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

Characteristics of immunoglobulin gene usage of the xenoantibody binding to gal-alpha(1,3)gal target antigens in the gal knockout mouse

BACKGROUND

Natural antibodies that react with galactose-alpha(1,3)galactose [galalpha(1,3)gal] carbohydrate epitopes exist in humans and Old World primates because of the inactivation of the alpha1,3-galactosyltransferase (alpha1,3GT) gene in these species and the subsequent production of antibodies to environmental microbes that express the galalpha(1,3)gal antigen. The Gal knockout (Gal o/o) mouse, produced by homologous disruption of the alpha1,3GT gene, spontaneously makes anti-galalpha(1,3)gal antibodies and can be used to study the genetic control of humoral immune responses to this carbohydrate epitope.

METHODS

Six hybridomas that produce monoclonal antibodies (mAbs) to galalpha(1,3)gal were generated in Gal o/o mice. The mAbs were tested to characterize the binding activity with flow cytometry using pig aortic endothelial cells and ELISA with galalpha(1,3)gal carbohydrates. The VH and VK genes of these hybridomas were cloned, sequenced, and analyzed.

RESULTS

The mAbs showed distinct patterns of antibody binding to galalpha(1,3)gal antigens. The VH genes that encode the mAb binding activity were restricted to a small number of genes expressed in their germline configuration. Four of six clones used closely related progeny of the same VH germline gene (VH441). Comparison of the mouse gene VH441 to the human gene IGHV3-11, a gene that encodes antibody activity to galalpha(1,3)gal in humans, demonstrates that these two genes share a nonrandom distribution of amino acids used at canonical binding sites within the variable regions (complimentary determining regions 1 and 2) of their immunoglobulin VH genes.

CONCLUSIONS

These results demonstrate the similarity of the Gal o/o mice and humans in their immune response to galalpha(1,3)gal epitopes. Gal o/o mouse can serve as a useful model for examining the genetic control of antibody/antigen interactions associated with the humoral response to pig xenografts in humans.

Murine immune response to Neisseria meningitidis group C capsular polysaccharide: analysis of monoclonal antibodies generated in response to a thymus-independent antigen and a thymus-dependent toxoid conjugate vaccine

Antibody (Ab) responses to polysaccharides (PSs) such as Neisseria meningitidis group C PS (MCPS) are characterized as being thymus independent (TI) and are restricted with regard to clonotype and isotype expression. PS conjugated to proteins, e.g., MCPS coupled to tetanus toxoid (MCPS-TT), elicits a thymus-dependent (TD) response. In order to understand the influence of the form of a vaccine (TI versus TD) on the Ab repertoire, we generated monoclonal antibody (MAb) panels from mice immunized and boosted with MCPS or MCPS-TT in different ways. The panels of MAbs were examined for isotype, fine specificity, affinity, and V(H) gene family usage. The use of MCPS-TT resulted in a shift in the isotype from immunoglobulin M (IgM) and IgG3 elicited in response to the MCPS to primarily IgG1. This isotype shift was accompanied by a change in the fine specificity of the response to the conjugate compared to that of PS. New fine specificities and increased affinity were observed in response to the TD antigen (Ag). Dot blot and Northern analyses of MCPS MAbs revealed that V(H) gene family usage is dominated by V(H)J558, used by 23 of 39 MAbs. V(H)3609 was seen in three MAbs of restricted fine specificity. V(H)Q52, V(H)7183, and V(H)VGAM3-8 were seen in more than one MAb across these panels, while V(H)10 and V(H)X24 were detected only once in response to the TI-2 Ag. All MAbs in the panels utilized kappa light chains, and all functional J(kappa) genes were expressed.

Structure-function studies of an anti-asialo GM1 antibody obtained from a phage display library

Although gangliosides elicit human autoantibodies, they are extremely weak immunogens in mice. We obtained a monoclonal antibody Fab fragment (clone 10) that is specific for asialo GM1 (GA1), from a phage display library. The Vkappa domain of clone 10 could be replaced by two different Vkappa domains without changing the specificity of the antibody. Mutagenesis of the third hypervariable regions of the heavy and light chains of clone 10 yielded three mutants that exhibited a 3 to 4 times increase in avidity for GA1. A molecular model of clone 10 indicated that the putative antigen-binding site contained a shallow surface pocket. These data illustrate the use of recombinant DNA techniques to obtain anti-ganglioside antibodies, and to explore the molecular basis of their antigen-binding activity.

Natural polyreactive immunoglobulin A antibodies produced in mouse Peyer's patches

To understand the biological function of natural immunoglobulin A (IgA) antibodies in Peyer's patches (PP), we generated IgA monoclonal antibody (mAb) clones from the PP of normal, unimmunized, specific pathogen-free BALB/c mice and examined their reactivities by enzyme-linked immunosorbent assay (ELISA). Many of these antibodies reacted with more than one antigen examined, suggesting that they were polyreactive Abs. Two mAbs agglutinated several different strains of commensal bacteria isolated from mice. To examine the genetic features of these polyreactive mAbs, the VH genes of seven different IgA mAbs were sequenced. The VH genes from the VGAM, J558 and 7183 families were compared with sequence from the mAbs with distinct VDJ rearrangements. One of the mAbs that agglutinated bacteria was encoded by a germline VH gene, but the VH region of the other polyreactive mAbs contained between seven and 11 mutated sites. No indication of antigenic selection was observed in the pattern of these mutated sites. Our results show that polyreactive IgA Abs are present in PP as a part of the normal B-cell repertoire. These polyreactive Abs may establish a natural immune homeostasis, and function as a polyreactive sensor to detect pathogenic invasion and to control immune response in the gut.

Conservation of sequence in recombination signal sequence spacers

The variable domains of immunoglobulins and T cell receptors are assembled through the somatic, site specific recombination of multiple germline segments (V, D, and J segments) or V(D)J rearrangement. The recombination signal sequence (RSS) is necessary and sufficient for cell type specific targeting of the V(D)J rearrangement machinery to these germline segments. Previously, the RSS has been described as possessing both a conserved heptamer and a conserved nonamer motif. The heptamer and nonamer motifs are separated by a 'spacer' that was not thought to possess significant sequence conservation, however the length of the spacer could be either 12 +/- 1 bp or 23 +/- 1 bp long. In this report we have assembled and analyzed an extensive data base of published RSS. We have derived, through extensive consensus comparison, a more detailed description of the RSS than has previously been reported. Our analysis indicates that RSS spacers possess significant conservation of sequence, and that the conserved sequence in 12 bp spacers is similar to the conserved sequence in the first half of 23 bp spacers.

Restricted VH gene usage by murine hybridomas directed against the human N, but not M, blood group antigen

The M and N human blood group antigens are complex glycopeptide determinants at the amino terminus of the red blood cell membrane glycoprotein, glycophorin A. The heavy and light chain variable region cDNA sequences were determined for seven murine monoclonal antibodies recognizing glycophorin A. Three of the antibodies were anti-M and four were anti-N. Each of the anti-M antibodies was composed of VH and VL regions derived from distinct germline gene families (VH1 (J558), VH4 (X24), VH5 (7183), VK5, VK8, and VK19). In contrast, all four anti-N heavy chains were composed of VH regions derived from the VH2 (Q52) germline gene family and all used the same J4 gene segment. In addition, two of the anti-N light chains were composed of VK regions from the VK8 germline gene family and used the J1 gene segment. Since each anti-N hybridoma was derived from different mice immunized by different protocols, these results suggest that the murine immune response to the N, but not the M, human blood group antigen is restricted.

Germline-encoded IgG antibodies bind mouse cartilage in vivo: epitope- and idiotype-specific binding and inhibition

Autoantibodies specific for type-II collagen (CII) occur in mice and rats with collagen-induced arthritis (CIA). The binding in vitro and in vivo of mouse monoclonal antibodies (MoAbs) specific for separate epitopes in CII have been investigated. Two-day-old mice were injected intraperitoneally (i.p.) with the anti-CII antibody CIID3 in both unlabelled and biotinylated form. It was found that antibodies binding to the same epitope in CII in vivo can inhibit others from binding in an epitope-specific fashion. The binding in vivo and in vitro of anti-CII antibodies could be inhibited also by an anti-idiotypic rat antiserum produced against the D3 antibody. The anti-idiotypic antiserum inhibited the binding of the antibody D3 and the idiotypically related antibody C2. The cDNA's of anti-CII antibodies D3, C2, and F4 were sequenced and found to contain germline encoded V-genes, apparently without somatic mutations. The variable heavy chain of D3 and C2 both expressed the same VH rearrangement, confirming that they share idiotypes. This report demonstrates that CII-specific germline-encoded IgG autoantibodies bind specifically to normal cartilage in vivo via their combining site.

Junctional diversification in the generation of the precursor of a discrete immune response

Phosphocholine (PC)-specific antibodies that arise in the mouse in response to Proteus morganii (PM) and use V1-DFL16.1-JH1 are characterized by a number of recurring mutations. Most striking is an invariant A for G substitution in codon 95 of VH which results in an asparagine instead of aspartate at that position. Because of the apparent importance of this substitution in an anti-PC(PM) response, we wanted to determine the molecular basis for this base change. A cDNA library derived from pre-immune splenic B cells was examined for the frequency of VDJ containing the A substitution at 95 and the presence of additional point mutations in these sequences. Six different cDNA were isolated which contained an A substitution at the VD junction (frequency 0.00009); a seventh positive cDNA could not be examined. The V segments of four of these cDNA matched known germline genes and were, therefore, unmutated. Two others closely matched V in families whose members have not all been characterized, hence, it is not known whether the mutations observed are somatic or germline in origin. Sequences of 35 cDNA clones, containing the same V segment but differing in D, J and junctional nucleotides, revealed no mutations. These results indicate that the A substitution generated at codon 95 is most likely a product of V-DJ joining.

A statistical examination of hypervariability in complementarity-determining regions of immunoglobulins

To determine the relative importance of gene conversion followed by natural selection and of natural selection for point mutation in generating variability in immunoglobulins, the numbers of synonymous and nonsynonymous substitutions in immunoglobulin sequences of various subgroups were estimated for complementarity-determining regions (CDRs) and for framework regions (FRs). Both the number of synonymous substitutions and the number of nonsynonymous substitutions in the CDR were found to exceed the corresponding numbers in the FR. Therefore, gene conversion is likely to be an important mechanism for providing variability in the CDR of immunoglobulins. The correlation coefficients between the number of synonymous substitutions and the number of nonsynonymous substitutions and between the substitution number in the CDR and that in the FR were found to be very low. Again, gene conversion is thought to be responsible for this finding.

Isolation and sequence of a cDNA coding for the immunoglobulin mu chain of the sheep

A sheep cDNA library was screened with a human C mu probe, and the complete nucleotide sequence of a 1923 nt cDNA was determined. It contains sequences corresponding to all the exons (VH, DH, JH, CH1, CH2, CH3 and CH4) characteristic of the immunoglobulin mu heavy chain regions. The deduced amino acid sequence shows a percentage of identical residues in the range 65-45% when compared with the mu chains of various species. The VH region of this clone is clearly related to a group of genes that includes mouse VH36-60 and VHQ52, human VH2, VH4 and VH6 gene families and Xenopus VHII gene families. The constant region shows an unusual repartition of cystein and proline residues at the beginning of the CH2 domain, that may result in a molecule with enhanced stability and reduced flexibility.

Binding studies on internal immunodeterminants: synthesis of beta-(1----6)-linked oligosaccharide methyl glycosides having one to four internal D-galactopyranosyl residues flanked by gentiobiose residues

The oligosaccharide glycosides beta-D-Glcp-(1----6)-beta-D-Glcp-(1----6)-[beta-D-Galp-(1----6)]n-beta-D - Glcp-(1----6)-beta-D-Glcp-1----OMe (n = 1-4) were prepared by a convergent block synthesis. Haloacetyl, tert-butyldiphenylsilyl, and dimethylthexylsilyl groups were used as temporary protective groups for the preparation of the intermediate glycosyl donors and acceptors. The deoxygenated trisaccharide glycosides beta-D-Glcp-(1----6)-beta-D-Galp-(1----6)-4-deoxy-beta-D-xylo-Hexp -1----OMe and beta-D-Glcp-(1----6)-4-deoxy-beta-D-xylo-Hexp-(1----6)-beta-D-Galp -1----OMe were also synthesized. The binding of each glycoside to the monoclonal antigalactan antibody IgA J539 was studied and the results support the previous finding that J539 can bind to internal antigenic epitopes. The data are consistent with the interpretation that subsite C of that antibody binds glucose with a Ka of approximately 6 (cf. 10.9 for galactose).

In vitro selection and affinity maturation of antibodies from a naive combinatorial immunoglobulin library

We have used a combinatorial immunoglobulin library approach to obtain monoclonal antibodies from nonimmune adult mice, thereby establishing the principles of (i) accessing naive combinatorial antibody libraries for predetermined specificities and (ii) increasing the affinity of the selected antibody binding sites by random mutagenesis. A combinatorial Fab library expressing immunoglobulin mu and kappa light-chain fragments on the surface of filamentous phage was prepared from bone marrow of nonimmunized, adult BALB/c mice with the multivalent display vector pComb8. Phage displaying low affinity Fabs (binding constants, 10(4)-10(5) M-1) binding to a progesterone-bovine serum albumin conjugate were isolated from the library. Random mutagenesis of the heavy- and light-chain variable regions expressed in the mono-valent phage display vector pComb3 was performed by error-prone PCR, and subsequently clones with improved affinity for the hapten conjugate were selected. We demonstrate that antibodies with desirable characteristics from a nonimmune source may be selected and affinity maturation may be achieved by using the twin vectors pComb8 and pComb3, thus opening the route to obtaining specific antibodies from a generic library and bypassing immunization.

Demonstration of a divergent transcript from the bidirectional heavy chain immunoglobulin promoter VH441 in B-cells

The mouse heavy chain immunoglobulin promoter VH441 can lead in vitro to bidirectional transcription, due to a symmetrical organization of immunoglobulin heavy chain promoters with two TATA-like sequences bracketing the upstream promoter element ATGCAAAT (the so called octamer). We demonstrate here that divergent transcription also occurs in vivo in mature B cells from a myeloma which expresses the VH441 gene and even from the spleen of BALB/c mice. The level of VH441 divergent transcript increases in the spleen of BALB/c mice after immunisation by beta-(1,6)-galactan, showing that it is expressed in B cells which actively transcribe the VH441 gene. The divergent transcript has been characterized: its major transcription start site was mapped within 33 base pairs from the divergent TATA-like region, it is unspliced and not polyadenylated. In the light of these results, the functions of the divergent transcript and the bidirectional promoter are discussed.

Blot-sequencing of antibodies: application to analysis of V gene usage among anti-steroid monoclonal antibodies

Automated gas-phase protein sequencing has been used to characterize variable regions of antibody heavy and light chains separated by SDS-polyacrylamide gel electrophoresis (PAGE) and electroblotted onto Immobilon polyvinylidene difluoride membranes ('blot-sequencing'). Starting from 100 micrograms of antibody, 20 or more residues of N-terminal VH and VL sequences can regularly be obtained, which is often sufficient to assign the V region to a known family or subgroup. We have applied the blot-sequencing method to analysis of VH and VL usage among a panel of monoclonal anti-steroid antibodies, namely anti-progesterone, anti-pregnanediol, anti-estrone and anti-testosterone. The results demonstrate restricted, repetitive usage of VL subgroups and VH families related to anti-steroid specificities. VL regions of the VK1 group were particularly associated with anti-progesterone, VK21 with anti-estrone, and VK8 and VK9 with anti-pregnanediol. VH regions of anti-progesterone antibodies were all derived from the VHVGAM3.8 family; anti-estrone and anti-pregnanediol antibodies were derived from the VH7183 and VH36-60 families. The latter two families appear to characterize antibodies raised against steroids conjugated to proteins via a sugar bridge. Differences in VH/VL combination were associated with diversity of antibody specificity. In order to extend the sequence data obtained by this technique and confirm family assignments, we have shown that internal V-region sequences can be obtained by limited chemical cleavage of whole antibody with cyanogen bromide, followed by separation of individual fragments by SDS-PAGE and blot-sequencing.

Significant conformational changes in an antigenic carbohydrate epitope upon binding to a monoclonal antibody

Transferred nuclear Overhauser enhancement spectroscopy (TRNOE) was used to observe changes in a ligand's conformation upon binding to its specific antibody. The ligands studied were methyl O-beta-D-galactopyranosyl(1----6)-4-deoxy-4-fluoro-beta-D-galactopyra nos ide (me4FGal2) and its selectively deuteriated analogue, methyl O-beta-D-galactopyranosyl(1----6)-4-deoxy-2-deuterio-4-fluoro-beta -D- galactopyranoside (me4F2dGal2). The monoclonal antibody was mouse IgA X24. The solution conformation of the free ligand me4F2dGal2 was inferred from measurements of vicinal 1H-1H coupling constants, long-range 1H-13C coupling constants, and NOE cross-peak intensities. For free ligand, both galactosyl residues adopt a regular chair conformation, but the NMR spectra are incompatible with a single unique conformation of the glycosidic linkage. Analysis of 1H-1H and 1H-13C constants indicates that the major conformer has an extended conformation: phi = -120 degrees; psi = 180 degrees; and omega = 75 degrees. TRNOE measurements on me4FGal2 and me4F2dGal2 in the presence of the specific antibody indicate that the pyranose ring pucker of each galactose ring remains unchanged, but rotations about the glycosidic linkage occur upon binding to X24. Computer calculations indicate that there are two sets of torsion angles that satisfy the observed NMR constraints, namely, phi = -152 +/- 9 degrees; psi = -128 +/- 7 degrees; and omega = -158 +/- 6 degrees; and a conformer with phi = -53 +/- 6 degrees; psi = 154 +/- 10 degrees; and omega = -173 +/- 6 degrees. Neither conformation is similar to any of the observed conformations of the free disaccharide.(ABSTRACT TRUNCATED AT 250 WORDS)

Heavy and light chain sequences of four monoclonal antibodies that bind galactosylgloboside (GalGb4)

We recently described IgM monoclonal antibodies directed against the glycospingolipid galactosylgloboside (GalGb4; Marcus, M. D. et al., Arch. Biochem. Biophys, 1988.262: 620). We now present the nucleotide and deduced amino acid sequences of the heavy and light chains of these antibodies. The antibodies were generated in a single fusion, their heavy as well as their light chains are almost identical, and they appear to be clonally related. The light chains were encoded by J kappa 5 and a V kappa gene belonging to the Ox1 family, but they are only 93% homologous to the most closely related germ-line gene, and they are probably encoded by a germ-line gene that has not yet been identified. The heavy chains were all encoded by VH441 and JH2, and have identical N segments. The VH441 germ-line gene encodes a potential glycosylation site at Asn58 in the complementarity-determining region 2. This site, which has been retained in all VH441-encoded monoclonal antibodies sequenced previously, was mutated out by a single base change in all four anti-GalGb4 antibodies.

Synthesis of specifically deoxygenated ligands related to (1----6)-beta-D-galacto-oligosaccharides, and studies on their binding to monoclonal antigalactan antibodies

Synthetic deoxygenated derivatives of methyl beta-glycosides of (1----6)-beta-D-galacto-oligosaccharides were prepared, and their binding to antigalactan monoclonal antibodies X24 and J539 (Fab') was studied. The results suggest the involvement of an additional, critical hydrogen bond in the highest affinity subsite (A), which now appears to require two hydrogen bonds from the 2- and 3-hydroxyls of the galactosyl residue to the protein, and one from the protein to O-4 of that residue. The data obtained with a series of oligosaccharides deoxygenated at position 3(1), 3(2), 3(3), 4(1), 4(2), or 4(3) support the binding patterns and subsite-arrangement inferred previously from studies with large numbers of deoxyfluoro-substituted ligands and this family of antibodies.

A synthetic heptasaccharide reveals the capability of a monoclonal antibody to read internal epitopes of a polysaccharide antigen

The binding of the synthetic heptasaccharide,beta-D-Galp-(1----3)-beta-D-Galp-(1----6)-beta-D-Galp-(1 ----6)-beta-D-Galp-(1----6)-beta-D-Galp-1-OCH3 (10) with two monoclonal IgAs of the X24 gene-family has been investigated. The ligand 10 was synthesized by silver triflate mediated coupling of O-(2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl)-(1----3)-O-(2,4,6,-t ri-O-benzoyl-beta-D-galactopyranosyl)-(1----3)-2,4,6-tri-O-benzoyl-alpha -D-galactopyranosyl chloride (5) to the benzoylated, all-beta-(1----6)-linked methyl galactotetraoside 13, having O-6(4) free, followed by debenzoylation of the formed, fully protected methyl galactoheptaoside. The blockwise synthesis of the nucleophile 13 from readily available monosaccharides, and the synthesis of 5 from the corresponding beta-1-O-benzoylated trisaccharide, is also described. Heptasaccharide 10 binds with the (1----6)-beta-D-galactan-specific monoclonal antibodies X-24 and J539 with essentially the same Ka-values (5.4 x 10(5) M-1 and 6.4 x 10(5) M-1, respectively) as does the methyl beta-glycoside of all-beta-(1----6)-linked galactotetraose 14 (5.7 x 10(5) M-1 and 5.9 x 10(5) M-1, respectively). Of the series of homologous oligosaccharides studied previously (di- through a hexa-saccharide), 14 was found to show the highest affinity of interaction with both these immunoglobulins. The beta-(1----3)-linked galactotriose, which forms the bulky terminus of 10, does not appear to bind to these IgA. Thus, the observation that the affinity of 10 is the same as that of 14 confirms that these immunoglobulins bind internal tetrasaccharide sequences of the antigenic (1----6)-beta-D-galactopyranan.

Eleven distinct VH gene families and additional patterns of sequence variation suggest a high degree of immunoglobulin gene complexity in a lower vertebrate, Xenopus laevis

Lower vertebrate species, including Xenopus laevis, exhibit restricted antibody diversity relative to higher vertebrates. We have analyzed more than 180 VH gene-containing recombinant clones from an unamplified spleen cDNA library by selective sequencing of JH and CH positive clones following iterative hybridization screening with family-specific VH probes, 11 unique families of VH genes, each associated with a unique genomic Southern blot hybridization pattern, are described and compared. Considerable variation in the number of hybridizing components detected by each probe is evident. The nucleotide sequence difference between VH families is as great as, if not more than, that reported in other systems, including representatives of the mammalian, avian, and elasmobranch lineages. Some Xenopus Ig gene families encode alternative amino acids at positions that are otherwise invariant or very rarely substituted in known Igs. Furthermore, variations in complementarity determining region sequences among members of the same gene family and high degrees of DH and JH region complexity are described, suggesting that in at least this lower vertebrate species, the diversity of expressed Ig VH genes is not restricted.

Restricted usage of VH and V kappa genes by murine monoclonal antibodies against 3-fucosyllactosamine

We are studying the structure and regulation of murine antibodies against the 3-fucosyllactosamine antigenic determinant. Analysis of the sequences of seven BALB/c IgM, kappa monoclonal antibodies (mAb), obtained from four fusions, indicates that these antibodies exhibit restriction in their usage of VH and VL genes. Based on a combination of mRNA sequences and Southern filter hybridization data, all seven light chains are encoded by V kappa 24B and J kappa 1 gene segments. Complete mRNA sequences of the heavy chains revealed that all seven mAb are encoded by VH441, six antibodies are encoded by JH4 and one uses a JH3 gene segment. The VH441 gene segment and all seven mAb contain a potential glycosylation site at Asn 58 in complementarity-determining region (CDR)2. In contrast to the similarity of the VH regions, the heavy chain CDR3 segments exhibit considerable heterogeneity. They are encoded by three D segments, they vary in length from 7-9 amino acids and display differences in their deduced amino acid sequences. The VH441 gene segment also encodes antibodies against four other carbohydrate antigens, levan, galactan, dextran and galactosyl globoside. The use of a single gene segment to encode antibodies against five different antigens suggests that the domain encoded by VH441 might be particularly well adapted for forming sites that bind carbohydrate determinants. Glycosylation of CDR2 might contribute to the unique properties of this VH domain.

The 5' splice site: phylogenetic evolution and variable geometry of association with U1RNA

The 5' splice site sequences of 3294 introns from various organisms (1-672) were analyzed in order to determine the rules governing evolution of this sequence, which may shed light on the mechanism of cleavage at the exon-intron junction. The data indicate that, currently, in all organisms, a common sequence 1GUAAG6U and its derivatives are used as well as an additional sequence and its derivatives, which differ in metazoa (G/1GUgAG6U), lower eucaryotes (1GUAxG6U) and higher plants (AG/1GU3A). They all partly resemble the prototype sequence AG/1GUAAG6U whose 8 contigous nucleotides are complementary to the nucleotides 4-11 of U1RNA, which are perfectly conserved in the course of phylogenetic evolution. Detailed examination of the data shows that U1RNA can recognize different parts of 5' splice sites. As a rule, either prototype nucleotides at position -2 and -1 or at positions 4, 5 or 6 or at positions 3-4 are dispensable provided that the stability of the U1RNA-5' splice site hybrid is conserved. On the basis of frequency of sequences, the optimal size of the hybridizable region is 5-7 nucleotides. Thus, the cleavage at the exon-intron junction seems to imply, first, that the 5' splice site is recognized by U1RNA according to a "variable geometry" program; second, that the precise cleavage site is determined by the conserved sequence of U1RNA since it occurs exactly opposite to the junction between nucleotides C9 and C10 of U1RNA. The variable geometry of the U1RNA-5' splice site association provides flexibility to the system and allows diversification in the course of phylogenetic evolution.

The molecular origin of regulatory idiotypes

A complete immunochemical and molecular profile was generated for a group of hybridoma and myeloma antibodies bearing the A48 regulatory idiotype (RI). These A48 RI+ antibodies were derived from normal or idiotypically manipulated mice and were selected either for utilization of a VHX24 VH gene or expression of the A48 RI. Among the hybridomas selected for VHX24 VH utilization a variety of antibody specificities were seen with the fructosan specificity occurring least frequently and the N-acetylglucosamine specificity occurring most frequently. A variety of Vk families were used with a bias for the Vk1 family by the antibodies deriving from untreated mice. The A48RI was expressed by only 3 of these antibodies, none of which were fructan specific. Two used the canonical VHX24-Vk10 combination utilized by the A48 and UPC 10 prototypes, and one used the VHX24-Vkl combination. This demonstration of A48 RI expression ny non-fructan specific, non-VHX24+Vk10+ antibodies was extended by showing expression of this Id by two monoclonal antibodies specific for the Sm self-antigen, one rheumatoid factor and two monoclonal antibodies specific for influenza virus hemagglutinin molecule. They used different VH-VL combinations. Among the monoclonal antibodies selected for A48 RI expression all exhibited fructan binding activity and the vast majority used the VHX24-Vk10 association. A collective analysis of the VH and VL sequences of all these A48RI+ antibodies showed idiotype expression was not associated with any particular germline VH or VL gene. D, Jk or JH sequence. Three positions on the light chain and one on the heavy chain were identified which could represent the structural correlates for the A48 regulatory idiotype.

A Vh region synthetic peptide induces antibodies which bind native immunoglobulins and augment an immune response to antigen

The BALB/c myeloma protein ABPC48 (A48) binds the polysaccharide bacterial levan; its Vh is encoded by a gene derived from the VhX24 family. This antibody has been shown to cross-react idiotypically with the phosphorylcholine-binding BALB/c myeloma protein MOPC167 whose Vh shares homology with A48 from residues 32-44. We have synthesized a peptide corresponding to residues 32-44 of the Vh encoded by a germline gene of the VhX24 family. Anti-peptide antisera from rabbits were purified by affinity chromatography with peptide or intact antibody. Several myeloma proteins and monoclonal antibodies with varying degrees of homology to the peptide have been analyzed for reactivity with purified rabbit antibodies in solid-phase RIA. We observed that the specificities within rabbit antisera are heterogeneous, and that purification with antibody versus peptide yields preparations containing different specificities, albeit demonstrably peptide-related. We also show that injection of mice at birth with small amounts of purified rabbit antibodies can affect the magnitude of the response to bacterial levan and the expression of A48 idiotopes in that response.

Molecular and serological diversity of anti-DNA autoantibodies from NZB and (NZB X NZW) F1 mice

We have carried out an analysis of the serological and molecular diversity of a panel of monoclonal anti-DNA autoantibodies and serum autoantibodies from NZB and (NZB X NZW) F1 mice, in an attempt to obtain insights into the mechanisms responsible for the development of systemic autoimmune disease. Our data show that the autoantibodies are quite diverse. A dominant, binding-site idiotope on one of our monoclonal autoantibodies is expressed at variable levels in anti-DNA binding antibodies in the sera of both NZB and (NZB X NZW) F1 mice, but on none of the other monoclonal autoantibodies in our panel. We have cloned and sequenced the heavy chain variable region (VH) gene of one anti-DNA hybridoma and by hybridization have determined the VH and V kappa gene segments expressed by 14 others. All of the autoantibodies express members of known V gene subfamilies. A total of four different VH and at least six V kappa subfamilies are expressed by the hybridomas. Thus, a broad spectrum of the total murine Ig repertoire is represented in the anti-DNA autoantibodies present in these strains.

Immunoglobulin VH region genes of the mouse are organized in overlapping clusters

Restriction fragment length polymorphism has been compared between the Igh loci of C57BL/6 and MOLF/EI (Mus musculus molossinus) mice utilizing probes which detect the C gamma 2b gene and genes from nine VH-gene families. Distinct restriction site patterns were found for the CH genes and for VH families PC7183, Q52 and X24. VH families V31 and J558 showed identical patterns. Mixed patterns of identical and distinct bands were detected in VH families S107, J606, V3660 and VGAM3.8. This indicates that a recombination took place involving the Igh loci of a M. m. molossinus and a progenitor of the C57BL/6 strain. The breakpoint of recombination maps to the chromosomal region carrying VH families S107, J606, VGAM3.8 and V3660. VH families PC7183, Q52 and X24 map 3' to the recombination breakpoint and proximal to the DH-JH-CH region, whereas VH families V31 and J558 accordingly map 5' to the recombination breakpoint and distal to DH-JH-CH. This order of VH families was confirmed by deletion mapping utilizing hybridomas which are haploid either for the Ighb or for the Igha locus. The mapping data indicate that the VH families of the mouse are organized in overlapping clusters. This notion is confirmed by demonstration of the physical linkage of VH genes from families V31 and J558 in the Igha locus.

A novel family of variable region genes of the human immunoglobulin heavy chain

We isolated and sequenced six variable-region (V) gene segments of the human immunoglobulin heavy-chain (H) using the V71-2 segment as probe. These VH segments were more than 90% homologous to each other and less than 65% homologous to members of the three known VH families. The VH fragments hybridized to an identical set of restriction fragments on Southern blots of human placenta DNA. The new family was designated as the VH-IV family. The complexity of the VH-IV family was estimated to be at least nine genes, of which the sequenced seven were functional genes. The VH-IV family is homologous (76%) to the mouse Vh36-60 family.

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.

High connectivity, natural antibodies preferentially use 7183 and QUPC 52 VH families

Twenty-seven B cell hybridomas derived from spleen cells of nonimmunized, 6-day-old BALB/c mice and previously characterized serologically were screened for VH-gene expression: hybridomas expressing the two most D-proximal VH-gene families, 7183 and QUPC 52 were over-represented in this sample. Strikingly, clones serologically characterized by high degree of degenerate "specificity" and high idiotypic connectivity were found to use almost exclusively these two VH-gene families. As these serological properties are a unique feature of "natural" antibody repertoires, the results may reflect a functional relationship between expression of these VH genes and activation of B cells in the internal environment, particularly in the context of idiotypic interactions.

Analysis of promoter and enhancer cell type specificities and the regulation of immunoglobulin gene expression

We have analysed the properties of IgH promoter (VH) and enhancer (Ig) regions which were used to drive the expression of the chloramphenicol acetyl transferase (CAT) gene (cat) in recombinant plasmids. We observe little synergistic effect between the VH promoter and Ig enhancer on cat gene expression in our constructs. Replacing the VH promoter by the thymidine kinase (TK) promoter does not affect the enhancer-mediated B-cell-specific expression of the cat gene. However, replacement of the VH promoter by the mouse renin gene promoter, which is not normally expressed in B cells, completely abolishes cat gene expression in cells of this lineage. When the Ig enhancer is replaced by the SV40 enhancer (SV), CAT activity is restricted to B cells. The VH promoter is as efficient as the TK promoter in a preB cell line. Extending the size of the VH promoter fragment to include sequences between 126 to 639 bp upstream from the transcription start point results in an eight-fold decrease in CAT activity. In this situation, the tissue specificity of the promoter cat fusion is maintained. Among the various combinations tested here, the association of the TK promoter and the Ig enhancer expresses the cat gene most efficiently. The implications of these observations are discussed.

Immunochemical and molecular characterization of regulatory idiotopes expressed by monoclonal antibodies exhibiting or lacking beta 2-6 fructosan binding activity

Hybridomas secreting antibodies bearing the ABPC48 (A48) regulatory idiotype (Id) were generated from BALB/c mice treated at birth or as adults with minute amounts of anti-A48-Id antibodies. The majority of these antibodies were recognized by the syngeneic monoclonal anti-A48-Id and anti-UPC-10-Id antibodies, IDA10 and 10-1, respectively. In Northern blotting experiments, most of these hybridomas were shown to use VH (heavy chain variable region) genes related to the 441-4 germline VH gene that encodes the A48 VH region. Hybridization was detected between polyadenylated H chain mRNA, isolated from the majority of the hybridomas, and the VH probe. Southern blots confirmed these results by showing a rearrangement of VH-related sequences to the JH (H chain joining segment) clusters on these same hybridomas. The antibodies from all of the hybridomas that derived from neonatal mice and half of those derived from adult mice showed specificity for fructosan determinants that, in most cases, was different from the beta 2-6 fructosan linkage specificity of A48. Surprisingly, several of the non-fructosan-binding hybridomas generated from the adult mice and the MOPC-173 myeloma demonstrated a clear specificity for the beta 1-6-D-galactan determinant. Of four galactan-binding myeloma proteins studied. XRPC 44 alone shared idiotypy with the UPC-10 myeloma. These findings suggest a possible clonal crossreactive regulation mediated by regulatory idiotopes. The crossreactive regulation concept is discussed.

Antigen-binding specificities of antibodies are primarily determined by seven residues of VH

Although the antigen-binding pocket of all antibodies consists of VL + VH dimers (where VL and VH represent immunoglobulin light and heavy chain regions, respectively), subgroups of their VH largely determine their antigen-binding specificities. This VH subgroup dependence automatically relegates subsidiary roles to VL as a whole and to the complementarity-determining region 3 (CDR-3) of VH encoded by independent diversity (D) and joining (J) coding segments in determining antigen-binding specificities of individual antibodies. As a sequel to our previous paper, which emphasized the role conserved residues in CDR-1 and CDR-2 of VH play in general shaping of the primordial antigen-binding cavity, here we propose that the three short clusters of amino acid sequences in CDR-1 and CDR-2 that are placed in the immediate vicinity of the tryptophan loop primarily determine subgroup-dependent antigen preference of individual VH, therefore, antibodies. The three clusters are the 31st to 35th positions of CDR-1 and the 50th to 52nd and 58th to 60th positions of CDR-2. Of those, the 32nd, 34th, 51st, and 59th positions tend to be occupied by tyrosine, methionine, isoleucine, and tyrosine, respectively. Nevertheless, free amino acid substitutions at the remaining seven sites can generate 20(7) or 1.28 X 10(9) varieties of amino acid sequence combinations. Some of these astronomically numerous sequence combinations no doubt contribute to the maintenance of the vast repertoire of antigen-combining diversity, which might be as large as 10(7), whereas others serve to vary binding affinities toward the same antigen. Ironically, but not surprisingly, a single nonconservative amino acid substitution at one of these sites often suffices to change the antigen preference of VH from one to another, whereas more substitutions affecting two or more clusters are apparently required to change the binding affinity toward the same antigen. In the case of mouse anti-p-azophenylarsonate antibodies, the principle of VH subgroup dependence is violated, their VH belonging to either subgroup 1 or 3. It appears that the mouse genome lacks anti-p-azophenylarsonate germ line VH, residues of CDR-3 derived from one particular JH coding segment coming to rescue to cope with this unnatural man-made antigen.

A single VH-gene associated with a variety of D- and J-segments encodes for a large family of ABPC48-related antibodies induced by antiidiotypic immunization

Two series of monoclonal antibodies have been obtained from BALB/c mice immunized against two antiABPC48 antiidiotypic antibodies. They are divided into two serologically different classes. Class I antibodies bind only the immunizing antibody; class II antibodies display a broad binding capacity to various antiidiotypic antibodies, and some bind levan, as does ABPC48. Northern blot analyses and partial mRNA sequencing show that all class II antibodies express the VH-gene coding for ABPC48 and UPC10 antilevan antibodies associated with a variety of D- and J-segments. The third hypervariable region of the sequenced antibody with antilevan activity is structurally related to that of ABPC48 and UPC10 antibodies but has a different genetic origin. This study indicates that the identification of idiotype-related antibodies arising from antiidiotypic immunization may be misleading, if based on their antigen-binding properties; and it stresses the importance of structural approaches for the analysis of regulatory mechanisms ruling immune responses.

Immunoglobulin VH gene structure and diversity in Heterodontus, a phylogenetically primitive shark

A mouse VH probe has been used to identify and isolate VH homologs in a DNA library of Heterodontus francisci (horned shark). The complete nucleotide sequence of one VH gene, HXIA, has been determined and found to exhibit striking organizational homology and nucleotide identity with mammalian prototype VH genes. Metric analysis of the complete sequence is consistent with the early phylogenetic diversification of framework and complementarity-determining regions (CDR). Both the predicted amino acid sequence and the specific hybridization of the CDR2-specific, synthetic oligodeoxynucleotide probe in spleen mRNA suggest that HXIA is functionally expressed. A probe consisting of the entire coding region of this gene hybridizes with multiple components in Southern blot analysis of Heterodontus genomic DNA and together with the identification of additional unique VH+-lambda clones indicates that considerable complexity is associated with the germline VH gene family in a contemporary species that represents an early stage in the phylogenetic development of the vertebrates.

Immune response induced by a single or several syngeneic monoclonal antiABPC48 antiidiotypic antibodies: no predominant coexpression of ABPC48 idiotopes

BALB/c mice were immunized with monoclonal BALB/c antibodies IDA10, IDA16 and IDA17 raised against the BALB/c ABPC48 myeloma protein. Several procedures of immunization--copolymers with lipopolysaccharide or keyhole limpet hemocyanin, simultaneous or sequential injections of different IDAs--were performed in an attempt to orient the immune response towards the production of ABPC48-like idiotypes. We used a binding assay which identifies two idiotopes on the same molecule to measure the population of antibodies induced in these responses. The expression of ABPC48 cross-reactive idiotypes in immune sera was analyzed. The results show that, with all immunization protocols, immune responses to different monoclonal antiidiotypic antibodies are mostly independent of each other: the coexpression of ABPC48 idiotopes, either private or recurrent on the induced antibodies, is rarely found; it makes it difficult to discriminate by a serological approach between cross-reactive idiotypes and anti-antiidiotypic antibodies. We discuss the interest of combining molecular and serological approaches to identify these two populations of antibodies.

Complete nucleotide sequences of three VH genes in Caiman, a phylogenetically ancient reptile: evolutionary diversification in coding segments and variation in the structure and organization of recombination elements

Complete nucleotide sequences are described for three caiman (Caiman crocodylus crocodylus) immunoglobulin VH genes (C3, E1, and G4) that hybridize with a murine VH probe. The E1 and G4 genes are physically linked (intergenic distance, approximately equal to 6.5 kilobases) in the same transcriptional orientation but are not directly contiguous with the C3 gene. When the coding segments, including both framework and complementarity-determining regions, of these genes and the murine probe sequences are compared by metric analysis, it is apparent that the caiman genes are only slightly more related to each other than to the mammalian sequence, consistent with significant preservation of nucleotide sequence over an extended period of phylogenetic time. Based on the presence of transcriptionally critical 5' sequences and the absence of terminator codons, frameshift mutations, or other recognizable alterations, the genes do not appear to be pseudogenes. The E1 gene, however, is distinguished from other VH genes because (i) the spacer region within the 3' recombination signal sequence is 12 base pairs, typical of VK genes but not of VH genes, which possess 22- to 23-base-pair spacers and (ii) a near-perfect VH recombination signal sequence is present within the intervening sequence that splits the segment encoding the leader. These studies establish VH gene multiplicity in a species that arose prior to mammalian radiation and provide a description of differences in the configuration and location of recombination elements associated with an otherwise potentially functional gene.

The internal image and the structural idiotypic network (Ab1, Ab2, Ab3) in the GAT system

The GAT repertoire expressed at the different levels of the classical idiotypic cascade Ag----Ab1----Ab2----Ab3 has been analysed by direct nucleotide sequencing of H- and L-enriched mRNA. Ab1 and Ab3 expressing the major public idiotypes used similar, if not identical, VH and VK genes. The VH Ab3 of the Ab1 type (Ab1') appeared highly conserved. Ab2 also use a small number of germ-line genes. The D region of Ab2 is of particular interest since it contains either a Tyr-Tyr-Glu or a Glu-Glu-Tyr sequence, characteristic of the GAT major determinants. It is therefore suggested that this D region contains the internal image of the antigen. A large number of VH germ-line genes have been isolated and sequenced. They all pertain to the VH-II family, which contains a large number of members, some of them being very close in sequence.

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.

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.

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.

Regulatory idiotopes, parallel sets and internal image of the antigen within the polyfructosan-A48 idiotypic network

The study of the A48 idiotype anti-beta 2----6-polyfructosan immune response was used as a tool to investigate the various postulates of the immune network theory. The results of this study have shown: that only certain idiotopes, designated as regulatory idiotopes, play a role in idiotype-regulated immune responses; that some of the A48 idiotopes were expressed on a myeloma protein with unknown binding activity (MOPC173) and on MOPC167, a phosphorylcholine-binding myeloma protein; that one out of six monoclonal antiidiotypic antibodies tested carried the internal image of the antigen and could elicit an antibacterial levan immune response in mice treated at birth with bacterial levan or polyclonal anti-A48Id antibodies.

Structural relationships among mouse and human immunoglobulin VH genes in the subgroup III

The mouse VHIII subgroup is composed of four families which share sequence homology. We isolated a VH germ-line genomic clone, which cross hybridizes with a cDNA probe from one of these families, derived from a myeloma secreting an antigalactan antibody. We report here the nucleotide sequence of the cross hybridizing gene and show that very likely it has an anti-sheep red blood cell specificity. Comparison of its nucleotide sequence with those of the three other VHIII families shows that these genes share segmental homologies of variable lengths. This suggests that interchanges of sequence blocks between VH genes could be an important evolutionary mechanism for diversifying the germ-line repertoire. The strong homology (82%) with human VHIII genes suggests that efficient antibody sequences are strongly conserved. This conservation of homology is particularly striking when compared to the more limited homology (63%) between mouse and human C kappa genes.

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.

Three T cell hybridomas do not contain detectable heavy chain variable gene transcripts

We attempted to determine whether T cells express any VH gene segments. cDNA libraries were constructed from one suppressor and two helper T cell hybridomas. Both the library construction and screening were designed to maximize detection of a wide range of VH gene segments. One screening method should detect about half of the sequenced VH genes, while the second should detect most of these genes. The probability of detecting a VH gene homologous to the probes and present at 10 copies per cell was 77% for one helper cell cDNA library, 88% for the second helper cell library, and greater than 99% for the suppressor cell library. No cDNA clones with VH gene segments were detected. From this result, we conclude that VH gene segments are not likely to encode the antigen-specific receptor in the cells we tested.