Structural analysis of monoclonal anti-arsonate antibodies: idiotypic specificities are determined by the heavy chain

Recognition by anti-Fab antibodies in rheumatoid arthritis of structure(s) widely distributed on human Fab molecules

Anti-Fab antibodies (aFABA) of restricted clonality and acidic spectrotypes were isolated from the sera of patients with rheumatoid arthritis (RA). These aFABA reacted with multiple populations of pooled human Fab molecules, which had been charge separated by chromatofocusing techniques (CF), indicating that the structures recognized by these aFABA were present on a polyclonal population of Fab molecules. The structures were also widely distributed among the Fab repertoires of normal individuals, as well as individual autologous and heterologous RA patients. Thus, the aFABA did not appear to recognize highly restricted epitope(s), i.e. a private idiotope, limited in its expression to RA individuals. The determinants of the Fab molecules recognized by affinity purified aFABA could be defined by linear and/or conformational structures, depending upon the individual from which the aFABA were isolated. Additionally, some of the affinity purified aFABA also reacted with Fc fragments, suggesting the presence of epibody-like autoantibodies in this population. Lastly, size analysis of the circulating IgG4 aFABA complexes indicated that these autoantibodies were not complexed with intact IgG, but rather with a molecule of 40-60 kDa, further suggesting the potential for these autoantibodies to react with multiple antigens.

Molecular characterization of the A/J J558 family of heavy chain variable region gene segments

The nucleotide sequences of the coding as well as the flanking regions of 11 A/J J558 heavy chain variable region (VH) gene segments are presented. Among these J558 VH segments was the unrearranged germline VH gene segment recruited in the predominant A strain-specific anti-arsonate response. Three other VH gene segments that are greater than 92% related to the p-azophenylarsenate (Ars) A VH gene segment were also isolated. Detailed analysis of the nucleotide sequences of these as well as the remaining seven J558 VH gene segments reveal that the J558 VH gene family is composed of distinct, but related, J558 VH subfamilies. Deletion mapping analyses were used to position the Ars A VH gene segment proximally with respect to the DH-JH clusters within the J558 VH gene family and distally with respect to its own J558 subfamily. The documentation of J558 VH subfamilies is discussed in the context of J558 VH family evolution and diversification.

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.

Idiotype-anti-idiotype interactions of VHIX-coded anti-progesterone and anti-arsonate antibodies. Comparison of passive haemagglutination and radioimmunoassays

The reactivity and specificity of polyclonal and monoclonal anti-idiotypic antibodies raised against monoclonal anti-progesterone and anti-arsonate antibodies have been studied by solid phase radioimmunoassay (RIA) with immobilized idiotype and by passive haemagglutination with idiotype-coupled red cells. The sensitivity of the two methods was comparable, though some cross-reactions were only detected by RIA. Passive haemagglutination was found to be especially suitable in screening for monoclonal anti-idiotypes in hybridoma supernatants and ascites, and had advantages over RIA in detection of syngeneic anti-idiotypes. Demonstration of binding site-associated idiotopes was possible by haemagglutination inhibition. RIA and haemagglutination were used to investigate the idiotypic relationships between BALB/c antiprogesterone and anti-arsonate monoclonal antibodies which share heavy chains encoded by VHIX variable region genes.

Somatic diversification of the chicken immunoglobulin light chain gene is limited to the rearranged variable gene segment

Previous studies have shown that the chicken lambda immunoglobulin light chain gene undergoes a single rearrangement that results in functional VJ joining of the unique variable (V lambda 1) and joining (J lambda) coding regions. The immunologic repertoire of lambda genes is created through extensive sequence diversification within the rearranged locus during B cell development in the bursa of Fabricius. This sequence diversification was detected only at the rearranged V lambda 1 segment and not within the 5' leader sequence, the J lambda segment, or the unrearranged V lambda 1 segment. The selective diversification of the rearranged V lambda 1 segment was associated with unique DNAase I-hypersensitive sites on the rearranged allele. While probes for V lambda 1 sequences detect multiple homologous V lambda segments, probes for both the 5' leader and J lambda segments fail to detect homologous sequences. Taken together, these results suggest that a highly selective process, possibly gene conversion, operates during B cell ontogeny to generate diversity within the lambda gene.

Clustering of extensive somatic mutations in the variable region of an immunoglobulin heavy chain gene from a human B cell lymphoma

Following treatment of a human B cell lymphoma with an anti-idiotype antibody, a subpopulation of tumor cells remained that had lost the tumor-specific heavy chain idiotypic determinant. Nucleotide sequence analyses of eight independent heavy chain variable region isolates showed extensive point mutations, so that no two sequences were identical. Comparison of pretreatment and posttreatment sequences implicated an amino acid in CDR2 as being involved in the idiotypic determinant. Apparently the malignant B cells escaped the therapeutic effects of the anti-idiotype antibody through an ongoing process of somatic mutation in their immunoglobulin genes. Non-random clustering of amino acid replacements in CDR2 suggested that growth of the tumor may have been influenced by endogenous selective forces interacting with the tumor cell-surface immunoglobulin.

Complete amino acid sequence of heavy chain variable regions derived from two monoclonal anti-p-azophenylarsonate antibodies of BALB/c mice expressing the major cross-reactive idiotype of the A/J strain

The primary structure of A/J anti-p-azophenylarsonate (anti-Ars) antibodies expressing the major A-strain cross-reactive idiotype (CRIA) has provided important insights into issues of antibody diversity and the molecular basis of idiotypy in this important model system. Until recently, this idiotype was thought to be rarely, if ever, expressed in BALB/c mice. Indeed, it has been reported that BALB/c mice lack the heavy chain variable segment (VH) gene that is utilized by the entire family of anti-Ars antibodies expressing the A/J CRI. Recently, however, it has been possible to elicit CRIA+, Ars binding antibodies in the BALB/c strain by immunizing first with anti-CRI and then with antigen. Such BALB/c, CRIA+ anti-Ars antibodies can be induced occasionally with antigen alone. VH region amino acid sequences are described for two CRIA+ hybridoma products derived from BALB/c mice. While remarkably similar to each other, their VH segments (1-98) differ from the VH segments of A/J CRIA+, anti-Ars antibodies in over 40 positions. Rather than the usual JH2 gene segment used by most A/J CRIA+ anti-Ars antibodies, one BALB/c CRIA+ hybridoma utilizes a JH1 gene segment, while the other uses a JH4. However, the D segments of both of the BALB/c antibodies are remarkably homologous to the D segments of several A/J CRIA+ antibodies sequenced previously, as are the amino terminal amino acid sequences of their light chains. These data imply that BALB/c mice express the A/J CRIA by producing antibodies with very similar, if not identical, light chain and heavy chain D segments, but in the context of different VH and JH gene segments than their A/J counterparts. The results document that molecules that share serologic specificities can have vastly different primary structures.

Structural and serological analysis of cross-reactive idiotypes: comparison of heavy and light chain families of anti-arsonate antibodies

The amino acid sequences of VH and VL regions of 16 cross-reactive idiotype-positive (CRI+) and ten CRI-negative (CRI-) monoclonal anti-arsonate antibodies from a range of laboratories were compared. Analysis of the data demonstrates the existence of several pairs of hybridoma proteins (within CRI+ and CRI- families) which have identical or very similar sequences for VH and VL. This strongly suggests the existence of at least 4 germ-line genes in A/J mice coding for CRI+VH, CRI+VL, CRI-VH and CRI-VL regions. The CRI+ family, however, consists of VH structures which represent either (1) germ-line sequences, (2) VHVL variants with a few substitutions, or (3) VHVL variants with extensive substitutions. The latter two consist of antibodies which have lost either the CRI or arsonate binding capacities. The CRI- family consists of two very different groups. The first group appears to be the product of CRI- VHVL germ-line genes and their variants. The second group contains antibodies coded by CRI+ germ-line genes but which, due to somatic diversification, become CRI-. Comparison of VHVL of all anti-arsonate antibodies clearly indicates that light chain selection by the heavy chain is a non-random process. Also, there appears to be a parallel diversification of VH and VL. Comparative data on H and L chain structures and serological evidence obtained by three monoclonal antiidiotypic antibodies indicates that formation of the original cross-reactive idiotypic determinant(s) requires an equal contribution for both H and L chains; moreover, CRI consists of a single (or few) idiotopes.

A serologic marker for the Ars-C family of anti-arsonate antibodies

Attempts are being made to define, at the serologic, structural and genetic levels, the anti-arsonate repertoire. We previously identified three families of anti-arsonate antibodies based on the amino acid sequence of the heavy chain V regions. The present report establishes the serologic correlates of one of these families, the Ars-C family. The determinants defining this family are expressed by anti-Ar molecules displaying the A/J minor idiotype or the BALB/c major idiotype; these determinants are also expressed on molecules of different specificity, notably by the DNP-binding myelomas, MOPC-460 and MOPC-315. All strains tested employed the Ars-C family in the response to arsonate.

Monoclonal antibodies reveal the structural basis of antibody diversity

Hybridoma technology has made it possible to introduce into continuous culture normal antibody-forming cells and to obtain large amounts of the immunoglobulin produced by each of these cells. Examination of the structure of a number of monoclonal antibodies that react with a single antigen has provided new information on the structural basis of the specificity and affinity of antibodies. Comparisons of families of monoclonal antibodies derived from a single germ line gene revealed the importance of somatic mutation in generating antibody diversity. Monoclonal antibodies that react with variable regions of other monoclonals allow the further dissection and modulation of the immune response. Finally, the continued somatic instability of immunoglobulin genes in cultured antibody-forming cells makes it possible to determine the rate of somatic mutation and to generate mutant monoclonal antibodies that may be more effective serological reagents.

Amino acid sequence diversity within the family of antibodies bearing the major antiarsonate cross-reactive idiotype of the A strain mouse

VH region amino acid sequences are described for five A/J anti-p-azophenylarsonate (anti-Ars) hybridoma antibodies for which the VL region sequences have previously been determined, thus completing the V domain sequences of these molecules. These antibodies all belong to the family designated Ars-A which bears the major anti-arsonate cross-reactive idiotype (CRI) of the A strain mouse. However, they differ in the degree to which they express the CRI in standard competition radioimmunoassays. Although the sequences are closely related, all are different from each other. Replacements are distributed throughout the VH region and occur in positions of the chain encoded by all three gene segments, VH, DH, and JH. It is likely that somatic diversification processes play a dominant role in producing the sequence variability in each of these segments. The number of differences from the sequence encoded by the germline is smallest for antibodies that express the CRI most strongly, suggesting that somatic diversification is responsible for loss of the CRI in members of the Ars-A antibody family. There is an unusual degree of clustering of differences in both CDR2 and CDR3 and many of the substitutions are located in "hot spots" of variation. The large number of differences between the chains prohibits the unambiguous identification of positions at which alterations play a major role in reducing the expression of the CRI. However, the data suggest that the loss of the CRI is associated with a definable repertoire of somatic changes at a restricted number of highly variable sites.