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

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.

Human and mouse monoclonal antibodies to blood group A substance, which are nearly identical immunochemically, use radically different primary sequences

A human monoclonal antibody (HuA) specific for blood group A substance with two fucose groups was found to be immunochemically almost identical with that of a previously characterized mouse monoclonal anti-A, AC-1001. The VH and VL chain cDNAs of HuA were sequenced and compared with those of AC-1001. The human and mouse antibodies used VH and Vk genes that came from different families and shared minimal nucleotide and amino acid sequence identity. Thus, two antibodies from two different species can use evolutionarily unrelated sequences to bind the same carbohydrate epitope. The cloned HuA VH and VL genes were then transfected into a mouse myeloma cell line and re-expressed, together, and each separately with an irrelevant VH or VL. Only the original HuA VH and Vk had anti-A activity, demonstrating that both the heavy and light chains contributed to specificity.

Molecular characterization of the humoral responses to Cryptococcus neoformans infection and glucuronoxylomannan-tetanus toxoid conjugate immunization

The molecular characteristics of the humoral immune response to a serotype A Cryptococcus neoformans infection were compared with the response elicited by a cryptococcal glucuronoxylomannan-tetanus toxoid (GXM-TT) conjugate. Anticryptococcal monoclonal antibodies (mAbs) isolated from both responses have previously been shown to recognize the same antigenic determinant of cryptococcal GXM. Southern blot and sequence analyses indicate that the hybridomas isolated from each response arose from only a few precursor B cells. All the mAbs generated from the infected and GXM-TT conjugate-immunized mice utilize the same VH7183 family member: JH2/JH4, v kappa 5.1, and J kappa 1; mAbs generated by different B cells had complementarity-determining region 3's (CDR3s) composed of seven amino acids with a common sequence motif. Thus, the molecular analysis of these anticryptococcal mAb-producing hybridomas indicated that the response to both cryptococcal infection and conjugate immunization was oligoclonal and highly restricted with regard to immunoglobulin gene utilization. The GXM-TT conjugate primarily stimulated isotype switching and clonal proliferation, and did not result in hybridomas expressing additional immunoglobulin repertoires. The mAbs from both responses had a number of replacement mutations at the 5' end of CDR2 that appear to be the result of antigen-driven selection. Somatic mutation also resulted in altered epitope specificity for one mAb, 13F1. Passive administration of representative mAbs from different clones generated in response to the GXM-TT conjugate prolonged survival of lethally infected mice.

An insertion-deletion event in murine immunoglobulin kappa gene resembles mutations at heavy-chain disease loci

The analysis of spontaneous somatic mutants gives insights into the regulation of gene expression. Human heavy-chain disease (HCD) is a monoclonal lymphoproliferative disorder characterized by the presence of truncated immunoglobulin (Ig) heavy chains without associated light chains. To better understand the molecular mechanisms leading to the loss of light-chain production, we have examined a murine cell line model of heavy-chain disease. R15, a spontaneous mutant of the IgA, kappa-producing myeloma cell line W3129, produces heavy chain but no light chain. The variant delta 15 derived from R15 resembles human HCD in that it secretes a shortened heavy chain with no associated light chain. Cloning and analysis of the R15 kappa light-chain gene revealed that a 358-nucleotide insertion of unknown origin replaced 22 bases of the wild-type leader-variable region (L-V) intron (IVS). Although this genomic change left the light-chain exons and known regulatory elements intact, it altered the mRNA processing pathway, yielding two alternative RNA products, neither of which encodes a functional protein. This mutant therefore provides new insights into how genomic changes can influence gene expression.

Analysis of the interaction between an alpha (1----6)dextran-specific mouse hybridoma antibody and dextran B512 by affinity electrophoresis

Carbohydrates are common environmental antigens. As dextran B512 is composed of a repeating structure of simple antigenic determinants, it is widely used to study the immunochemical properties of immunoglobulins. Two-dimensional affinity electrophoresis patterns of a mouse monoclonal antidextran antibody (35.8.2H; IgG1, BALB/c) were produced to obtain insights into the microheterogeneity of the monoclonal antibody. The monoclonal antibody was separated into about six spots which had an identical affinity to dextran B512, but differed in their isoelectric points (pI). In addition, the pH dependence of the binding affinity of this antidextran to dextran B512 was examined. By comparing affinities obtained by affinity electrophoresis between weakly basic (pH 9.5) and weakly acidic (pH 3.8) discontinuous buffer systems, the latter showed an affinity about 500 times lower than the former. The change in the affinity was investigated with a continuous pH gradient by an affinity titration curve and was seen to change markedly at about pH 6. This suggests that the histidine at residue 34 in the light-chain CDR1 is largely responsible for the dextran binding.

The mouse antibody response to infection with Cryptococcus neoformans: VH and VL usage in polysaccharide binding antibodies

Cryptococcus neoformans is a ubiquitous fungus that can cause serious infections in humans. The fungus has a polysaccharide (C. neoformans capsular polysaccharide; CNPS) capsule that contributes to its pathogenicity and can elicit an antibody response. Nevertheless, only 4 of 60 BALB/c mice chronically infected with C. neoformans had a detectable increase in serum anti-CNPS. The sera of three responder mice contained both IgM and IgG anti-CNPS antibody, and the titers of lambda and kappa anti-CNPS antibody were approximately equal. Eight IgM and one IgG3 monoclonal antibodies (mAbs) were generated from the spleen of one responder mouse, and one IgA was generated from the spleen of another mouse. Seven of the IgMs, the IgG3, and the IgA mAb had lambda light chains and were specific for serotype D CNPS. Molecular analysis confirmed that this was a highly restricted antibody response. All of the D-specific antibodies used VH441, JH3, and either V lambda 2/J lambda 2 or V lambda 1/J lambda 1, and all had the same heavy chain CDR3 amino acid sequence, even though there were differences in the nucleotide sequence of the N/D segment. One IgM mAb reacted with both serotype A and D CNPS, and this mAb used different VH and JH genetic elements and had kappa light chains. All the anti-CNPS mAbs used J proximal VH gene elements that have previously been shown to bind dextran and other polysaccharides. Sequence and Southern blot analysis indicate that the serotype-D CNPS-specific mAbs arose from only a few precursor B cells.

The influence of T cells on the immunoglobulin repertoire and the affinity maturation of the immune response against dextran B512 in C57BL/6 mice

A collection of hybridomas from C57BL/6 mice producing antibodies to dextran B512 was analysed and found to reflect the immune response in vivo with regard to immunoglobulin class expression, T cell dependency and antibody affinity. IgM-, IgG-3, and IgG-2b, and IgA-producing hybridomas were found. IgG3-producing hybridomas were obtained from nude mice, indicating T cell independent IgG3 synthesis. All monoclonal antibodies were of kappa light chain. A major anti-dextran idiotype was expressed in many monoclonals. Secondary immune responses to dextran were also suppressed at the hybridoma cell level. However, hybridomas from secondary responses produced antibodies expressing the major idiotype, suggesting that anti-idiotype mediated suppression was not responsible for the reduced secondary response. Most monoclonals belonged to the VHJ558 family, but the IgG3-producing hybridomas showed a preferential use of genes from the VHX24 family. All monoclonals were directed against internal structures of the dextran molecule. The affinity for dextran of the IgG antibodies produced in secondary immune responses was drastically increased, even when the mice were immunized with thymus-independent forms of dextran, indicating that T helper cells need not be involved in affinity maturation of the immune response.

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.

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 subsites of monoclonal anti-dextran IgA W3129

Synthetic deoxyfluoro derivatives of methyl alpha-D-glucopyranoside, as well as methyl alpha-glycosides of isomalto-oligosaccharides, some having fluorine substituted for hydroxyl groups at selected positions, have been evaluated for their binding with a myeloma monoclonal IgA known to bind only to an oligosaccharide sequence at the nonreducing end of alpha-(1----6)-linked D-glucopyranans (dextrans). The results are compatible with the antibody's possessing one subsite of high affinity for its D-glucosyl group, the remaining three subsites having low affinities for their respective D-glucosyl residues. The high-affinity antibody-subsite occurs at the interior end of the sequence of four subsites, appears to be relatively accessible, and binds the (terminal) nonreducing D-glucosyl group of the oligosaccharidic determinant using two, and possibly three, hydroxyl groups in hydrogen bonding.

Functional immunoglobulin light chain genes are replaced by ongoing rearrangements of germline V kappa genes to downstream J kappa segment in a murine B cell line

A murine B cell lymphoma (38C13) was subjected to immunoselection with mAbs directed against the idiotypic determinants of its cell surface Ig. Variants emerged with altered Ig receptors containing identical heavy chains but different light chains. The functional light chain genes in these variants were composed of V kappa segments drawn from the V kappa Ox-1 family, which had replaced the V kappa gene expressed by the parental tumor by rearranging to downstream J kappa segments. Rearrangement at the kappa locus continued to occur spontaneously, giving rise to secondary and tertiary variants at a rate of 1.9 x 10(-4) per cell per generation. Variants were isolated that had ceased production of surface Ig but went on to rearrange again and to become surface Ig+. The Ig- state may be an intermediate step providing a stimulus for continued rearrangement. This process provides an additional mechanism for generating diversity within B cell clones and expands the use of the available repertoire of Ig genes.

Mouse Vk gene classification by nucleic acid sequence similarity

Analyses of immunoglobulin (Ig) variable (V) region gene usage in the immune response, estimates of V gene germline complexity, and other nucleic acid hybridization-based studies depend on the extent to which such genes are related (i.e., sequence similarity) and their organization in gene families. While mouse Igh heavy chain V region (VH) gene families are relatively well-established, a corresponding systematic classification of Igk light chain V region (Vk) genes has not been reported. The present analysis, in the course of which we reviewed the known extent of the Vk germline gene repertoire and Vk gene usage in a variety of responses to foreign and self antigens, provides a classification of mouse Vk genes in gene families composed of members with greater than 80% overall nucleic acid sequence similarity. This classification differed in several aspects from that of VH genes: only some Vk gene families were as clearly separated (by greater than 25% sequence dissimilarity) as typical VH gene families; most Vk gene families were closely related and, in several instances, members from different families were very similar (greater than 80%) over large sequence portions; frequently, classification by nucleic acid sequence similarity diverged from existing classifications based on amino-terminal protein sequence similarity. Our data have implications for Vk gene analyses by nucleic acid hybridization and describe potentially important differences in sequence organization between VH and Vk genes.

Model-building study of the combining sites of two antibodies to alpha (1----6)dextran

Models of the Fv portion (containing the variable regions of the heavy and light chains) of two monoclonal anti-alpha (1----6)dextran antibodies, W3129 and 19.1.2, were constructed from amino acid sequences and the known three-dimensional structures of the Fv portions of McPC603 and J539. The modeled combining site of W3129 has a protrusion on one side, formed by the long complementarity-determining region 1 of the light chain and the long complementarity-determining region 3 of the heavy chain, and has a cavity accommodating a glucose moiety. The model of the 19.1.2 site is basically flat with a shallow groove that can accommodate several internal glucose units. These results support the earlier conclusions, from ligand binding data, that W3129 has a cavity-type site, involving the terminal nonreducing glucose residue (endbinder), whereas 19.1.2 has a groove-type site.