Multiplicity of constant kappa light chain genes in the rabbit genome: a b4b4 homozygous rabbit contains a kappa-bas gene

We have constructed a genomic library of homozygous b4b4 rabbit DNA in the pJB8 cosmid vector. Clones containing Ckappa-like sequences were screened with a b4 cDNA probe and were characterized by restriction mapping. One of the clones contained a Ckappa sequence different from the b4 allotype normally expressed by the animal. We report here the nucleotide sequence of this gene and show that it probably corresponds to a kappa-bas form of the Basilea allotype. It appears to be a structurally complete gene without any stop codons within the coding region and containing the dinucleotide AG as a splice site acceptor for the J-C junction, just 5' of the coding block. Comparison with the b4 cDNA nucleotide sequence shows a separate evolution of the Ckappa-coding and 3'-untranslated sequences, since the 3'-untranslated regions are more conserved than the coding regions. Genomic blot analysis would suggest that the kappa-bas gene is isotypic in the domestic rabbit population, since it lies within a genomic EcoRI or PstI restriction fragment, which was shown to be common to all homozygous b4, b5, b6 and b9 rabbit DNAs.     

Identification of a novel substitution in the constant region of a gene coding for an amyloidogenic kappa1 light chain.

Current concepts regarding the association between immunoglobulin (Ig) light chain structure and AL amyloidosis (AL) emphasize Ig variable region amino acid substitutions because the majority of light chain amyloid fibrils that have been sequenced contain amino termini of the variable region with only small amounts of the constant region. In this report, we describe a patient with rapidly progressive AL whose amyloid deposits contained primarily monoclonal kappa light chain constant region fragments. We sequenced and analyzed this AL protein, determining that it was an O18-O8 kappa1 variant and that the constant region possessed an unusual Ser-->Asn substitution at position 177. Using pre-mortem bone marrow cells, we cloned and sequenced the cDNA for this AL protein (HCAK1) and, using DNA from post-mortem somatic tissue, we cloned and sequenced the patient's kappa germline O18-O8 donor and kappa constant region (Ckappa) gene segments. The cDNA that coded for HCAK1 contained a variable region that was derived from O18-O8, showing 96.1% homology to germline, and a Ckappa that had a nucleotide substitution (AGC to AAC), resulting in the 177Ser-->Asn replacement. Two Ckappa genes were cloned from somatic tissue DNA, one identical to a known Ckappa sequence and another containing this substitution which likely is a new Ckappa allotype. Our findings indicate that further investigation is warranted into the contributions genetic polymorphisms and light chain constant regions may make to amyloidogenesis.     

Serologic and structural characterization of immunoglobulin chains secreted by rabbit-mouse hybridomas

Serologic and primary structural analyses of Ig chains secreted by several rabbit-mouse hybridomas have shown that these hybrid cells produce heavy (H) or light (L) chains identical to those isolated from rabbit sera. Two of the cell lines (7D2, 7D6) secreted rabbit H chains with a m.w. of 55,000 each of which expressed a full complement of variable and constant region allotypes (a3, d11, e15). These apparently normal rabbit H chains were secreted in a complex with a m.w. about 130,000, and serologic studies indicated that this complex contained a covalently linked mouse kappa L chain. Two other cell lines (4C1, 12F2) produced allotype b4 L chains with m.w. of 23,000 and 25,000, and a third (1D4P5) produced an allotype b5 L chain with a m.w. of 23,000. Serologic analyses indicated that the allotypes on these chains are equivalent to those expressed by normal rabbit Ig molecules. Partial amino acid sequence data obtained for the L chain products showed them to be typical of rabbit L chains, and to be significantly different from mouse L chains.     

The rabbit kappa 1 b5 immunoglobulin gene: another J region gene cluster with only one functional J gene segment?

Our previous analysis of an immunoglobulin gene encoding the rabbit kappa chain of b4 allotype revealed that of the five J-like sequences in the J kappa cluster of this gene, only one, J2, appeared to be functional. This unusual ratio of J pseudogenes to functional J genes is unique among all J clusters of light and heavy chain genes of all species examined to date, including the cluster from the rabbit kappa 2 isotype, and must have consequences for diversity generation of b4 immunoglobulins. The fact that the only two known b5 J kappa sequences are different from the functional J2 of the b4 allotype prompted investigation of the b5 J kappa cluster to determine whether it resembled the b4 cluster, or the more typical mouse or human J kappa clusters. Our analysis of the b5 gene reveals a J kappa cluster strikingly similar to that of b4; apparent defects occur in all J sequences except J2. Although J2 is apparently functional, it differs from the J2 of the b4 locus by four nucleotide and three amino acid substitutions. The unusually high degree of sequence similarity previously observed between the b4 and b5 loci in the noncoding (vs the coding) regions extends through the newly sequenced DNA segment and remains an enigma.     

Partial amino acid sequence of a rabbit immunoglobulin light chain of allotype b5

The amino acid sequence of a rabbit immunoglobulin light chain of allotype b5 has been nearly completed. A comparison of its structure with that of light chains of allotypes b4, b6, and b9 confirms that the constant regions of these various kappa chains differ by 20-35%. The substitutions are clustered in parts of the second half of the chain, and the b5 form bears more resemblance to the b6 chain than to any other, in good agreement with previous serological data. The analysis of the variable region reveals the existence of certain allotype-associated residues which have also been reported in other b5 chains, but not in proteins of the other allotypes. An examination of the rabbit light chain sequences between positions 96 and 107 suggests that this portion of the chain may be encoded separately by a joining "J" DNA segment, as has been described previously for murine and human immunoglobulins. In the rabbit, however, these J kappa regions appear to differ from one allotype to another. Together with the extensive variations of the constant regions, these data suggest that the rabbit kappa gene organization more closely resembles the murine gamma system (four different C gamma genes each flanked by its J segment) than the murine kappa system (a single C kappa gene).     

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

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

Characterization and DNA sequence of the b6w2 allotype of the rabbit immunoglobulin kappa 1 light chain (b locus)

The b6w2 allotype of the constant region of the rabbit immunoglobulin kappa 1 (k1) light chain (b locus) was discovered in wild populations from northern Spain. At the serological level, the b6w2 allotype is characterized by the presentation of all b6-specific epitopes, while an allotypic determinant which is shared between the nominal b5 and b6 allotypes is lacking. The DNA fragment encoding the b6w2 allotype was amplified by means of the polymerase chain reaction, and sequenced directly by dideoxy-DNA-sequencing. When compared with the sequence of the nominal b6 allele, the b6w2 sequence differs at eleven nucleotide positions (96.5% similarity). This variation corresponds to amino acid replacements at 1) the three positions C-terminal to the peptidyl junction with the variable region (amino acid positions 109–111);2) the four positions N-terminal to the interdomain disulfide bond (167–170); and 3) two positions in the vicinity of the interchain disulfide bond (190 and 210). The nature and distribution of the observed nucleotide substitutions strongly suggest a possible role of the extra interdomain disulfide bond in the unusual evolutionary dynamics of the rabbit K1 light chain.The nucleotide sequence data reported in this paper have been submitted to the EMBL nucleotide sequence database and have been assigned the accession number Z48308     

Analysis of the diversity of a sheep antibody repertoire as revealed from a bacteriophage display library

We have applied bacteriophage display technology to construct and analyze the diversity of an IgG library of >1 x 108 clones from an adult sheep immunized against the hapten atrazine. We have identified eight new VH gene families (VH2-VH9) and five new Vkappa gene families (VkappaV-VkappaIX). The heavy and kappa light chain variable region gene loci were found to be far more diverse than previously thought.     

RNA conversion of lymphoid cells to synthesize allogeneic immunoglobulins in vivo

Ribonucleic acid extracts (“5 day immune” and “nonimmune”-RNA) obtained from lymph nodes and spleens of rabbits homozygous for the b⁴ or b⁵ allele of light chain immunoglobulin allotypes were injected iv into nonimmunized rabbits homozygous for the alternate allele. The recipient rabbits were then given multiple iv injections of sheep red blood cells (SRBC). The spleens were assayed 13, 21, and 37 days following the RNA injection for “direct” IgM and “indirect” IgG plaque forming cells (PFC) specific for SRBC. The b4 or b5 light chain allotype and the a1, a2, and a3 heavy chain allotype of the antibody in the plaques was identified by radioautography and by inhibition of plaque formation using anti-allotype antibodies. The b light chain allotype of the RNA donor was identified in 22–32% of the IgM plaques and in 25–42% of the IgG plaques. The allotype of the host rabbit b light chain allotype was identified in 56–67% of the IgM plaques and in 57–71% of the IgG plaques. Likewise the a heavy chain allotype of the RNA donor was identified in 10–19% of the IgM plaques and in 12–19% of the IgG plaques. The allotype of the host rabbit a heavy chain allotype was identified in 51–60% of the IgM plaques and in 55–63% of the IgG plaques. The concentrated lysates of spleen and lymph node cells were also analyzed for immunoglobulins of each light chain allotype by immunodiffusion with radiolabeled antibody. The allotype of both the RNA donor rabbit and host rabbit were found in most of the lysates of lymphoid tissues and in some of the IgG isolated from the serum and concentrated.     

Structural analysis of a rabbit immunoglobulin kappa 2 J-C locus reveals multiple deletions.

We previously reported that domestic rabbits harbor at least two DNA sequences that hybridize strongly to immunoglobulin kappa C region probes in Southern blots. One of these was cloned from a domestic b4 rabbit and identified as the gene for the nominal b4 allotype kappa chain which is expressed at high levels. We now have cloned (from a b4 rabbit) the other homologous sequence and find that it encodes a kappa chain nearly identical to the kappa 2 chain of "bas" rabbits, which is not normally expressed at detectable levels in domestic rabbits. Sequence analysis of this kappa 2 chain reveals a J kappa -C kappa locus with no obvious coding sequence defects that could explain its low expression. However, several base changes in a putative enhancer region as well as deletions (totalling about 1.5 kb) in the J-C intron might be related to low expression. The comparison between these two kappa genes raises questions about the selective pressures operating during the evolution of this gene system.     

Antibody repertoire development in fetal and neonatal pigs. VII. Characterization of the preimmune kappa light chain repertoire

Combinatorial diversity is highly restricted in the preimmune porcine H chain repertoire compared with that in humans and mice. This raised the question of whether similar restriction characterized the preimmune L chain repertoire. In this study we present evidence that >90% of all expressed Vkappa genes in the porcine preimmune repertoire belong to three subfamilies of Vkappa genes that share 87% sequence similarity with human IGKV2. This porcine Vkappa family also shares sequence similarity with some, but not all, Vkappa genes from sheep. Hybridization with sperm DNA and sequence analyses of polynucleotides from overlapping bacterial artificial chromosome clones suggest swine possess approximately 60 IGVK2 genes. The latter method also revealed that certain IGKV2 subfamilies are not expressed in the preimmune repertoire. Six members of an IGVK1 family were also expressed as part of the preimmune repertoire, and these shared 87% sequence similarity with human IGVK1. Five Jkappa segments, complete with recombination signal sequences and separated by approximately 300 nt, were identified approximately 3 kb upstream of a single Ckappa. Surprisingly, Jkappa2 accounted for >90% of all framework region 4 sequences in the preimmune repertoire. These findings show that swine use approximately 10 IGVK2 genes from three of six subfamilies and preferentially one Jkappa segment to generate their preimmune kappa repertoire. These studies, like those of porcine Ig constant regions and MHC genes, also indicate unexpected high sequence similarity with their human counterparts despite differences in phylogeny and the mechanism of repertoire diversification.     

Multiple sequences related to a constant-region kappa light chain gene in the rabbit genome

Four allelic genes control kappa light chain allotypes in the rabbit. Amino acid sequence studies have revealed an extensive divergence (22%--33%) in the alternative forms of the kappa constant region (b4, b5, b6 and b9). Furthermore, independent studies have shown that a rabbit could express a wrong allotype. To assess the hypothesis that b allotypes are encoded by duplicated genes with a polymorphic control mechanism, we have analyzed the DNAs of four different homozygous rabbits using the Southern blot hybridization technique, with a cloned b4 C kappa probe. DNAs of individual b4, b5, b6 and b9 rabbits were cleaved with Eco RI, Kpn I and Pst I restriction endonucleases. Comparative analysis of restriction patterns shows that all four rabbit DNAs contain multiple DNA fragments hybridizing with the probe under low- and high-stringency washing conditions. In addition, each restriction pattern is distinct, suggesting that the C kappa genes are organized differently in animals expressing different allotypes.     

Rabbit Ig kappa 1b6 gene structure

Previous studies employing Southern blot analyses have detected multiple kappa-homologous sequences within EcoRI-digested DNA isolated from kappa 1b6 homozygous rabbits and kappa 1b6 L chain secreting RMH H158 cell line. These results are very unexpected because the published partial protein sequence for the kappa 1b6 C region is incompatible with an EcoRI restriction endonuclease recognition sequence at the nucleotide level for this allotype. To determine their identity, the kappa-homologous sequences were isolated from DNA extracted from a kappa 1b6 L chain secreting RMH H158 cell line by molecular cloning. Structural analyses demonstrated these sequences to contain genetic information encoding the majority of the kappa 1b6 L chain gene locus. The protein sequence deduced from the kappa 1b6 C region gene was shown to differ from the published partial kappa 1b6 C region protein sequence at five amino acid positions. One of these differences results in a glycine to serine interchange that introduces an EcoRI restriction endonuclease recognition site within the kappa 1b6 C region gene. Subsequent genomic Southern blot analyses confirmed this structural assignment. Based on these data, the EcoRI-sensitive kappa-homologous fragments present within the genomes of the RMH H158 cell line and kappa 1b6 homozygous rabbits represent the nominal kappa 1 gene and not an alternative kappa isotype or kappa pseudogene. Rabbit Ig kappa 1 allelic nucleotide sequence homology comparisons have shown the isolated kappa 1b6 J-C gene locus to display common structural features previously identified in other kappa 1 alleles.     

Cloning and expression of human anti-tumor necrosis factor-alpha monoclonal antibodies from Epstein-Barr virus transformed oligoclonal libraries

Peripheral blood was obtained from a healthy human volunteer and transformed with Epstein-Barr virus (EBV). This produced an oligoclonal cell library in culture medium that was screened by ELISA for anti-human tumor necrosis factor-alpha (TNFalpha) activity. RNA from two positive clones was applied to RT-PCR using antibody-specific primers, and the light (kappa and lambda) and heavy chain genes (gamma and mu) were cloned into the plasmid vector pFab1-His2. The antibodies produced in Escherichia coli as Fab fragments were assayed for anti-TNFalpha activity utilizing ELISA. Two IgG1/kappa anti-TNFalpha antibodies and two IgM/kappa anti-TNFalpha antibodies were isolated. DNA sequence analysis showed that the VL and VH gene families of IgM and IgG were the same. Both the antibodies showed almost the same activity on ELISA-testing. Ten clones randomly selected from light (kappa and lambda) and heavy (gamma and mu) chain genes in the oligoclonal cell library 1D5 were sequenced, and each gene (kappa, lambda, gamma, and mu) was found to be composed of one to three different genes. These data support the conclusion that the cell clone is oligoclonal at the molecular level.     

Rabbit variable kappa light chain regions: subgroups contain polypeptides encoded by multiple genes.

Two identical light chain variable regions were identified in anti-streptococcal Group A-variant antibodies elicited in litter-mate rabbits by hyperimmunization with vaccine. In addition, one rabbit produced two additional clonally restricted antibodies to this polysaccharide antigen. The partial amino acid sequence of the light chain of one of these antibodies was identical with the dominant antibody light chain sequence, while the light chain of the other antibody, also partially established, showed significant variations in the framework-associated regions with identical CDRI and II. Since all of these light chains were from a small subset of rabbit kappa light chain pools (b4 allotype) the data suggest, together with other light chains reported in the literature, that more than one copy of variable region genes are present in the germ-line per subgroup. Furthermore, framework associated amino acid substitutions are not random; this suggests the existence of some "ordered" mechanism for linked amino acid substitutions (presumably recombination). Furthermore one light chain can pair with more than one heavy chain to yield functional antibodies.     

Influence of the immunoglobulin heavy chain locus on expression of the VK1GAC light chain

The VK1GAC light chain represents the dominant V kappa structure employed in the antibody response of A/J mice to streptococcal group A carbohydrate ( GAC ). Two anti-idiotypic antisera, anti- Id5 and anti- Id20 , with specificity for the VK1GAC light chain were used to examine anti- GAC antibody responses in a series of inbred mouse strains that differ at the heavy chain constant region ( IgCH ) allotype locus. Both idiotypes were expressed in normal and immune sera from mice of most IgCH allotypes, except IgCHb (C57BL/6J) and IgCHf (CE/J). C57BL/6J mice expressed Id5 , but not Id20 , whereas CE/J mice did not express either idiotype. Testing of recombinant inbred strains between BALB/c and C57BL/6 indicated that the pattern of idiotype expression did not correlate with IgCH allotype. The C X B recombinants expressed all three idiotype patterns that were observed in the panel of inbred strains. Testing of allotype congenic mice between BALB/c and C57BL/6 showed that CB.20 and BC.8 mice were Id20 -, whereas BAB-14 mice were Id20 +, indicating that both VH and background (V kappa or regulatory) loci must be derived from BALB/c to obtain Id20 expression. The difference in the frequency of idiotype expression observed between BALB/c and BAB-14 mice indicates that the IgCH locus may exert a quantitative influence on the expression of this light chain. To examine the Id20 -, Id5 + antibodies of C57BL/6 mice, anti- GAC hybridomas were prepared. Of 16 C57BL/6-derived anti- GAC monoclonal antibodies, six were reactive with anti- Id5 and not with anti- Id20 . Isoelectric focusing of the purified kappa light chains from three of these antibodies revealed two distinct spectrotypes that co-migrated with the two known VK1GAC spectrotypes observed with A/J anti- GAC light chains. Idiotypic analysis of in vitro recombinants between the heavy and light chains of A/J and C57BL/6 monoclonal antibodies demonstrated that the C57BL/6 light chains were idiotypically similar to A/J light chains when they were free in solution or paired with A/J heavy chains. These results demonstrate that C57BL/6 mice can express a light chain that is very similar, if not identical, to the VK1GAC light chain, although the light chain is expressed in lower frequency and is paired with a distinct VH structure, which can mask expression of one of the VK1GAC idiotypes. These effects on V kappa expression map to at least three genetic loci: VH, CH, and an unlinked locus.     

The organization of genes tightly linked to the Ha locus in Aegilops tauschii, the D-genome donor to wheat.

The grain hardness locus, Ha, is located at the distal end of the short arm of chromosome 5D in wheat. Three polypeptides, puroindoline-a, puroindoline-b, and grain softness protein (GSP-1), have been identified as components of friabilin, a biochemical marker for grain softness, and the genes for these polypeptides are known to be tightly linked to the Ha locus. However, this region of the chromosome 5D has not been well characterized and the physical distance between the markers is not known. Separate lambda clones containing the puroindoline-a gene and the puroindoline-b gene have been isolated from an Aegilops tauschii (the donor of the D genome to wheat) genomic lambda library and investigated. Considerable variation appears to exist in the organization of the region upstream of the gene for puroindoline-b among species closely related to wheat. Using in situ hybridization the genes for puroindoline-a, -b, and GSP-1 were demonstrated to be physically located at the tip of the short arm of chromosome 5 of A. tauschii. Four overlapping clones were isolated from a large-insert BAC library constructed from A. tauschii and of these one contained genes for all of puroindoline-a, puroindoline-b, and GSP-1. The gene for puroindoline-a is located between the other two genes at a distance no greater than approximately 30 kb from either gene. The BAC clone containing all three known genes was used to screen a cDNA library constructed from hexaploid wheat and cDNAs that could encode novel polypeptides were isolated.