The expressed lysozyme-specific B cell repertoire. I. Heterogeneity in the monoclonal anti-hen egg white lysozyme specificity repertoire, and its difference from the in situ repertoire

A structurally based approach to determine HLA compatibility at the humoral immune level

HLAMatchmaker is a structurally based matching program. Each HLA antigen is viewed as a string of epitopes represented by short sequences (triplets) involving polymorphic amino acid residues in antibody-accessible positions. HLAMatchmaker determines which triplets are different between donor and recipient, and this algorithm is clinically useful in determining HLA mismatch acceptability. Triplets provide however an incomplete description of the HLA epitope repertoire and expanded criteria must be used including longer sequences and polymorphic residues in discontinuous positions. Such criteria should consider the structural basis of antibody-antigen interactions including contact areas and binding energy, the essence of antigenicity. This report describes the development of a structurally defined HLA epitope repertoire based on stereochemical modeling of crystallized complexes of antibodies and different protein antigens. This analysis considered also data in the literature about contributions of amino acid residues to antigen-antibody binding energy. The results have led to the concept that HLA antigens like other antigenic proteins have structural epitopes consisting of 15-22 residues that constitute the binding face with alloantibody. Each structural epitope has a functional epitope of about 2-5 residues that dominate the strength and specificity of binding with antibody. The remaining residues of a structural epitope provide supplementary interactions that increase the stability of the antigen-antibody complex. Each functional epitope has one or more non-self residues and the term "eplet" is used to describe polymorphic HLA residues within 3.0-3.5 A of a given sequence position on the molecular surface. Many eplets represent short linear sequences identical to those referred to as triplets but others have residues in discontinuous sequence positions that cluster together on the molecular surface. Serologically defined HLA determinants correspond well to eplets. The eplet version of HLAMatchmaker represents therefore a more complete repertoire of structurally defined HLA epitopes and provides a more detailed assessment of HLA compatibility.

Mapping epitopes and antigenicity by site-directed masking

Here we describe a method for mapping the binding of antibodies to the surface of a folded antigen. We first created a panel of mutant antigens (beta-lactamase) in which single surface-exposed residues were mutated to cysteine. We then chemically tethered the cysteine residues to a solid phase, thereby masking a surface patch centered on each cysteine residue and blocking the binding of antibodies to this region of the surface. By these means we mapped the epitopes of several mAbs directed to beta-lactamase. Furthermore, by depleting samples of polyclonal antisera to the masked antigens and measuring the binding of each depleted sample of antisera to unmasked antigen, we mapped the antigenicity of 23 different epitopes. After immunization of mice and rabbits with beta-lactamase in Freund's adjuvant, we found that the antisera reacted with both native and denatured antigen and that the antibody response was mainly directed to an exposed and flexible loop region of the native antigen. By contrast, after immunization in PBS, we found that the antisera reacted only weakly with denatured antigen and that the antibody response was more evenly distributed over the antigenic surface. We suggest that denatured antigen (created during emulsification in Freund's adjuvant) elicits antibodies that bind mainly to the flexible regions of the native protein and that this explains the correlation between antigenicity and backbone flexibility. Denaturation of antigen during vaccination or natural infections would therefore be expected to focus the antibody response to the flexible loops.

IL-4 promotes Stat6-dependent survival of autoreactive B cells in vivo without inducing autoantibody production

Persistent cross-linking of hen egg lysozyme (HEL)-specific B cell membrane Ig (mIg) in double transgenic mice that express soluble HEL as a self Ag (HEL-Ig mice) decreases B cell mIgM expression, responsiveness, and life span. Because in vitro treatment with IL-4 inhibits T cell apoptosis through a Stat6-independent mechanism, increases mIg expression, and suppresses activation-induced B cell death, we studied IL-4 effects on B cell mIg expression, survival, and Ab secretion in Stat6-sufficient and deficient HEL-Ig mice. IL-4 treatment nearly normalized B cell number and greatly increased the percentage of mature B cells in HEL-Ig mice, but failed to normalize mIgM expression or spontaneous LPS-induced IgM secretion. IL-4 effects on B cell survival and maturation were CD4(+) T cell independent, but Stat6 dependent, and did not involve receptor editing. IL-4 had to be present while B cells were generated to have a detectable effect on autoreactive B cell survival; however, the survival of B cells generated in the presence of IL-4 was substantially increased even after IL-4 was withdrawn. These observations suggest that: 1) activation-induced B cell death and anergy are independent processes; 2) B cells that survive to maturity develop increased resistance to Ag-induced deletion; and 3) IL-4 promotes B and T cell survival through different mechanisms.

Protein kinase Cdelta controls self-antigen-induced B-cell tolerance

Interaction of a B cell expressing self-specific B-cell antigen receptor (BCR) with an auto-antigen results in either clonal deletion or functional inactivation. Both of these processes lead to B-cell tolerance and are essential for the prevention of auto-immune diseases. Whereas clonal deletion results in the death of developing autoreactive B cells, functional inactivation of self-reactive B lymphocytes leads to complex changes in the phenotype of peripheral B cells, described collectively as anergy. Here we demonstrate that deficiency in protein kinase Cdelta (PKC-delta) prevents B-cell tolerance, and allows maturation and terminal differentiation of self-reactive B cells in the presence of the tolerizing antigen. The importance of PKC-delta in B-cell tolerance is further underscored by the appearance of autoreactive anti-DNA and anti-nuclear antibodies in the serum of PKC-delta-deficient mice. As deficiency of PKC-delta does not affect BCR-mediated B-cell activation in vitro and in vivo, our data suggest a selective and essential role of PKC-delta in tolerogenic, but not immunogenic, B-cell responses.

Prolonged antigen persistence within nonterminal late endocytic compartments of antigen-specific B lymphocytes

Although Ag-specific B lymphocytes can process Ag and express peptide-class II complexes as little as 1 h after Ag exposure, it requires 3-5 days for the immune system to develop a population of Ag-specific effector CD4 T lymphocytes to interact with these complexes. Presently, it is unclear how B cells maintain the expression of cell surface antigenic peptide-class II complexes until effector CD4 T lymphocytes become available. Therefore, we investigated B cell receptor (BCR)-mediated Ag processing and presentation by normal B lymphocytes to determine whether these cells have a mechanism to prolong the cell surface expression of peptide-class II complexes derived from the processing of cognate AG: Interestingly, after transit of early endocytic compartments, internalized Ag-BCR complexes are delivered to nonterminal late endosomes where they persist for a prolonged period of time. In contrast, Ags internalized via fluid phase endocytosis are rapidly delivered to terminal lysosomes and degraded. Moreover, persisting Ag-BCR complexes within nonterminal late endosomes exhibit a higher degree of colocalization with the class II chaperone HLA-DM/H2-M than with the HLA-DM/H2-M regulator HLA-DO/H2-O. Finally, B cells harboring persistent Ag-BCR complexes exhibit prolonged cell surface expression of antigenic peptide-class II complexes. These results demonstrate that B lymphocytes possess a mechanism for prolonging the intracellular persistence of Ag-BCR complexes within nonterminal late endosomes and suggest that this intracellular Ag persistence allows for the prolonged cell surface expression of peptide-class II complexes derived from the processing of specific AG:

In vivo survival of autoreactive B cells: characterization of long-lived B cells

To determine the effects of chronic Ag stimulation on B cell survival and phenotype, we compared survival and surface markers of hen egg lysozyme (HEL)-specific B cells in Ig transgenic (Tgn) mice, which lack HEL, and in HEL-Ig transgenic mice, which express soluble HEL. Serum HEL levels were maximized in HEL-Ig Tgn mice by feeding them zinc, which activates the metallothionein promoter that regulates HEL expression. B cell age was characterized by expression of heat-stable Ag, and B220 and B cell survival was studied by evaluating changes in B cell number when lymphopoiesis was suppressed with anti-IL-7 mAb and by identifying newly generated B cells through 5-bromo-2'-deoxyuridine incorporation. Our observations show that the mean B cell life span is considerably reduced in HEL-Ig Tgn compared with Ig Tgn mice, but also demonstrate that some HEL-Ig Tgn B cells survive to maturity. Some of these surviving B cells have undergone receptor editing (substitution of an endogenous Ig light chain for the transgenic Ig light chain), so that their ability to bind HEL is decreased or absent. Surviving HEL-Ig Tgn B cells that retain HEL specificity express decreased mIgD and little or no mIgM. mIgD expression progressively decreases with increasing HEL-Ig Tgn B cell age. These observations suggest that self Ag-specific B cells can survive in the presence of soluble self Ag by down-regulating mIg expression, which should limit B cell signaling by Ag that might otherwise cause deletion of these cells.

Functional Characterization of the Somatic Hypermutation Process Leading to Antibody D1.3, a High Affinity Antibody Directed Against Lysozyme

The impact of somatic hypermutation on the affinity of Abs directed against protein Ags remains poorly understood. We chose as a model the secondary response Ab D1.3 directed against hen egg lysozyme. During the maturation process leading to this Ab, five replacement somatic mutations occurred. After reconstituting the germline Ab from which D1.3 originated, we assessed the energetic and kinetic importance of each of the somatic mutations, individually or combined, using the BIAcore apparatus. We found that the mutations induced an overall 60-fold improvement of affinity, principally due to a decrease in the kinetic rate of dissociation. We showed that their effects were additive and context independent; therefore, in the case of D1.3, the order in which somatic mutations were introduced and selected is unimportant. Interestingly, most of the affinity improvement was due to a single somatic mutation (Asn50→Tyr in VL), involving a residue that belongs to the functional interface between Ab D1.3 and lysozyme. This replacement could either establish new Van der Waals contacts between the Ab and the Ag or help stabilize the conformation of a closely situated crucial residue of the Ab paratope. The four other mutations played only a marginal part in affinity maturation; potential reasons for which these mutations were nevertheless selected are discussed.

Glycoprotein B of Aujeszky's disease virus: topographical epitope mapping and epitope-specific antibody response

A panel of 26 monoclonal antibodies (mAbs) against glycoprotein B (gB) of Aujeszky's disease (pseudorabies) virus (ADV), a glycoprotein complex consisting of three glycoproteins, gBa, gBb, and gBc, was produced by two research groups and was used for the topographical epitope mapping of gB. An epitope map was constructed in which the identified epitopes of gB were situated in 14 topologically distinct antigenic domains; ten antigenic domains represented by 22 mAbs were localized on gBc, while four antigenic domains represented by four mAbs resided on gBb of the gB complex. All the epitopes located on gBc appeared to be conformation-dependent, whereas all the epitopes on gBb were conformation-independent. The identified epitopes of gB were conserved among laboratory, vaccine and field ADV strains. Conformation-dependent epitopes were shown to contribute largely to the overall antibody response to gB in naturally infected swine and immunized mice. Moreover, it was found that most of the infected animals responded relatively weakly to the identified conformation-independent epitopes of gB, while a group of immunodominant epitopes that induced a strong antibody response was represented exclusively by conformation-dependent epitopes from different antigenic domains. The results clearly demonstrated that conformation-dependent epitopes of gBc play a crucial role in inducing the humoral immune response to gB of ADV during the natural infection of swine and immunization of mice. The application of mAbs of our panel as research and diagnostic tools is discussed.

Immunological characterisation of glycoprotein E of Aujeszky's disease virus

A panel of 14 monoclonal antibodies (MAbs) against glycoprotein E (gE) of Aujeszky's disease (pseudorabies) virus (ADV), which constitutes a representative sample of naturally occurring gE-specific antibodies in sera from infected animals, was produced and characterised. Eleven topologically distinct antigenic domains represented by one or more MAbs were identified on gE by using these MAbs and three additional gE-specific MAbs. Three of the MAbs available recognised conformation-independent epitopes on gE, while the other 14 MAbs bound to conformation-dependent epitopes. By using the recombinant protein encompassing the N-terminal part of gE, which was expressed in Escherichia coli, all the conformation-independent epitopes of gE were mapped within the first 125 amino-terminal amino acids of gE. The epitopes of gE were demonstrated to be conserved among gE-positive laboratory, field and vaccine ADV strains. Conformation-dependent epitopes were shown to contribute largely to the overall antibody response to gE in naturally infected swine and immunised mice. Most of the infected animals responded weakly to the identified conformation-independent epitopes of gE, while the group of immunodominant epitopes of gE was represented exclusively by conformation-dependent antigenic determinants from different antigenic domains. The results clearly demonstrated that conformation-dependent epitopes play a crucial role in inducing the humoral immune response to gE of ADV during the natural infection of swine and immunisation of mice. The application of MAbs of our panel as research and diagnostic tools is discussed.

The crystal structures of complexes formed between lysozyme and antibody fragments

Type c lysozymes, and hen egg lysozyme in particular, have been extensively used to study the immune response because of their strong immunogenicity, the availability of many natural variants to study cross-reactivity, and the possibility to correlate these results with the known three-dimensional structure of lysozymes from several species. To date, the structure of six different murine monoclonal anti-lysozyme antibodies has been studied as a complex between the Fab fragment and antigen. In some cases, the structure of the uncomplexed Fab is also available, giving detail at the atomic level of the changes which take place during the formation of the antibody-antigen complex. The bacterially-expressed Fv molecule, the simplest fragment of an immunoglobulin retaining an intact antigen-binding site, has been studied for three of the monoclonal anti-lysozyme antibodies. Recombinant Fv fragments have opened up the possibility of using site-directed mutagenesis to study the effect of amino acid changes at the antibody-antigen interface. The six monoclonal antibodies appear to recognize epitopes which are localised on three different regions of the lysozyme surface.

Molecular recognition of lysozyme by monoclonal antibodies

HEL was one of the first proteins to be mapped antigenically using mAb, and panels of mAb have been used as a measure of antigenicity in order to study regulation of the immune response and the apparent 'antigenic structure' of HEL. These studies have confirmed the multideterminant hypothesis derived from pAb. However, although the entire surface of HEL is potentially antigenic, the mature immune response appears to be dominated by three functionally nonoverlapping antigenic regions, defined operationally by antibody complementation assays. Recent structural studies have confirmed the existence of three distinct epitope clusters. Functional epitopes, defined by immunoassays, are generally only a subset of the structural epitope, the 14-17 amino acid residues which contact antibody in the X-ray structure of the complex. An even smaller subset of 'critical residues', the 'energetic' epitope, may predominate the interaction energetically. Antibody complex formation with HEL is enthalpically driven, and is accompanied by an unfavorable entropy change. Mutations of either antibody or antigen which lower affinity appear to do so primarily by increasing dissociation rates, and also appear to be accompanied by entropy/enthalpy compensation. The current availability of six structurally defined antibody-lysozyme complexes presents excellent opportunities for comparative studies in order to understand the structural bases of affinity, specificity, and thermodynamic properties, as well as the interrelationships of functional, structural, and energetic epitopes.

Induction of plasmacytomas secreting antigen-specific monoclonal antibodies with a retrovirus expressing v-abl and c-myc

ABL-MYC, a recombinant murine retrovirus that expresses v-abl and c-myc, rapidly induces transplantable mono- or oligoclonal plasmacytomas in BALB/c mice. To determine if the targets for transformation of this retrovirus are antigen-committed B lymphocytes and to explore this system as an alternative technique for producing antigen-specific monoclonal antibodies, plasmacytomas were induced in mice that had been immunized with two different types of immunogens, hen egg white lysozyme and sheep red blood cells. The majority of these plasmacytomas secreted immunogen-specific antibodies. Plasmacytomas induced in unimmunized mice did not react with hen egg white lysozyme or sheep red blood cells. The specific antibodies were comparable in concentration, specificity, and affinity to monoclonal antibodies obtained with conventional hybridoma technology, but, in addition to IgGs and IgMs, they included specific IgA antibodies, which are rare among splenic-derived hybridomas. Our results demonstrate that a principal target for ABL-MYC is an antigen-committed B lymphocyte. In addition this procedure provides an alternative method for the production of monoclonal antibodies, without a requirement for hetero-caryon formation by cell fusion techniques.

Evidence for idiotypic sharing between conventional and naturally activated B cells

In the primary immune response to hen egg-white lysozyme (HEL), approximately 50% of the primary anti-HEL antibody-forming cells (AFC) express IdXE, an idiotype absent from the secondary response. Spontaneous IgM enzyme-linked immunosorbent assay (ELISA)-AFC in spleen cells from naive A/J mice were analyzed for the occurrence of IdXE by use of two affinity-purified rabbit antisera, R213 and R8, each raised against a different primary IdXE+, anti-HEL mAb. Two ELISA-AFC assay methods were used: direct coating of immunoplates with R213 or development of IgM-producing ELISA-AFC with biotinylated R8. From ages 7 days until 6 months, 10-20% of spontaneous IgM AFC were found to be IdXE+. IdXE+ anti-HEL IgG1 monoclonal antibodies, 2F4 or 3C11 (100 micrograms/ml), completely inhibited binding of biotinylated R8 (0.5 micrograms/ml) to spontaneous IgM-AFC while IdXE-, anti-HEL IgG1, 5E11 and 2C7, showed no significant inhibition. Greater than 90% of IdXE+ spontaneous IgM-AFC were not HEL specific. We conclude that a dominant set of idiotopes found in a conventional antigen-driven immune response can also play a major role in the spontaneously activated B cell repertoire. Our data argue against a bifurcation of the immune system into a compartment of idiotypic network-related cells and an independent set of non-network cells subject to antigenic stimulation.

Application of a sol particle immunoassay to the determination of affinity constants of monoclonal antibodies

The affinity constants (Ka) of monoclonal antibodies (MAb) for binding to their corresponding antigens (Ag), unlabelled and in buffered solution were determined by the following procedure: 1. Incubation of MAb (fixed concentration) with Ag (concentration dilution series). 2. Rapid bound/free separation by adding immobilized second antibody, followed by centrifugation. 3. Determination of free Ag in the supernatant using a gold sol particle agglutination immunoassay (SPIA) in a microtitration plate format. 4. Calculations and interpretation were based on Scatchard and Sips plots. Ka values found by this procedure were found to be similar to those obtained by a radio-immunoassay (RIA) procedure. The present method avoids possible artefacts in Ka values introduced by the procedure or chemical modification due to labelling of MAb or Ag. It enables rapid, simultaneous screening of a considerable number of different MAbs under non-specialized (i.e. RIA) laboratory conditions.

Affinity of monoclonal antibodies. Interpretation of the positive cooperative nature of anti-hCG/hCG interactions

The interaction of some individual MAbs and human chorionic gonadotrophin (hCG) showed apparent positive cooperativity as observed by equilibrium binding studies. This form of cooperative interaction has now been further characterized. The main results were: (1) the apparent positive cooperativity was strongly dependent upon concentration and temperature; (2) the cooperativity was strongly reduced by using peptic F(ab')2 fragments of IgG and became undetectable when the MAb was replaced by the corresponding Fab fragment; (3) the molecular weight of the complex changed from 226 kDa to 450 kDa upon increasing the hCG/MAb ratio. From these and additional results it is hypothesized that the apparent positive cooperativity results from self (Fc-Fc) associations mediated or facilitated by prior antigen binding.

Inhibition of offspring response to HEL-CFA by administration of anti-HEL MAB to the mother is not related to the predominant idiotype, IdXE, or specificity of the MAB

In the neonatal suckling mouse, the antibody response to HEL-CFA can be inhibited by administration of certain anti-HEL monoclonal antibodies to the mother. The murine primary response to hen egg-white lysozyme (HEL), which can be elicited in A/J mice as early as 7 days of age, is characterized by a predominant specificity that includes the 3 N-terminal amino acids of HEL (TIP-dependence) and by a predominant idiotype, IdXE. A panel of murine IgG1 anti-HEL mAbs was administered to the suckling offspring via the mother. These mAbs were not equivalent in their effects on the offspring. Only two of six IgG1 mAbs, 2F4/2E5 (IdXE-positive, TIP-dependent) and 2D1 (IdXE-negative, TIP-independent), consistently induced suppression of the response of A/J offspring when immunized at 16-20 days of age with HEL-CFA. Suppression averaged 71% for 2F4/2E5 and 74% for 2D1 and was always statistically significant (P less than .05) when 275 micrograms mAb was administered IP to the mother within 24 hr postpartum. Since 2D1 is IdXE-negative and TIP-independent, neither of these properties appears to be crucial for suppression. Differences in transfer of the mAbs from the mother to the offspring or differences in catabolism of the mAbs in the offspring were not detected. When various characteristics of the mAbs such as affinity, idiotypy, and fine specificity were considered, there was no single factor which determined suppression. One of the two mAbs that suppressed the offspring response, 2D1, is idiotypically highly connected in the anti-HEL mAb panel. This observation suggests that idiotypic interactions in the developing neonatal repertoire with subsequent perturbation of T and B cell repertoire development may be an area for future investigation.

Monoclonal antibodies to cyclosporin are representative of the major antibody populations present in antisera of immunized mice

Two series of mouse antisera raised against cyclosporin (Cs)-carrier conjugates exposing opposite sides of the Cs molecule and more than sixty monoclonal antibodies (mAbs) derived from the same animals were compared in terms of isotype and fine specificity for Cs. The predominant isotypes of the mAbs reflected the in situ distribution of the circulating anti Cs antibodies. The fine specificity of the antibodies was studied by determining their cross-reactivity for a series of Cs-derivatives and Cs-metabolites in competitive ELISA. The antisera raised by different immunizations showed very different cross-reactivity patterns for the Cs-derivatives. However, the in situ anti Cs antibody populations and the majority of mAbs derived from the corresponding animals showed a striking similarity in fine specificity for restricted clusters of residues on the Cs molecule. These results indicate that the mAbs produced against Cs are representative of the major antibody population present in the sera of the mice used for the fusion. By determining the characteristics of antibodies found in the serum of immunized mice it may thus be possible to select animals that are likely to give rise to mAbs of a certain isotype and specificity.

A substantial proportion of the adult BALB/c available B cell repertoire consists of multireactive B cells

A variety of studies have documented multireactive antibodies in both the preimmune and naturally activated repertoire, but the relationship of these primarily IgM multireactive antibodies to antigen-specific primary and secondary response antibodies is currently not defined. In order to characterize the BALB/c preimmunization specificity repertoire and the baseline of naturally activated antibodies from which the immune response to a specific antigen (hen egg-white lysozyme, HEL) develops, panels of polyclonally activated blast-derived hybridomas (BlAbs) and natural antibody hybridomas (NAbs) from the spleens of unimmunized mice were screened for binding to a panel of nine complex antigens. Over half of the IgM-secreting BlAbs produced antibodies that were antigen-reactive; of these, over half were multireactive, i.e. capable of binding more than one complex antigen. There was no bias towards self vs foreign or thymus-dependent vs thymus-independent antigens. The frequency of antigen-reactive NAbs was about half the frequency of antigen-reactive antibodies found among the BlAbs. However, over half of the antigen-reactive NAbs were also multireactive, and the reactivity profile within the antigen-reactive subset of NAbs was similar to that within the antigen-reactive subset of BlAbs. These results suggest that the available repertoire of adult spleen cells contains a high proportion of multireactive antibodies, and that a subset of the available repertoire is randomly activated, yielding a small proportion of natural antibodies which closely reflect a random sampling of the available repertoire. Although monospecific precursor cells are rare, monospecific IgM BlAbs were found for all antigens in the panel except staphylococcal nuclease and mouse IgG. Monospecific as well as multireactive HEL-binding BlAbs were found at frequencies comparable to other protein antigens in the panel, and HEL-reactive NAbs were also present. On the other hand, it has previously been shown that HEL-reactive IgM antibodies (including multireactive antibodies whose specificities include HEL) are rare or absent in both the primary and secondary response to HEL. This cannot be attributed to an absence of available precursor B cells, and most likely reflects an early recruitment of HEL-reactive clones into the peripheral B cell pool. The possibility that polyreactive B cells may serve as precursors for some HEL-specific IgG antibodies is discussed.

Terasaki-ELISA for murine IgE. III. Determination of concentration and functional affinity by sequential equilibrium binding analysis

A simple Terasaki tray-based ELISA technique with a fluorescent detecting system has been used to determine the affinity of murine IgE antibodies. The system was shown to be sensitive enough to measure affinities in the range of 10(-6)-10(-10) M as well as detect IgE antibodies down to a limit of 0.1 ng/ml. The results, expressed as arbitrary fluorescence units (AFU), were compared with those obtained using equilibrium dialysis for several DNP-specific IgE monoclonal antibodies of known affinities yielding KD values. The relationship between KAFU and KD established a conversion factor which could then be used to compute KD from KAFU, provided the detection system remained identical. Based on the equations proposed, an alternative method for the quantitation of murine IgE is described which is independent of the affinity of IgE for the coated antigen.

Serological differentiation of the potato-cyst nematodes Globodera pallida and G. rostochiensis: II. Preparation and characterization of species specific monoclonal antibodies

Hybridomas producing antibodies which react with thermostable protein antigens isolated from the potato cyst nematode species Globodera rostochiensis (TSRoP) and G. pallida (TSPaP) were isolated. Three of the isolated hybridomas (WGP 1, WGP 2 and WGP 3) produce antibodies that react with preferent affinity with protein antigens isolated from G. pallida, and two (WGR 11 and WGR 12) produce antibodies which bind preferentially to G. rostochiensis. Binding constants were determined to quantitate the differences in affinity of WGP 1, WGP 2, WGP 3, WGR 11 and WGR 12 for the protein antigens from both nematode species, and to asses the similarity in affinity for either protein antigen with respect to the other non-specific antibodies. In immunoblotting experiments a binding could be demonstrated, for most antibodies, to two thermostable proteins with apparent molecular weights of 20.6/20.8 kD for G. rostochiensis and 20.5/21.0 kD for G. pallida. the reactivity of the monoclonal antibodies with thermostable protein antigens from other common cyst nematodes was also investigated. All monoclonal antibodies, which are not specific for TSRoP or TSPaP, bind to thermostable proteins of these cyst nematode species. The use of some of the isolated monoclonal antibodies to improve the diagnosis of potato cyst nematodes in soil samples is discussed.

Organ reactive autoantibodies from non-immunized adult BALB/c mice are polyreactive and express non-biased VH gene usage

To examine the naturally activated autoreactive B cell repertoire, we analyzed a panel of hybridomas from unmanipulated adult BALB/c spleen cells for reactivity patterns and VH gene usage. We found a pattern of VH usage that was diverse and appeared to reflect the germline repertoire. Although all but one natural antibody hybridoma (NAb) were initially selected for organ rather than antigen binding, the majority of organ reactive IgM NAbs were polyreactive, expressing a broad range of reactivity patterns for both self and foreign antigens, that were unique for each NAb and were not indiscriminate. Our results are consistent with the hypothesis that many naturally activated adult B cells are highly polyreactive and that autoreactivity is a consequence of polyreactivity. We suggest that the population of NAbs exhibiting organ reactivity overlaps the populations of other IgM autoantibodies that have been described previously, and that these all derive from a pool of polyreactive IgM antibodies which are polyclonally activated in the early immune response. These polyreactive natural antibodies may represent a first line of defense and offer protection for the host against a variety of foreign agents.

A predominant idiotype independent of specificity, or Ig and H-2 allotypes, is found in the primary but not the secondary murine antibody response to lysozyme

Removal of just the three N-terminal residues Lys-Val-Phe (TIP) on hen egg white lysozyme (HEL), by aminopeptidase cleavage, eliminates an antigenic determinant which is a recurrent and dominant focus of primary but not secondary antibody responses to HEL in a variety of mouse strains. We have generated an anti-idiotypic rabbit antiserum against such a TIP-dependent monoclonal antibody (mAb). This antiserum reacts with many different primary anti-HEL mAb, but fails to react with all of a variety of secondary anti-HEL mAb. The idiotype defined by this antiserum, termed IdXE, is a common feature of early anti-HEL antibody responses but does not appear in secondary responses. Although the presence of IdXE and TIP dependence is correlated in primary responses, studies of idiotype expression on mAb and on plaque-forming cells (PFC) using mixed erythrocyte monolayers clearly show that at the single-cell level the properties are separable, i.e., not all TIP-recognizing PFC display IdXE and a sizable proportion of cells producing non-TIP-dependent antibodies are IdXE+. The restricted idiotypy and specificity of early antibody responses to HEL occur in each of eight diverse mouse strains tested: it is not associated with a particular MHC haplotype, heavy chain allotype or light chain allotype. The finding of such strain-independent restriction in the early response pattern to a typical protein antigen is novel and suggests the involvement of highly conserved, potent regulatory mechanisms which are manifested as a limitation in the initial expression of the available repertoire.

Assessment of neuromedin B polyclonal antibodies as molecular probes in neural tissue

Five unique, high affinity rabbit polyclonal antibodies against neuromedin B were characterized in a radioimmunoassay in terms of the following parameters: pH and type of buffer, ionic strength, and non-ionic detergents in order to optimize immunoglobulin-peptide interaction; specificity using peptides of the bombesin family, in addition to the tachykinin substance P; and affinity to neuromedin B. Optimum conditions included acidic pH (5.25), high ionic strength (greater than 0.1 M) and absence of non-ionic detergents, which inhibited the assay. Affinities for the 5 antibodies ranged from 10 to 48 fmol neuromedin B with titers from 1:1,000 to 1:10,000 and the sequence-specificity covered the entire peptide; cross-reactivity towards substance P was negligible. As a model tissue, rat spinal cord was homogenized with 5 different extraction solvents, including acetone, methanol, acid and alkaline conditions, and assayed by each polyclonal antiserum; neuromedin B immunoreactivity levels were highest in acid and alkaline extracts and reflected the specificity of the antibody used. Applying these antisera to rat brain extracts, the posterior pituitary gland contained the highest concentration of immunoreactive equivalents of neuromedin B followed by the anterior pituitary, hypothalamus, and hippocampus. The immunoreactive content in the pituitary and hypothalamus, however, depended on the particular antisera used with significant (P less than 0.01) differences existing between them. Further application of these polyclonal antibodies to a spinal cord extract analyzed by isocratic reverse-phase HPLC conditions also revealed differences in their cross-reactivity with the immunoreactive peptides. These antisera may now be used as molecular probes for the determination of extractable immunoreactive neuromedin B from neural tissue and in situ localization by immunohistochemical techniques.

Profile of the continuous antigenic regions on the extracellular part of the alpha chain of an acetylcholine receptor

Reaction of overlapping synthetic peptides spanning the extracellular part (residues 1-210) of the alpha chain of the Torpedo californica acetylcholine receptor (an alpha 2 beta gamma delta pentamer) with anti-receptor antibodies produced the profiles of the continuous antigenic regions of the correlate segment. Essentially similar profiles were recognized by rabbit and outbred mouse antibodies against isolated receptor or mouse antibodies against membrane-bound receptor. The antigenic sites reside within eight continuous regions: residues 1-14, 25-36, 41-53, 63-75, 102-114, 128-138, 172-182, and 188-198. Five of these regions (the second and the fifth through the eighth) appeared to be immunodominant. Significantly, two of these antigenic regions (i.e., those residing within residues 128-138 and 188-198) coincided with known toxin-binding regions. The antigenic profile suggests that recognition is directed to the intact molecule and only very slightly to the processed (fragmented) protein.

A three-dimensional model of an anti-lysozyme antibody

The primary amino acid structure of the lysozyme-binding antibody, HyHEL-10, as determined by amino acid and nucleotide sequencing was utilized to construct a scale model of the Fv (variable region domain of immunoglobulin) using energy-minimized torsional angles of the McPC603 Fv as a prototype template. This model was in turn used as a template for generating a computer-built set of co-ordinates, which were subjected to a total of 600 steps of Adopted Basis Newton-Raphson energy minimizations using the program CHARMM. Only minimal shifts of the backbone (root-mean-square 0.76 A) were required to give an energetically stable structure with a favorable van der Waals' energy. Several notable features were evident from both the scale model and the energy-minimized computer model: (1) the shape of the antibody combining region is that of a very shallow concavity approximately 20 A X 25 A; (2) the concavity is acidic and non-hydrophobic and is bordered by hydrophobic segments; (3) the lower portion of the combining site is dominated by a cluster of tyrosine residues over the L3 and H2 areas; (4) a somatic mutation encoded by the J region of the heavy chain (JH) may contribute significantly to the complementarity of heavy chain H3 to the epitope on hen egg white lysozyme. In addition, the space-filling energy-minimized model revealed that residue 49L, a framework residue, was prominently exposed and accessible in the center of the combining-site concavity. The model suggests that variation in length of complementarity-determining regions may function not only to change directly the shape of the antibody combining site, but may also influence indirectly the nature of the antibody surface by changing the accessibility of residues not usually involved in antigen binding.

Immune recognition of human major histocompatibility antigens: localization by a comprehensive synthetic strategy of the continuous antigenic sites in the first domain of HLA-DR2 beta chain

A comprehensive synthetic approach, previously developed in this laboratory, has been applied to screen the entire first domain (residues 1-95) of the HLA-DR2 beta chain for the full profile of continuous regions that are recognized by human allo-antisera and anti-DR or anti-beta chain antisera raised in other species. Nine consecutive peptides, that were 15 residues each and overlapped by 5 residues, covering the first domain of the DR2 beta chain were synthesized, purified and characterized. The antibody-binding activities of the peptides were determined by radioimmunosorbent titrations. This established the full profile of peptides having specific antibody-binding activity with these various antisera. Three continuous antigenic sites were localized in this domain by all of antisera tested. Peptide 81-95 appeared to be the most immunodominant (i.e. bound the highest amounts of antibodies) in most antisera tested. Although their immunodominance varied with the antisera and boundary shifts were present, the submolecular regions recognized on the first domain of DR2 beta appeared to be similar with antisera against the DR2 (alpha beta I) complex or against the isolated beta chain. Furthermore, recognition was independent of the host species from which the antisera were obtained.

Chemistry of antibody binding to a protein

The chemistry of antibody recognition was studied by mapping the antigenicity of the protein myohemerythrin with peptide homologs of the protein sequence. The results suggest that the entire protein surface is antigenic, but the probability of there being antibodies to a given site is influenced by local stereochemistry. Although accessible to an antibody binding domain, the least reactive positions cluster in the most tightly packed and least mobile regions and are closely associated with narrow, concave grooves in the molecular surface containing bound water molecules. The most frequently recognized sites form three-dimensional superassemblies characterized by high local mobility, convex surface shape, and often by negative electrostatic potential.

Antigen specificity and cross-reactivity of monoclonal anti-lysozyme antibodies

Twenty-seven murine monoclonal anti-hen egg-white lysozyme (HEL) antibodies were tested with a panel of nine antigens; eight avian lysozymes and human lysozyme. The antibodies were arranged into 10 groups based on their antigen specificity and cross-reactivity. Antigenic determinants recognized by each group of antibodies were tentatively identified. They are located at different points of the HEL accessible surface in agreement with the notion that its entire surface has an antigenic potential. The affinity constants of antibodies representative of seven of the 10 groups range from 0.79 X 10(7) to 5.3 X 10(7) M-1. Heteroclitic antibodies occurring in some of the groups bind heterologous lysozymes with somewhat higher association constants than those for the homologous antigen (HEL). Their broader specificities do not correlate with overall lower association constants, but rather with the occurrence of public epitopes in the panel of avian lysozymes. Although the reaction of two antibodies with the solid-phase coupled antigen is not always additive, detailed interpretation of these results and the observation of actual ternary complexes Fab-HEL-Fab rules out the occurrence of conformational changes in the complexed antigen.

Three-dimensional structure of an antigen-antibody complex at 2.8 A resolution

The 2.8 A resolution three-dimensional structure of a complex between an antigen (lysozyme) and the Fab fragment from a monoclonal antibody against lysozyme has been determined and refined by x-ray crystallographic techniques. No conformational changes can be observed in the tertiary structure of lysozyme compared with that determined in native crystalline forms. The quaternary structure of Fab is that of an extended conformation. The antibody combining site is a rather flat surface with protuberances and depressions formed by its amino acid side chains. The antigen-antibody interface is tightly packed, with 16 lysozyme and 17 antibody residues making close contacts. The antigen contacting residues belong to two stretches of the lysozyme polypeptide chain: residues 18 to 27 and 116 to 129. All the complementarity-determining regions and two residues outside hypervariable positions of the antibody make contact with the antigen. Most of these contacts (10 residues out of 17) are made by the heavy chain, and in particular by its third complementarity-determining region. Antigen variability and antibody specificity and affinity are discussed on the basis of the determined structure.

Mouse monoclonal antibodies induced by anti-allotype antibody display internal images of the rabbit VHa1 allotype: direct visualization by immunoelectron microscopy

We have previously shown that injection of adult rabbits with anti-immunoglobulin (Ig) antibody (Ab) induces the expression of genetically unexpected Ig markers, i.e., a1 allotypic determinants. We now show that these rabbit Ig markers can also be induced in mice by a similar treatment; in the latter case the a1 determinants are located in the antigen-combining site and thus represent "internal images". Two monoclonal antibodies (mAb) were developed from mice treated with anti-allotype Ab. These mAb were reactive with all homologous and heterologous anti-a1 Ab but not normal Ig; efficiently inhibited the binding of rabbit a1 Ig to anti-a1 Ab; and elicited the production of anti-allotype Ab when injected into normal mice. To determine whether the a1-like determinants on these mAb were located in the antigen-combining site, immunoelectron microscopy was utilized to directly visualize Ab complexes. Complexes composed of intact Ab and anti-a1 Fab fragments yielded uniform binding patterns which were identical to those produced by anti-idiotypic reactions. In each case, an identical tip-to-tip binding configuration was observed with a single Fab fragment attached at an approximate 180 degree angle to the V region terminus of each Ab arm. In contrast, rabbit a1 Ig bound as many as two anti-a1 fragments per Ig arm; these fragments were attached laterally and at right angles to the intact molecule. These mAb thus provide the first direct evidence that Ab2 beta determinants are located in, or near, the antigen-combining site.

Evolutionary origin of autoreactive determinants (autogens)

The question addressed in this report focuses on the autoantigenicity of self antigens, principally cytochrome c and lysozyme. Of interest is whether the immune system produces autoantibodies to its host proteins reacting randomly with all potential antigen sites or is autoreactively selective for certain determinants. Based on experimental evidence from autoantibodies against cytochromes c, Jemmerson and Margoliash [Jemmerson, R. & Margoliash, E. (1979) Nature (London) 282, 468-471] have described a striking correlation between autoreactive sequence regions and evolutionary instability. While their analysis of evolutionary variation was based on simple sequence variability plots, we present here a refined approach that takes into account the distinction between evolutionary substitutions that induce a change in the protein surface from those that do not (surface-neutral substitutions). A quantitative aspect of surface variation (surface consensus) is included in the algorithm that produces a ranked order for autoantigenic determinants. The final plot, called surface variability, indicates sequence regions having a preference for autoimmune reaction. We propose the term "autogen" to designate such protein determinants.

Identification of antigenic determinants on insulin recognized by monoclonal antibodies

The specificities of nine monoclonal antibodies raised to bovine insulin were investigated. The probable binding sites of the antibodies were determined by correlation of cross-reactivity with heterologous insulins and amino acid differences in the primary structures. Most antibodies recognized topographic determinants composed of both A- and B-chain residues but were capable of binding either one or both free chains independently. Only one antibody was completely conformation-dependent. A number of antibodies showed heteroclitic binding to particular insulin variants. All the antibodies were autoreactive in that they recognized rat insulin which has the same primary sequence as the mouse molecule.

Antibody recognition of ragweed allergen Ra3: localization of the full profile of the continuous antigenic sites by synthetic overlapping peptides representing the entire protein chain

A comprehensive synthetic approach, for the localization of the full profile of the continuous antigenic sites on proteins, previously introduced by this laboratory, was applied here to localize the continuous antigenic sites of ragweed allergen, Ra3. The following 10 consecutive peptides, each comprising 15 residues (except for peptide 91-101) and overlapping each of its neighbors by 5 residues, were synthesized and purified: 1-15, 11-25, 21-35, 31-45, 41-55, 51-65, 61-75, 71-85, 81-95 and 91-101. Quantitative radiometric titrations of protein and peptide adsorbents were performed with 125I-labeled anti-Ra3 IgG antibodies from rabbit, outbred mouse and human antisera. The specificity of antibody binding to peptide adsorbents was confirmed by inhibition experiments. These studies established the full profile of antigenic (IgG-binding) sites of Ra3 and permitted comparison with the allergenic (IgE-binding) sites recently localized. It was found that the recognition by IgG antibodies was independent of the host species in which the antibodies were raised. Furthermore, the regions recognized by human IgE antibodies coincided with those recognized by IgG antibodies in three different species. Thus, Ra3 was found to have 4 continuous antigenic sites which occupy the same locations as the allergenic sites.

Antigenic structure of human haemoglobin. Localization of the antigenic sites of the beta-chain in three host species by synthetic overlapping peptides representing the entire chain

A comprehensive synthetic approach is applied here to localize the continuous antigenic sites of the beta-chain of haemoglobin. The approach was based on the synthesis and purification of the following consecutive 15-residue peptides (each overlapping by five residues at both ends with the peptides preceding it and following it in the sequence): 1-15, 11-25 etc. Quantitative radiometric titrations of protein and peptide adsorbents were performed with 125I-labelled anti-haemoglobin antibodies from three different host species. The specificity of antibody binding to peptide adsorbents was confirmed by inhibition studies and by the binding specificity of antibodies isolated from peptide adsorbents. These studies established the full profile of antigenic beta-chain regions, which was found to be independent of the host species. Five major antigenic sites were localized, and their three-dimensional and structural characteristics are discussed in relation to the immune recognition of haemoglobin and other proteins.

An evaluation of some in vivo immunization strategies for the production of monoclonal antibodies to insulin and ACTH

Immunization schedules for the production of monoclonal antibodies to bovine insulin and porcine adreno-corticotrophic hormone (ACTH) have been investigated. Specifically, prime dose, prime route, pre-fusion boost dose and immune status have been evaluated for their effect on both the number of hybrids observed after fusion, and the proportion of wells containing antibody which bound to the immunogen. Although a single optimum protocol was not identified, the results indicate that spleen cells from mice primed at multiple sites should be used for fusion after the peak of the primary antibody response. Excessive hyperimmunization should be avoided. Dose regimes combining a low prime amount and a high pre-fusion boost amount or a high prime amount and a low pre-fusion boost amount (except in the presence of circulating antibody) were favoured. Monitoring of the immune response of animals used in fusion experiments is of paramount importance.

Theoretical considerations of the ability of monoclonal antibodies to detect antigenic differences between closely related variants, with particular reference to heterospecific reactions

In theory monoclonal antibodies can be used to analyse antigenic determinants in great detail by correlating differences in antibody affinity for variant antigens with their amino acid differences. In particular, heteroclitic antibodies should be detected, which would normally be masked in a polyclonal antiserum. Recognition of such antibodies may be important for our understanding of the scope of antibody repertoires particularly when the immunogen is closely related to a component of the immunised animal. In practice the immunoassays commonly used to measure affinity differences between different antigens fall short of these capabilities. Mathematical studies were carried out to identify factors controlling the sensitivity of 4 types of assay to differences in affinities for different antigens. The most important factors controlling assay sensitivity were found to be the ratio of antibody affinity (K) to epitope density in direct binding assays, the ratio of K to antibody concentration in liquid phase competition assays, and the ratio of solid phase to liquid phase values of K for solid-phase competition assays. It is predicted that a combination of solid-phase competition assay with high epitope density and direct binding assay with low epitope density would result in optimal detection of heteroclitic antibodies and small differences in antibody affinity for cross-reactive antigens.

Quantitation of the immunogenic potential of protein antigens

A procedure to quantitate the immunogenic potential of protein antigens is presented. It is hypothesized that the intrinsic immunogenicity of an accessible region on the protein arises from the overall structural effect of the presence of the particular assemblage of amino acid residues in the given region. Structural parameters previously derived by Grantham [Science 185, 862-864 (1974)] to differentiate the various amino acids are assigned to each residue position. At each point chosen on the molecule, an av. value is computed due to all residues within 8.5 A of this point; it is proposed that this local average is proportional to the immunogenic potential of the region centered at this point. The method can be used to locate the immunodominant regions of a molecule and to compare the antigenicity of related molecules. Test calculations on hen egg-white lysozyme, sperm whale myoglobin and horse cytochrome c show that segments in these molecules, that have been shown in immunochemical studies to possess antigenic activity, are predicted by this method to be immunodominant.

Intrinsic and extrinsic factors in protein antigenic structure

Recent advances in the preparation of synthetic peptide vaccines and the use of synthetic peptides as probes of antigenic structure and function have led to renewed interest in the prediction of antigenic sites recognized by antibodies and T cells. This review focuses on antibodies. Features intrinsic to the antigen, such as hydrophilicity and mobility, may be useful in the selection of amino acid sequences of the native protein that will elicit antibodies cross-reacting with peptides, or sequences which, as peptides, will be more likely to elicit antibodies cross-reactive with the native protein. Structural mobility may also contribute to protein-protein interactions in general. However, the entire accessible surface of a protein is likely to be detectable by a large enough panel of antibodies. Which of these antibodies are made in any individual depends on factors extrinsic to the antigen molecule, host factors such as self-tolerance, immune response genes, idiotype networks, and the immunoglobulin structural gene repertoire.

Three-dimensional structure of an antigen-antibody complex at 6 A resolution

Present understanding of the three-dimensional structure of antibody combining sites is based on X-ray diffraction studies of myeloma immunoglobulins. The structures of the antigen-binding fragment (Fab) complexes of two of these immunoglobulins with small ligands have also been determined. However, there is no crystallographic information concerning the interactions of an antibody with an antigen, nor do we know the precise structure of antigenic determinants on protein molecules. We now report the first structure determination of an antigen-antibody complex at 6 A resolution. The structure of the complex between hen egg-white lysozyme and the Fab of a monoclonal anti-lysozyme antibody (D1.3) shows that the combining site of antibodies is not merely a cleft delineated by the complementarity-determining regions of the variable regions of the light and heavy chains, but is a larger area extending beyond it. A correspondingly large area of the antigen makes close contacts with the antibody, in agreement with the notion of a 'topographical' rather than 'sequential' antigenic determinant. The structural basis of cross-reactivities of an antibody with heterologous antigens and the effect of a single amino acid substitution on antigenic specificity can thus be visualized in the structural model presented here.

A rapid method for comparing monoclonal antibodies by limited proteolysis and electrophoresis

A rapid and sensitive method for comparing the primary structure of proteins has been adapted to the study of monoclonal antibodies. Samples were digested with alpha-chymotrypsin in the presence of sodium dodecyl sulfate after which peptide fragments were separated into distinctive banding patterns by polyacrylamide gel electrophoresis. This method could easily detect differences in the primary structure of antibodies with related as well as unrelated binding specificities. In addition, antibody molecules derived by somatic diversification from the same germ line gene segments could be distinguished from one another.