Acid-treated, naked bacteria as immune carriers for protein antigens

Salmonella minnesota R595 bacteria were stripped of their natural antigenic determinants to yield acid-treated, naked bacteria. The proteins, human apolipoprotein A1 and carcino-embryonic antigen, were adsorbed to naked bacteria and these complexes were used to immunise rabbits. Although the antibody titres obtained were comparable to those achieved using Freund's adjuvant emulsions, much less antigen was needed for immunisation. This technique could be of great value where the amount of protein available for immunisation is very small.     

The use of peroxidase anti-peroxidase (PAP) complexes in the detection of plant viruses by ELISA

An ELISA test system for detection of plant viruses in field samples is described, based on the unlabelled antibody method using a peroxidase-antiperoxidase (PAP) complex. Novel features of the system include the use of acid-treated naked bacteria as combined carrier-adjuvants for the production of rabbit antiviral antibodies, and the use of acid-treated chicken antibodies (IgY) for antigen trapping in the ELISA. Systems for detection of potato virus Y (PVY), potato leafroll virus (PLRV), grapevine fanleaf virus (GFV) and grapevine virus A (GVA) were developed and compared with conventional direct double antibody sandwich (DAS) systems in tests with both purified virus and field samples. The PAP systems offer improved sensitivity, no background problems in the outer rows of the microtitre plates and are much easier to visualize with the naked eye if no plate reader is available.     

The production of highly specific anti-testosterone antisera using acid-treated bacteria as immunogenic carrier

A novel and effective procedure for the production of highly specific anti-testosterone antibodies is described. It involved pretreatment of experimental animals with tolerogens followed by immunization with conjugates of testosterone covalently linked to acid-treated Salmonella minnesota R595 bacteria as immunogenic carriers. Antibodies elicited by this procedure showed minimal cross-reactivity towards 5 alpha-dihydrotestosterone and some of them were successfully used in radioimmunoassays for the determination of serum testosterone levels, even without the need for prior extraction.     

The Production of Highly Specific Anti-Testosterone Antisera Using Acid-Treated Bacteria as Immunogenic Carrier

A novel and effective procedure for the production of highly specific anti-testosterone antibodies is described. It involved pretreatment of experimental animals with tolerogens followed by immunization with conjugates of testosterone covalently linked to acid-treated Salmonella minnesota R595 bacteria as immunogenic carriers. Antibodies elicited by this procedure showed minimal cross-reactivity towards 5α-dihydrotestosterone and some of them were successfully used in radioimmunoassays for the determination of serum testosterone levels, even without the need for prior extraction.     

Active in situ immune complex glomerulonephritis using the hapten-carrier system: role of epitope density in cationic antigens.

The role of epitope density in cationic antigen was investigated in an active model of in situ immune complex glomerulonephritis (ICGN) using the hapten-carrier system. Trinitrophenol (TNP) was conjugated with variable density to cationic human immunoglobulin (C-HIgG) to yield TNP6.2-C-HIgG (low-valency antigen) and TNP31.3-C-HIgG (high-valency antigen). In rats preimmunized with TNP17.3-bovine serum albumin (BSA), endocapillary proliferative GN with proteinuria developed in rats receiving high-valency antigen. In contrast, no significant abnormalities in renal histology or urinalysis were observed when a low-valency antigen was injected. These results indicate that glomerular injury produced by hapten-specific immune reaction is affected by the number of haptenic groups conjugated to the carrier molecule (epitope density) in active in situ ICGN.     

Mechanism of formation of subepithelial electron-dense deposits in active in situ immune complex glomerulonephritis.

The influences of the epitope density on cationic antigens on the fate of immune reactants and the formation of subepithelial electron dense deposits (EDD) were studied in a model of active in situ immune complex glomerulonephritis (ICGN), using a hapten-carrier system. Three weeks after immunization with trinitrophenol conjugated bovine serum albumin (TNP17.3-BSA), the left kidneys of rats were perfused with 500 micrograms of TNP6.2-cationized human immunoglobulin G (C-HIgG) or TNP31.3-C-HIgG. The renal tissues were then examined at intervals by light, immunofluorescence, and electron microscopies. The perfused kidneys of rats given high-valency antigens (TNP31.3) showed marked subepithelial EDDs with foot process retraction associated with proteinuria. In contrast, those of rats given low-valency antigens (TNP6.2) showed only small subepithelial EDDs beneath the slit membrane, which consisted of apparently normal epithelial cells, and did not develop proteinuria. Kinetic studies on immunofluorescence showed that glomerular depositions of immune reactants (TNP-carrier conjugate, rat IgG, and C3) were present longer in rats treated with high-valency antigens than in those treated with low-valency antigens. We conclude that the epitope density on cationic antigens strongly influences the retention of immune reactants and the formation of subepithelial EDDs, as well as development of glomerular injury.     

Self versus non-self carrier in primary and secondary anti-TNP B cell response: I. specificity of help

Humoral anti-hapten responses are supposed to require carrier-specific help. Yet, «TNPspecific» help can be activated with TNP coupled to syngeneic lymphocytes. To further clarify the role of hapten-specific vs. carrier-specific helper T cells (T_H) in the humoral anti-TNP response, BALB/c mice were immunized with TNP coupled to cellular or soluble self or nonself carriers, we analyzed primary and secondary B cell responses as well as the apparent specificity of help. TNP bound to syngeneic red blood cells (sRBC), syngeneic albumin (sA) and syngeneic polyclonal or monoclonal immunoglobulin (s1g/smIg) and TNP coupled to non-self carriers initiated equivalent primary anti-TNP responses. On the other hand, a secondary anti-TNP response was only obtained with heterologous carriers or with smIg. Even with heterologous carriers or with smIg, the magnitude of the secondary anti-TNP response exceeded only slightly the amplitudes of a primary anti-TNP response. Furthermore, if animals were challenged shortly after priming, they appeared un/-hyporesponsive.In vitro analysis revealed that in the primary as well as in the secondary anti-hapten response, TNP-specific T_H were involved, i.e., the primary response to s1g, sA and sRBC was exclusively due to TNP-specific help, the response after priming with TNP-smIg or TNPheterologous carrier was due to the additive effects of carrier- and TNP-specific help. Since «carrier-specific» help with smIg was independent of the antibody specificity as well as of the Ig class, we suppose that sm1g activated idiotype-specific TH, which functioned like «carrier» T_H.Two mechanisms were responsible for the low magnitude of the secondary anti-hapten response: competition for carrier-specific help (using heterologous carriers), antibody (AB)-dependent suppression.     

Tolerance induction during ontogeny II. Distinct unresponsive states in immature mice question the generality of clonal abortion

Multivalent trinitrophenyl (TNP) conjugates of both human γ-globulin (HGG) and bovine serum albumin (BSA) are capable of inducing hapten-specific unresponsiveness in neonatal mice, as assessed by challenge with TNP on thymus-dependent carriers. When such mice are challenged with TNP on thymus-independent carriers, however, only TNP-HGG- but not TNP-BSA-treated mice are found to be substantially unresponsive to the hapten. Moreover, unresponsiveness induced by BSA, but not HGG, as a carrier was associated with the presence of antigen-specific suppressor cells. Thus, contrary to predictions made by defendants of the classical clonal abortion hypothesis, functional deletion of hapten-specific B cells appears to depend on the nature of the hapten-carrier complex. This conclusion is supported by B cell-precursor frequency estimates indicating that the number of hapten-specific precursor cells is significantly lower in TNP-HGG-treated mice, but remains unaltered in TNP-BSA-treated mice relative to the precursor frequency in untreated animals. While it remains a formal possibility that the differences in tolerogenicity seen between the two carriers can be interpreted in terms of a difference in serum half-life, we favor the interpretation that the distinction lies in molecular aspects of the carrier, which allow for differences in antigen handling by sets of interacting cells.     

Tolerogenic properties of human IgG subclasses in mice

The tolerogenic properties of the purified myelomatous human IgG subclasses IgG1, IgG2, IgG3 and IgG4 were investigated in mice, when given at a dose of 1 or 5 mg either, chemically nonmodified or trinitrophenylated. A complete tolerance at the helper T cell level was obtained with IgG1, IgG2 and IgG3, and a partial tolerance with IgG4 at the dose of 5 mg. At a dose of 1 mg, tolerance was observed only with IgG3. The ability of these human IgG subclasses to induce tolerance at the helper T cell level was modified after trinitrophenylation. Each subclass induced a complete tolerance when given at a dose of 1 mg. At higher doses (5 mg), a complete tolerance was obtained at the B cell level, using trinitophenyl (TNP) IgG1, TNP IgG2, TNP IgG3 or TNP IgG4 as carriers.     

The "patchy" immunodeficiency of CBA/N mice.

The in vivo responses of CBA/N (which have an X-linked defect of B lymphocyte differentiation) and CBA/J normal mice to 2,4,6-trinitrophenylated (TNP) bacteriophage T4 and Diplococcus pneumoniae CS variant have been compared. Both antigens are thymus-independent (TI), and TNP-CS additionally contains the phosphorylcholine (PC) epitope, CBA/N and CBA/J mice give TNP plaque-forming cell responses similar in magnitude and avidity although only CBA/J give a PC response when challenged with TNP-CS. These results indicate that CBA/N mice have a "patchy" defect of antigen-induced humoral responses. This defect is manifested only in certain subpopulations of B cells and is not restricted to TI responses.     

Generation of adult-like antibody avidity profiles after early-life immunization with protein vaccines

The capacity to induce high-avidity antibodies following early-life immunization has long been questioned, and the possibility of inducing such antibodies soon after birth is a recognized goal for a number of vaccination strategies. Therefore, we assessed the capacity to develop high-avidity antibodies to peptidic vaccines in 1-week-old BALB/c mice. The dynamics of the generation of antibody molecules of increasing avidity were analyzed on circulating serum antibodies and, where feasible, at the single-cell level on spleen and bone marrow antibody-secreting cells. Two alum-adsorbed protein-based human vaccines, tetanus toxoid (TT) and pertussis toxin, induced neonatal antibody responses with adult-like avidity profiles. This was confirmed at the level of spleen and bone marrow ASC. In contrast, immunization with TT-P30, a 21-mer synthetic peptide containing a TT-immunodominant epitope, trinitrophenyl hapten (TNP) conjugated to ovalbumin or TNP conjugated to Ficoll, induced a much lower avidity profile in early life than in adults. These observations indicate that in murine models the avidity maturation of T cell-dependent antibody responses induced by structurally complex protein vaccines can be fully elicited after early life immunization, as opposed to the maturation of responses induced with short peptides or hapten-based vaccines.     

Assay of preS epitopes and preS1 antibody in hepatitis B virus carriers and immune persons

The diagnostical significance of the large hepatitis B surface protein with its preS1 attachment site and of anti-preS antibodies are not yet well known. We investigated the epitope of the preS1 attachment site to see whether it is a marker of viremia and whether antibodies against it occur in convalescents and vaccinees. For comparison, sera were also tested for the presence and relative amount of a preS2 epitope. The epitopes were detected by binding to specific monoclonal antibodies (mAb MA18/7 for the preS1 epitope and mAb Q19/10 for the preS2 epitope) at the solid phase of a sandwich enzyme-linked immunosorbent assay. Antibody against the preS1 epitope was detected by inhibition of binding to mAb MA18/7. This mAb inhibits attachment of preS1 antigen to hepatocytes and reacts with a subtypeindependent sequential epitope at the surface of hepatitis B virus between amino acid 29–36. This preS1 epitope occurs in most hepatitis B surface antigen (HBsAg) carriers, irrespective of viremia. Free preS2 epitope Q19/10 is present in samples with more than 8 g/ml total HBsAg and it is masked in sera with less HBsAg. Antibodies which compete with mAb MA18/7 for its viral preS1 epitope occur in one third of HBsAg carriers who were negative for hepatitis B e antigen. It also occurs in one third of convalescents and in most good responders to plasma-derived vaccines.     

Monoclonal antibodies specific for Shigella flexneri lipopolysaccharides: clones binding to type IV, V, and VI antigens, group 3,4 antigen, and an epitope common to all Shigella flexneri and Shigella dysenteriae type 1 stains.

Monoclonal antibodies reactive with Shigella flexneri O antigens were generated in both mouse and rat systems. Antibody-producing hybridomas were screened in an enzyme-linked immunosorbent assay using chemically defined lipopolysaccharides as antigens, and the epitope specificities were determined with a panel of lipopolysaccharides and synthetic O-antigen-specific glycoconjugates as antigens. To verify the specificity seen in the enzyme-linked immunosorbent assay, the antibodies were used in agglutination against a large number of S. flexneri strains. Monoclonal antibodies with the following specificities were identified: type, antigen IV (reactive with serotype 4a and 4b bacteria); type antigen V (reactive with serotype 5a and 5b bacteria); type antigen VI (reactive with serotype 6 bacteria); group antigen 3,4(reactive with serotype 1a, 2a, 3b, 4a, 5a, and Y bacteria); and group antigen 1 (reactive with an epitope present on all S. flexneri and Shigella dysenteriae type 1 bacteria). Furthermore, a monoclonal antibody defining a new O-antigenic epitope present on some S. flexneri strains of serotypes 4a, X, and Y was characterized (4X). The monoclonal antibodies analyzed in this study define epitopes described by polyclonal antisera (type antigens IV, V, and VI), define a hitherto uncharacterized epitope (group antigen 1), and finally identify new epitopes in what has previously been considered as one epitope (group antigen 3,4 and type antigen IV). These immunochemically characterized monoclonal antibodies may have a powerful potential in studies of the importance of humoral immunity in shigellosis.     

Immune response of rabbits to lipid A: influence of immunogen preparation and distribution of various lipid A specificities.

Sixty-two rabbit anti-lipid A serum samples were compared with respect to the immunogens used (synthetic lipid A and partial structures, natural lipid A, or acid-treated bacteria). Immunoglobulin (Ig) type-specific differences in rabbit response between liposomal membrane-embedded (LME) and other lipid A immunogens were found: LME lipid A elicited predominantly IgM antibodies. Previous findings of equally good immune responses to synthetic lipid A and acid-treated bacteria (L. Brade, E.T. Rietschel, S. Kusumoto, T. Shiba, and H. Brade, Infect. Immun. 51:110-114, 1986, and L. Brade, E.T. Rietschel, S. Kusumoto, T. Shiba, and H. Brade, Prog. Clin. Biol. Res. 231:75-97, 1987) turned out to be restricted to complement-fixing antibodies; IgG titers of sera against free lipid A (whether synthetic or natural) were significantly lower than those raised with bacteria. The results indicated an increase in IgG content of sera from LME lipid A over other free lipid A immunogens to acid-treated bacteria. These data underline the importance of the physicochemical environment for the immunogenicity of lipid A. As a second objective, the presence of various lipid A antibody specificities was tested with synthetic lipid A antigens. Antibodies to monophosphoryl lipid A were detected only in sera raised with monophosphoryl immunogens. Reactivity with monosaccharide partial structures of lipid A was found both in sera against monophosphoryl lipid A and in 60% of sera against bisphosphoryl lipid A. In the former, monosaccharide reactivity was of a magnitude similar to that of reactivity with lipid A; in sera against bisphosphoryl lipid A, it was lower. No reactivity or only marginal reactivity was found with phosphate-free lipid A, thus emphasizing the role of phosphate substitution for the lipid A epitopes recognized.     

Characterization of two different antibody specificities recognizing distinct antigenic determinants in free lipid A of Escherichia coli.

Antisera were raised in rabbits with acid-treated Re mutant bacteria from Salmonella minnesota and Escherichia coli and tested in a passive hemolysis assay with di- and monophosphorylated free lipid A of E. coli (LipA-Ac and LipA-HCl, respectively) coated onto sheep erythrocytes. Depending on the acid used to prepare the immunogen (acetic versus hydrochloric acid), different antibody specificities were obtained. Antiserum prepared against HCl-treated bacteria was found to react with both antigens to the same extent (i) in the passive hemolysis test, (ii) in the passive hemolysis inhibition test, and (iii) in absorption experiments, suggesting that antibodies in this antiserum recognize an antigenic determinant equally present in LipA-Ac and LipA-HCl. Antiserum raised against acetic acid-treated bacteria reacted with the homologous antigen (LipA-Ac) in the passive hemolysis and passive hemolysis inhibition test as well as in absorption experiments. However, the antiserum failed to react with the heterologous antigen (LipA-HCl) in the hemolysis test and during absorption, whereas in inhibition studies interaction of this antiserum with both antigens was observed. The inhibiting capacity of LipA-Ac was lower compared with that of LipA-HCl, indicating that the antigenic determinant of LipA-Ac is partly expressed by LipA-HCl in solution, but not when fixed on the surface of sheep erythrocytes. The role of glycosidically linked phosphate in lipid A is discussed with respect to antigenicity.     

A synthetic multi-epitope antigen enhances hepatitis C virus-specific B- and T-cell responses

Combining results from previous studies, a multi-epitope antigen PCXZ against the hepatitis C virus was synthesized in this study. The antigenic specificity of PCXZ was determined by recognizing antibodies in serum samples from hepatitis C virus patients, but not from healthy subjects or subjects who had the hepatitis B virus. The characteristics of PCXZ immunogenicity were evaluated in BALB/c mice. Strong antibody responses were generated in mice immunized with either naked PCXZ or PCXZ in Freund's adjuvant. As for the T-cell responses, Freund's adjuvant significantly increased interferon-γ secretion and enhanced the lytic activity of cytotoxic T lymphocytes. The epitope Pa, one component of PCXZ, made the most significant contribution to specific CTL lysis; this epitope was also a B-cell epitope and was able to induce high IgG titers. In summary, PCXZ was found to be highly immunogenic, and elicited both humoral and cellular immune responses in mice.     

Reactivity and crossreactivity of mouse helper T cells to malaria parasites.

The mouse helper T-cell response to four plasmodial and babesial parasites was measured by using them as carriers for a standard hapten (TNP). Helper T cells appeared to recognize all the parasites, but not to be able to distinguish between them. Helper T-cell responses could be augmented by vaccination with formalin-fixed parasites. However vaccination did not always confer protection against infection. Conversely, mice resistant to infection because of prior recovery from a homologous or heterologous infection had normal or reduced helper T-cell responses. It is concluded that resistance to infection with these parasites, though dependent on T cells, may not only involve the helper T-cell subpopulation.     

Immunoassay for Transthyretin Variants associated with Amyloid Neuropathy

An anti-transthyretin (TTR) mouse monoclonal antibody (88.6.FD6)of IgG1 subclass, obtained using as immunogen TTR from the serum of a patient with familial amyloidotic polyneuropathy, was found to bind to sera from carriers of several amyloidogenic TTR variants associated with peripheral neuropathy, but not to normal sera or sera from carriers of non-pathogenic or cardiomyopathic variants, in an ELISA performed under special conditions. Further characterization suggests that it recognizes an epitope near the N-terminal side of the TTR monomer. We propose that this epitope is exposed in amyloid and could be implicated in fibril deposition in the peripheral nervous system.     

Polymeric Display of Immunogenic Epitopes from Herpes Simplex Virus and Transmissible Gastroenteritis Virus Surface Proteins on an Enteroadherent Fimbria

The strong immunogenicity of bacterial fimbriae results from their polymeric and proteinaceous nature, and the protective role of these immunogens in experimental or commercial vaccines is associated with their capacity to induce antiadhesive antibodies. Fimbria-mediated intestinal colonization by enteropathogens typically leads to similar antibody responses. The possibility of taking advantage of these properties was investigated by determining whether enteroadhesive fimbriae, like the 987P fimbriae of enterotoxigenic Escherichia coli, can serve as carriers for foreign antigens without losing their adhesive characteristics. Random linker insertion mutagenesis of the fasA gene encoding the major 987P subunit identified five different mutants expressing wild-type levels of fimbriation. The linker insertion sites of these mutants were used to introduce three continuous segments of viral surface glycoproteins known to be accessible to antibodies. These segments encode residues 11 to 19 or 272 to 279 of herpes simplex virus type 1 (HSV-1) glycoprotein D [gD(11–19) and gD(272–279), respectively] or residues 379 to 388 of the transmissible gastroenteritis virus (TGEV) spike protein [S(379–388)]. Studies of bacteria expressing fimbriae incorporating mutated FasA subunits alone or together with wild-type FasA subunits (hybrid fimbriae) indicated that foreign epitopes were best exported and displayed on assembled fimbriae when they were inserted near the amino terminus of FasA. Fimbriated bacteria expressing FasA subunits carrying the HSV gD(11–19) or the TGEV S(379–388) epitope inserted between the second and third residues of mature FasA elicited high levels of foreign epitope antibodies in all rabbits immunized parenterally. Antibodies against the HSV epitope were also shown to recognize the epitope in the context of the whole gD protein. Because the 987P adhesive subunit FasG was shown to be present on mutated fimbriae and to mediate bacterial attachment to porcine intestinal receptors, polymeric display of foreign epitopes on 987P offers new opportunities to test the potential beneficial effect of enteroadhesion for mucosal immunization and protection against various enteric pathogens.     

Structural and functional analysis of spontaneous anti-nitrophenyl antibodies in three cyprinid fish species: carp (Cyrinus carpio), goldfish (Carassius auratus) and tench (Tinca tinca)

High spontaneous anti-trinitrophenyl (TNP) activities were found in three Cyprinid fish species: Carp (Cyprinus carpio), Goldfish (Carassius auratus) and Tench (Tinca tinca). The molecules involved, isolated by affinity chromatography on dinitrophenyl-lysine Sepharose (DNP-lysine-Sepharose), had the main characteristics of a high molecular weight immunoglobulin (IgM-like). Affinity measurements were performed on natural anti-DNP/TNP antibodies isolated from nine individual tench sera, using the inhibition of DNP-T4 bacteriophage inactivation technique. The antibodies analysed were more specific for TNP than for DNP. No activity was found against paranitrophenyl hapten. Affinities were all very low, even for TNP. In the three species, natural anti-DNP/TNP antibodies constitute as much as 11 to 16% of the total immunoglobulin concentration. This high level of nitrophenyl-binding serum immunoglobulins either suggests the existence of a particular regulatory mechanism in fish or reflects a generally low antibody diversity in these species.