Immunochemical studies of mouse monoclonal antibodies to dextran B1355S--II. Combining site specificity, sequence, idiotype and affinity

Affinity electrophoresis and its applications to studies of immune response

Affinity electrophoresis (AEP) is a useful technique for separation of biomolecules such as plasma proteins, enzymes, nucleic acids, lectins, receptors, and extracellular matrix proteins by specific interactions with their ligands in electric fields and for the determination of dissociation constants for those interactions. Two-dimensional affinity electrophoresis (2-D AEP), which was newly developed by a combination of isoelectric focusing with AEP, has been used for studies on immune response to haptens. Antihapten antibodies, which were induced by immunization of a mouse with the hapten-conjugated bovine serum albumin, were separated by 2-D AEP into a large number of groups of IgG spots with a few microliters of antiserum. Each group of spots showed an identical affinity for the hapten but different isoelectric points as in the case of monoclonal antibodies specific to the hapten. This enabled us to study the diversification and affinity maturation of antihapten antibodies in the course of immunization of a single mouse. Furthermore, effects of a carrier and a hapten array on the production of antihapten antibodies and the cause of charge heterogeneity of monoclonal antibodies were also examined to understand the molecular basis of the immune response in vivo.

Stimulation of the same B-cell population by thymus-independent dextran and by thymus-dependent oligosaccharide-carrier

The immune response of adult BALB/c mice against the bacterial antigen dextran B1355S (Dex) is well characterized as thymus independent (TI type 2) and Igha linked. The antisera consist of mainly IgM/lambda antibodies directed against the alpha(1-->3) glucosidic linkage. This study describes the immune response against the alpha(1-->3) linkage in the thymus dependent form (TD), i.e. tetra- or heptasaccharides (N4 or N7) of glucose as hapten coupled to chicken serum albumin (CSA) as carrier. Whereas athymic BALB/c-nu/nu mice did not respond to the TD antigens N4-CSA and N7-CSA, euthymic BALB/c showed high anti-Dex antibody titres of IgM and, after 2 degrees immunization, a class switch to IgG (mainly IgG1) isotypes with lambda light chains. The hapten N4 inhibited Dex-binding of M104E or of antisera from Dex or N4-CSA or N7-CSA immunized mice at 1.7-10 x 10(-4)M. The idiotype composition of these antibodies resembled those after Dex immunization. We conclude that the same Dex-specific precursor B cells have been stimulated by either form of antigen. The ontogenic development of a Dex-specific response could not be accelerated by the aid of T cells, even of adult origin. It seems, therefore, that the maturation of antigen specific B cells is the limiting step in ontogeny.

Reaction of germinal centers in the T-cell-independent response to the bacterial polysaccharide alpha(1-->6)dextran

Primary immunization of BALB/c mice with alpha(1-->6)dextran (DEX), a native bacterial polysaccharide, induces an unexpected pattern of splenic B-cell responses. After a peak of antibody-secreting B-cell response at day 4, deposition of dextran-anti-dextran immune complexes, as revealed by staining with both dextran and antibodies to dextran, occurs and persists in splenic follicles until at least the fourth week after immunization. Antigen-specific B cells appear and proliferate in such follicles, leading by day 11 to development of DEX-specific germinal centers as characterized by the presence of distinct regions of DEX+ peanut agglutinin-positive (PNA+) cells. At this time, fluorescence-activated cell sorter analysis also reveals the appearance of a distinct population of DEX+ PNA+ splenic B cells. In contrast, DEX+ PNA- cells, characterized by intense cytoplasmic staining, are present outside of splenic follicles, peak at day 4 to day 5, and persist until at least day 28. The frequency of these cells correlates with DEX-specific antibody-secreting cells, as detected by the ELISA-spot assay. Thus, in addition to the expected plasma cellular response, the typical T-cell-independent type II antigen, DEX, surprisingly also elicits the formation of antigen-specific germinal centers. These observations raise fundamental questions about the roles of germinal centers in T-cell-independent immune responses.

Molecular characterization of a cross-reactive idiotope on human immunoglobulins utilizing the VH4-21 gene segment

The anti-idiotypic (anti-Id) antibody (Ab) 9G4 binds a cross-reactive idiotope (CRI) present in a select group of human autoantibodies. This Id has been localized to the portion of immunoglobulin (Ig) heavy (H) chains encoded by the VH4-21 gene segment, a member of the human VH4 family. This gene segment is utilized by essentially all cold agglutinin (CA) Abs with I/i specificity isolated from patients with CA disease stemming from chronic lymphoproliferative disorders. In this study, mutational analysis of a CA has been used to determine the structural basis for 9G4 binding to Abs utilizing the VH4-21 gene segment. Recombinant CA H chain mutants were produced and their 9G4 reactivity determined. Mutants were generated by exchanging VH4-21 sequences in the FR1, CDR1, and CDR2 with corresponding sequences from a closely related gene segment V71-2, a VH4 family member that is associated neither with Abs having CA activity nor with Abs that react with 9G4. The results indicate that the motif AVY at amino acid positions 23-25 in FR1 defines the 9G4 idiotope. Reaction of these recombinant Abs with a polyclonal rabbit anti-CA antiserum absorbed to render it specific for a CA CRI also maps predominantly to FR1. These findings indicate that the solvent-exposed FR1 plays an important role in eliciting an immune response to Igs.

Neonatal complement depletion results in predominant expression of a myeloma M 104E private idiotope among anti-dextran antibodies

Myeloma M 104E (IgM, lambda 1) with specificity for the alpha(1----3) glucosidic linkage of dextran B 1355 S (Dex) carries two idiotopes (Id) as defined by isogenic anti-idiotype mAb. The public Id is not influenced by two amino acid replacements in CDR 2 nor by an alternative D region sequence. It is shared by all or nearly all humoral antibodies in the primary immune response against Dex of mice carrying haplotype Igha. The private Id-5' appears to depend on the integrity of the VH germ-line sequence and on the particular M 104E D region sequence. It is present on a highly fluctuating but usually small fraction of primary anti-Dex antibody. We report here that this situation is changed when mice are treated with Cobra venom anti-complement factor (CVF), after birth and thereby were deprived of complement for the first two weeks of life. When immunized with Dex as adults the majority of anti-Dex Ab carried the M 104E Id-5. Thus, humoral antibody in CVF-treated animals resembled the Ly-1+ anti-Dex precursor B cell population in the peritoneal cavity, while anti-Dex Ab in animals not treated with CVF more closely corresponded to the Ly-1- precursor B cell pool in spleen (H.-P. Lehmann and G. Lehle, Eur. J. Immunol. 1991. 21: 1201).

A myeloma M 104E private idiotope is represented predominantly among anti-dextran, peritoneal cavity Ly-1+ precursor B cells

Public and private idiotopes (Id) had been defined in the BALB/c anti-dextran B1355 fraction S (Dex) response by means of syngeneic monoclonal anti-M 104E Id antibodies. Most of the primary anti-Dex antibodies shared the public Id-1 while the private Id-5 constituted a comparatively low, but highly variable proportion of humoral anti-Dex antibodies of individual mice. In the present work we have analyzed by limiting dilution the expression of these two Id by anti-Dex B cell precursors from the spleen and peritoneal cavity of BALB/c mice. Testing spleen cells we found about 65% of anti-Dex precursors to be Id-1+ and only a minority to be Id-5+. Treatment with anti-Ly-1 and complement was without any effect on anti-Dex precursors from spleen. Anti-Dex B cell precursors among peritoneal cavity lymphocytes differed from those found in the spleen in two ways. First, on average, 50% of them were Id-5+; second, about 80% carried the Ly-1 marker. Both markers are, therefore, expressed on at least 30% of anti-Dex B cell precursors from the peritoneal cavity but rarely on anti-Dex precursors from the spleen.

Specificity and variable region cDNA sequence of an isogeneic monoclonal antiidiotype to an anti-alpha(1----6)dextran

We have characterized a monoclonal isogeneic antiidiotype, IdB5.7, from a BALB/c mouse immunized with the anti-alpha(1----6)dextran C57BL/6 45.21.1. It defined a hapten-inhibitable idiotope expressed on four of the 2 myeloma and 37 hybridoma anti-alpha(1----6)dextrans tested. Sequence comparison of Id+ and Id- anti-alpha(1----6)dextrans suggested that two extra amino acids at VH 100A and 100B and different residues at VH 101 abolish the expression of the idiotope in the Id- anti-alpha(1----6)dextrans. Sequence analysis of the VH of IdB5.7 showed a CDR1 longer than usual and a D segment in CDR3 formed by the fusion of two D minigenes. The IdB5.7 V kappa uses the V kappa 1 germline gene K5.1 with a few substitutions. The D-D fusion in VH CDR3 is a feature which has been reported in several other antiidiotypic antibodies.

Characterization of lambda class antibodies from the BALB/c memory response to a [glucosyl-alpha(1----3) glucosyl]-protein conjugate

Both dextran B-1355 and nigerosyl-KLH (N-KLH) contain alpha(1----3) diglucosyl moieties and both induce lambda class serum antibodies which recognize the alpha(1----3) linkage. However, as shown here, some of the antibodies induced by the thymus-dependent form, N-KLH, have a distinct fine specificity. It is known that B-1355 induces antibodies which resemble the anti-alpha(1----3) myeloma proteins MOPC 104E and J558. The new fine specificity which does not resemble such antibodies is found in the serum of N-KLH primed mice challenged with N-KLH. The two fine specificity types are distinguished by their sensitivity to inhibition by nigerose in ELISA using B-1355 or N-BSA as bound antigen. Twelve hybridomas were produced from N-KLH primed mice boosted with either N-KLH or B-1355. Six of the 12 had the new fine specificity; only two out of the 12 expressed the IdX determinant commonly associated with the B-1355 response and neither of these possessed the new reactivity pattern. Comparative inhibition with the disaccharide nigerose and the tetrasaccharide nigerantetraose indicated that 11 out of the 12 hybridoma proteins have combining sites larger than a disaccharide. Southern and Northern blot analysis of eight hybridomas revealed that all expressed VH genes from the J558 family, but that at least two distinct VH genes from this family were used. The data support the hypothesis that immunization with an alpha(1----3) diglucosyl-protein conjugate alters the composition of the B cell pool capable of producing lambda class antibodies from that ordinarily observed following immunization with B-1355.

Interaction between phage G13 and its oligosaccharide receptor studied by equilibrium dialysis

The reversible binding of phage G13, a phi X174-like single-strand DNA phage, to a 3H-labelled nonasaccharide from the lipopolysaccharide of its natural host Escherichia coli C was studied with equilibrium dialysis. The binding constant (Ka) was determined to 1.3 x 10(7) M-1 in Scatchard and Lineweaver-Burk plots. Approximately one saccharide bound per G13 phage particle which suggests that only one of the 12 spikes in each G13 virion was engaged in the phage/receptor saccharide interaction. Equilibrium dialysis inhibition experiments with saccharides from lipopolysaccharides of an isogenic series of Salmonella typhimurium mutants showed that hepta- and pentasaccharides from two G13-sensitive bacteria, i.e., with efficiencies of plating of 0.1-1.0 compared to E. coli C, were efficient inhibitors with Ka-values greater than or equal to 1.2 x 10(7) M-1. The octa- and hexasaccharides from two G13 resistant strains, with efficiency of plating less than or equal to x 10(-4), were either greater than 1000-fold or greater than 15-fold less efficient as inhibitors with Ka-values less than or equal to 8.8 x 10(5) M-1. The results show that phage G13 binds in a specific and reversible way to penta-, hepta-, and nonasaccharides from G13 sensitive bacteria with the specificity residing in the hexose and heptose region of the core lipopolysaccharide.

Immunochemical analyses of C57BL/6J monoclonal anti-alpha (1----3) dextran antibodies

Twelve C57BL/6J anti-B-1355S monoclonal antibodies (five IgM lambda and seven IgM kappa) were characterized immunochemically by binding and inhibition ELISA. All 12 were negative for the expression of the cross-reactive idiotype (IdX) of BALB/c mice, as expected from previous work; no kappa IdX+ antibodies have been reported and IdX- lambda class antibodies were observed in B-1355-Con A induced immune sera [Geckeler W., Blomberg B., dePreval D. and Cohn M. (1977) Cold Spring Harb. Symp. quant. Biol. 41, 743-748]. The antibodies studied bind to B-1355 coated plates and this binding is inhibited by B-1355 but not by dextrans B-512 (F) or B-742S; the latter two have no linear alpha (1----3; 1) linkages. The nomenclature of Jeanes is used [Jeanes A. (1986) Molec. Immun. 23, 999-1028]; alpha (1----3; 1) refers to glucosyl diose residues linked alpha (1----3) linearly. In the case of B-1355 these linear stretches alternate with alpha (1, 6) linkages and are non-contiguous; alpha (1----3; b) refers to the linkage at a branching residue, e.g., a 1,3,6 linked moiety. The IgM kappa class antibodies are not inhibited by nigerose or nigerantetraose, suggesting that they have binding site sizes which are unusually large for B-1355 specific antibodies. The five IgM lambda antibodies are inhibited identically by equimolar amounts of nigerose and nigerantetraose, suggesting that their binding sites accommodate a disaccharide epitope. These antibodies are also inhibited by the alpha (1----6), alpha (1----4) triose, panose. The kappa class antibodies do not bind to alpha (1----3)-diglucosyl-(nigerosyl; N)-BSA. Four of the five lambda class antibodies show weak binding to N-BSA, while the fifth binds N-BSA better but less well than MOPC 104E (the BALB/c myeloma protein). All 12 antibodies are unique when compared to BALB/c antibodies derived from B-1355 immunization. The primary response of 15 C57BL/6J mice to B-1355 was re-assessed for kappa and lambda class antibody contribution. A patchy lambda class response was observed suggesting that previous lambda class responses may have been overlooked.

Estimation of the avidity of antibodies in polyclonal antisera against Streptococcus pneumoniae type 3 by inhibition ELISA

The reliability of the determination of antibody avidity in polyclonal sera by indirect sandwich ELISA was studied. Binding of IgM and IgG (sub)classes in unpurified serum to Streptococcus pneumoniae type 3 capsular polysaccharide, which was coated onto ELISA plates, was inhibited with different inhibitors. The inhibitor concn at which 50% inhibition of antibody binding to the ELISA coat was achieved, was used as a measure for antibody avidity. As this 50% inhibition value is dependent upon the dilution of the serum and thus upon the initial amount of free antibody, it is necessary to define (a narrow range of) final ELISA absorbance values to which the dilutions of non-inhibited sera have to be adjusted. The shapes of the serum dilution curves have a good correlation with the numerical 50% inhibition values of the antibody avidity. The inhibition ELISA is suitable to compare the avidity values of the different antibody isotypes, but two remarks should be made: (1) antibody heterogeneity should be considered to influence the results and prevent the accurate measurement of absolute numerical avidity values. Because in the ELISA system merely antibody "activity" is measured, comparison of the efficacy of vaccines by means of the 50% inhibition (avidity) value of various antibody (sub)classes can still be performed in a reliable way; (2) results of the determination of the 50% inhibition values of the different antibody (sub)classes showed them to be dependent on the molecular ratio between antibody (sub)class levels. More aspects of the determination should be taken into account, like shapes of simple dilution curves, influences of various inhibitor concns in the diluent and whole (extended) inhibition curves.

The use of defined peptides in characterizing idiotypes

The structural correlates of idiotypes have been sought in several antibody systems. The cumulative results suggest that the hypervariable regions (or complementarity-determining regions) of the heavy and light chains are the structural basis of idiotypes. However, in most cases, it is exceedingly difficult to associate a particular idiotypic determinant with a specific amino acid sequence. Recently, synthetic peptides were used to induce antibodies specific for predefined determinants in intact proteins. These findings led us and others to use synthetic peptides corresponding to the hypervariable regions/complementarity-determining regions to induce anti-idiotypes. These novel anti-idiotypic antibodies are easy to prepare, and are ideal reagents for structural and genetic studies of antibody responses.

Immunochemical and related interactions with dextrans reviewed in terms of improved structural information

Structurally diverse dextrans from Leuconostoc mesenteroides and related bacteria have been used extensively in fundamental immunochemical studies such as induction and characterization of anti-dextran antibodies, as well as in studies of their interaction with pneumococcal antisera, normal bovine serum, concanavalin A, dextran-binding myeloma immunoglobulins and hybridoma antibodies. The inherent lack of specificity of structural data obtained by POSA and general lack of insight into other limitations of these analyses has often led to inaccurate and superficial interpretations. Proper interpretation of past and future studies necessitates pointing out previous inadequacies of dextran structural data and detailing more recently acquired structural information on the dextrans. Unambiguous terminology has been achieved by a new system of linkage symbols that includes the designation of structural positions, such as (1----3; l)- and (1----3; b) as linear-chain and branch-point positions, respectively. Results of immunological studies are reviewed. Improved interpretations and correlations are made on the basis of structural data from MSA and several other techniques which have become available on the dextrans.