Structure and genetic control of V kappa-1 light chains

Only Selected Light Chains Combine with a Given Heavy Chain to Confer Specificity for a Model Glycopeptide Antigen

The M and N human blood group glycopeptide Ags are carried on RBCs by glycophorin A. Previous results suggested that the murine humoral immune response against the N, but not the M, Ag is restricted. In addition, these results suggested that particular highly homologous heavy chains might be able to combine promiscuously with various light chains to yield anti-N specificity. To examine this, the current study used Fab phage methodology to couple an array of light chains, obtained from cDNA libraries isolated from immunized mice, to single Fd obtained from N61, N92, and 425/2B hybridomas. Interestingly, for the chimeric Fab to retain M or N specificity, the new light chains needed to belong to the same Vk gene family as the light chain from the parental, hybridoma-derived mAb. In some cases the new light chains modified the Fab affinity and fine specificity. For example, library-derived light chains coupled with the N92 Fd yielded chimeric Fab with increased affinity. In particular, the affinity of these univalent chimeric Fab for the N Ag was equivalent to that of the bivalent parental IgG mAb. Taken together, these results demonstrate that particular structures formed by the light chain V region are required to cooperate with a particular heavy chain V region to create a functional binding site for these glycopeptide Ags. They also demonstrate a lack of heavy chain promiscuity in the formation of murine anti-M and anti-N Abs.

Regeneration of antidigoxin binding activity in an antibody by changes surrounding the original binding defect

A panel of antibodies which differ in their L chain structures and which bind to structurally defined haptens, would be useful in investigating L chain structure and function. In a previous study, chain recombinant antibody CR24 (26-10 H, 45-20 lambda) was produced by hybridoma-hybridoma fusion. Although both parental antibodies bound digoxin with high affinity, CR24 lacked detectable digoxin-binding activity. Hybridoma CR24 was subsequently fused with H chain-loss hybridomas in order to produce a panel of antibodies composed of 26-10 H chains and 26-10 "like" L chains. Two antibodies produced were CR260 which demonstrated digoxin-binding activity and CR256 which did not. CR260 and CR256 expressed only one amino acid difference (Pro to Leu at L-96). This difference resulted in the CR256 binding defect. In this report, two new antidigoxin antibodies are described. One, SR2E7, contained the Pro to Leu (L-96) defect, but still bound digoxin. Binding affinities and binding specificity patterns, as well as complete VL DNA sequence and corresponding protein sequence of the new digoxin binding antibody L chains (SR2E7 and SR1C7) are presented. Both kappa L chains are highly homologous to the 26-10 kappa L chain as well as the BALB/c germline gene K5.1. These results suggest that antibodies which are initially defective in binding activity can be cured by changing specific amino acids involved in determining the binding-site structure. Molecular modelling studies of the binding-site region were completed to address L chain structural changes induced by specific amino acid substitutions.

Primary structure of the murine monoclonal IgG2a antibody mAb735 against alpha(2-8) polysialic acid. 1) Amino-acid sequence of the light (L-) chain, kappa-isotype

Here we report the complete amino-acid sequence of the anti-alpha(2-8)polysialic acid antibody mAb735 light chain. The sequence was determined after digestion of the reduced and carboxymethylated L-chain with trypsin, SV-8 proteinase, and Asp-N proteinase, isolation of the generated peptides by RP-HPLC and characterization of these fragments by sequence analysis, amino-acid analysis and/or plasma desorption mass spectrometry. According to Kabat et al. the variable region belongs to the V kappa-II subgroup, whilst according to Hum et al. it belongs to the V kappa-1B subgroup. With the exception of proline at position 46, the sequence from position 1 to 95 is identical to the translated DNA sequence of a V kappa-germline gene segment previously reported.

The role of germline gene expression and somatic mutation in the generation of autoantibodies to DNA

Several distinctive features of anti-DNA autoantibodies have been identified by a detailed analysis of the available heavy and light chain sequences. They include unique VH gene segments that are not normally expressed in antibodies to external antigens, somatic mutations which may serve to change the antigenic specificity as well as to increase affinity, a less stringent choice of light chains, and a unique basic peptide in the heavy chain CDR3. It is proposed that in the majority of cases, the regulatory mechanism of self-tolerance in the healthy animal operates via VH gene expression to prevent the synthesis of potentially high affinity anti-DNA autoantibodies.

Structural correlates of a regulatory idiotope

The A48RI expressed on the ABPC48 and UPC10 beta 2----6 fructosan-binding myeloma proteins is a conformational antigenic determinant encoded by V genes deriving from the VHX24 and VK10 families. In the preimmune repertoire the clones using VHX24 genes rarely express A48 idiotopes, clearly demonstrating that this regulatory idiotope is a minor or silent idiotope. Furthermore, these same VHX24-utilizing preimmune clones are frequently associated with the VK1 gene family which is highly represented in the neonatal and adult repertoires. The clonal expansion occurring subsequent to neonatal injection of minute amounts of anti-Id antibodies leads to selective expansion of A48Id+ clones associated with class switching. Few somatic mutations are observed in preimmune clones, or in those expanded by anti-Id antibodies. The fact that few mutations were observed in the IgG1 clones obtained from animals injected with anti-A48Id antibodies after birth indicates that, in contrast to antigen-induced class-switching, the anti-Id-induced switching is not associated with a highly active mutational process. In contrast to the preimmune clones, or those expanded by anti-Id (in the absence of antigenic stimulation) in which VHX24 is associated with VK regions deriving from various gene families, the clones expanded by anti-Id and fructan resemble A48 by using VHX24 and VK10 genes. Few apparent mutations were also observed in these IgM or IgG3 clones expressing A48 idiotopes. The A48 RI can be expressed on clones producing antibodies specific for various self and foreign antigens, and encoded by V genes deriving from various VH and VK families. These results indicate that key contacting residues bearing A48 conformational idiotypic determinants can be made up by various VH-VK combinations. A comparison of the VH and VL sequences of A48 RI+ mAbs showed that many of the observed somatic mutations could be correlated to decreased IDA10 binding. This comparison allowed identification of specific idiotope-determining regions of VH and VK which could represent contacting residues with anti-idiotypic antibodies. The contributions of these regions to the expression of the A48Id was tested by generating a transfectoma antibody expressing the rearranged VHJ558 gene of the ricin 45 hybridoma and the VK10-Ars-a gene of the 36-65 hybridoma. This transfectoma antibody expresses the idiotope recognized by IDA10 and confirms the conformational nature of this idiotope. There are three amino acid residues shared by VHX24 and VHJ558 antibodies expressing the A48 RI which are important for its expression.(ABSTRACT TRUNCATED AT 400 WORDS)

Variable region sequences of murine IgM anti-IgG monoclonal autoantibodies (rheumatoid factors). II. Comparison of hybridomas derived by lipopolysaccharide stimulation and secondary protein immunization

We have obtained the complete variable region mRNA sequences of 11 LPS-derived and 14 secondary immunization-derived monoclonal IgM anti-IgG antibodies (rheumatoid factors, RFs). A comparative analysis of these sequences showed that monoclonal RFs derived after polyclonal activation are structurally very similar to RFs derived after secondary protein immunization. This study was undertaken to evaluate the potential relationship between two previously described phenomena: (a) during a secondary response to a protein antigen, RF is produced in quantities that equal or exceed the immunogen-specific antibody; and (b) the frequency of B cells that make RF after polyclonal activation is quite high; 3-10%. It has been unclear whether LPS-stimulated cells that produce IgM anti-IgG that is detected by an in vitro assay are related to the cells that produce RF after in vivo stimulation. The similarity of the antigen receptors found in the two types of RF, however, suggests that most or all of the RF-producing B cells detected after LPS stimulation would also be stimulated during the secondary immune response. Thus, the presence of relatively large number of B cells that can make RF after nonspecific stimulation provides an explanation for the magnitude of RF production accompanying the secondary immune response.

Monoclonal BALB/c anti-progesterone antibodies use family IX variable region heavy chain genes

Variable region nucleotide sequences and respective translated amino acid sequences for three heavy chains (DB3, 11/32 and 10/8) and two light chains (DB3 and 11/32) of monoclonal mouse IgG1 anti-progesterone antibodies have been determined by primer extension mRNA sequencing. The three VH regions exhibit the same rarely observed VH IX gene family and have greater than 88% homology between them. Two associated light chain sequences are 95% homologous and belong to the V kappa I group. The N-terminal twenty two amino acids of the kappa light chain of the third antibody 10/8 have been determined by automated protein sequencing and are identical to those of 11/32. Thus, these three monoclonal anti-progesterones derived from separate fusions all use VHIX-V kappa 1 gene combinations.

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.