Diversity at the variable-joining region boundary of lambda light chains has a pronounced effect on immunoglobulin ligand-binding activity

Structural, functional, and physiological properties of anti-(4-hydroxy-3-nitrophenyl)acetyl antibodies during the course of affinity maturation

Structural and functional analyses of antibodies in the affinity maturation pathway can help us understand the molecular mechanisms of protein recognition. Using one of the haptens, (4-hydroxy-3-nitrophenyl)acetyl (NP), various monoclonal antibodies have been obtained, either at the early or late stage of immunization. The variable regions of monoclonal antibodies and their site-directed mutants can also be obtained as single-chain Fv (scFv) antibodies. The change in antigen-binding affinity and avidity of matured-type antibodies from germline-type antibodies could be evaluated based on binding kinetics and thermodynamics, proposing the antigen recognition mode. Crystal structures of a germline-type antibody, N1G9, and a matured-type antibody, C6, in complex with NP were determined, revealing different antigen-binding mode at atomic resolution. Notably, the Tyr to Gly mutation at the 95th residue of the heavy chain is critical for changing the configuration of complementarity determining region 3, which is involved in antigen binding. Furthermore, thermal stability analyses of scFv antibodies have revealed trade-off between antigen-binding affinity and thermal stability in the antigen-unbound state. To increase affinity, the stability of the variable region may be decreased, possibly due to protein architecture. The high stability of germline-type antibodies and the low stability of matured-type antibodies, which increase upon antigen binding, can be explained by the stability of antibodies required at the respective stages of immunization.

Molecular evolution of catalytic antibodies in autoimmune mice

Catalytic Abs (catAbs) preferentially evolved in autoimmune MRL/MPJ-lpr/lpr (MRL/lpr) mice upon immunization with the phosphonate transition-state analogue (TSA), but this did not happen in normal BALB/c mice. The majority of the catAbs from MRL/lpr mice were from several independent clones of the same family. Most of them had a lysine at position 95 in the heavy chain (H95), which is at the junctional region. This residue, which interacts with the phosphonate moiety of the TSA and presumably is involved in the catalytic activity, was not changed even after expansive evolution following multiple mutations. By contrast, the majority that arose from BALB/c mice were the non-catAbs, which were quite different in the sequence from the catAbs from MRL/lpr mice, but they were clonally related to one another, so most of them were originated from a single clone. In the MRL/lpr mice, the catalytic subsets that existed in the initial repertoire were effectively captured by the phosphonyl oxygens in the TSA by interacting with the lysine at H95. In the BALB/c mice, however, another noncatalytic subset with only the binding capability directed to a moiety other than the phosphonate moiety was alternatively evolved, because of the lowest abundance or elimination of the catalytic subsets.

Somatic hypermutation in mouse lambda chains

The frequency and distribution of somatic hypermutation in immunoglobulin genes and the effect of amino acid substitution on the structure/function of antibodies were studied using hybridomas that secrete anti-(4-hydroxy-3-nitrophenyl)acetyl (NP) monoclonal antibodies bearing lambda 1 chains. A high frequency of mutation was observed in V-J exons and J-C introns of rearranged and active lambda 1 chains but not in the 5'-non-coding regions of these chains. Since a similar distribution was observed in inactive lambda 2 chain genes, 5'-non-coding regions containing a promoter were considered to be protected from mutation in view of their apparent importance. Using transgenic mice carrying chloramphenicol acetyl transferase transgenes driven by the VH promoter and heavy-chain intron enhancer, it was also revealed that these cis-acting elements are important in the induction of somatic hypermutation and are capable of inducing mutation even in non-immunoglobulin genes. Affinity of anti-NP Abs to NP increased with time after immunization to approximately 8,000-fold (affinity maturation); however, fine specificity, such as heteroclicity, remained unchanged. Memory B cells, which are responsible for affinity maturation, were analyzed in terms of the mutation from Trp to Leu at position 33, a change known to raise affinity about 10-fold and considered to be a memory B-cell marker. These cells were found predominantly in the early stage (2-3-week) hybridomas but rarely in late stage (> 12-week) ones, suggesting that a dynamic change in the memory B-cell population occurs during the immunization process.

The role of VL gene structural determinants in the fine specificity of anti-DNA antibodies

To investigate the structural contribution of the light chain of anti-DNA antibodies to fine specificity, the VKappa genes of two monoclonal anti-DNA antibodies, termed H241 and H102, were cloned and sequenced. H102 and H241 are independently derived from MRL-lpr/lpr mice and differ in their fine specificity: H241 binds dsDNA and normal glomeruli in vitro and deposits in the kidney in vivo, whereas H102 binds only ssDNA and does not deposit in the kidney. Both are encoded by nearly identical VH genes but different N and D regions. Our previous results have demonstrated that the VH gene for H102 and H241 encodes eight other anti-DNA antibodies that also differed in fine specificity. This suggested that the gene product encoded by the VH 102/241 gene, may have intrinsic affinity for DNA, but is unlikely to determine fine specificity or nephritogenicity. In the present study we examined whether the VKappa gene might account for the difference in nephritogenicity. The complete nucleotide and deduced amino acid sequence of VK 102 and VK241 revealed that they are very dissimilar to each other (< 60% homology). VK 241 defined a new member of the VKappa gene family and was moderately homologous to two other VK genes encoding anti-DNA antibodies and to one VK gene encoding an anti-histone antibody all from lupus strains of mice. In addition, sequence diversity in the VK CDR1 region and position 96 of the CDR3 region was observed that may be of significance in determining fine specificity. VK 102 was highly homologous to two other VKappa genes, VKs17.2 and VK C8.5, both encoding anti-DNA antibodies and members of the VK20 gene family. It was striking that all three members of the VK 20 gene family code for DNA reactivity. This suggests that certain VKappa genes may also be used to repeatedly code for anti-DNA reactivity.

The human antibody V region repertoire to the type B capsular polysaccharide of Haemophilus influenzae

The V region repertoire of the human antibody response to the type b capsular polysaccharide of Haemophilus influenzae (Hib-PS) is being defined at the molecular level using antibodies purified from serum of immunized adults. The VH of this response is restricted to the VHIII subgroup while the VL can be divided into two categories. The most common VL, expressed in > 90% of adults and usually constituting the majority of a subjects anti-Hib-PS antibody response, is restricted to the product of a single V kappa II gene known as A2 that probably lacks somatic mutations. The product of the A2 gene is invariably joined to one of several J kappa products by an inserted arginine at the V kappa-J kappa junction. In contrast to the restricted nature of the dominant VL clonotype, the second category of VL constitutes a heterogeneous group of at least seven different VL gene products that often contain somatic mutations and generally exhibit crossreactivity with a related polysaccharide from E. coli. Elucidation of anti-Hib-PS V regions at the molecular level will permit examination of structure-function relationships among these clinically important antibodies and should make the V region repertoire to Hib-PS a useful model for studying human V gene responses.

T cell receptor delta diversity of freshly isolated T lymphocytes in rheumatoid synovitis

In some patients with rheumatoid synovitis the distribution of V delta gene families used by freshly isolated T lymphocytes from the synovial fluid and peripheral blood is different: peripheral blood T lymphocytes preferentially use the V delta 2 gene segment, whereas the majority of synovial fluid T lymphocytes use the V delta 1. The antigenic diversity of T cell receptor gamma/delta is mainly dependent upon base sequences in the V-J junction. In the present study we investigated whether the synovial fluid T lymphocytes expressing the V delta 1 gene segment were derived from a polyclonal or monoclonal expansion. The sequences encoding the V-J junctions of 11 cDNA clones derived from the synovium of two patients with chronic arthritis were determined. Our data demonstrate that the V delta 1 cDNA clones have different V-J junction sequences. This indicates that the V delta 1-expressing T cells found in the synovial compartment are polyclonally expanded.

Computer analysis of mutations that affect antibody specificity

The mouse hybridoma cell line 40-150 secretes antibodies with high affinity toward the cardiac glycosides digoxin and digitoxin. A spontaneous mutant, 40-150 A2.4, produces an antibody which carries a single residue mutation, Ser----Arg, in its heavy chain (H94) and has an altered specificity. A second-order mutant, 40-150 A2.4 P.10, produces two antibody molecules, one the same as 40-150 A2.4, the other lacking two residues at the N-terminus of its H chain, and having a specificity profile approaching that of 40-150 antibody. The N-terminus and the position H94 are distant from the antigen-binding site of the antibody; thus, the structural basis of the specificity changes was not immediately clear. Approximate structures of the 40-150 antibody and its mutants were constructed in the computer, based on atomic coordinates of the homologous mouse antibody McPC 603. Using the program CONGEN, the torsional space of the polypeptide backbone and side chains around position H94 was uniformly sampled, and the lowest energy conformations were analyzed in detail. The results indicate that when Arg-H94 is substituted for Ser, Arg-H94 can hydrogen bond to side chains of Asp-H101, Arg-L46, and Asp-L55. This results in a change in the surface of the combining site which may account for the affinity changes. Deletion of the two N-terminal residues increases solvent accessibility of Arg-H94. The solvation may cause a hydrogen bond between Arg-H94 and Asp-H101 to be lost, restoring the structure to one similar to that of 40-150.

Diversity in T-cell receptor gamma gene usage in intestinal epithelium

The intraepithelial cells of the murine small intestine include a significant number of CD3+ T cells that use T-cell receptor gamma genes rather than T-cell receptor beta genes. As with other sites of T-cell receptor gamma expression, combinatorial diversity is limited, but there is junctional diversity, and this, together with the specific variable region gamma gene segments used, distinguishes gamma gene expression in the gut epithelium from that in cells derived from the dermal epithelium. The restriction of productive gamma gene expression largely to one V-J-C (V, variable; J, joining; C, constant) gene combination may result from nonproductive joining of other V-J combinations and from productively rearranged genes rendered nonfunctional by incorrect splicing.

T-cell receptor delta-chain diversity in peripheral lymphocytes

A small percentage (approximately 5%) of the cells in the adult thymus expresses a heterodimeric receptor, gamma delta, that exhibits extensive clonal diversity. The specificity and function of these cells are unclear. Furthermore, it is not known if their role in the immune system is primarily one that operates within the thymus during the selection of the T-cell repertoire or if they function primarily in an antigen-recognition capacity in the peripheral lymphoid system. To examine if gamma delta+ T cells in the periphery are as diverse as those in the thymus, we used the polymerase chain reaction to amplify delta-chain transcripts from polyclonal populations of thymic and splenic lymphocytes (the latter were derived from allogeneic mixed lymphocyte cultures). The nucleotide sequences of delta chains from the spleen, like those from the thymus, were all different. Most of the diversity was present in the region between the variable (V) and joining (J) gene segments and was generated through the use of the two known diversity (D) elements, D delta 1 and D delta 2, and by the addition or deletion of bases at the V delta D delta 1, D delta 1D delta 2, and D delta 2J delta junctions. The extensive gamma delta repertoire among peripheral cells suggests that they have the potential to recognize an array of ligands that could be as diverse as those recognized by alpha beta+ cells. The amplification strategy described here can be used to analyze rapidly the diversity exhibited by any of the members of the immunoglobulin-like gene families that undergo rearrangement.

Two M315 idiotopes defined by isologous monoclonal antibodies: one depends on germline and the other on mutated murine lambda 2 light chain sequences

We have previously reported that T helper cells of BALB/c mice recognize the unique mutated sequence Phe94, Arg95, Asn96 of the lambda 2 L chain of isologous (BALB/c) myeloma protein 315. Here we study two Id (Id-315.1.4 and Id-315.TH) of the DNP-Lys binding M315 defined by two monoclonal isologous anti-Id Ab (Ab 2-1.4 and Ab 2-TH). Both Id were (1) totally expressed by Fv-315, but not by free unpaired V domains, (2) specifically dependent on VH-315, since lambda 2-315 recombined with four other H chains did not express the Id, (3) related to the hapten-binding site because their expression was blocked by the haptens DNP-Lys and DNP-Gly, and (4) topographically related because Ab 2-1.4 and Ab 2-TH competed with each other for binding to M315. The contribution of lambda chain V regions was studied with the aid of reconstituted Ig molecules of H-315 paired with lambda 1, lambda 2, and lambda 3 L chains. Id-315.TH was expressed equally well by reconstituted Ig containing three different lambda 2 chains (lambda 2-5-7, lambda 2-T952, and lambda 2-315), but its expression was profoundly reduced when H-315 was associated with lambda 3-SAPC15 or lambda 1-J558 L chains; it therefore depended upon amino acids encoded by germline lambda 2 genes. By contrast, Id-315.1.4 was only restored by the lambda 2-315 chain paired with H-315. Since lambda 2-5-7 and lambda 2-T952 differ from lambda 2-315 at positions 38, 94, 95, 96, and 98 or 99, respectively, Id-315.1.4 probably requires the unique mutated amino acids Phe94, Arg95, Asn96 of lambda 2-315. This resembles the effects on Id expression of previously reported unique amino acids of the D region. We failed to confirm that hyperimmunization of BALB/c mice with Ab 2-1.4 cross-linked to KLH induced M315-like Ab. The results are discussed in terms of the contribution of the third hypervariable loop of lambda chains to Id and the immunogenicity of isologous Ig.

Identity of the V kappa 10-Ars-A gene segments of the A/J and BALB/c strains

To characterize the light chain gene segments involved in the murine immune response to keyhole limpet hemocyanin p-azophenylarsonate (Ars), we have determined the amino acid and/or nucleotide sequences of several anti-arsonate antibodies of the Ars-A family in the A/J, C.AL-20, and BALB/c strains. These structures have been compared to certain BALB/c anti-phenyloxazolone and anti-levan antibodies previously sequenced and to the A/J V kappa 10-Ars-A genomic sequence (where V kappa = kappa chain variable). These primary structural studies were complemented by Southern filter hybridization analyses utilizing V kappa and kappa chain joining (J kappa) molecular probes. We found a surprising uniformity of structure among these antibody light chains derived from different murine strains. Thus, in contrast to the heavy chain variable (Vh) regions of the Ars-A antibody family where the BALB/c strain lacks the VH gene segment utilized in the A/J Ars-A response, the light chain variable region gene segments at the V kappa 10-Ars-A locus appear to be identical between the two strains.

The T lymphocyte response to syngeneic lambda 2 light chain idiotopes. Significance of individual amino acids revealed by variant lambda 2 chains and idiotope-mimicking chemically synthesized peptides

In the present study we have investigated the structure of the helper T cell (Th)-defined idiotope (Id) of myeloma protein 315 lambda 2 light chain (lambda 2(315] in BALB/c (H-2d) mice which carry a high-responder immune response gene for this Id. Three peptides were synthesized which spanned the third hypervariable region (HV3) of lambda 2(315): peptides 88-99, 94-108 and 91-108. Only peptide 91-108 was capable of eliciting carrier-specific Th that recognized M315 or free lambda 2(315). These Th did not recognize lambda 2(5-7) chain which differs from lambda 2(315) at 4 positions in this region; these are Tyr94, Ser95, Thr96, Tyr98 for lambda 2(5-7) and Phe94, Arg95, Asn96, Phe98 for lambda 2(315). Immunization with peptide analogues revealed that substitution of Tyr for Phe94 was compatible with Id-lambda 2(315) mimicry, but substitution of Ser for Arg95 or Thr for Asn96 destroyed the Th-recognized Id. Furthermore, Th primed with lambda 2(5-7) chain did not cross-react with lambda 2T952; these lambda 2 chains only differ from each other at positions 98 and 99 at the V lambda 2-J lambda 2 junction. The data indicate that individual amino acids of short peptide segments are critical for Th-recognized Id of the lambda 2 HV3 loop and V lambda 2-J lambda 2 junction. Furthermore, the immunogenicity of a small peptide suggests that the carrier (lambda 2)-specific Th recognize Id that have been processed by antigen-presenting cells (APC). This implies the existence of two categories of "internal images" of foreign or of self antigens: (a) serologically defined and (b) T lymphocyte defined. We propose that as a rule, Id processing by APC, including B cells, destroys the first and reveals the second category. The possible physiological function of these Id-specific T cells in network interactions with B cells is discussed.

Repertoire of murine lambda-positive variable domains: polyclonal induction of lambda isotypes and their associated pattern of antibody specificities

The diversity of lambda variable (V lambda) domains is extremely restricted when compared to those of VH and V kappa. In addition, each V lambda domain is determined by the C lambda domain. For these reasons, the lambda system is an excellent model for the study of the associated VH region repertoire. The study of V lambda domain diversity has been limited by the small contribution (approximately 5%) of lambda-bearing proteins to the total Ig pool. We now show that treatment of BALB/c mice with rabbit anti-lambda 1 antibodies coupled to lipopolysaccharide induces a production of polyclonal lambda 1 light chain-bearing Ig whereas, conversely, treatment with rabbit anti-lambda 2 antibodies induces a production of polyclonal lambda 2 + lambda 3 light chain-bearing Ig. The antigenic specificities of these two distinct lambda populations were then studied using B1355 dextran, (4-hydroxy-3-nitrophenyl)acetyl (NP) and 2,4-dinitrophenyl (DNP) as antigens. The anti-alpha(1-3)dextran antibody specificity was found to be mediated exclusively by antibodies bearing the lambda 1 isotype whereas the anti-NP and anti-DNP antibody specificities are mediated by both the lambda 1 and lambda 2 + lambda 3 isotypes. In addition, various mouse strains with the VHa or VHb allotypic haplotype and the rlo lambda 1 or r+ lambda 1 phenotype were treated with rabbit anti-lambda 1 antibodies. The lambda 1 anti-NP and anti-DNP antibody specificities were similar in all strains whereas the lambda 1 anti-alpha(1-3)dextran specificity was linked to the presence of the VHa allotypic haplotype. The mouse strains with the rlo lambda 1 or r+ lambda 1 phenotype did not differ in terms of their patterns of lambda 1 antibody specificities.

Secondary, tertiary, and quaternary structure of T-cell-specific immunoglobulin-like polypeptide chains

To explore the possibility that the difference in antigen recognition between B and T cells derives from a structural difference in their respective antigen-specific receptors (immunoglobulins on B cells and immunoglobulin-like molecules on T cells), we compared the extracellular segments of the T-cell receptor alpha, beta, and gamma polypeptide chains and the N-terminal segment of the T-cell T8 (Lyt-2) antigen chain with the corresponding regions of immunoglobulins whose three-dimensional structures are known. The results indicate that the four T-cell polypeptide chains are organized into immunoglobulin-like domains consisting of multistranded antiparallel beta-sheet bilayers. Invariant amino acid side chains that are conserved in diverse immunoglobulins, including those that mediate domain-domain interactions and form a constant scaffold for antibody binding sites, are also conserved in the chains encoded by the T-cell receptor genes and in the N-terminal domain of T8 (Lyt-2). It appears that the binding sites of the antigen-specific T-cell alpha beta-chain receptors and of antibodies are very similar in their overall dimensions and geometry: a T-cell alpha beta receptor molecule probably has an antigen-specific binding site that is fundamentally no different than the conventional binding site of an antibody.

Heavy chain variable region. Multiple gene segments encode anti-4-(hydroxy-3-nitro-phenyl)acetyl idiotypic antibodies

The hapten (4-hydroxy-3-nitrophenyl)acetyl (NP), when conjugated to carrier proteins, elicits a characteristic idiotypic response (NPb) in C57BL/6 mice. The response can be divided serologically into two distinct NPb-positive groups of antibodies. The first group consists of four crossreacting subgroups (I-IV), the second of two subgroups (V, VI). Some antibodies of subgroups I and II have been shown to express the unmutated heavy chain variable region (VH) germline gene 186.2. Antibodies of subgroups V and VI crossreact extensively with the NPa-positive antibodies of BALB/c mice. We sequenced heavy chain complementary DNA from eight hybridomas producing anti-NP antibodies. Six of these belong to subgroups V and VI, and two were NPa-positive hybridomas of BALB/c origin. All sequences were homologous to each other, and differed by approximately 80 basepairs from the 186.2 C57BL/6 germline VH gene. From our sequence and Southern blot analyses we suggest: (a) the NPb idiotypic response is the product of several VH germline genes, (b) some of these genes are very homologous to the gene coding for the BALB/c NPa idiotype, and might represent the C57BL/6 allelic forms of this gene, (c) the diversity regions of NPb and NPa-positive antibodies are diverse in length and amino acid composition, except for the first residue, which is always tyrosine, (d) all four heavy chain joining region gene segments are expressed without mutation. We discuss our data in terms of diversity in the germline VH gene repertoire, as well as diversity created by gene segment-joining events and somatic mutation.

Limited diversity of the rearranged T-cell gamma gene

The immunoglobulin-related, T-cell specific gamma gene is rearranged in a wide variety of murine T lymphocytes. We detected gamma-gene transcripts in all cloned cytotoxic T lymphocytes examined but in only 1 of 11 T-helper cell lines or hybridomas. Although in cytotoxic T cells, the rearranged gamma gene seems to have been assembled from the same germ-line variable and joining gene segments, the transcribed gene exhibited distinct sequence diversity near the junction between these segments.