Structural evidence for independent joining region gene in immunoglobulin heavy chains from anti-galactan myeloma proteins and its potential role in generating diversity in complementarity-determining regions

Immuno-receptors: from recognition to signaling and function

The vertebrate adaptive immune response is initiated by specific recognition of antigens. This is carried out by molecules, soluble or cell surface receptors that are members of the Multichain Immune Recognition Receptors (MIRR) group of proteins. The soluble arm of the response is based on antibodies. Kinetic analysis of antibody-antigenic epitope interactions pioneered insights into the complexity underlying the capacity of relatively limited repertoires of antibodies to recognize an essentially unlimited range of epitopes by employing conformational diversity of a given single sequence. The arm responsible for recognition of cellular targets involves a considerably more elaborate process, predominantly of antigen-derived peptides presented bound to molecules encoded by the major histocompatibility complex (MHC). This remarkable cellular recognition process performed by T-cell receptors requires earlier steps of peptide presentation and involves interactions of the receptor sites with the array of its MHC-peptide composite ligand. In both cases, antigen recognition needs to be followed by its coupling, by biochemical cascades, to different specific responses, namely activation of effector functions. The parameters required for coupling to functional responses are still a focus of intense research. In solution, antigen-antibody aggregation is one established activation process. Those required for coupling antigen recognition to cell activation, whether by Fc receptor bound antibodies or by the B-cell antigen receptor, are also still subject to active research efforts. Though activation by immune-receptors requires antigen recognition, considerable differences could exist among the requirements set by distinct cell types. Moreover, antigen binding requiring intercellular interactions introduces additional complexity.

Isolation of a vascular cell wall-specific monoclonal antibody recognizing a cell polarity by using a phage display subtraction method

Using a strategy consisting of (i) the isolation of cell walls from synchronously differentiating cells of Zinnia, (ii) the generation of mAbs with an antibody phage display method, and (iii) screening with a subtraction method, we isolated mAbs recognizing vascular development-specific cell wall components without prior antigen identification. One of the isolated mAbs, designated CN 8, recognized a cell wall component contained in the hemicellulosic fraction. Immunohistochemical analyses showed that the CN 8 epitope was localized to the cell wall of immature tracheary elements and xylem parenchyma cells. In immature tracheary elements, the CN 8 epitope had a polarized localization pattern regardless of whether the cells are formed as parts of vessels in situ or as single tracheary elements in vitro, suggesting that cell polarity autonomously formed on the cell wall may function in tracheary element differentiation.

The alternative binding site for protein A in the Fab fragment of immunoglobulins

Twenty-six new human or murine monoclonal immunoglobulins (IgM, IgA, murine IgG1 or human IgG3) with a known V-region sequence were tested for alternative (non-Fc) binding to Staphylococcal protein A. Seven of them did not bind at all. Four immunoglobulins (all mouse IgG1) were bound but easily eluted (at pH 6). They were probably bound via the Fc part. All eleven were classified as negative for alternative binding. Fifteen immunoglobulins were found to bind more firmly; they came off the protein A column at pH 4-3 (alternative binders). Amino acid sequences of immunoglobulins that have been typed in the present work or earlier (25 binders and 26 non-binders) were compared. The light chain, the C region of the heavy chain and the D and JH segments look irrelevant for alternative binding. The N-terminal portion (amino acids 1-94) of the H chain probably forms the ligand of protein A. A peptide making the ligand cannot be reliably localized within this stretch but binder proteins had a high homology in residues 6-29. All mouse immunoglobulins expressing VH genes of families J606 or S107 were alternative binders; those expressing other families were non-binders.

Cloning and sequence analysis of two isotypic IgM heavy chain genes from Atlantic salmon, Salmo salar L

A leukocyte cDNA library from Atlantic salmon, based on oligo-dT priming, was constructed in lambda-gt10. Immunoglobulin heavy chain (IgH) cDNA were isolated from the library using a specific probe generated by polymerase chain reaction (PCR) between two conserved areas within the variable region (second and fourth frame region). Two cDNA clones encoding the entire constant region of membrane-bound IgH, and one cDNA encoding the entire constant region of secretory IgH were sequenced, revealing messages from two isotypic IgM genes. Both genes were shown to be present in haploid embryos and have been isolated from a genomic library, the exons and deduced amino acid sequences of which are presented here (salmon CHA and CHB). The splicing of transcripts encoding the membrane-bound IgH excises the whole fourth exon as in other teleosts. The nucleotide and amino acid identity between salmon CHA and CHB are 98.2%, and 96.2%, respectively. Two subfractions of IgM from Atlantic salmon separated by ion chromatography can be explained by a net exchange of basic residues in salmon CHB compared to CHA. The finding of two closely related salmon CH genes is in accordance with the quasi-tetraploid state of the Atlantic salmon genome.

Nucleotide sequence of the cDNAs encoding the variable region heavy and light chains of a myeloma protein specific for the terminal nonreducing end of alpha(1----6)dextran

The complete nucleotide sequences of the cDNAs encoding the heavy- and light-chain variable regions (VH and VL) of myeloma protein W3129, an anti-alpha(1----6)-dextran with a unique combining site, have been determined. The VH region is encoded by a germ-line gene highly homologous to VH441, which also appears to be used in some anti-galactans and anti-levans. W3129 VH uses a diversity region that is not found in any of the galactan- or levan-specific antibodies and whose germ-line counterpart is unknown. The W3129 light chain differs from complete light-chain sequences thus far reported but is identical in the first 23 amino acids with NZB IgA myeloma PC118.

The amino acid sequences of the myelin-associated glycoproteins: homology to the immunoglobulin gene superfamily

The myelin associated glycoproteins (MAG) are integral plasma membrane proteins which are found in oligodendrocytes and Schwann cells and are believed to mediate the axonal-glial interactions of myelination. In this paper we demonstrate the existence in central nervous system myelin of two MAG polypeptides with Mrs of 67,000 and 72,000 that we have designated small MAG (S-MAG) and large MAG (L-MAG), respectively. The complete amino acid sequence of L-MAG and a partial amino acid sequence of S-MAG have been deduced from the nucleotide sequences of corresponding cDNA clones isolated from a lambda gt11 rat brain expression library. Based on their amino acid sequences, we predict that both proteins have an identical membrane spanning segment and a large extracellular domain. The putative extracellular region contains an Arg-Gly-Asp sequence that may be involved in the interaction of these proteins with the axon. The extracellular portion of L-MAG also contains five segments of internal homology that resemble immunoglobulin domains, and are strikingly homologous to similar domains of the neural cell adhesion molecule and other members of the immunoglobulin gene superfamily. In addition, the two MAG proteins differ in the extent of their cytoplasmically disposed segments and appear to be the products of alternatively spliced mRNAs. Of considerable interest is the finding that the cytoplasmic domain of L-MAG, but not of S-MAG, contains an amino acid sequence that resembles the autophosphorylation site of the epidermal growth factor receptor.

The galactan-binding immunoglobulin Fab J539: an X-ray diffraction study at 2.6-A resolution

The crystal structure of the Fab of the galactan-binding immunoglobulin J539 (a mouse IgA,kappa) has been determined at a resolution of approximately 2.6 A by X-ray diffraction. The starting model was that obtained from the real space search described previously (Navia, M.A., Segal, D.M., Padlan, E.A., Davies, D.R., Rao, D.N., Rudikoff, S. and Potter, M. "Crystal structure of galactan-binding mouse immunoglobulin J539 Fab at 4.5 A resolution." Proc. Nat. Acad. Sci. USA, 76:4071-4074, 1979). This Fab structure has now been refined by restrained least-squares procedures to an R-value of 19% for the 11,690 unique reflections between 8.0 A and 2.6 A. The rms deviation from ideal bond lengths is 0.025 A. The overall structure differs from McPC603 Fab, another mouse IgA,kappa antibody, in that the elbow bend, relating the variable and constant parts of the molecule, is 145 degrees vs. 133 degrees for McPC603. The region of the molecule expected to be the antigen binding site contains a large cavity with two clefts leading away from it. This has been fitted with a model of an oligo-galactan.

Inter- and intraclonal diversity in the antibody response to influenza hemagglutinin

This study focuses on 10 BALB/c anti-influenza virus (A/PR/8/34) hemagglutinin antibodies that have light chains encoded by the same variable region kappa chain (V kappa) gene, V kappa 21C. A comparison of antibodies from lymphocytes of independent origin reveals the contribution of germline diversity (combinatorial joining and association) to this response. Although combinatorial joining and association contribute to sequence diversity, they appear to have little effect on the fine specificity of these antibodies. Somatic mutation, in addition to contributing to the sequence diversity of these antibodies, creates differences in their fine specificity. The extent of mutation and its effect on fine specificity can be seen by comparing antibodies of lymphocytes from the same clone. These intraclonal comparisons also indicate that somatic mutation is an ongoing process occurring at a high rate (estimated to be at least 10(-3) mutations per base pair per division) in the expressed V region heavy chain (VH) and V kappa genes. Furthermore, both the nature and distribution of these mutations suggest that amino acid replacement mutations in the light but not the heavy chain are selected for by 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.

Evidence for gene conversion among immunoglobulin heavy chain variable region genes

We have previously reported that the VH region amino acid sequence of a phosphocholine (PC)-binding hybridoma antibody of CBA/J origin, HP101 6G6 (6G6), differs extensively from the VH regions of other PC-binding antibodies. The sequence of 6G6 VH appears to be derived from a gene homologous to the BALB/c V11 gene, a member of the PC VH (T15 VH) gene family not normally used to encode PC-binding antibodies. The 6G6 VH sequence differs from the translated sequence of V11 by six amino acids, four of which occur at the same position in other members of this gene family. This coincidence led to the proposal that the 6G6 VH gene was derived by gene conversion involving three genes of the PC VH gene family. We report here the nucleic acid sequence of the rearranged VH gene of hybridoma 6G6. This sequence supports our previous suggestion of gene conversion by confirming those differences, relative to the BALB/c V11 gene sequence, that are encoded by other members of this gene family, and extends this correlation to include three silent base pair substitutions as well. In addition, 5' noncoding region sequence and Southern blot analysis using probes derived from the coding and 5' noncoding regions confirm that the 6G6 VH gene is likely to be derived from the V11 homologue in CBA/J mice, and suggest that all three genes believed to be involved in the generation of the 6G6 VH gene are present in the CBA/J genome, a prerequisite for their involvement in gene conversion.

Antigen binding to lymphoid cells from unimmunized mice. VII. Restriction of antigen-binding capacity by maturing B lymphocytes

Neonatal spleen populations have been studied for antigen-binding capacity in an attempt to determine if the frequency of double antigen-binding cells changes as the population matures. Just after birth, the frequencies of total ABC, double ABC and Ig-bearing cells were similar to the frequencies seen in the adult bone marrow. During the first week after birth, the proportion of total ABC and Ig-bearing cells rose sharply so that by 8 days after birth, these cells were about half of adult levels. The proportion of total double ABC, after a brief rise at day 1, remained constant throughout the test period. Thus, the proportion of total ABC which are doubles gradually decreases with age. Sedimentation velocity studies indicate that double ABC's tend to co-sediment with cells which require a period of maturation before they can respond to a thymus-independent antigen in irradiated hosts. Single ABC, on the other hand, tend to co-sediment with cells which are immediately responsive to antigen, or require a shorter maturational period before they become responsive to antigen. All of these data, taken together with our other work, suggest the possibility that multiple ABC are clonally-derived lymphocyte populations which become more restricted in their antigen-binding capacity as they mature.

Characterization of idiotypes on antibodies to galactan

The correlation between the primary structure and the expression of idiotypy in the anti-galactan antibody system is extremely precise. Amino-acid residues, which are implicated in the expression of recurrent or private idiotopes, are localized in the CDR3 region of all hybridomas and of at least 2 out of 4 myeloma proteins. A single substitution in this region may, in some cases, suffice to abolish idiotope expression.

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 of the Fv region of a human monoclonal IgM (protein WEA) with antibody activity against 3,4-pyruvylated galactose in Klebsiella polysaccharides K30 and K33

We have determined the amino acid sequence of the Fv [variable heavy (VH) and variable light (VL)] region of a human monoclonal IgM-kappa with antibody activity against 3,4-pyruvylated galactose, isolated from the plasma of patient WEA with Waldenström macroglobulinemia. The VH region has 114 residues, belongs to subgroup III, and has a very short third complementarity-determining region (CDR3), probably due to a small D segment/or an unusual D-J rearrangement (D, diversity; J, joining). The VL region has 108 residues and belongs to subgroup V kappa I. Compared to other members of the human VHIII and V kappa I families, WEA Fv does not appear to have significant differences within the framework residues but has unique CDRs that might be responsible for the particular antibody activity. Another IgM-kappa (GAL), which has an as-yet-undetermined antibody activity, shares a striking homology in V kappa with WEA, including an identical CDR1.

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.

Molecular cloning and nucleotide sequencing of human immunoglobulin epsilon chain cDNA

DNA complementary to mRNA of human immunoglobulin E heavy chain (epsilon chain) isolated and purified from U266 cells has been synthesized and inserted into the PstI site of pBR322 by G-C tailing. This recombinant plasmid was used to transform E. coli chi 1776 to screen 1445 tetracycline resistant colonies. Nine clones (pGETI - 9) containing cDNA coding for the human epsilon chain were recognized by colony hybridization and Southern blotting analysis with a nick-translated human IgE genome fragment. The nucleotide sequence of the longest cDNA contained in pGET2 was determined. The results indicate that the sequence of 1657 nucleotides codes for 494 amino acids covering a part of the variable region and all of the constant region of the human epsilon chain. Most of the amino acid sequence deduced from the nucleotide sequence is in substantial agreement with that reported. Furthermore a termination codon after the -COOH terminal amino acid marks the beginning of a 3' untranslated region of 125 nucleotides with a poly A tail. Taking this into account, the structure of the human epsilon chain mRNA, except a part of the 5' end, is conserved fairly well in the cDNA insert in pGET2.

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.

Polymorphism in immunoglobulin heavy chains suggesting gene conversion

Complete heavy (H) chain variable region (V region; amino acids 1-118) sequences have been determined for three phosphocholine (PCho)-binding monoclonal antibodies of CBA mouse strain origin. Two of these were found to differ from the sequence of the BALB/c T15 germline VH segment (segment of the V region that includes amino acids 1-95) at four positions but were identical to the allelic form of T15 (C3) found in C57BL. The third VH segment, HP101.6G6 (6G6), was clearly the product of a second, related VH gene, probably the allele of the BALB/c V11 gene, a second member of the P-Cho VH gene family. Thus, more than one VH gene is capable of encoding heavy chains of PCho-binding antibodies. The 6G6 VH segment differs from VII at seven positions; four of these distinguishing amino acids are encoded in other membranes of the PCho VH gene family. We postulate that the origin of the 6G6 VH sequence can most easily be explained by a process of gene conversion occurring between the least three members of the PCho VH family.

A monoclonal antibody that defines an idiotope with two subsites in galactan-binding myeloma proteins

An IgG1 monoclonal antibody HyX24-14 was derived from A/J mice that were immunized with the IgA XRPC24 (X24) galactan binding myeloma protein (GalBMP) of BALB/c origin by the Kohler-Milstein hybridoma technology. HyX24-14 specifically binds some but all GalBMP. Different patterns of binding using a panel of nine Gal BMP were found, depending upon the concentration of antibody and the antigenic target. From molecular models and amino acid sequence data, ti was proposed that the idiotope defined by HyX24-14 had two subsites, each of which appeared to be able to bind independently to the antibody.

Amino acid sequence of the variable regions of heavy chains from two idiotypically cross-reactive human IgM anti-gamma-globulins of the Wa group

The amino acid sequences of the variable regions of the heavy chains derived from two idiotypically related human monoclonal rheumatoid factors are reported. The sequences were obtained through automated Edman degradations of the intact, pyroglutamate aminopeptidase cleaved heavy chains and peptides produced from digestion of the pentameric IgM with CNBr. The peptides generated from the CNBr reaction were further digested by trypsin and the Staphylococcus aureus V8 protease. Comparisons of these sequences and those of the light chains from these molecules [Andrews, D. W., & Capra, J. D. (1981) Biochemistry (preceding paper in this issue)] suggest that the idiotypic determinant(s) in this system may reside in the framework portions of these molecules or in their J segments.

Restricted reassociation of heavy and light chains from hapten-specific monoclonal antibodies

Six murine monoclonal antifluorescyl antibody clones encompassing a defined range of affinities and containing kappa light chains with IgG1 or IgG2 heavy chains were examined. As the fluorescence of the ligand is quenched greater than 90% when fluorescein is bound by antifluorescyl antibodies, fluorescence quenching was assayed to monitor polypeptide reconstitution and active site formation on mixing of resolved heavy (H) and light (L) chains. Of 36 possible experimental combinations of H- and L-chain reaction mixtures, only homologous H and L chains (derived from the same parental immunoglobulin molecule) bound fluorescein. Results from fluorescence polarization studies, conducted independently of fluorescence quenching, confirmed the findings. Competitive inhibition and molecular sieve experiments showed that, despite preferential association of homologous H and L chains, several heterologous H and L chains associated to form intact 7S molecules, although no active site was constituted. Thus, polypeptide recombination and formation of functional antigen binding sites are two processes that immunocytes must regulate during cell differentiation and generation of diversity. A mechanism and underlying the observed preferential reassociation of specific H and L chains and a means of generating affinity maturation, as exhibited by the antifluorescein system, is proposed.

Mouse heavy chain variable regions: nucleotide sequence of a germ-line VH gene segment

We have constructed a library of Balb/c mouse embryo DNA in the vector Charon 4A. The library was searched for sequences homologous to the VH region of a cloned cDNA of the UPC10 heavy chain mRNA. In this paper, we describe the structure and the partial nucleotide sequence of one of such clones (VH441). The nucleotide sequence of this germ-line gene indicates that it encodes amino-acids 1-98 of the X44 and J601 galactan-binding VH regions, but that it differs from the UPC10 VH segment by four single base changes. The VH gene appears to contain a 101 bases long intervening sequence within a precursor sequence identical to the precursor sequence of UPC10. The 3' non coding sequence of the V gene contains the two conserved sequences found in embryonic V DNA segments, CACAGTG and ACATGAACC, separated by 23 nucleotides and a sequence CACTGTG separated by 33 nucleotides from the first heptamer.

Lack of heterogeneity in antihapten antibodies of a phylogenetically primitive shark

Individual mammals have the capacity to express at least one million distinct antigen binding specificities, implying a high degree of structural heterogeneity in the variable heavy and light chain (VH and VL) portions of the antibody molecules. Studies of higher vertebrate species suggest that this heterogeneity is created both through a sizeable repertoire of germ-line VH and VL genes and through random rearrangements of V and joining genes. Additional somatic mechanisms probably also contribute to the ultimate heterogeneity; one-third of murine plasmacytomas producing lambda 1 immunoglobulin carry a somatically mutated Ig1-V gene. The relative contributions of these various mechanisms to the overall imunoglobulin variability are difficult to evaluate. The production of different antibodies to a defined determinant in different individuals of an inbred mouse strain [for example, (3-iodo-4-hydroxy-5-nitrophenyl) acetyl (NIP) in CBA mice] suggests the involvement of somatic mutations or rearrangement but does not rule out the possibility that each individual CBA mouse expresses only a small random fraction from a large germ-line repertoire of V genes determining different anti-NIP binding sites. The opposite finding, that different individuals produce nearly identical antibodies to a defined determinant, would suggest the presence and expression of a limited number of germ-line genes without somatic alterations. Data presented here suggest that primitive sharks (Heterodontus fransisci) produce such antibodies to the hapten furyloxazolone.

Antibody diversity in amphibians: evidence for the inheritance of idiotypic specificities in isogenic Xenopus

Two families of isogenic Xenopus and the progeny from one individual of each family were immunized with dinitrophenylated keyhole limpet hemocyanin. Antisera were raised in mice and in guinea pigs against purified antibodies from one individual of the first generation of each family. These were rendered anti-idiotypic by absorption with immunoglobulins of unimmunized isogenic frogs. In the first generation, antibodies from individuals of each family exhibited a high degree of idiotypic cross-reactivity. Antibodies from individuals of the second generation displayed idiotypic cross-reactivity, but to a lesser extent. Some idiotypic cross-reactivity was seen between members of one family with members of the other family: no sharing of idiotypic specificity was detected among anti-DNP antibodies isolated from individual outbred frogs. Isoelectric focusing (IEF) patterns of the anti-DNP antisera showed a high degree of restriction and overlap within members of each family and across two generations. Furthermore, the N-terminal sequence of the L chains from X. laevis anti-DNP antibodies was unique, and there was a low degree of structural heterogeneity in the H chain N-terminal region. A correlation between the IEF banding pattern and idiotypic reactivity was apparent. The data suggest the inheritance of variable region genes through two generations of isogenic Xenopus.

J genes for heavy chain immunoglobulins of mouse

A 15,8-kilobase pair fragment of BALB/c mouse liver DNA, cloned in the Charon 4A lambda phage vector system, was shown to contain the mu heavy chain constant region (CHmu) gene for the mouse immunoglobulin M. In addition, this fragment of DNA contains at least two J genes, used to code for the carboxyl terminal portion of heavy chain variable regions. These genes are located in genomic DNA about eight kilobase pairs to the 5' side of the CHmu gene. The complete nucleotide sequence of a 1120-base pair stretch of DNA that includes the two J genes has been determined.

Two types of somatic recombination are necessary for the generation of complete immunoglobulin heavy-chain genes

At least two types of somatic recombination are necessary for the generation of a complete immunoglobulin gamma 2b gene from germ-line DNA sequences. The first type of recombination consists of the assembly of three separate DNA segments, each encoding a different part of the variable region. The second type of recombination replaces the exons coding for the constant region of the mu chain with those coding for the same region of the gamma 2b chain. The DNA sequencing studies suggest that the two types of recombination operate by different mechanisms.

J segment in human delta chains

We report the complete sequence of a cyanogen bromide fragment of a human delta chain (ErI). Its interest lies in the fact that it contains the peptide joining the V delta to the C delta 1 region. The presented sequence is compared with the homologous region of other human heavy chain classes and subclasses. The possibility that human delta chains and other human heavy chains have in their chromosomal DNA a short J sequence, is discussed.

kappa Chain joining segments and structural diversity of antibody combining sites

Immunoglobulin kappa light chains are coded for by at least three distinct gene segments designated variable, joining, and constant. The joining gene codes for the 13 amino acid segment linking the variable and constant regions. This peptide includes the last amino acid (96) in the third complementarity-determining region and thus could introduce structural diversity. We have determined the light chain variable region sequences from three myeloma proteins with beta(1,6)galactan-binding specificity, bringing to six the number of light chains sequenced from proteins demonstrating this specificity. Five of these have isoleucine at position 96 and the sixth tryptophan. This substitution appears to be accommodated with no significant change in association constant for a beta(1,6)galactan hapten. Additionally, as many as nine substitutions are found in both light and heavy chain complementarity-determining regions between members of this group although only minimal variations in hapten binding affinity are observed. The isoleucine found at position 96 in five of the kappa chains could not be coded for by any of the joining gene nucleotide sequences previously observed and would require a novel nucleotide sequence at the recombination site between variable and joining genes to produce the observed protein structure. Alternatively, there may exist joining gene segments not yet detected.

Amino acid sequence of the variable region of a human mu chain: location of a possible JH segment

The complete amino acid sequence of th variable (V) region of the mu heavy chain of a human IgM immunoglobulin (Cam) has been determined. The strategy for sequence determination involved sequenator analysis of the CNBr cleavage products of the succinylated carboxymethylated Fab mu fragment, and of tryptic peptides of the CNBr polypeptides and thermolytic subpeptides. The variable region of this heavy chain (VH) belongs to the VHIII subgroup; it has greater than 70% homology with other VHIII sequences and contains the VHIII marker peptide, Phe-Thr-Ile-Ser-Arg (residues 67-71). As more sequences have been published, the number of subgroup-specific residues has diminished to the point that no position is absolutely subgroup specific. An analysis of the available human VH sequences in the V/C switch region showed the likelihood of a human JH segment (residues 101-113) analogous to the J segments in mouse light chains. The JH region is highly conserved, has striking homology to proposed mouse JH regions, and has significant homology to known mouse J lambda and J kappa segments.

Isolation of variants of mouse myeloma X63 that express changed immunoglobulin class

We have used fluorescence-activated cell sorting with class-specific antisera to isolate spontaneous variants in the expression of immunoglobulin heavy chain class from the mouse myeloma cell line X63 (IgGI, kappa). In the wild-type cell population, only one type of variants was found, namely, cells expressing IgG2b. From an IgG2b variant clone we isolated secondary variants that had either reverted to IgGI expression or expressed IgG2a or IgG2a and IgG2b concomitantly. The variant heavy chains are of normal size. The variant immunoglobulins were characterized serologically, and all of them still expressed the wild-type idiotype. Wild-type and variant cell populations were screened for heavy chain class-switch variants by fluorescence microscopy. A variety of switch variants was found in addition to the ones isolated by cell sorting, and a clear pattern of class switching (gamma 1 leads to gamma 2b leads to gamma 2a leads to alpha) with frequent reversion emerges from this analysis. Cells expressing new heavy chain classes occurred at frequencies of about 10(-7)-10(-6)/cell per generation, whereas revertants were as frequent as 10(-6)-10(-5)/cell per generation.

Contribution of immunoglobulin heavy-chain variable-region genes to antibody diversity

A mouse cloned cDNA probe containing a variable (V) region belonging to the VHIII subgroup has been used in filter hybridisations to estimate the number of heavy-chain V-genes in this subgroup of mouse and human DNA. There seem to be about 10 and 20 VH-genes hybridising to this probe in mouse and human DNA, respectively. Studies of cross-hybridisation of the related VK-genes from MOPC21 and MPC11 myelomas indicate that the experiments detect all members of the VHIII subgroup.

Self-association of human immunoglobulin kappa I light chains: role of the third hypervariable region

Gel electrophoresis and molecular sieve chromatography were used to compare 17 different human kappa I type Bence Jones proteins including 5 for which the amino acid sequence is known. Although electrophoresis in the presence of NaDodSO4 showed uniformity of covalent dimer and monomer molecular weights, Sephadex chromatography under nondissociating conditions showed that monomers eluted with different apparent molecular weights. These differences were attributed to heterogeneity in light chain self-association; dimerization constants of the 17 proteins, calculated from a computer simulation of their behavior upon gel filtration, ranged from less than 10(3) to greater than 10(6) M-1. The variable region, more specifically the third hypervariable region, appears to be responsible for the variation in the dimerization constant. Association properties of light chains of known sequence suggest that the presence of an aromatic or hydrophobic residue at position 96 enhances dimer formation whereas a charged residue at that position results in light chains remaining stable monomers. The location of hypervariable residue 96 within the amino-terminal portion of the joining segment of the variable region suggests that the joining region may account for the variability of self-association of light chains and, moreover, that it has a function in determining the selective association of immunoglobulin polypeptide chains.

Rearrangement of immunoglobulin gamma 1-chain gene and mechanism for heavy-chain class switch

Cloning and nucleotide sequence determination suggest that the rearranged gamma 1-chain gene in a gamma 1-chain-producing myeloma a-pears to be formed by the recombination between the 5' flanking regions of the gamma 1- and mu-chain genes of undifferentiated cells. The recombination site is distinct from the putative J region and is a novel region that we call the S region. We have extended our previous model that explains the heavy-chain class switching by two or more successive recombination events.

The role of gene deletion in the immunoglobulin heavy chain switch

We have examined the arrangement of the genes for the mouse heavy chain subclasses gamma 2b, gamma 2a and gamma 1 by the Southern hybridisation procedure. Evidence has been found for rearrangement involving the gamma 2b and gamma 2a CH genes in the DNA of cells making IgG2b and IgG2a respectively. The DNA of an IgG2b-secreting line lacks detectable C gamma 1 gene, whilst the DNA of an IgG2a-secreting line lacks detectable C gamma 1 and C gamma 2b genes. The DNA of a cell line secreting IgA lacks detectable C gamma genes. These observations implicate deletion in the mechanism of the H-chain switch and allow a preliminary ordering of some of the CH genes in the mouse genome.

Amino acid sequence of homogeneous antibodies to dextran and DNA rearrangements in heavy chain V-region gene segments

The complete variable region sequences from ten antibodies and two myeloma proteins binding alpha-1,3 dextran have been determined. The diversity patterns of these homogeneous antibody molecules suggest that the variable regions of heavy chains are encoded by separate variable (V) and joining (J) gene segments. The most striking feature of these data is the extensive sequence variability of a region that we denote the D (diversity) segment which is located at the junction between the V and J segments in the centre of the third hypervariable region. The D segment diversity may arise from a novel somatic mutational mechanism or may be encoded by multiple D gene segments. For the first time, the amino acid sequence correlates of several V region idiotypes are determined.

Intervening sequences divide the gene for the constant region of mouse immunoglobulin mu chains into segments, each encoding a domain

To elucidate the structure of the gene for the constant region of immunoglobulin mu chains, we have cloned a 9.9-kilobase-pair fragment of mouse DNA bearing a gene for the constant region of the mu chain (C mu gene) from an IgM-secreting mouse plasmacytoma. The sequence around this gene has apparently undergone somatic rearrangement; the gene occurs in an EcoRI restriction endonuclease fragment of a different size from that in embryo or liver DNA and no C mu-bearing fragment of embryo size remains in the plasmacytoma. The cloned sequence lacks a variable region gene; hence, if this C mu gene is active, its position within the clone indicates that the gene for the variable region of a heavy chain (VH gene) must be more than 3.7 kilobase pairs away. The C mu gene is divided by three intervening sequences into four coding segments, each of which encodes one of the domains (homology units) of the polypeptide. The nucleotide sequence coding for amino acids near the V-C junction is not present within the C mu clone or clones bearing homologous embryonic VH genes. This suggests that an immunoglobulin heavy chain, in common with light chains, is encoded not only by a V and C gene, but also by an independent joining region (JH) gene.

Some sequence similarities among cloned mouse DNA segments that code for lambda and kappa light chains of immunoglobulins

A comparison between the cloned mouse DNA segments that were found to code for the lambda and kappa light chains of immunoglobulins established that there were seven short nucleotide sequences, two of which matched 6 out of 7, two 7 out of 8, two 8 out of 9, and one 9 out of 10 bases; these sequences were located either at homologous amino acid positions or at positions displaced by four amino acids or less. They all occurred in the framework regions (FRs), five next to the complementarity-determining regions (CDRs). Three of these were unique and did not occur elsewhere in the immunoglobulin nucleotides sequenced thus far or in DNA's of phage phi X174, phage G4, or simian virus 40. Five could serve as sites of joining by recombination or insertion of CDR to FR segments, and the invariant tryptophan that is the first residue of the second FR might serve as a sixth. These sites are consistent with the mini-gene or insertional hypotheses for the generation of antibody diversity but could also serve as points of recognition for a mutator enzyme or could serve to limit somatic mutation to the CDRs.

Sequences of five potential recombination sites encoded close to an immunoglobulin kappa constant region gene

Immunoglobulin kappa chain gene formation involves site-specific somatic recombination between one of several hundred germ-line variable region genes and a joining site (or "J segment") encoded close to the constant region gene. We have cloned and determined the nucleotide sequence of major portions of the recombination region of the mouse kappa gene and discovered a series of five such J segments spread out along a segment of DNA 2.4 kilobases from the kappa constant region gene. These J segments encode the 13 COOH-terminal amino acids of the variable region, probably including amino acids involved in the antigen combining site and in heavy/light chain contacts. The J segments also display striking sequence homology to one another in both their coding and immediately flanking sequences. Major elements of a short palindrome--CAC(TA)GTG--are preserved adjacent to the recombination sites of both variable and J region genes and constitute inverted repeats at both ends of the sequences to be joined. These palindromes can be written as a hypothetical stem structure that draws variable and J regions together, providing a possible molecular basis for the DNA joining event. Four of the J segments that we have discovered encode amino acid sequences already found in myeloma proteins. By altering the frame of recombination, we can account for additional light chain amino acid sequences, suggesting that the V/J joining event might generate antibody diversity somatically both by using different combinations of variable and J region genes and by using alternative joining frames.