variable region with limited numbers of nucleic acid substitutions (>98% identity with their germline progenitors) although others demonstrated increased variation in nucleotide sequences (95-97% identity) when compared with germline V(H) genes. Analysis of the canonical binding site structure from the predicted amino acid sequences demonstrated that the majority of IgG clones (9/10) displayed a similar pattern of conserved configurations for their combining sites.

CONCLUSIONS

The change in IgM to IgG antibody production in the later stages of the humoral immune response of rats to hamster xenografts is associated with an IgM to IgG isotype switch and an increased production of antibodies of the IgG1 isotype. Rat anti-hamster IgG xenoantibodies continue to express the V(H)HAR family of V(H) genes, many in their original germline configuration, to encode antibody recognition of the hamster target antigens. There are, however, a majority of antibodies for which the V(H) genes express evidence of increased nucleic acid sequence variation when compared to currently available germline sequences. The source of this variation is not known but may represent the expression of as yet unidentified germline genes and/or the introduction of T cell-driven somatic mutations. Despite the appearance of this variation, the unusual level of conservation in key antigen binding sites within the V(H) region suggests the variation, independent of its origin, may have a limited influence on the restricted nature of the host antibody response to xenografts.

[Urine free light chains kappa in multiple sclerosis]

The evaluation of free light chains kappa in urine was performed in 77 cases of multiple sclerosis, including 52 patients before and after treatment with 2 CDA and in 25 patients before and after therapy with high doses of prednisone. The high variations in the level of free kappa chains indicate a limited diagnostic value, and only for cases with very high level. We have found effect of 2 CDA therapy in chronic progressive MS group on free kappa light chain value. A significant effect of prednisone treatment was observed in early onset cases of multiple sclerosis and in cases with clinical improvement after therapy. In conclusion, the study suggests that urinary free light chains level may be considered as one of markers for monitoring of the effect of therapy on the activity of the immunological processes in multiple sclerosis.

The effects of E mu, 3'alpha (hs 1,2) and 3'kappa enhancers on mutation of an Ig-VDJ-Cgamma2a Ig heavy gene in cultured B cells

The Ig kappa intronic and 3'kappa light chain enhancers have been shown to be necessary for V region hypermutation in kappa light chain transgenes. To investigate the role of the E mu intronic enhancer in V region hypermutation of heavy chain genes, E mu and its associated matrix attachment regions (MAR) were replaced with the SV40 or the cytomegalovirus (CMV) enhancer in a gamma2a construct that hypermutates its rearranged VDJ region in the NSO plasmacytoma and 18.81 pre-B cell lines. In this model in vitro system, mutation rates of stable transfectants were determined by reversion analysis using a V region stop codon that, when mutated, allowed the detection of cellular revertants by ELISA spot assay. The gamma2a constructs with the E mu, SV40 and CMV enhancers mutated at comparably high rates in the B cell lines, but not in L cells, indicating that the E mu enhancer and its associated MAR were not specifically required for IgH hypermutation in this system. In parallel experiments, the addition of the 3'alpha heavy chain enhancer (hs 1,2) or the 3'kappa light chain enhancer did not increase the mutation rate of a related mu reporter construct in which the associated VDJ mutates at a moderately low rate in NSO cells or in cell hybrids made between 18.81 and NSO. These results imply that cis-acting IgH elements that promote hypermutation may not be restricted to Ig-specific transcriptional enhancers.

[Construction and screening of type 1 human immunodeficiency virus specific phage antibodies combinatorial library]

Human monoclonal antibodies to type 1 immunodeficiency virus (HIV-1) gp120 were generated from phage antibody combinatorial library.

METHODS

The human immunoglobulin heavy chain Fd and light chain k genes were amplified by half-nested PCR from PBMC of patient infected with HIV. Phage antibody combinatorial library was constructed with the Fd and k chain genes using Pcomb3 as vector. The affinity selection and ELISA were adopted for generating specific phage antibodies. Partial DNA of a positive clone was sequenced and its soluble Fab was expressed in E coli. HIV-1 specific phage antibodies combinatorial library were constructed using the Fd and k genes and Pcomb3 vector. The library capacity was about 1.95 x 10(7). The specific phage antibodies were highly enriched after three rounds of biopanning selection against HIV-1 gp120 and 32% positive clones were detected by ELISA screening. DNA fragment coding for CH1 and CL derived from a positive clone was sequenced and its product was successfully expressed as soluble Fab which was specific for HIV-1 gp120. The HIV-1 specific phage antibody combinatorial library, and human monoclonal antibodies to HIV-1 gp120 have been used as tools for screening of neutralizing antibody to HIV-1, and the methods seem to be very crucial and applicable.