Specificity of the antibody response of rabbits to a self-antigen

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.

Generation of epitope-specific antibodies to rat GHBP in the sheep using an interspecies switching strategy involving site-directed mutagenesis of ovine GHBP

Site-directed antibodies to the growth hormone receptor could be potentially useful as growth hormone mimics but, in previous attempts, we found that antisera generated using peptides derived from growth hormone receptor sequences failed to recognize the intact protein. As an alternative approach to this problem, we have now adopted a strategy of epitope-switching between rat and ovine growth hormone receptors to produce rat epitopes in the correct structural context. Using site-directed mutagenesis, we altered the two dominant linear epitopes in the ovine growth hormone binding protein to the analogous sequences in rat growth hormone binding protein. Site A, between Thr28 and Leu34, is equivalent to epitope 1 in ovine growth hormone binding protein and site B, between Ser121 and Asp124, corresponds to epitope 5. The wild-type ovine growth hormone binding protein and the two mutant proteins were bacterially expressed, refolded and, following purification by metal-chelate affinity chromatography, used to raise antisera in sheep. We showed using RIA, in which wild-type ovine growth hormone binding protein acted as a competitor for the binding of rat growth hormone binding protein, that only the site A mutant protein elicited a specific anti-rat growth hormone binding protein response. This was confirmed in subsequent RIA studies using the antiserum to the site A mutant protein in which only peptides corresponding to the site A sequences in mutant ovine growth hormone binding protein and rat growth hormone binding protein, but not that in wild-type ovine growth hormone binding protein, were able to act as competitors for rat growth hormone binding protein. Antibodies specific for rat growth hormone binding protein could be separated from the antiserum to the site A mutant protein by means of affinity chromatography using immobilized wild-type ovine growth hormone binding protein to remove antibodies which cross-reacted with the ovine protein. The work lays the foundations for further studies in which the biological effects of these antibody fractions will be investigated and demonstrates an approach with general applicability in the production of antibodies directed towards specific epitopes on protein molecules.

Major histocompatibility complex as an antigen pump: self-declaration in somatic cell society

Self-recognition by the immune system is a basic mechanism of vertebrates. Mechanisms of antigen presentation by somatic cells are based on the coupling of small peptides produced in cytoplasm and major histocompatibility complex major histocompatibility complex. The antigen pumps, including major histocompatibility complex, can present various internal molecules which are possible targets of autoimmunity, using a peptide binding mechanism. The antigen pump can transfer external signals by autoantibody and cellular immunity without a specific receptor system. This self-declaration mechanism continuously presents 'self' rather than 'non-self'. It is qualitatively impossible to differentiate self antigens from non-self antigens in this process at all. Somatic cell society is non-self for germ line DNA, since germ line DNA is symbiotic with somatic cell society. Consequently, non-self can be recognized through self-declaration.

Transplantation and chimera as extended self

Transplantation can be considered as an artificial reconstitution of symbiosis called chimera, since the donor and recipient carry different DNAs. In successful transplantation, engrafted tissues and cells should be recognized as self by the immune system, as shown in external pathogens. The external milieu introduced by transplantation and infection can only be immunologically recognized as self when it forms a symbiotic relationship with somatic cell society. Immunological identity is a posteriori educated recognizing immunological self and genetic self may be ignored in self-recognition. For example, transplanted bone marrow immunocytes recognize somatic cell society which is selected previously by other immunological standards as self. Dissociation between genetic self and immunological self originates in the development and differentiation of multicellular organisms a priori, since alteration of DNA sequences is necessary in the development and differentiation of multicellular organisms and symbiosis is the essential nature of it.

Major and minor epitopes on the self antigen mouse cytochrome c mapped by site-directed mutagenesis

Variants of rat (mouse) cytochrome c, prepared by site-directed mutagenesis or represented by closely-related cytochromes c from different species, were employed to map the functional boundaries of a number of mouse monoclonal antibodies (mAb) specific for the major antigenic region on the self antigen (Ag) around residue 62 and the minor antigenic region around residue 44. The recombinant mouse cytochromes c tested were, unlike the tissue-derived Ag, trimethylated at position 72, and included the wild-type which was acetylated at the amino terminus, a variant that was unacetylated at the amino terminus, and variants with the following single amino acid residue replacements: V11I (valine to isoleucine at position 11), Q12M, A15S, A44P, F46Y, D50A, T58I and G89E. Of these, only the A44P variant affected the binding of mAb to the region previously localized to the vicinity of residue 44, thus confirming that assignment. Loss of the acetyl group at the amino terminus affected the binding of most of the mAb to the region around residue 62. The other mutations had little, if any, affect on mAb binding. The epitopes of mAb binding the region around residue 62 were shown in this study to have similar functional boundaries. This site on the self Ag, which encompasses at least three discontinuous segments of the polypeptide chain, is comparable in size to epitopes on other protein Ag that have been mapped by X-ray crystallography and is similar to an epitope in the corresponding region of the foreign Ag, horse cytochrome c, that has been mapped by hydrogen-deuterium exchange. In addition to the mAb binding the regions around residues 44 and 62, a third group of mouse cytochrome c-specific mAb known to be broadly reactive with mammalian cytochromes c and that represents a minor portion of the mAb was tested for binding the site-directed mutants of mouse cytochrome c. None of these mAb were affected by the mutations, indicating the presence of at least one more antigenic region on the self Ag in an area not encompassed by these mutations that is structurally highly conserved.

The immune response to cytochrome c in BALB/c mice is delayed due to inability of their non-specific antigen-presenting cells to provide its immunodominant epitope

The antibody response to horse cytochrome c (cyt.c) in BALB/c mice developed slowly and a substantial production of IgG antibodies was observed only 26-30 days after immunization. Lymph node cells (LNC) of unimmunized mice proliferated weakly in response to both native cyt.c and its synthetic peptides. On day 8 after immunization, LNC could not be stimulated with native cyt.c and peptide 92-104. However, they did proliferate in response to cyt.c peptides 1-6, 1-13, 2-13, 14-22, 46-56, 57-77, 61-77 and 61-69 which are closely related in horse and mouse cyt.c. On day 26, both native cyt.c and the peptides, including 92-104, were equally active in stimulating LNC proliferation. Both plastic-adherent and cyt.c-specific cells panned from day 8 cells enhanced the response of unprimed cells to native cyt.c. Elimination of B cells demonstrated that primary recognition of cyt.c was mediated, at least partly, by non-specific antigen-presenting cells (APC) while later B cells of additional specificities were involved. It is concluded that immunization with horse cyt.c initiated an autoimmune response resulting in T-dependent anergy. Peptide determinants processed by non-specific APC stimulated corresponding autoreactive T cells. Specific B cells which appeared as a result of the response maturation processed successfully the immunodominant epitope and finally mediated proliferative and antibody responses.

Antibodies to carbonic anhydrase in systemic lupus erythematosus and other rheumatic diseases

OBJECTIVE

Autoantibodies to CA were demonstrated in the sera of patients with systemic lupus erythematosus (SLE) and some other rheumatic diseases. This study was undertaken to define the isoform and species specificity of these reactions, as well as to develop a method for detecting immune complexes.

METHODS

Antibodies to CA were sought by enzyme-linked immunosorbent assay (ELISA) and by Western immunoblotting.

RESULTS

An increased prevalence of CA autoantibodies was detected, by both methods, in patients with SLE, scleroderma, and polymyositis, compared with controls. In SLE patients, CA autoantibodies occurred preferentially in those with anti-U1 RNP or anti-U1 RNP and Ro/SS-A. Some sera reacted with only the CA I or CA II isoform, while approximately 50% of sera that were CA positive reacted with both isoforms. The autoantibodies reacted preferentially with the human enzymes, rather than the bovine CA, both on Western blot and by ELISA: Selected IgG F(ab')2 fragments from anti-CA-containing sera specifically inhibited the enzyme activity of CA, and the CA inhibitor acetazolamide partially inhibited the binding of anti-CA to CA. Thus, at least a part of autoanti-CA is directed toward the active site of CA. Finally, CA molecules were detected as immune complexes in sera from selected anti-CA-positive patients.

CONCLUSION

Autoantibodies to CA represent a previously unrecognized autoantibody to an abundant intracellular protein of the human erythrocyte.

Sera from patients with autoimmune disease recognize conformational determinants on the 60-kd Ro/SS-A protein

Anti-Ro antibodies are found in a large proportion of patients with systemic lupus erythematosus and primary Sjögren's syndrome. These antibodies also characterize neonatal lupus, subacute cutaneous lupus erythematosus, and vasculitis associated with Sjögren's syndrome and rheumatoid arthritis. Anti-Ro-positive sera may contain either or both of 2 sets of antibodies, recognizing either a 60-kd or a 52-kd polypeptide component of the Ro particle. We found in this study that the immune response to the 60-kd Ro antigen is heterogeneous. Some sera specifically recognize the native Ro antigen but fail to bind the corresponding denatured polypeptides. In addition, after immunodepletion using the denatured 60-kd Ro polypeptide, all anti-Ro-positive sera tested still contained high titers of antibodies recognizing conformational determinants on the Ro antigen. The frequent immunodominance of anti-Ro antibodies targeted to conformational determinants suggests that native autoantigens may directly drive the autoimmune response.

Evolution of the glycophorin gene family in the hominoid primates

Analysis of nucleotide sequences of the human glycophorin A (GPA) and glycophorin B (GPB) genes has indicated that the GPA gene most closely resembles the ancestral gene, whereas the GPB gene likely arose from the GPA gene by homologous recombination. To study the evolution of the glycophorin gene family in the hominoid primates, restricted DNA on Southern blots from man, pygmy chimpanzee, common chimpanzee, gorilla, orangutan, and gibbon was probed with cDNA fragments encoding the human GPA and GPB coding and 3'-untranslated regions. This showed the presence in all of the hominoid primates of at least one GPA-like gene. In addition, at least one GPB-like gene was detected in man, both chimpanzee species, and gorilla, strongly suggesting that the event that produced the GPB gene occurred in the common ancestor of man-chimpanzee-gorilla. An unexpected finding in this study was the conservation of EcoRI restriction sites relative to those of the other four enzymes used; the significance of this observation is unclear, but raises the question of nonrandomness of EcoRI restriction sites in noncoding regions. Further analysis of the evolution of this multigene family, including nucleotide sequence analysis, will be useful in clarification of the evolutionary relationships of the hominoid primates, in correlation with the structure and function of the glycophorin molecules, and in assessment of the role of evolution in the autogenicity of glycophorin determinants.

Antigenic sites on cytochrome c2 from Rhodospirillum rubrum

The antigenic determinants for three monoclonal antibodies against cytochrome c2 from Rhodospirillum rubrum were partially characterized by differential chemical modification of free and antibody-bound cytochrome c2 and by cross-reactivity analysis with different antigens. Circular dichroism spectroscopy was used to probe the effect of antibody binding on the conformation of cytochrome c2. The binding of two antibodies was strongly dependent on the native folding of the antigen. The first antibody bound to a determinant around the exposed heme edge on the 'front side' of the molecule which is not antigenic in mitochondrial cytochrome c2. Binding of this antibody to cytochrome c increased the induced CD of the ferric heme in a manner similar to that observed previously when mitochondrial cytochrome-c oxidase bound to the front side of cytochrome c. This observation points to a subtle conformational adaptation of the antigen induced by the antibody. The determinant for the second antibody, which also affected the heme CD spectrum of the antigen, was on a polypeptide loop where cytochrome c2 differs from mitochondrial cytochrome c by an eight-residue insertion. The third antibody, which did not induce a change in CD, bound to a sequential determinant near the amino end of cytochrome c2. Only this antibody cross-reacted with isolated cytochrome-c-derived peptides and with apo-cytochrome c2. A preliminary analysis of the polyclonal immune response of five rats against cytochrome c2 indicates that, unlike in eukaryotic cytochrome c, antigenic determinants are distributed over the whole polypeptide chain of the prokaryotic immunogen.

Selection of antibody epitopes in an immunopathogenic neural autoantigen

Results with two well-characterized self-antigens, cytochrome c and myelin basic protein, have led to differing opinions regarding the predominant specificities of autoantibodies, whether regions of sequence diversity or 'structurally inherent features' of a protein determine favored antigenic sites. To further examine this question, 16 antibody epitopes have been mapped on a highly immunopathogenic autoantigen, retinal S-antigen (S-Ag). The epitopes were characterized for: (1) sequence diversity and cross-reactivity on S-antigens from several species; (2) conformational dependency; and (3) probability of their occurrence on the surface of S-antigen. A single C-terminal region containing sequence diversity was most frequently recognized, but no evidence for recognition of any other regions of sequence diversity was found. Thirteen of 16 monoclonal antibodies raised to native S-Ag bound epitopes strongly predicted to be on the surface of S-antigen. Conversely, only one of six antibody preparations raised to peptides or affinity-purified on peptides was found to recognize an epitope predicted to be on the surface, suggesting a good correlation between specificity for conformation-dependent sites and surface probability based on the surface prediction algorithm. Three of these six antibodies which preferred denatured epitopes bound sites which overlapped or coincided with T cell sites; two of these T cell sites are immunopathogenic. The epitopes recognized on denatured antigen and peptides were similar whether the antibodies were elicited with intact human or bovine S-antigen or with cyanogen bromide-cleaved peptides. Our data suggests that in the case of S-antigen, structural features are more significant factors in epitope selection than sequence diversity.

The Ro ribonucleoprotein particle: induction of autoantibodies and the detection of Ro RNAs among species

High titers of autoantibody specific for the Ro(SSA) ribonucleoprotein are frequently found in patients with systemic lupus erythematosus and Sjogren's syndrome. In this study we have analyzed the immune responses to the Ro particle when utilized as an immunogen in animal hosts. Anti-Ro autoantibodies which bound autologous Ro ribonucleoprotein particles were induced in rabbits. In immunodiffusion studies using crude rabbit tissue extracts, the rabbit antibody made a precipitin line of identity with a prototype human anti-Ro serum. In solid-phase assays, the human autoimmune serum and the antigen-induced rabbit serum competed for similar or overlapping epitopes on the Ro particle. The rabbit and human sera precipitated the four Ro RNAs from human cells as well as four previously uncharacterized Ro RNAs from a bovine cell line, three Ro RNAs from a rabbit cell line, and two Ro RNAs from duck cells. While total numbers of cellular Ro RNAs differ among species, all possess an RNA of common size which comigrated with the hY1 of human cells.

Biochemical and immunological heterogeneity of the Ro ribonucleoprotein particles. Analysis with sera specific for the RohY5 particle

Anti-Ro autoantibodies found in sera from patients with systemic lupus erythematosus and related diseases precipitate four RNAs (hY1-hY5) from human cell extracts. We identified two patient sera that selectively immunoprecipitated from such extracts the Ro particle containing the hY5 RNA (RohY5 particle). Using cell fractions either enriched in or depleted of RohY5 particles, we have shown that these sera contain autoantibodies that target an antigenic determinant on the 60-kD Ro polypeptide that is expressed only on RohY5 particles and is absent on the Ro particles containing the hY1-hY4 RNAs (RohY1-hY4 particles). In a competitive inhibition assay using a cell fraction enriched in RohY1-hY4 particles but depleted of RohY5 particles, four of six control anti-Ro sera were also shown to contain antibodies reactive with the epitope specific for the RohY5 particle. Thus anti-RohY5 antibodies frequently occur in tandem with anti-Ro antibodies, but are not detected unless inhibition assays are performed. Finally, anti-RohY5 specific sera do not immunoprecipitate any Ro particles from various nonhuman cell lines. In contrast to other autoantibodies in systemic lupus and related diseases that bind conserved regions on conserved polypeptides, this observation suggests that a portion of the anti-Ro response targets a nonconserved epitope on a conserved autoantigen.

The autoantigenic response to rabbit cytochrome c

In this report we describe the production and characterization of autoantibody responses to rabbit cytochrome c (cyt c) in rabbits immunized with either the native monomeric or polymerized form of rabbit cyt c. Fine-specificity analyses of the response indicated that the majority of the response was to the evolutionarily conserved amino-terminal region of the molecule. The relative affinity of the autoantibody interaction with rabbit cyt c was assessed by a solid-phase assay and was found to be lower than that observed for rabbit anti-horse cyt c antibody populations. These findings are consistent with the prediction that low-affinity self-reactive B cells may escape tolerance induction.

Identification of the main immunogenic region of retinal S-antigen: subordinate influence of MHC, IGH, species or strain differences on the specificity of the antibody response

The factors which lead to selection of dominant antigenic sites concentrated in discreet regions of proteins and polypeptides are important to the development of antigen-specific immunotherapies for autoimmune diseases and for vaccine design. In this study, the main immunogenic regions of the immunopathogenic autoantigen, retinal S-antigen, have been identified by examination of the specificity of antibody responses of different species. Using cyanogen bromide and synthetic peptides in western blots and the ELISA, the specificities of antisera from rabbits, guinea pigs, rats and 19 inbred strains of mice were tested. All animals produced high titers of antibody to S-antigen with the exception of PL/J mice. Antibodies which bound epitopes contained in peptide CB46, a 46 amino acid-containing peptide located at the C-terminus of S-antigen, were dominant in all species and strains tested. The epitopes in CB46 were multiple, overlapping, and concentrated in a stretch of approximately 30 residues. Two overlapping synthetic peptides from that region substantially competed the anti-CB46 response of all animals. Antibodies which recognized peptide CB47, a 47 residue peptide from the N-terminus, comprised the next most common group. This epitope was similar in all mice and overlapped the epitope defined by rat antibodies. All anti-CB47 antibodies mapped to an 11 residue region of CB47. Eleven strains of mice did not respond to CB47 after one immunization with S-antigen; however, multiple immunizations readily converted all animals so tested to CB47 responders. Rabbits and guinea pigs exhibited very weak responses to CB47 following one immunization; multiple immunizations increased the response minimally. Rats produced a strong antibody response to peptide CB123, which contains the known uveitogenic sites, while very little activity to CB123 was raised in rabbits and guinea pigs. Only 3 murine strains, LP, LP.R3, and B10.R3-71, responded with antibodies to CB123 and the epitope was mapped to a 30 residue region which in rats also contains two distinct pathogenic sites and an antibody epitope. Only rats and rabbits made antibody to the CB35 peptide; the epitopes were contained within an 18 residue sequence. The results show that a main immunogenic region is located in S-antigen near the C-terminus and is independent of species or MHC. Less dominant, species and strain-dependent immunogenic regions were found in three other areas, i.e. peptides CB47, CB123 and CB35.

Role of antibodies in T cell-mediated experimental allergic encephalomyelitis

The role of the humoral phase of the immune response in development of T cell-mediated experimental allergic encephalomyelitis (EAE) had not been clearly defined previously even though studies of the myelin basic protein (MBP) molecule had demonstrated the presence not only of T cell but also B cell epitopes capable of inducing cell-mediated immunity and antibody formation. Particularly relevant to this report are the immunological expressions of the region which induces EAE in the Lewis rat. The development of primary demyelination in Lewis rats is preceded by a cell-mediated immune response as well as antibody formation, both of which are highly specific to the encephalitogenic 14-residue peptide that defines the 69-84 region of the parent MBP. Our results are consistent with the dogma that EAE is a T cell-mediated disease, but they also clearly demonstrate an important role for specific antibodies in the development of these T cells responsible for demyelination. The antibody response, which may be heteroclitic, is necessary for T cells to develop into an effector T cell subset. Without this B cell response the subsequent T cell response does not lead to demyelination. In this report we shall discuss these findings and further show that the T cell and B cell epitopes, which are located within the 14-residue sequence, are physically separated and dependent upon the form of synthetic peptides known to induce T cell-mediated and/or humoral immunity.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of the ribosomal P2 protein autoantigen are similar to those of foreign protein antigens

Approximately 15% of patients with systemic lupus erythematosus have autoantibodies that bind to a shared epitope previously shown to be located on the carboxyl-terminal 22 amino acids of three 60S ribosomal proteins, P0, P1, and P2 ("P proteins"). A hydrophilicity plot and fine epitope mapping with seven synthetic peptides revealed that the properties of the antigenic site were similar to certain properties of epitopes on foreign protein antigens--namely, the epitope was located in the most hydrophilic portion of the P2 protein and also in the terminal region of the molecule. However, this site has been highly conserved during evolution. A mouse monoclonal antibody induced by immunization with ribosomal proteins had a fine specificity similar to the lupus antibodies. This finding indicates that a highly conserved region of a lupus autoantigen may also be antigenic in some normal animals. Therefore, lupus autoantibodies may be similar in most, if not all respects, to antibodies produced by immunization.

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.

Immunochemistry of scorpion alpha-toxins: study with synthetic peptides of the antigenicity of four regions of toxin II of Androctonus australis Hector

Sequences 19-29 and 28-39 of toxin II of the North African scorpion Androctonus australis Hector have been synthesized. These two peptides correspond to the highest peaks in the hydrophilicity profile of toxin II and were thus believed to account for a significant proportion of toxin antigenicity. Affinity chromatography of solid-phase-bonded peptides allowed us to purify two sub-populations from the total IgGs raised against the native toxin. They both still bound to 125I-toxin II and showed a restricted heterogeneity in their specificity. Solid-phase immunoassays confirmed the antigenicity of these synthetic peptides and also that of two other previously described synthetic replicates of the antigenic regions of toxin II: sequences (5-14) S-S (60-64) and 50-59. The location of the four antigenic regions relative to the postulated location of the receptor-binding site of the toxin is discussed.

Differential effects of defined chemical modifications on antigenic and pharmacological activities of scorpion alpha and beta toxins

Specific chemical modifications of scorpion alpha and beta toxins have been used to study the involvement of particular residues in both the pharmacological and the antigenic sites of these toxins. Modification by 1,2-cyclohexanedione of arginine-27 of a beta toxin, Centruroides suffusus suffusus toxin II, drastically decrease the antigenic activity without any influence on the pharmacological activity. Conversely, modification by the same reagent of arginine-2 of an alpha toxin, Androctonus australis Hector toxin III, led to a 100-times less pharmacologically potent derivative and did not induce a significant loss of antigenic activity. Excision of the N-terminal pentapeptide of another alpha toxin, Buthus occitanus mardochei toxin III, by pepsin digestion led to a non-toxic derivative retaining full antigenic activity. Thus, the N-terminal part of the conserved hydrophobic surface of the toxin is highly implicated in the pharmacological activity, whereas the region of arginine-27, located in the alpha helix situated on the back surface, opposite the conserved hydrophobic region, is fully implicated in the antigenic activity and is far from the pharmacological site. These results are good arguments in favor of the idea that in scorpion toxins the surfaces implicated in the pharmacological and the antigenic activities do not overlap. Since the antigenic sites are present in highly variable sequence the development of an efficient polyvalent serotherapy is questionable.

Rational design and application of idiotope vaccines

Current emphasis on risk factors associated with established vaccines and pressing needs for vaccines against certain viral transmitted diseases have stimulated the search for new conceptual and practical approaches to vaccine production. Among these developments, the idiotope vaccine method has produced promising results. In this review the basic and conceptual principles for idiotype vaccine design are discussed. A novel approach for identifying idiotopic structures in the three dimensional structure of internal idiotope antigens is developed. The method is based on the relationship of the immune response with the evolutionary variation and diversity of the immunoglobulin family. Idiotopic structures are found in specialized topographic regions on the surface of the immunoglobulin molecule. The knowledge of these idiotope domains will facilitate the synthesis of idiotope expressing peptides and the computer modeling of the three dimensional structure of internal idiotope antigens. Finally, the existing evidence for successful application of the idiotope vaccine method is summarized and new disease groups are identified which could benefit from the development of idiotope vaccines.

cDNA cloning of a human autoimmune nuclear ribonucleoprotein antigen

Sera from patients with systemic lupus erythematosus and other autoimmune disorders contain antibodies against nuclear proteins. One such autoantibody system, known as Sm, reacts with antigens associated with small nuclear RNA molecules. In this paper we report the use of Sm autoantibodies to isolate a cDNA clone for the mRNA of one of these nuclear antigens. A HeLa cell cDNA library was screened by message selection followed by autoantibody reaction of cell-free translation products. This led to the identification of a cDNA clone, p281, containing sequences complementary to mRNA for an Sm autoantibody-reactive, 11,000 Mr protein. This cloned Sm antigen comigrated with the small nuclear RNA-associated protein known as "E" and reacted with four out of four Sm autoantibodies that precipitate E protein from total mRNA translation products. RNA gel blot hybridization with clone p281 DNA revealed a poly(A)+ mRNA of approximately equal to 600 nucleotides in human and marmoset (New World primate) cells. Southern blot hybridization of HeLa cell and human lymphocyte DNA indicated the presence of 6-10 copies of p281-homologous sequences. Similar copy numbers were observed with genomic DNA from baboon, cat, and mouse, indicating that the Sm antigen mRNA sequence represented in p281 is conserved across three classes of the Mammalia (primates, carnivores, and rodents). However, no cross-hybridization of p281 was observed with frog or Drosophila DNA. In light of existing evidence that the mammalian Sm antigen E is a weaker autoantigen than other small nuclear RNA-associated proteins, these results suggest a possible correlation between a protein's capacity to serve as an autoantigen during breakdown of the host's immunological tolerance and its extent of evolutionary conservation, whereas the inverse relationship applies to conventional immunity. We suspect, as have others, that this is a clue to the mechanism of autoimmunity.

Analysis of an evolutionarily conserved antigenic site on mammalian cytochrome c using synthetic peptides

Two synthetic peptides inclusive of the NH2-terminal N-acetyl-Gly-Asp-Val-Glu tetrapeptide of mammalian cytochrome c (cyt c) were used in this study to address the question of whether mammals can respond immunologically to an evolutionarily conserved region of a protein. These peptides were assessed for their capacity (i) to act as immunogens for the production of anti-self cyt c antisera and (ii) to bind rabbit anti-rodent cyt c antibody. The findings from these studies indicate the existence of an immunogenic determinant in an evolutionarily conserved region of cyt c that contains residues 1-4. This determinant can induce anti-self cyt c antibodies whether presented as a peptide on a carrier protein or in the context of the intact molecule as polymerized mammalian cyt c.

Delineation and conformational analysis of two synthetic peptide models of antigenic sites on rodent cytochrome c

Two regions of rodent cytochrome c, one within the first four residues of the molecule, which is N-acetylated, and one at a beta bend around residue 44, are known to be immunogenic and antigenic in rabbits. Using sequential peptide synthesis, we have determined the residues required for linear synthetic peptides within these sequences to bind to antibody raised in rabbits to intact rat cytochrome c. The residues that were important in binding the N-terminal peptides were N-acetylglycine at position 1 and valine at position 3. The smallest peptide sequence around residue 44 that would bind to antibodies was Gln-Ala-Ala-Gly-Phe. A theoretical conformational analysis of these peptides showed that the amino-terminal tetrapeptide adopts a wide statistical ensemble of conformational states and that the addition of residues beyond 41 and 45 in the other sequence does not appear to stabilize longer peptides in the native beta-bend conformation. Thus, the antigenicity conferred by Phe-46 and Gln-42 in this peptide is most likely due to the direct interaction of the side chains of these residues with the antibody binding site. The demonstration here that native conformation is not essential for antigenic peptides to bind to antibodies raised against the whole protein indicates that the association energy between antigen and antibody can be sufficient to induce conformation in conformationally flexible peptides. This supports the concept that anti-protein and anti-peptide antibodies may invoke conformational changes in cross-reactive protein antigens and may explain why longer peptides, which may adopt stable nonnative secondary structure, often do not bind to antibodies raised to the whole molecule.

Mapping epitopes on the insulin molecule using monoclonal antibodies

A panel of 18 monoclonal antibodies (mAb) delta to insulin have been prepared and used to begin to map antigenic determinants on the insulin molecule. All 18 mAb were of the IgG class, with 14 IgG1, 2 IgG2a and 2 IgG2b. The affinities of these mAb for their immunizing insulin ranged from 1 X 10(6) to 3 X 10(8) 1/M. The epitope recognized by three of the mAb, 1, 7 and 16 involves the three residues of the A chain, A 8-10, the so called A chain-loop determinant. This A chain loop is one of the most evolutionarily diverse regions of insulins from different species. Another mAb, 10, has been hypothesized to recognize a nearby epitope composed of the A chain residues, A4 and A8 and a B chain residue, B29, that are adjacent on the surface of the insulin molecule. Four of the mAb bind to synthetic B chain. The epitopes recognized by these 4 mAb and the last 10 mAb are unknown but the mAb are grouped according to their ability to bind to different species of insulin or proinsulin. The results of an 18 X 18 matrix analysis of pairs of mAb binding simultaneously to insulin indicate that, despite the finding that some mAb see similar antigenic sites on the insulin molecule, each of the mAb recognizes a unique site on the insulin molecule. Finally, a lower estimate of the number of possible antibodies made to insulin has been calculated to be greater than or equal to 115, a number only 10-fold lower than the lower limit of antibodies made to dinitrophenyl (DNP) or (4-hydroxy-5-iodo-3-nitrophenyl)acetyl (NIP), following hapten protein immunization.

A natural model of immunologic tolerance. Tolerance to murine C5 is mediated by T cells, and antigen is required to maintain unresponsiveness

A unique experimental model is described, where natural immunologic tolerance to a well-defined soluble native antigen (murine C5) is examined in congenic strains of mice that differ only by the presence or the absence of C5. A highly sensitive hemolytic assay was developed to detect nanogram amounts of C5 as well as an assay of anti-C5 inhibition of C5 hemolytic activity. The latter was more sensitive than immunodiffusion. Two reciprocal approaches were used to study the cellular basis of tolerance in irradiated hosts of either strain. In the first, lymphoid cells from either strain were transferred to irradiated B10.D2OSN hosts that were lacking C5 and so would not hinder detection of anti-C5 antibody upon challenge with murine C5. Second, lymphoid cells from either strain were transferred to irradiated B10.D2NSN hosts, whose native C5 provided the antigenic stimulus. The immune response of whole nonadherent spleen cell suspension as well as mixtures of T and B cells (separated on the basis of surface immunoglobulin) from either strain were studied. In addition, the duration of tolerance and the antigen requirement to maintain it in irradiated C5-deficient hosts repopulated with C5-sufficient spleen cells was examined. The positive control of irradiated C5-deficient hosts repopulated with syngeneic spleen cells showed a primary and secondary response to immunization. In contrast, C5-sufficient spleen cells failed to respond both in the primary and the secondary response. Because the unresponsiveness was not caused by antigen carryover and was not antigen specific, it represents central tolerance. In C5-sufficient irradiated hosts (where immunization was not required and antigen was present in natural form and physiological concentration), transfer of C5-deficient cells mediated a drop in C5 levels to 10-20% of that noted in unreconstituted controls. T and B cell mixing experiments from the two strains into deficient or sufficient hosts demonstrated that tolerance is T cell dependent and that C5-sufficient or -deficient B cells could cooperate with nontolerant C5-sufficient T cells to produce significant anti-C5 antibody or mediate a significant drop in C5 levels. In addition, the presence of antigen was necessary to maintain tolerance. In conclusion, these results show that (a) natural tolerance to C5 is an active process that is T cell dependent and requires the presence of antigen; (b) in this natural model, clonal abortion does not seem to occur; and (c) both tolerant and nontolerant B cells retain the capacity to produce autoantibody.

The major B and T cell determinant on pigeon cytochrome c in B10.a mice

The specificities of B10.A B and T cells responding to pigeon cytochrome c have been examined. Proliferating T cells recognize glutamine 100 and lysine 104 and can be stimulated in vitro by either native cytochrome c molecules or certain of their CNBr-cleavage fragments. In contrast only molecules with the native cytochrome c conformation were found to interact with B10.A antipigeon cytochrome c antibodies. Antibodies appear to recognize a determinant or determinants which overlaps with that which elicits the T cell proliferative response.

Evolution of cytochrome C investigated by the maximum parsimony method

Rates of evolution for cytochrome c over the past one billion years were calculated from a maximum parsimony dendrogram which approximates the phylogeny of 87 lineages. Two periods of evolutionary acceleration and deceleration apparently occurred for the cytochrome c molecule. The tempo of evolutionary change indicated by this analysis was compared to the patterns of acceleration and deceleration in the ancestry of several other proteins. The synchrony of these tempos of molecular change supports the notion that rapid genetic evolution accompanied periods of major adaptive radiations. Rates of change at different time in several structural-functional areas of cytochrome c were also investigated in order to test the Darwinian hypothesis that during periods of rapid evolution, functional sites accumulate proportionately more substitutions than areas with no known functions. Rates of change in four proposed functional groupings of sites were therefore compared to rates in areas of unknown function for several different time periods. This analysis revealed a significant increase in the rate of evolution for sites associated with the regions of cytochrome c oxidase and reductase interaction during the period between the emergence of the eutherian ancestor to the emergence of the anthropoid ancestor.