Organization, structure, and assembly of immunoglobulin heavy chain diversity DNA segments

Novel immunoglobulin heavy chains are produced from DJH gene segment rearrangements in lymphoid cells

It has been found that most immunoglobulin heavy(H)-chain gene diversity (D) segments carry their own 5' transcriptional promoter element. Transcription of rearrangements which use heavy-chain D and joining (J) segments in B-lymphoid cells ultimately leads to the production of a Dmu messenger RNA which contains the DJH segments linked to the mu heavy-chain constant region. If the D is joined to the JH segment in the appropriate translational reading frame, this Dmu mRNA is translated to yield a short Dmu protein with a variable DJH N-terminus.

The D segment defines the T15 idiotype: the immunoresponse of A/J mice to Pneumococcus pneumoniae

In the immune response of BALB/c mice (Igha) to Pneumococcus the majority of antibodies express the idiotype of the myeloma protein TEPC 15 (T15). In contrast mice of the A/J strain (Ighe) do not express this idiotype. Using (BALB/c X A/J)F1, F2 or backcross mice it could be shown that in allotype heterozygous animals (Igha/e) Pneumococcus pneumoniae preferentially stimulates B cells expressing a heavy chain (H) encoded by genes in the BALB/c H chain gene complex. Phosphorylcholine (PC)-specific hybridoma lines were established from BALB/c and A/J spleen cells and idiotypically analyzed using monoclonal antibodies (mAb) specific for the T15 idiotopes 32/65, 10/13, 16/13 or 21A5. Whereas the majority of the BALB/c PC-binding mAb express these idiotopes, only some of the A/J mAb are positive for one or the other of the idiotopes formed by the variable (V) regions of the H and the light chain of the myeloma protein T15. However, 80% of the A/J PC-binding hybridoma proteins were bound by the anti-idiotopic mAb 21A5. This mAb is specific for a determinant partially formed by the C alpha and partially by the V regions of the myeloma protein T15. The mRNA of one of these T15- A/J PC-binding hybridoma lines was sequenced. VH and V kappa were identical with sequences found for BALB/c T15-like antibodies. The sequence of the D segment was structurally very different. The importance of the D segment in the dominant expression of the T15 idiotype is discussed.

Preferential utilization of the most JH-proximal VH gene segments in pre-B-cell lines

The most JH-proximal VH gene segments are used highly preferentially to form VHDJH rearrangements in pre-B-cell lines. This result demonstrates that the rate at which immunoglobulin VH gene segments recombine is influenced by their chromosomal organization, and that the initial repertoire of VH genes expressed in pre-B cells is strikingly different from that seen in mature populations.

Insertion of N regions into heavy-chain genes is correlated with expression of terminal deoxytransferase in B cells

The variable regions of immunoglobulin heavy chains are encoded in the germ line by three discrete DNA segments: VH (variable) elements, D (diversity) elements and JH (joining) elements. During the differentiation of B lymphocytes, individual segments from each group are brought together by recombination to form the complete VHDJH variable region. To understand these processes better, we have now isolated and sequenced molecular clones representing intermediates (DJH fusions) and final products (VH-to-DJH joins) of heavy-chain gene rearrangement in two cell lines that represent analogues of cells at early stages of B-lymphocyte differentiation. Heavy-chain gene assembly in one cell line but not in the other is accompanied by the appearance of short nucleotide insertions at the recombinational junctions. The generation of such insertions is positively correlated with the expression of terminal deoxynucleotidyl transferase in these lines.

A murine T cell receptor gene complex: isolation, structure and rearrangement

We describe here our efforts to develop a systematic strategy for the enumeration and isolation of genes encoding T cell-specific, membrane-associated polypeptides. Of particular importance among the cDNA clones that we have isolated is one which encodes the beta chain of the murine T cell receptor for antigen. The gene product is strikingly similar to immunoglobulin in its variable (V), constant (C), joining (J), and diversity (D) - like elements and the ability of the latter three types of element to assort independently during differentiation. The genomic organization of the constant region locus which encodes this molecule consists of two tandemly arrayed units of the form JC/JC, where the J clusters consist of fourteen distinct elements, many of which may be functional. The two constant regions differ by only four amino acids and both are apparently expressed in T cells of the same phenotype, so they probably do not represent isotypes in the classical sense. The sequences flanking the V, D and J elements are also similar to the conserved heptamer and nonomer sequences of immunoglobulins thought to be important in the recombination of the specific gene segments. These similarities indicate both the common evolutionary origins of these loci and the strong selective pressure that must be operative. The T cell receptor locus differs somewhat from immunoglobulins in the large number of possible J region elements and to some extent in the hypervariable-framework regions of the V region. We and others have mapped this gene to chromosome 6 of the mouse, in the same portion of the chromosome but not closely linked the kappa locus. The significance of the predicted protein structure of the beta chain and its support of the one-receptor model of MHC-antigen recognition are discussed.

Complete amino acid sequence of heavy chain variable regions derived from two monoclonal anti-p-azophenylarsonate antibodies of BALB/c mice expressing the major cross-reactive idiotype of the A/J strain

The primary structure of A/J anti-p-azophenylarsonate (anti-Ars) antibodies expressing the major A-strain cross-reactive idiotype (CRIA) has provided important insights into issues of antibody diversity and the molecular basis of idiotypy in this important model system. Until recently, this idiotype was thought to be rarely, if ever, expressed in BALB/c mice. Indeed, it has been reported that BALB/c mice lack the heavy chain variable segment (VH) gene that is utilized by the entire family of anti-Ars antibodies expressing the A/J CRI. Recently, however, it has been possible to elicit CRIA+, Ars binding antibodies in the BALB/c strain by immunizing first with anti-CRI and then with antigen. Such BALB/c, CRIA+ anti-Ars antibodies can be induced occasionally with antigen alone. VH region amino acid sequences are described for two CRIA+ hybridoma products derived from BALB/c mice. While remarkably similar to each other, their VH segments (1-98) differ from the VH segments of A/J CRIA+, anti-Ars antibodies in over 40 positions. Rather than the usual JH2 gene segment used by most A/J CRIA+ anti-Ars antibodies, one BALB/c CRIA+ hybridoma utilizes a JH1 gene segment, while the other uses a JH4. However, the D segments of both of the BALB/c antibodies are remarkably homologous to the D segments of several A/J CRIA+ antibodies sequenced previously, as are the amino terminal amino acid sequences of their light chains. These data imply that BALB/c mice express the A/J CRIA by producing antibodies with very similar, if not identical, light chain and heavy chain D segments, but in the context of different VH and JH gene segments than their A/J counterparts. The results document that molecules that share serologic specificities can have vastly different primary structures.

The immunoglobulin heavy chain variable region (Igh-V) locus in the mouse. I. One hundred Igh-V genes comprise seven families of homologous genes

Seven families of Igh-V genes have been defined by Southern blot analysis of genomic DNA from eighteen inbred strains of mice. Each of twenty-four cloned Vh genes hybridized to one of seven nonoverlapping sets of Eco RI restriction fragments. These families contain from 2 to approximately 40 hybridizing fragments. From these data we estimate that the mouse Igh-V locus consists of one hundred Vh genes. Genes within a Vh family share greater than 80% sequence homology while the sequence homology between families is generally less than 70%. There is extensive restriction fragment length polymorphism among the strains analyzed allowing the assignment of complete (Igh-V + Igh-C) Igh haplotypes for eighteen inbred mouse strains.

The structure, rearrangement and expression of D beta gene segments of the murine T-cell antigen receptor

It has been postulated that the variable region of the beta-polypeptide of the murine T-cell antigen receptor is encoded by three distinct germ-line gene segments--variable (V beta), diversity (D beta) and joining (J beta)--that are rearranged to generate a V beta gene. Germ-line V beta and J beta gene segments have been isolated previously. Here we report the isolation and characterization of two germ-line D beta gene segments that have recognition signals for DNA rearrangement strikingly similar to those found in the three immunoglobulin gene families and in V beta and J beta gene segments. The D beta and J beta segments can join in the absence of V beta gene segment rearrangement and these rearranged sequences are transcribed in some T cells.

A biological consequence of variation in the site of D-JH gene rearrangement

One mechanism which generates diversity in immunoglobulin variable (V) regions is flexibility in the site of recombination among the constituent genetic elements. Within a specific antibody family (that is, a particular VH-VL combination), variability in V-D-J rearrangement not only leads to sequence diversity at the boundary of the juxtaposed genes, but also enables the total length of the third complementarity-determining region (CDR-3) of the heavy chain to be conserved. We demonstrate here that the junctional diversity inherent in rearranged immunoglobulin genes can have consequences for the biology of the immune system. Sequence analysis of the expressed immunoglobulin genes of idiotypically variant as opposed to conventional B lymphocytes of a dominant antibody family showed that the variant B cells undergo a novel D-JH joining event such that an extra amino acid is inserted into the heavy chain CDR-3. The unique D-region conformation possessed by the variant B cells accounts for previous observations which showed that variant and conventional B cells could be differentially regulated in vivo by an autologous set of idiotope-specific B lymphocytes. Our findings indicate that D-region structure can determine the expression of regulatory idiotopes and suggest that the conservation of heavy-chain CDR-3 length within an antibody family may reflect regulatory as well as functional constraints.

Illegitimate recombination generates a class switch from C mu to C delta in an IgD-secreting plasmacytoma

We present here the sequence characterization of a C mu----C delta immunoglobulin (Ig) heavy chain class switch. In the murine IgD-secreting plasmacytoma TEPC 1017, deletion of most of the mu switch recombination region (S mu) and the entire C mu gene occurred in the absence of switch region sequences 5' to C delta. This unique rearrangement resulted from an illegitimate recombination of sequences with only patchy homology to each other. The infrequent and variable nature of illegitimate recombination may explain the low frequency of IgD-secreting plasma cells in normal mouse tissues.

Ordered rearrangement of immunoglobulin heavy chain variable region segments

The immunoglobulin heavy chain variable region is encoded as three separate libraries of elements in germ-line DNA: VH, D and JH. To examine the order and regulation of their joining, we have developed assays that distinguish their various combinations and have used the assays to study tumor cell analogs of B-lymphoid cells as well as normal B-lymphoid cells. Abelson murine leukemia virus (A-MuLV) transformed fetal liver cells - the most primitive B-lymphoid cell analog available for analysis - generally had DJH rearrangements at both JH loci. These lines continued DNA rearrangement in culture, in most cases by joining a VH gene segment to an existing DJH complex with the concomitant deletion of intervening DNA sequences. None of these lines or their progeny showed evidence of VHD or DD rearrangements. Heavy chain-producing tumor lines, representing more mature stages of the B-cell pathway, and normal B-lymphocytes had either two VHDJH rearrangements or a VHDJH plus a DJH rearrangement at their two heavy chain loci; they also showed no evidence of VHD or DD rearrangements. These results support an ordered mechanism of variable gene assembly during B-cell differentiation in which D-to-JH rearrangements generally occur first and on both chromosomes followed by VH-to-DJH rearrangements, with both types of joining processes occurring by intrachromosomal deletion. The high percentage of JH alleles remaining in the DJH configuration in heavy chain-producing lines and, especially, in normal B-lymphocytes supports a regulated mechanism of heavy chain allelic exclusion in which a VHDJH rearrangement, if productive, prevents an additional VH-to-DJH rearrangement.

Somatic recombination in a murine T-cell receptor gene

A putative T-cell receptor gene was isolated from the DNA of the helper hybridoma, 2B4 . Analysis of the sequence components of this rearranged gene indicates the presence of separate variable (V), diversity (D) and joining (J) region elements analogous to those of heavy-chain immunoglobulins. These findings further support the belief that the products of this locus are involved in antigen recognition by T cells. There is no evidence of somatic mutation between the putative germ-line and the expressed variable-region gene.

Site-specific recombination between immunoglobulin D and JH segments that were introduced into the genome of a murine pre-B cell line

A recombinant plasmid containing the herpes simplex virus thymidine kinase (tk) gene, flanked on one side by two murine immunoglobulin heavy chain diversity (D) elements and on the other by two murine immunoglobulin heavy chain joining (JH) elements, was introduced into a tk- variant of a pre-B cell line transformed by Abelson murine leukemia virus. The four possible site-specific joining events between the D and JH segments within the integrated construct occurred frequently during passage of the cloned line under nonselective conditions, and deletion of the internal tk gene as a result of these joining events was, by far, the predominant mechanism of resistance to BUdR within this line. These studies demonstrate that a precise chromosomal location is not essential for the assembly of D and JH elements and provide a model system for mechanistic and genetic studies of this recombination process.

Sequence relationships between putative T-cell receptor polypeptides and immunoglobulins

Comparison of the sequence of a cloned T cell-specific cDNA with those of cross-reacting cloned cDNAs isolated from a thymocyte library indicates the presence of variable, constant and joining regions remarkably similar in size and sequence to those encoding immunoglobulin proteins. Together with the evidence for somatic gene rearrangements reported in the accompanying paper, this strongly suggests that the TM86 cDNA clone encodes one chain of the T-cell receptor for antigen.

Somatic diversification of immunoglobulins

A series of three IgM, kappa monoclonal antibodies arising from a fusion of BALB/c spleen cells from mice immunized with beta-(1,6)-galactan-containing antigens have been analyzed. These three lines were found (i) to have homologous protein sequences in the heavy chain D region and at the sites of recombination between the heavy chain variable and D segment (VH-D) and the D and joining segment (D-JH), although amino acid substitutions were observed in both the heavy and light chain variable regions; (ii) to use identical heavy and light chain joining segments; and (iii) to demonstrate two identical (productive and nonproductive) kappa-chain rearrangements. A likely explanation for these observations is that the three lines are clonally related (arise from a common precursor) and that the observed heavy and light chain variable segment substitutions represent somatic point mutations. Because these antibodies are all of the IgM class, the results indicate that a somatic mutational mechanism is activated early in B-cell ontogeny and operates at both the heavy and light chain loci. Furthermore, the somatic mutation process appears to continue during the development of a given cell line, but is independent of class switching.

Translocation of the myc cellular oncogene to the immunoglobulin heavy chain locus in murine plasmacytomas is an imprecise reciprocal exchange

The 15;12 translocations in murine plasmacytomas represent recombination of the myc oncogene with the immunoglobulin CH locus, often within CH switch recombination (SH) regions. Chromosome junctions cloned from four plasmacytomas confirmed that the translocation generates reciprocal CHSH-myc and 5'myc-SH structures. H locus targets included S alpha fused to Smu, Smu fused to S gamma 2b, and a germline S alpha region. The nature of two H locus targets suggests that the target need not be highly active transcriptionally. Switch recombination machinery is implicated in the translocation by the SH targets and by homology of certain c-myc breakpoints with normal switch recombination sites. Fusion regions revealed deletions, extraneous nucleotides, and one duplication. These results prompt a translocation model in which staggered single-stranded breaks on each chromosome are followed by single-strand excision or polymerization prior to ligation to the other chromosome.

The role of a novel VH sequence (V11) in the formation of anti-phosphocholine antibodies

The immune response to phosphocholine (PC) in mice is highly restricted. Most anti-PC antibodies use heavy-chain variable-region (VH) sequences derived from single VH gene segment, V1. In order to investigate whether a highly homologous VH gene segment, V11, could contribute to the formation of PC-binding antibodies, we carried out chain recombination experiments with M47A, a non-PC binding myeloma protein whose H-chain is encoded by the V11 gene segment, and two PC-binding antibodies, HP101.6G6 (HP6G6) and M511. The H-chains from the non-PC-binding myeloma protein, M47A, formed a functional PC-binding site when paired with L-chains from both PC-binding antibodies. These results suggest that a second VH gene segment, V11, could theoretically be used to form PC-binding antibodies. In addition, these results provide direct evidence that a single H-chain can be used in combinatorial association with different L-chains to form antibodies of differing specificities.

A pattern of partially homologous recombination in mouse L cells

Herpes simplex virus thymidine kinase gene and pBR322 DNA (in large excess to the thymidine kinase gene) were introduced into mouse L cells by calcium phosphate DNA-mediated gene transfer. DNA fragments encompassing six junctions between the exogenous DNAs have been cloned and their nucleotide sequences determined. Analysis of these sequences has shown that stretches of partial homology involving from 20-50 base pairs are present near the points at which joining occurs between the donor molecules. The structure of the junction sequences suggests that the recombination event involves the alignment of the two donor DNA molecules at partially homologous regions followed by staggered cutting and joining. One donor molecule is always cut in the region of partial homology, while the second is cut at some distance that is a small multiple of 13.5 +/- 0.5 base pairs away (at 0, 14, 27, 39, 41, and 54 base pairs). In the three junctions where the second cut is far from the region of homology, a 17- to 19-base-pair segment of DNA separates the donor sequences. In all cases the origin of this "filler" DNA appears to be oligonucleotides derived from pBR322.

An attempt to correlate an idiotype with antibody structure

The expression of different idiotypic families encountered in the anti-phosphorylcholine antibodies depends on the association of a heavy chain with one of the VL sub-families. Manipulation of the response by idiotypic suppression leads to formation of a T15cr family whose structural correlates are analysed by determination of the mRNA sequence of hybridoma heavy and light chains.

Multiple VH gene segments encode murine antistreptococcal antibodies

Most mouse strains are able to mount a diverse antibody response against group A streptococcal carbohydrate (GAC). We have previously reported that murine anti-GAC antibodies are for the most part restricted to IgM and IgG3 subclasses. In addition, despite extensive heterogeneity in their isoelectric focusing patterns, greater than 50% of A/J anti-GAC antibodies share a common light chain defined by spectrotypic and idiotypic (VK1GAC) criteria. We have used protein and DNA sequencing strategies to examine the genetic basis of diversity in murine anti-GAC antibodies. In particular, we report that, (a) multiple, closely homologous VH gene segments contribute to the generation of anti-GAC antibodies, (b) a common framework sequence, related to the VK27 subgroup, probably defines VK1GAC, and (c) the A/J anti-GAC VH regions and BALB/c anti-inulin VH sequences are 95% homologous at the protein level and are likely encoded by overlapping VH gene families. Lastly, we discuss the genetic mechanisms that might permit the evolution of multiple, closely homologous germline VH gene segments in the context of highly divergent flanking region sequences.

Monoclonal AKR/J thymic leukemias contain multiple JH immunoglobulin gene rearrangements

We have examined the patterns of heavy-chain immunoglobulin gene rearrangement and provirus integration in seven murine leukemia virus-induced thymic leukemias from AKR/J mice. In five of the seven tumors examined, there were between two and five rearrangements of the heavy-chain immunoglobulin J (JH) segment. Except for one case, the rearranged JH segments are present in less than one copy per cell, indicating that these tumors contain subpopulations of thymocytes with differing JH rearrangements. Nevertheless, each tumor is probably of monoclonal origin because the cells in a given tumor contain a common set of randomly integrated murine leukemia proviruses. Our results indicate that the JH segments rearranged within a few cell divisions after tumor cell proliferation began and may, therefore, identify a specific stage in T-cell differentiation when tumorigenesis occurs.

The D-JH complex is an intermediate to the complete immunoglobulin heavy-chain V-region gene

We have examined the organization of the immunoglobulin JH segments in three clones derived from a single Abelson murine leukemia virus-transformed cell. Cloning and nucleotide sequence analyses of the JH-containing fragments have revealed the rearrangement from the preformed D-JH complex to the complete VH-D-JH gene, which was accompanied by the expression of the intra-cytoplasmic mu chain. In one case a JH segment downstream to the preformed D-JH was used to create a new VH-D-JH gene. Upon the D-JH and VH-D-JH rearrangements the intervening D segments were deleted from the chromosome. One of the expressed VH genes suffered from a large deletion of the 3' portion (including the 95th cysteine residue) of the VH segment. We discuss the possible mechanism of the allelic exclusion.

Galactan-binding antibodies. Diversity and structure of idiotypes

A group of eight IgM hybridoma proteins induced with beta(1,6)-D-galactan-containing antigens has been characterized in terms of primary amino acid sequence and idiotype expression. The H chain amino acid sequences reveal very strong homology in the VH segment although several substitutions are seen that suggest the occurrence of somatic mutation in these IgM molecules. Significant sequence variation was observed in CDR-3, the region generated by the D segment, and the two recombination events, VH-D and D-JH. The number of amino acids in this region contributed by the D segment was found to vary from two to six, yet the overall length of CDR-3 was precisely maintained by the addition of amino acids on either side of D during the recombination processes. These additional amino acids are suggested to result from nucleotide addition by repair enzymes. Idiotypic analysis of these proteins, in conjunction with an assessment of the H chain sequences, has permitted an identification of the molecular basis of both cross-reacting and unique idiotypic determinants expressed by these molecules.

Amino acid sequence diversity within the family of antibodies bearing the major antiarsonate cross-reactive idiotype of the A strain mouse

VH region amino acid sequences are described for five A/J anti-p-azophenylarsonate (anti-Ars) hybridoma antibodies for which the VL region sequences have previously been determined, thus completing the V domain sequences of these molecules. These antibodies all belong to the family designated Ars-A which bears the major anti-arsonate cross-reactive idiotype (CRI) of the A strain mouse. However, they differ in the degree to which they express the CRI in standard competition radioimmunoassays. Although the sequences are closely related, all are different from each other. Replacements are distributed throughout the VH region and occur in positions of the chain encoded by all three gene segments, VH, DH, and JH. It is likely that somatic diversification processes play a dominant role in producing the sequence variability in each of these segments. The number of differences from the sequence encoded by the germline is smallest for antibodies that express the CRI most strongly, suggesting that somatic diversification is responsible for loss of the CRI in members of the Ars-A antibody family. There is an unusual degree of clustering of differences in both CDR2 and CDR3 and many of the substitutions are located in "hot spots" of variation. The large number of differences between the chains prohibits the unambiguous identification of positions at which alterations play a major role in reducing the expression of the CRI. However, the data suggest that the loss of the CRI is associated with a definable repertoire of somatic changes at a restricted number of highly variable sites.

The sequences of rabbit kappa light chains of b4 and b5 allotypes differ more in their constant regions than in their 3' untranslated regions

We report the sequence of a cDNA clone encoding the entire variable and constant regions of a rabbit kappa light chain of b5 allotype. The deduced amino acid sequence of the variable region (positions 1-95) is 86% homologous to that of a b4 light chain protein [BS-1) (1) but the b4 and b5 constant regions are only 74% homologous. Comparison of this DNA sequence to that of a cDNA clone encoding a b4 constant region shows that the kappa allotypes b4 and b5 have diverged significantly more in their coding region than in the 3' untranslated regions (86% vs 96% nucleotide sequence homologies). This implies either a function for the 3' untranslated region with evolutionary pressures to conserve or an accelerated divergence of the coding regions.

Diversity in the rabbit immunoglobulin kappa chain variable regions is amplified by nucleotide deletions and insertions at the V-J junction

To analyze the rabbit immunoglobulin kappa locus, we isolated, from a phenotypically homozygous b4/b4 rabbit genomic library, a C kappa gene corresponding to the b4 var allelic form of the b4 C kappa gene. We also determined the nucleotide sequence of the J kappa cluster 3 kb upstream of the b4 var C kappa gene. Southern blot experiments with rabbit J kappa probes indicate that the bas C kappa gene is an isotype probably associated with its own J kappa segment(s). The rabbit b4 J kappa gene region contains a cluster of five J kappa segments, homologous to the human J kappa cluster, and two remnant J kappa segments approximately 5 kb upstream of the b4 C kappa gene. Nucleotide sequence analyses of the coding J kappa segments and their recombination signal sequences show only one functional J kappa segment. Comparisons with the protein data indicate that the rabbit kappa gene family, unlike its human and mouse homologs, increases kappa light chain variability by deletions and insertions at the V-J junction.

Reciprocal chromosome translocation between c-myc and immunoglobulin gamma 2b genes

Specific chromosome translocations have been observed in transformed cell lines of both man and mouse and may be implicated in the origin or maintenance of malignancy. In mouse plasmacytomas, translocations have been identified that bring the immunoglobulin alpha heavy-chain gene (C alpha, normally located on chromosome 12) into proximity with c-myc (normally located on chromosome 15), c-myc being the mouse cellular homologue of the avian myelocytomatosis virus transforming gene (v-myc). Here we identify a DNA rearrangement in a mouse hybridoma that has brought c-myc close to C gamma 2b and show that this rearrangement occurred by reciprocal chromosome translocation, as recombinant clones were isolated from the same cell line in which a rearranged variable-region (VH) gene has been brought close to 5' c-myc sequences. The translocation has resulted in the net loss of 7 base pairs (bp) of chromosome 15 sequence as well as in the presence of an additional base of unknown provenance. This reciprocal translocation was analysed in DNA from a mouse hybridoma cell line but is shown to be characteristic of the X63Ag8 myeloma parent.

Amino acid sequence of the heavy chain variable region from the A/J mouse anti-arsonate monoclonal antibody 36-60 bearing a minor idiotype

In addition to the predominant idiotype family (IdCR) associated with the murine A/J anti-azophenylarsonate response, a second idiotype family (Id36-60) was defined on the basis of serologic cross-reactivity and amino acid sequence homology among monoclonal antibodies [Marshak-Rothstein, A., Margolies, M.N., Benedetto, J.D., & Gefter, M.L. (1981) Eur. J. Immunol. 11, 565-572]. The complete variable region amino acid sequence of the A/J IgG2a hybridoma protein 36-60 heavy chain was obtained by automated Edman degradation of the intact chain and fragments generated by cleavage with CNBr and by tryptic digestion of a succinylated CNBr peptide. A comparison of the Id36-60 heavy chain sequence to that of the IdCR heavy chain variable region reveals only 45% homology between them. The structural data indicate that different genes encode the VH, D, and JH gene-encoded sequences in the two idiotypes.

Recombination between antibody heavy chain variable-region genes: evidence for gene conversion

The murine hybridoma line B1-8.delta 1 secretes monoclonal IgD lambda 1 antibodies specific for the hapten (4-hydroxy-3-nitrophenyl)acetyl (NP). The variable (V) region of these antibodies is defined by a characteristic pattern of idiotopes. A spontaneous V-region variant (B1-8.V1) with altered idiotope pattern was selected. The structural variation is confined to the V region of the heavy chain. It was shown previously that the variant V region is encoded by a gene that was generated by a crossover between the rearranged VDJ gene of the wild type (B1-8.delta 1) and a neighboring germ-line VH gene. In the present study the nucleotide sequence of coding and flanking regions of the VH gene expressed in variant B1-8.V1 was determined. Wild-type and variant VH genes differ at 15 positions in a region between leader sequence and codon 66. The sequence of the region carrying the substitutions is identical to the sequence of the corresponding region in a neighboring germ-line VH gene. This implies that the variant VH gene was generated by a mechanism of recombination more complicated than single crossover. Gene conversion as the mechanism of the recombination is discussed.

mRNA sequences define an unusually restricted IgG response to 2-phenyloxazolone and its early diversification

Light and heavy chain mRNAs of 15 anti-oxazolone antibodies were sequenced directly using synthetic primers. Hybridomas obtained 7 days after primary immunization show that they are of restricted heterogeneity. The majority expressed a single sequence with minor differences concentrated in the D region and joining boundaries D--JH and V kappa--J kappa.

T and B cells that recognize the same antigen do not transcribe similar heavy chain variable region gene segments

We have attempted to determine whether T cells and B cells that have the same antigenic specificity and whose receptors share idiotypic determinants in fact express similar VH gene segments. To do this, we have obtained and characterized a cDNA clone containing the entire coding sequence for the VH gene from a glutamic acid60/alanine30/tyrosine10 (GAT)-binding immunoglobulin that carries the CGAT idiotype. The GAT-VH clone was hybridized to Northern blots of GAT-specific T cell RNAs; there was no evidence of a T cell transcript that hybridized to the GAT-VH probe. The T cells analyzed included: (a) 10 GAT-binding suppressor T cell hybridomas, 6 of which secreted factors with CGAT idiotypic determinants, (b) one GAT-specific helper T cell hybridoma, and (c) two GAT-specific helper T cell lines grown in the absence of feeder cells. The detection limit of the Northern blot analysis was 1-2 copies of a particular mRNA species per cell for the hybridomas and 5-10 copies per cell for the T cell lines. Therefore, we conclude that T and B lymphocytes responding to GAT do not utilize similar VH gene segments. Furthermore, the presence of idiotypic determinants on T lymphocytes does not necessarily imply close structural similarity between T and B cell antigen receptors.

Restricted adult clonal profiles induced by neonatal immunization. Influence of suppressor T cells

The effects of neonatal antigen exposure on the adult B cell repertoire have been examined by characterizing the influenza hemagglutinin (HA)-specific response of adult BALB/c mice given antigen soon after birth. Ligand exposure during early life exerts a profound and lasting effect upon the B cell repertoire, characterized by the expansion and preservation of particular antigen-reactive clones and the apparent loss of others. The precise subset of clonotypes selectively preserved depends upon the age at which antigen is first encountered; and is predictable given a knowledge of the emerging primary pool's dynamics and composition. The preserved (secondary) B cells differ from their unprimed precursors with respect to (a) expression of the surface marker detected by the monoclonal antibody J11d, and (b) susceptibility to T cell-mediated suppression. These studies thus demonstrate a strong relationship between the heritable dynamics of the emerging primary B cell repertoire and the effect of ligand-driven events upon repertoire phenotype. In addition, they provide a mechanistic model for certain forms of antigen-induced oligoclonal dominance, especially the phenomenon of original antigenic sin.

Immunoglobulin diversity: analysis of the germ-line VH gene repertoire of the murine anti-GAT response

A cDNA clone was constructed from a mRNA encoding an anti-GAT (Glu60 Ala30 Tyr10) BALB/c monoclonal antibody heavy chain. Its sequence, covering codons -5 to 162 and therefore encompassing the complete V-D-J region, was determined. Surprisingly, the sequence of the VH gene-encoded region was almost identical with that of the BALB/c VH anti-HNP (4-hydroxy-3-nitrophenyl) acetyl VH region, suggesting that the same VH germ-line might be used to encode two heavy chains contributing to antibodies of discrete specificities. A specific VH probe was derived and annealed to Eco RI and Bg1 II restriction fragments of liver (unrearranged) DNA extracted from the BALB/c, DBA/2 and C57BL/6 mouse strains that differ in their H chain allotypes. Under stringent conditions, only a few bands were identified by Southern blotting. The different patterns observed suggest that the VH anti-GAT repertoire differs between these strains even though their various anti-GAT antibodies express the same public idiotypic specificities.

Diversity and joining segments of mouse immunoglobulin heavy chain genes are closely linked and in the same orientation: implications for the joining mechanism

We have mapped 12 diversity (D) gene segments of mouse Ig heavy chains between 80 and 1 kilobases 5' to the four joining (JH) gene segments by molecular analysis of DNA clones isolated from recombinant phage and cosmid libraries. All identified D and JH segments are in the same 5'-3' orientation. The significance of these findings with respect to the joining mechanism for Ig gene segments is discussed.

Somatic generation of antibody diversity

In the genome of a germ-line cell, the genetic information for an immunoglobulin polypeptide chain is contained in multiple gene segments scattered along a chromosome. During the development of bone marrow-derived lymphocytes, these gene segments are assembled by recombination which leads to the formation of a complete gene. In addition, mutations are somatically introduced at a high rate into the amino-terminal region. Both somatic recombination and mutation contribute greatly to an increase in the diversity of antibody synthesized by a single organism.

Sequential generation of antibody diversity during B-cell development

It has become increasingly apparent that generation of and variation in antigen-combining sites of antibodies occurs sequentially during B-cell development. Allelic and isotypic exclusion mechanisms ensure that a B cell produces antibody molecules having a single kind of combining site. A major reason for evolution of mechanisms which result in asynchronous formation of functional H and L chain genes may be the need for allelic and isotypic exclusion; but this may not be the only advantage of asynchronous formation of H and L chain genes. The evolution of mechanisms causing nonjunctional somatic mutation late in B cell development - only after antigen exposure apparently - may result from the biological advantages of: (1) 'fine tuning' of the combining site; (2) a response to an anti-idiotype regulatory network, or (3) expanded memory.

Structural correlates of immunoglobulin diversity

VL and VH domains, from different species and with widely different primary structures, interact with each other in the same way to create the globular FV region. Much of the FV is a highly conserved framework structure that is probably common to most, if not all, mammalian FV regions. The extensive contoured frontal surface of the FV is composed of highly variable polypeptide segments (Wu-Kabat complementarity-determining regions). These segments are derived from parts of VL, VH, JH gene products and most of the D gene product. This surface is currently considered to be the most likely location of the antigen-binding sites. The firm immunochemical data based on identification of contacting amino acids supporting this location are still, however, very fragmentary. VL and VH gene products form a large part of the potential antigen-reactive surface. Hence, combinations of different VL and VH gene products are the largest source of structural diversity. The JL and JH gene products have chiefly structural functions in maintaining domain architecture and controlling some interactions between VL and VH domains. The VL-J junction amino acid can provide unique structural properties in the deeper accesses of the potential antigen reaction surface. The VHD-JH junction is more superficial and could be, but has not yet been, directly implicated in antigen binding. The D gene product and the additional amino acids associated with the (VH-D-JH) rearrangement process do determine a substructural part of the potential antigen reactive surface. The D gene product (a connecting segment between two beta strands) can have many different secondary structures. Functionally, the D region product could interact with VL-CDR-1 amino acids to create a specific contour of the antigen reaction surface. Curiously, primary structural variations in H3 have not yet been directly implicated in antigen binding. Much remains to be learned about the role of VH-D-JH rearrangement in antibody diversity. The major genetic factors in creating structural diversity are the multiple VL and VH gene libraries. The gene rearrangement process provides a further amplification. Somatic mutations are yet another additional mechanism.

Somatic cells efficiently join unrelated DNA segments end-to-end

Molecular substrates for probing nonhomologous recombination in somatic cells were constructed by inserting pBR322 sequences at selected sites on the simian virus 40 (SV40) genome. The chimeric products are too large to be packaged into an SV40 capsid. Therefore, production of viable progeny requires that most of the pBR322 sequences be deleted without altering any SV40 sequences that are essential for lytic infection. As judged by plaque assay, these recombination events occur at readily detectable frequencies after transfection into CV1 monkey kidney cells. Depending on the site of pBR322 insertion, the infectivities of the full-length circular or linear chimeras ranged from 0.02 to 2% of the infectivity of linear wild-type SV40 DNA. Nucleotide sequence analysis of several recombinant progeny revealed three distinct classes of recombination junction and indicated that the causative recombination events were minimally dependent on sequence homology. Potential mechanisms involving recombination at internal sites or at ends were distinguished by measuring the infectivity of chimeric molecules from which various lengths of pBR322 had been removed. These data support end-to-end joining as the primary mechanism by which DNA segments recombine nonhomologously in somatic cells. This end joining appears to be very efficient, since SV40 genomes with complementary single-stranded tails or with short non-complementary pBR322 tails were comparably infectious. Overall, this study indicates that mammalian somatic cells are quite efficient at the willy-nilly end-to-end joining of unrelated DNA segments.

Polymorphism in anti-phosphocholine antibodies reflecting evolution of immunoglobulin families

Complete variable (V) region amino acid sequences were determined for four heavy (H) and one light (L) chain from C57BL phosphocholine (PC)-binding monoclonal antibodies. Additional NH2-terminal sequences were obtained from H and L chains of C57BL and CBA/J origin. When these V regions were compared with previously reported anti-PC sequences, a number of observations could be made regarding the function and evolution of L and H chain segments used in these antibodies. (a) L and H chain V segments are remarkably conserved in these inbred strains, although there has been an accumulation of point mutations identifying apparently allelic forms of VK and VH. (b) Mice of each genotype use the same three VK segments in combination with a single VH segment to produce most anti-PC antibodies. An exception has been noted that indicates the occasional use of a second VH gene segment. (c) Multiple, different DH regions are used by mice of each strain, which suggests that the DH segment sequence plays no critical role in either antigen binding or VH-VL pairing. Furthermore, the DH segments and their corresponding gene families appear to be highly conserved in the inbred strains studied. (d) Most PC-binding antibodies use the JH1 joining segment. All JH1 sequences from C57BL mice differ from the BALB/c JH1 at position 105, which identifies allelic forms of the JH1 region. These studies are a first assessment of the nature of mutational events associated with the evolution of specific multigene immunoglobulin families and indicate that homologous VH, DH, JH, VK, and JK genes are similarly assembled and expressed in PC antibodies from three diverse genotypes.

A switch region inversion contributes to the aberrant rearrangement of a mu immunoglobulin heavy chain gene in MPC-11 cells

We describe the unique features of an aberrantly rearranged mu immunoglobulin heavy chain gene isolated from MPC-11 cells (a gamma 2b producing Balb/c plasmacytoma). A novel rearrangement has occurred 1.5 Kb 5' of the MPC-11 mu gene (denoted 18b mu) resulting in the deletion of the majority of the repetitive switch region (S mu) and 5' flanking DNA including the Joining (JH) sequences. The remainder (275 bp) of the S mu repeat has undergone a complete sequence inversion. DNA sequences 5' of the inverted S mu sequence do not resemble Variable (VH), Diversity (D), JH or their conserved flanking sequences. A DNA sequence localized 5' of the inverted S mu sequence, (p18b mu-1.4) detects a small family of homologous sequences in Balb/c DNA. The 18b mu-1.4 like sequences lack homology to S mu, exhibit flanking sequence polymorphisms in 5 out of 6 inbred mouse strains and undergo partial or complete deletion in 5 out of 10 plasmacytomas tested. Two 18b mu-1.4 homologous sequences display a higher copy number in C57Bl/6, AL/N and CAL9 mouse strains.