Rational design and application of idiotope vaccines

The promise of the anti-idiotype concept

A basic tenet of antibody-based immunity is their specificity to antigenic determinates from foreign pathogen products to abnormal cellular components such as in cancer. However, an antibody has the potential to bind to more than one determinate, be it an antigen or another antibody. These observations led to the idiotype network theory (INT) to explain immune regulation, which has wax and waned in enthusiasm over the years. A truer measure of the impact of the INT is in terms of the ideas that now form the mainstay of immunological research and whose roots are spawned from the promise of the anti-idiotype concept. Among the applications of the INT is understanding the structural implications of the antibody-mediated network that has the potential for innovation in terms of rational design of reagents with biological, chemical, and pharmaceutical applications that underlies concepts of reverse immunology which is highlighted herein.

Human immune response to a peptide mimic of Neisseria meningitidis serogroup C in hu-PBMC-SCID mice

An anti-idiotype-based peptide mimic vaccine for Neisseria meningitidis serogroup C polysaccharide (MCPS) has been developed and shown to induce a response in mice that is specific, functional, and T-dependent. In this study, the immunogenicity of the MCPS peptide mimic vaccine preparation, as a potential vaccine for use in humans, is shown using the hu-PBMC-SCID mouse model. The human antibody response to the MCPS peptide mimic vaccine is specific and functional as shown by inhibition enzyme-linked immunoadsorbent assay (ELISA) and bactericidal assay. These data support the usefulness of the peptide mimic vaccine strategy for humans.

Peptide mimotopes of carbohydrate antigens

Carbohydrate structures have been identified as significant antigens for bacterial, viral, and fungal pathogens as well as targets on human tumor cells. Many of these antigens are poorly immunogenic in humans, requiring extensive adjuvant sublimation. Although conjugate carbohydrate vaccines appear promising, there are limitations of using carbohydrate formulations. An alternative approach is to use surrogate antigens for some carbohydrates. We are developing peptides that mimic carbohydrates which might be further manipulated to induce responses that target biologically important carbohydrates expressed on pathogens and on tumor cells. We have shown that peptide mimotopes of carbohydrates induce immune responses to carbohydrate structures with in vivo and vitro functionality. Model systems include the Neisseria group C meningococcal polysaccharide; the histo-blood group-related antigens expressed on tumor cells; and mannose, sialyl, and histo-blood group-related carbohydrate epitopes expressed on human immunodeficiency virus.

Molecular characterization of a monoclonal antibody produced in response to a group C meningococcal polysaccharide peptide mimic

We have developed a monoclonal antibody, designated anti-anti-Id Ab3-2C4 which reacts with Neisseria meningitidis serogroup C polysaccharide (MCPS). Anti-anti-Id Ab3-2C4 was produced by immunizing Balb/C mice with a peptide mimic of MCPS. This monoclonal antibody reacts with native polysaccharide and its anti-idiotype antibody Ab2-6F9 by ELISA. The synthetic peptide mimic was constructed based on the sequence of the VHCDR3 region of the anti-idiotype Ab2-6F9. We compared the cDNA sequence of Ab3-2C4 to the sequence of idiotype antibody Ab1-1E4 produced in response to native MCPS. The predicted amino acid sequence of the unique VHCDR3 of anti-anti-Id Ab3-2C4 is similar to that of idiotype Ab1-1E4. Also the VHCDR3 of both antibodies is similar to some of the known or suggested carbohydrate binding motifs. A different VH gene family was utilized by Ab3-2C4 than by Ab1-1E4. These results suggest that immunization with the anti-idiotype-derived peptide mimic of the MCPS antigen stimulates the production of antibodies with a binding site structurally related to idiotype antibodies, even though the antibodies Ab1-1E4 and Ab3-2C4 are not related in gene families. Our results support the premise that the use of peptide antigens which are mimics of carbohydrates is an alternate vaccine strategy for polysaccharide antigens and results in an appropriate response.

Peptide mimicry of the meningococcal group C capsular polysaccharide

Sequence analysis of the variable regions of the heavy and light chains of the anti-idiotypic antibody 6F9, which mimics the meningococcal group C capsular polysaccharide (MCP), was performed. The immunogenic site on 6F9 responsible for inducing an anti-MCP antibody response was determined by means of sequence and computer model analysis of these data. Complementarity-determining region 3 (CDR3) was found to be unique in that the sequence tract YRY was exposed on the surface. A synthetic peptide spanning the CDR3 domain was synthesized and complexed to proteosomes (meningococcal group B outer membrane protein). Immunizations of BALB/c mice with the peptide-proteosome complex resulted in a significant anti-MCP antibody response. Immunized mice were protected against infection with a lethal dose of Neisseria meningitidis serogroup C.

An anti-idiotype antibody which mimics the inner-core region of lipopolysaccharide protects mice against a lethal challenge with endotoxin

Recently, we described the generation and characterization of an Armenian hamster Ab2 beta anti-idiotype monoclonal antibody (MAb4G2) specific for the binding site of a mouse monoclonal antibody, MAbY1-4A6, directed against the conserved 2-keto-3-deoxyoctulosonate (Kdo)-containing inner-core region of lipopolysaccharide (LPS) (S. K. Field, M. Pollack, and D. C. Morrison, Microb. Pathog. 15:103-120, 1993). In that study, mice and hamster immunized with MAb4G2 generated serum immunoglobulin G and M (IgG and IgM) antibodies which cross-react with Salmonella minnesota R595-chemotype rough mutant LPS (Re-LPS). In this report, we demonstrate that in C3Heb/FeJ mice, MAb4G2 elicits an immune response which is characterized by specific binding of antibody to Re-LPS, as assessed by enzyme-linked immunosorbent assay. The practical use of MAb4G2 as a potentially effective therapeutic agent against gram-negative bacterial sepsis is suggested by the demonstration that immunization of these mice with MAb4G2 results in significant protection of D-galactosamine-sensitized animals against an otherwise lethal dose of Re-LPS. Assessment of the temporal changes in Re-LPS-specific serum antibody titers from mice immunized with MAb4G2 or Re-LPS over a 40-day period indicates that immunization with Re-LPS elicits significantly higher titers of serum IgM antibodies compared with those in animals immunized with MAb4G2. Conversely, two immunizations with MAb4G2 result in an up to 10-fold increase in anti-Re-LPS-specific IgG serum antibody titers relative to those obtained in mice immunized with Re-LPS. Nineteen days after the secondary boost with MAb4G2, anti-Re-LPS-specific IgG serum antibody titers were significantly higher (three- to fourfold) compared with those in Re-LPS-treated animals. Initial immunization with the anti-idiotype antibody primes animals for enhanced secondary responses to Re-LPS, as assessed by the titers of anti-Re-LPS-specific IgG profiles. These data suggest the potential utility of MAb4G2 as a candidate vaccine against the lethal properties of gram-negative bacterial LPS.

Antiidiotype antibodies as surrogates for polysaccharide vaccines

In past studies we demonstrated that monoclonal antibody 6F9 is a surrogate image of the meningococcal C capsular polysaccharide. These studies indicated that immunization with this anti-id resulted in a T-dependent antibody response. In the studies reported in this paper, we show that the response which is elicited is protective. Using a model of meningococcal infection in BALB/c mice in which the animals are rendered susceptible with iron dextran, we studied the ability of this anti-id to protect adult mice against challenge. These studies encompassed the ability of 6F9 to prime neonatal mice and provide them with protection to later challenge. Adult BALB/c mice immunized with 6F9 had a 100% survival and a significantly reduced level of bacteremia at 24 hours. Neonatal mice primed within 24 hours of birth and immunized at 4 weeks of age with 6F9 had a 100% survival and cleared their bacteremia by 8 hours. Neonatal mice primed with 6F9 and challenged at 5 weeks had a 90% survival. These data indicate that anti-id 6F9 is a surrogate antigen for the meningococcal C polysaccharide and is capable of inducing protective immunity in immunologically mature as well as immature animals.

Use of a 35.5 kDa cell membrane composition of Pasteurella multocida and an anti-idiotype antibody to induce protective immunity in leghorn chickens

Using polyacrylamide gel electrophoresis and Western blot analysis, a 35.5 kDa cell membrane composition of Pasteurella multocida ATCC 11039 was identified as a dominant epitope of the bacterium. Mice inoculated with inactivated whole bacteria produce antisera primary reactive with the 35.5 kDa component (Pm35.5) in Western blot analysis. The outer membrane component was composed primarily of protein but did have lipopolysaccharide present at 133 micrograms mg-1 protein. In challenge trials (Trial 2), groups of white leghorn chickens vaccinated with Pm35.5 or an anti-idiotypic antibody (using Pm35.5 as the original antigen) had significant difference in mortality of 3.2% and 48.3%, respectively, when compared with unvaccinated controls (99%). Mortality in a group of chickens receiving a commercially available bacterin (9.2%) was higher but not significantly different from the mortality of the Pm35.5 vaccinated group (3.2%).

Investigation of the poultry idiotypic network using Pasteurella multocida

The idiotypic network in leghorn laying hens was investigated by inoculating hens with a 35.5 kD outer membrane protein of Pasteurella multocida (Pm35.5), idiotype (Id), or Pm35.5 anti-Id. Egg yolks were analyzed for the presence of Id, anti-Id, or anti-anti-Id. Anti-Pm35.5 antibodies (Id) were not titered to an end-point but were present in high concentrations. The presence of anti-Id antibody in yolk was demonstrated by the inhibition of Pm35.5 binding to Id by anti-Id using a flow microsphere inhibition immunoassay. Inhibition of Pm35.5 binding to Id caused by different anti-Id preparations ranges from 51.5 to 56.1%. Not all of the anti-Id bound to a paratope-associated Id, since 8.3-12.8% of the fluoresceinated anti-Id bound to Id-coated beads in the presence of excess Pm35.5. We confirmed that a portion of the anti-Id antibodies was an internal image of the Pm35.5 Id and could mimic antigen by demonstrating that anti-Id inoculated in naive hens caused the synthesis of anti-anti-Id antibodies that bound to Pm35.5 in enzyme linked immunosorbent assay. Monoclonal anti-Id antibodies were also capable of inhibiting Pm35.5 binding to Pm35.5 Id coated microspheres and inducing anti-anti-Id antibodies in BALB/cJ mice that reacted with the original antigen, Pm35.5. Our investigation has also shown that idiotypic antibodies to P. multocida were transferred from chicken to egg.

Anti-idiotype induced protection against Neisseria meningitidis serogroup C bacteremia

We have developed a monoclonal anti-idiotypic antibody, designated 6F9, which acts as the surrogate image of the meningococcal group C capsular polysaccharide (MCP). Murine immunization with 6F9 results in a T-dependent anti-MCP antibody response. To examine the protective nature of the antibody response elicited by 6F9 we performed a series of live challenge studies using a murine model for meningococcal infection in which mice were iron dextran treated and challenged with 10 x LD50 of meningococcal group C strain 35E. Adult BALB/c mice immunized with 6F9 had a 100% survival and a significantly reduced level of bacteremia at 24 h. Mice immunized with MCP had an 80% survival rate, all survivors were bacteremic at 24 h. Neonatal mice primed within 24 h of birth and immunized at 4 weeks of age with 6F9 had a 100% survival and cleared their bacteremia by 8 h, which was significantly faster than the MCP primed and immunized mice. Neonatal mice primed with 6F9 and challenged at 5 weeks of age had a survival rate of 90% which was significantly higher than mice primed with MCP and the control group (60% and 50% survival, respectively). Mice primed at birth and immunized at 8 days had a 100% survival and 90% of these mice had sterile blood cultures by 8 h. Mice primed and immunized with MCP all remained bacteremic at 24 h. These data indicate that the anti-Id 6F9 which mimics the capsular polysaccharide of group C meningococci is capable of inducing protective immunity in immunologically mature as well as immature animals.

Anti-idiotypic antibodies to feline leukemia virus: an approach for retroviral immunization strategies

The present study describes an approach to the development and use of anti-idiotypic antibodies as a possible immunization strategy to prevent retroviral infection. The rationale for using anti-idiotypes (anti-Ids) to try to elicit an antigenic-specific immune response is examined, and the production and characterization of polyclonal and monoclonal anti-Ids are described. Several techniques were used to determine antigenic mimicry and anti-Id subtypes. The potential use of anti-Ids in feline leukemia virus (FeLV) receptor studies and vaccine trials in vivo were investigated. Results from these studies suggest that the anti-Id strategy is feasible for the FeLV model. Polyclonal Ab2 reagents were developed that blocked virus-receptor binding and thus inhibited viral infection in vitro and induced humoral immune responses in 6- to 8-week old kittens characterized by production of Ab3 with the ability to bind the original FeLV envelope protein gp70 as assessed by Western blot analysis.

The thymus-dependent nature of the murine antibody response to a monoclonal anti-idiotypic antibody to the Neisseria meningitidis serogroup C capsular polysaccharide

Idiotype vaccines are proteins which may offer an alternative strategy for the conversion of a thymus-independent antigen into a thymus-dependent immunogen. To examine this question, we have studied the nature of the immune response to a monoclonal anti-idiotypic antibody, designated 6F9, which acts as a surrogate of Neisseria meningitidis serogroup C capsular polysaccharide, and compared this response to the nominal antigen, the meningococcal C-polysaccharide (MCP). BALB/c mice immunized with an optimal dose (100 micrograms) of 6F9 generate a specific anti-MCP IgG response which is maximal after 4 weeks. Secondary immunization with 6F9 results in a three- to five-fold increase in the specific IgG response. Mice given an optimal immunizing dose of MCP (5 micrograms) failed to generate an anti-MCP IgG response. No secondary response is detectable in mice immunized with MCP. Animals immunized with 6F9 and subsequently challenged with live meningococci group C show a significant anti-MCP IgG response. BALB/c nu/nu mice fail to generate an anti-MCP IgG antibody response to 6F9, while the nu/+ controls generate an anti-MCP IgG antibody titer 100 times that of the MCP-immunized mice. Neonatal mice that failed to respond to MCP developed early IgM and a subsequent IgG anti-MCP response after immunization with 6F9. These data demonstrate that the anti-idiotype 6F9, the combining site of which contains a surrogate image of the meningococcal group C capsular polysaccharide, evokes the responses expected of a T-dependent antigen.

Protection of mice against the lethal toxicity of a lipopolysaccharide (LPS) by immunization with anti-idiotype antibody to a monoclonal antibody to lipid A from Eikenella corrodens LPS

We produced anti-idiotype antibodies to antibody to lipid A from Eikenella corrodens. The ALA-1 monoclonal antibody (immunoglobulin M [IgM] isotype), which had already been produced in our laboratory (T. Kato, I. Takazoe, and K. Okuda, Infect. Immun. 57:656-659, 1989), had reacted strongly with lipid A from E. corrodens, Escherichia coli, and Salmonella minnesota. Four anti-idiotype monoclonal antibodies to ALA-1 (Ab1), designated A2LA-1 (IgG1 isotype), A2LA-2 (IgG2a isotype), A2LA-3 (IgG2a isotype), and A2LA-4 (IgG3 isotype), which recognized the idiotype Ab1, were produced. A2LA-1, A2LA-2, and A2LA-3 were capable of over 61% inhibition of ALA-1 reactivity to E. coli J5 lipid A in an enzyme-linked immunosorbent assay system. The sera of mice and rabbits immunized with the anti-idiotype antibodies revealed that the internal image anti-idiotype antibody induced the production of IgG antibodies that cross-reacted with or bound to lipid A. These studies indicate that A2LA-1 and A2LA-2 contained an antigenic epitope that mimicked lipid A. Immunization of mice with A2LA-1 resulted in prevention of lethal toxicity from E. coli J5 lipopolysaccharide.

Revised immune network concepts

The idiotype network concept needs to be revised in order to be in agreement with current data on protein/protein interactions, with the phenomenon of T and B cell recognition of idiotopes, and with the failure of certain anti-idiotypes to stimulate a given immune response. It is proposed that the distinction among Ab2 alpha, beta, and gamma is abandoned, as well as the concept of an internal image idiotope which mimics the three-dimensional shape of nominal antigen. In place of these definitions, the concept of "network antigen" is introduced. Network antigens are potentially the entire repertoire of anti-idiotypes. However, their biological effectiveness is controlled and established by two factors: (i) the affinity to the idiotype Ig receptor; and (ii) the preexisting regulatory network segment that controls the outcome of immune stimulation or suppression. Screening for effective idiotype therapeutic agents has to be done with panels of anti-idiotype and idiotype antibodies in order to establish correlations between idiotope expression and disease progression. Recognizing the importance of network segments will be the first step in the direction toward a rational design of idiotype-based therapies.

Antiidiotypic antibody vaccine in murine Schistosomiasis mansoni comprising the internal image of antigen

This study presents the characterization of an experimental immunotherapeutic approach for schistosomiasis utilizing antiidiotypic antibodies. Antiidiotype (31-3B6) was generated in rabbits using a protective murine monoclonal antibody 31-3B6 which recognizes a 68,000-D molecular mass glycoprotein present in extracts of Schistosomiasis mansoni adult worm homogenetics. Immunization of mice with antiidiotype (31-3B6) before S. mansoni cercariae infection resulted in protection levels ranging from 16 to 41% depending on the route of administration of antiidiotypic antibody and the use of adjuvant. Levels of protection as high as 25% could be obtained with a single injection of antiidiotype (31-3B6) without the use of adjuvant. Animals noted to be resistant to infection with S. mansoni cercariae were also noted to exhibit a humoral immune response that bound components of S. mansoni adult worm homogenetics. This induced antiantigen immune response was shown to bind to the surface of S. mansoni schistosoma by indirect immunofluorescence. Further characterization of the induced antiantigen response showed that a portion (3-32%) of the induced humoral immune response portrayed the binding specificities of the murine monoclonal antibody 31-3B6. The data indicate that antiidiotype antibodies generated utilizing defined monoclonal antibodies can act as surrogate antigens in the protection of infection in schistosomiasis.

Development and characterization of an anti-idiotype antibody to the capsular polysaccharide of Neisseria meningitidis serogroup C

A monoclonal anti-idiotypic antibody (Ab2) whose antibody combining site contained a surrogate image of the meningococcal group C capsular polysaccharide was developed. To accomplish this, a monoclonal antibody against the group C capsular polysaccharide was developed by the fusion of splenocytes from mice immunized with Neisseria meningitidis group C strain MP13 with Sp2/0-Ag14 plasmacytoma cells. Monoclonal antibody 1E4, an immunoglobulin M isotype, demonstrated binding to the serogroup C polysaccharide in enzyme-linked immunosorbent assay (ELISA). Monoclonal antibody 1E4 reacted with 30 of 30 group C strains and 1 of 36 group B strains in immunodot assay, slide agglutination, inhibition ELISA, and bactericidal assay. This monoclonal antibody was selected as idiotype (Ab1) for the development of hybridomas producing an anti-idiotype antibody. One of the hybridomas developed, designated 6F9, was capable of over 70% inhibition of 1E4 in binding in the meningococcal C polysaccharide-specific ELISA. Studies with convalescent human serum demonstrated 100% inhibition of a serogroup C-specific ELISA with 200 micrograms of 6F9 per ml and 50% inhibition of this ELISA was achieved with 50 micrograms of 6F9 per ml. Monoclonal anti-idiotype antibodies (Ab3) with specificities similar to Ab1, 1E4 were generated from BALB/c mice immunized with the Ab2 (6F9). Immunization of rabbits with 6F9 resulted in an immunoglobulin G response which was significantly greater than that of control to a titer of 1:160. These studies indicate that monoclonal 6F9 contained a surrogate image on the combining antibody site which mimicked meningococcal C polysaccharide. This surrogate image is capable of evoking antibodies to the meningococcal C polysaccharide in syngenic and xenogenic species.

Selective induction of T-cell subsets by antibodies to the T-cell antigen receptor and to the subset-specific differentiation antigens CD8 and CD4

This report shows that small, resting T lymphocytes from mouse and man can be activated to proliferation and function by submitogenic concentrations of antibodies to T-cell antigen receptor in combination with antibodies to either CD8 or CD4. The combined antibodies can be applied either in solid phase condition or as soluble dimeric heteroconjugates. Activation is more efficient than by high concentrations of anti-T-cell-receptor antibody alone. Most importantly, activation is subset-specific such that the antibody to CD8/CD4 determines which T-cell subset will be induced.

Structural basis of stimulatory anti-idiotypic antibodies

In order to design and produce effective vaccines based upon the idiotype network hypothesis of Jerne, a thorough understanding of the biological and structural aspects underlying the stimulating activities of anti-idiotypic antibodies is needed. Here we determined the nucleotide sequence of the variable heavy and light chain regions of two monoclonal anti-idiotypic antibodies which induce different anti-phosphorylcholine responses. The nucleotide sequences of the variable domains of two monoclonal anti-TEPC 15 (T15) antibodies (F6-3 and 4C11) were determined by the primer extension and Maxam-Gilbert techniques. The nucleotide sequence data show that 4C11 and F6-3 have homologous VH segments and JH segments, but different D regions. The VH segments of both clones belongs to the J558 VH family. Most of the differences among the VH segments are located in CDR2. The VK segments of 4C11 and F6-3 are homologous to the VK gene group 4 and group 8, respectively. Comparison of the sequences of 4C11 and F6-3 with other published anti-idiotype antibodies shows that there is no preferential utilization of immunoglobulin genes. An analysis of the distribution of charged residues and hydropathic comparison studies were used to interpret the sequence of 4C11 in terms of the biological mimicry of antigenic stimulation.

Perspectives on antigenicity and idiotypy

The recent crystal determination of a lysozyme-antilysozyme complex provides a three-dimensional prototype of the manner in which contacts in idiotype-anti-idiotype interactions may be realized. Such interactions can be approximated by two complementary "flat" surfaces. Each IDR (autoantigenic locus) location might provide a particular recognition feature between two interacting partners. The combinatorial manner in which IDR domains are recognized by anti-idiotypic antibodies describe the repertoire of private and public (crossreactive) idiotopes of an antibody. Several interesting features emerge from consideration of the Ab contact residues in the crystal structure. First, framework residues are implicated in contacting the antigen: Thr 30 (FR1) of the heavy chain and Tyr 49 (FR2) of the kappa light chain. Both of these residues lie within predicted IDRs. Framework regions have recently been suggested to be involved in several anti-idiotypic systems, although such regions have, in the past, been disregarded based solely upon sequence analysis. The surface variability analysis, which identifies the repertoire of complementary interacting surfaces, depicts the immunoglobulin as having more variability than generally thought. This variability may also extend to T cell receptors since T cell chains express an extensive surface variable repertoire similar to that of the immunoglobulin light chains (Kieber-Emmons and Köhler, unpublished). Second, the D region plays a critical role in the generation of the antilysozyme combining sites. Similarly, the D segment makes up the largest component of an IDR. Third, while the CDR3 of the heavy chain contributes most to the antibody-lysozyme complex it is not the most surface-exposed (see Novotny, this issue). Nevertheless, surface variability analysis indicates that this region is generally immunodominant which is also observed experimentally. Together, these results indicate that perhaps certain IDR regions are intrinsically more antigenic. Idiotypic structures must be accessible for antibody recognition and binding. From a structural viewpoint, a single antibody molecule has a continuum or several different combining sites. Subsequently, a single residue can be contained in several overlapping idiotypic determinants. Surface variability analysis suggests that the hypervariable regions of Igs provide a diverse idiotope repertoire that can be utilized for binding. Monoclonal antibodies have been shown to have multiple specificities and this capacity for multiple binding is also intrinsic to the definitions that have emerged for anti-idiotypic antibodies.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Immunoglobulin with complementary paratope and idiotope

A hybridoma antibody (11E7-1) was isolated from a myeloma fusion with nu/nu BALB/c immunized against the T15 idiotype. This IgM antibody exhibited a dual specificity, binding both to PC and to anti-PC antibodies from two idiotype families. Binding to PC and anti-PC antibodies are completely inhibited by PC analogs. Furthermore, the hybridoma antibody binds to itself. Self-binding is also inhibited by PC analogs. From these data, we suggest that 11E7-1 hybridoma antibody has a PC-specific paratope site, and at same time expresses the internal PC antigen idiotope. The term autobody is proposed to signify its self-binding and potential role in autoimmunity. Autobodies may have a unique role in the network of immune system. Furthermore, it may be a model for designing idiotype vaccines.