The influence of epitope density on the immunological properties of hapten-protein conjugates. I. Characteristics of the immune response to hapten-coupled albumen with varying epitope density

Preparation of Monoclonal Antibody against Pyrene and Benzo [a]pyrene and Development of Enzyme-Linked Immunosorbent Assay for Fish, Shrimp and Crab Samples

Polycyclic aromatic hydrocarbons (PAHs) are significant environmental and food pollutants that can cause cancer. In this work, a specific monoclonal antibody (mAb) to identify pyrene (PYR) and benzo [a]pyrene (BaP) was prepared, and an indirect competitive enzyme-linked immunoassay (ic-ELISA) was established to detect PYR and BaP residues in living aquatic products for the first time. The effects of complete antigens with different coupling ratios on the production of high-sensitivity mAb was explored. Under the optimal conditions, the IC₅₀ value was 3.73 ± 0.43 µg/L (n = 5). The limits of detection (LODs) for PYR and BaP in fish, shrimp, and crab ranged from 0.43 to 0.98 µg/L. The average recoveries of the spiked samples ranged from 81.5–101.9%, and the coefficient of variation (CV) was less than 11.7%. The validation of the HPLC-FLD method indicated that the ELISA method set up in this experiment provided a trustworthy tool for PAHs residues detection in aquatic products.

Construction of an enantiopure bivalent nicotine vaccine using synthetic peptides

Clinical outcomes of anti-nicotine vaccines may be improved through enhancements in serum antibody affinity and concentration. Two strategies were explored to improve vaccine efficacy in outbred mice: the use of enantiopure haptens and formulation of a bivalent vaccine. Vaccines incorporating natural (-) nicotine haptens improved relative antibody affinities >10-fold over (+) haptens, stimulated a two-fold boost in nicotine serum binding capacity, and following injection with 3 cigarette equivalents of nicotine, prevented a larger proportion of nicotine (>85%) from reaching the brain. The activity of a bivalent vaccine containing (-) 3’AmNic and (-) 1’SNic haptens was then compared to dose-matched monovalent groups. It was confirmed that antisera generated by these structurally distinct haptens have minimal cross-reactivity and stimulate different B cell populations. Equivalent antibody affinities were detected between the three groups, but the bivalent group showed two-fold higher titers and an additive increase in nicotine serum binding capacity as compared to the monovalent groups. Mice immunized with the bivalent formulation also performed better in a nicotine challenge experiment, and prevented >85% of a nicotine dose equivalent to 12 cigarettes from reaching the brain. Overall, enantiopure conjugate vaccines appear to improve serum antibody affinity, while multivalent formulations increase total antibody concentration. These findings may help improve the performance of future clinical candidate vaccines.

Novel Anti-Nicotine Vaccine Using a Trimeric Coiled-Coil Hapten Carrier

Tobacco addiction represents one of the largest public health problems in the world and is the leading cause of cancer and heart disease, resulting in millions of deaths a year. Vaccines for smoking cessation have shown considerable promise in preclinical models, although functional antibody responses induced in humans are only modestly effective in preventing nicotine entry into the brain. The challenge in generating serum antibodies with a large nicotine binding capacity is made difficult by the fact that this drug is non-immunogenic and must be conjugated as a hapten to a protein carrier. To circumvent the limitations of traditional carriers like keyhole limpet hemocyanin (KLH), we have synthesized a short trimeric coiled-coil peptide (TCC) that creates a series of B and T cell epitopes with uniform stoichiometry and high density. Here we compared the relative activities of a TCC-nic vaccine and two control KLH-nic vaccines using Alum as an adjuvant or GLA-SE, which contains a synthetic TLR4 agonist formulated in a stable oil-in-water emulsion. The results showed that the TCC's high hapten density correlated with a better immune response in mice as measured by anti-nicotine Ab titer, affinity, and specificity, and was responsible for a reduction in anti-carrier immunogenicity. The Ab responses achieved with this synthetic vaccine resulted in a nicotine binding capacity in serum that could prevent >90% of a nicotine dose equivalent to three smoked cigarettes (0.05 mg/kg) from reaching the brain.

Simple radiometric method for accurately quantitating epitope densities of hapten-protein conjugates with sulfhydryl linkages

Control of small molecule hapten epitope densities on antigenic carrier proteins is essential for development and testing of optimal conditions for vaccines. Yet, accurate determination of epitope density can be extremely difficult to accomplish, especially with the use of small haptens, large molecular weight carrier proteins, and limited amounts of protein. Here we report a simple radiometric method that uses ¹⁴C-labeled cystine to measure hapten epitope densities during sulfhydryl conjugation of haptens to maleimide activated carrier proteins. The method was developed using a (+)-methamphetamine (METH)-like hapten with a sulfhydryl terminus, and two prototype maleimide activated carrier proteins, bovine serum albumin (BSA) and immunocyanin monomers of keyhole limpet hemocyanin. The method was validated by immunochemical analysis of the hapten–BSA conjugates, and least-squares linear regression analysis of epitope density values determined by the new radiometric method versus values determined by matrix-assisted laser desorption/ionization mass spectrometry. Results showed that radiometric epitope density values correlated extremely well with the mass spectrometrically derived values (r² = 0.98, y = 0.98x + 0.91). This convenient and simple method could be useful during several stages of vaccine development including the optimization and monitoring of conditions for hapten–protein conjugations, and choosing the most effective epitope densities for conjugate vaccines.

Production of Group Specific Monoclonal Antibody to Aflatoxins and its Application to Enzyme-linked Immunosorbent Assay

Through the present study, we produced a monoclonal antibody against aflatoxin B1 (AFB1) using AFB1- carboxymethoxylamine BSA conjugates. One clone showing high binding ability was selected and it was applied to develop a direct competitive ELISA system. The epitope densities of AFB1-CMO against BSA and KLH were about 1 : 6 and 1 : 545, respectively. The monoclonal antibody (mAb) from cloned hybridoma cell was the IgG1 subclass with λ-type light chains. The IC50s of the monoclonal antibody developed for AFB1, AFB2, AFG1 and AFG2 were 4.36, 7.22, 6.61 and 29.41 ng/ml, respectively, based on the AFB1-KLH coated ELISA system and 15.28, 26.62, 32.75 and 56.67 ng/ml, respectively, based on the mAb coated ELISA. Cross-relativities of mAb to AFB1 for AFB2, AFG1 and AFG2 were 60.47, 65.97 and 14.83% in the AFB1-KLH coated ELISA, and 59.41, 46.66 and 26.97% in the mAb coated ELISA, respectively. Quantitative calculations for AFB1 from the AFB1-Ab ELISA and AFB1-Ag ELISA ranged from 0.25 to 25 ng/ml (R(2) > 0.99) and from 1 to 100 ng/ml (R(2) > 0.99), respectively. The intra- and inter-assay precision CVs were < 10% in both ELISA assay, representing good reproducibility of developed assay. Recoveries ranged from 79.18 to 91.27%, CVs ranged from 3.21 to 7.97% after spiking AFB1 at concentrations ranging from 5 to 50 ng/ml and following by extraction with 70% methanol solution in the Ab-coated ELISA. In conclusion, we produced a group specific mAb against aflatoxins and developed two direct competitive ELISAs for the detection of AFB1 in feeds based on a monoclonal antibody developed.

Production of a highly group-specific monoclonal antibody against zearalenone and its application in an enzyme-linked immunosorbent assay

A monoclonal antibody (mAb) against zearalenone (ZEN) was produced using ZEN-carboxymethoxylamine and -BSA conjugates. Antibody produced by one clone showing a very high binding ability was selected and found to have a higher affinity for ZEN compared to a commerciall ZEN antibody. We developed two direct competitive ELISA systems using the selected antibody (ZEN-coated and anti-ZEN antibody-coated ELISA). Quantitative ranges for the anti-ZEN antibody-coated ELISA and ZEN-coated ELISA were from 25 to 750 ppb and from 12.5 to 100 ppb, respectively. The detection limit of both methods as measured with standard solutions was 10 ppb. The intra-plate and inter-well variation of both ELISAs were less than 10%. The IC₅₀ values for α-zearalenol, β-zearalenol, α-zearalanol, and β-zearalanol compared to ZEN were 108.1, 119.3, 114.1, and 130.3% for the ZEN-coated ELISA. These values were 100.7, 120.7, 121.6, and 151.6% for the anti-ZEN antibody-coated ELISA. According to the anti-ZEN antibody-coated ELISA, the average recovery rates of ZEN from spiked animal feed containing 150 to 600 ng/mL of ZEN ranged from 106.07 to 123.00% with 0.93 to 2.28% coefficients of variation. Our results demonstrate that the mAb developed in this study could be used to simultaneously screen for ZEN and its metabolites in feed.

Synthesis and Characterization of Immunogens Based on Calix[4]arene-crown-6 for the Generation of Antibodies Directed Towards Cesium Ions

With the aim of generating antibodies directed towards cesium, a calix[4]arene-crown-6 in the 1,3-alternate conformation bearing an N-hydroxysuccinimide function was synthesized. The calixarene was coupled to bovine serum albumin using different calixarene/protein ratios, and cesium was loaded. Conjugates were characterized using trinitrobenzenesulfonic acid derivatization, matrix assisted laser desorption ionisation-mass spectrometry (MALDI-TOF-MS), and inductively coupled plasma-mass spectrometry (ICP-MS). Targeted lysines were determined after enzymatic cleavage followed by MALDI-TOF-MS, and a progressive targeting related to lysines accessibility was observed.

Application of a modified version of Habeeb's trinitrophenylation method for the characterization of hapten-protein conjugates in a reversed micellar medium

We describe here a protocol for determining the epitope density of hapten-carrier conjugates at the nanomolar level. Conjugates of bovine serum albumin (BSA) and hen egg albumin (OVA) were prepared with two model haptens: 4-acetyl benzoic acid (ABA) as a chromophoric carboxylic hapten and cholesterol hemisuccinate (Chol HS) as a carboxylic derivative of a nonchromophoric hydroxylated hapten. Small-scale but valuable haptenization of carriers was achieved (approximately 4.3 nmol with an input molar ratio of hapten to carrier within the range from 50:1 to 100:1) that proved yet compatible with immunogenicity and antibody detection. We used a modified version of the amide bond-generating mixed anhydride method of Erlanger performed in a reversed micellar medium. Microsample aliquots of the coupling reaction (carriers plus activated haptens) or control experiment (carriers plus nonactivated haptens) mixtures were directly subjected to trinitrophenylation in the reversed micellar medium. The results for carrier substitution were strongly correlated (r2=0.94; n=12) with those obtained by other methods such as UV analysis (for ABA) and chromatographic determination (for Chol HS). This method was found directly applicable to other hapten-carrier conjugates coupled by the same procedure, provided that the haptens do not absorb at about 335 and 420 nm (absorption peaks of trinitrophenyl groups). With this simple, rapid, reproducible and low-cost analysis method, the separation of uncoupled hapten and conjugate is unnecessary. This facilitates the optimization of reaction conditions. Finally, using this procedure, kinetic studies of conjugate formation can be carried out in a very simple manner.

An improved method for the microscale preparation and characterization of hapten-protein conjugates: the use of cholesterol as a model for nonchromophore hydroxylated haptens

A minute amount (0.446 micromol) of cholesterol (Chol) was converted into an hemisuccinate derivative (Chol HS) using an excess of succinic anhydride. The optimal conditions for synthesis of Chol HS were explored by checkerboard experiments in which various succinic anhydride/Chol molar ratios ranging from 5:1 to 30:1 were assayed over a wide temperature range (50-85 degrees C) and for various incubation times (3-8 h). Total conversion was obtained at the higher reagent ratios, temperatures, and incubation times. Subsequently, this carboxylic derivative was first covalently linked to bovine serum albumin (BSA) then to various proteins (casein, ovalbumin, and hemocyanins) or to a synthetic homopolymer (poly-DL-Lysine) via a modified version of the mixed anhydride method of Erlanger, performed in a reversed micellar medium. The assessment of the number of haptenic groups per mole of BSA (epitope density) was achieved chromatographically by two methods according to a Chol standard curve established at 207 nm with linearity in the range 0-50 microg. These procedures involving an alkaline hydrolysis of a sample of either the conjugate (direct method) or the unreacted Chol HS (indirect method) yielded an acceptable level of agreement and concordant results in all cases. The influence of the activated hapten/BSA molar ratio on the coupling efficiency was investigated by the direct method within the range 10:1 to 250:1. Using the optimal conditions determined for Chol HS synthesis (a molar reagent ratio of 30:1 with incubation at 65 degrees C for 6 h) and for BSA haptenation (a 100-fold molar excess of activated hapten, with a carrier stock concentration of 5 mg/mL), epitope density of the conjugates lied between 23 and 27. By reacting the same amount of activated hapten ( approximately 216 microg) with identical amounts of various carriers (300 microg), conjugation efficiency was found similar on a microgram of Chol bound per milligram of carrier basis. This simple and reproducible conjugation and analysis procedures should provide a general method applicable to poorly available and weakly immunogenic haptens bearing hydroxyl groups such as polyether-type marine toxins.

A V3 loop haptenic peptide sequence, when tandemly repeated, enhances immunogenicity by facilitating helper T-cell responses to a covalently linked carrier protein

Subunit immunogens containing tandemly repeated copies of T- and B-cell epitopes have been shown to be more immunogenic than the respective immunogen containing only a single copy of the sequence. It has been unclear, however, whether the increased immunogenicity of a tandemly repeated B-cell epitope necessarily results from increased helper T-cell responses to intrinsic T-cell epitopes in the tandemly repeated sequences, or to neodeterminant T-cell epitopes created at the junction of adjacent repeat sequences. We examined this question by comparing the immunogenicity in mice of two immunogens containing one or eight tandemly repeated copies of an HIV-1 V3 loop haptenic sequence. Our results show that the tandemly repeated haptenic sequence potentiates the immunogenicity of the protein construct, likely through the facilitation of enhanced B-cell interaction with the tandem repeat construct and the consequent elicitation of increased carrier protein-specific helper T-cell responses.

A novel and efficient method for synthetic carbohydrate conjugate vaccine preparation: synthesis of sialyl Tn-KLH conjugate using a 4-(4-N-maleimidomethyl) cyclohexane-1-carboxyl hydrazide (MMCCH) linker arm

STn (NeuAcalpha2 --> 6GalNAc alpha-O-Ser/Thr) is a carbohydrate epitope overexpressed in various human carcinomas. Clinical trials are underway using synthetic STn or STn trimeric glycopeptides [STn, cluster; STn(c)] conjugated with keyhole limpet hemocyanin (KLH) as active specific immunotherapy for these cancers. These vaccines have been prepared by conjugating a crotyl ethyl amide derivative of STn or STn(c) to KLH by direct reductive amination after ozonolysis. In the case of STn(c) the conjugation efficiency and the resulting epitope ratios were low. This may be due to steric hinderance of the short spacer arm. To overcome these difficulties, without resynthesis, the STn(c) glycopeptide was modified by attachment of an MMCCH (4-(4-N-maieimidomethyl) cyclohexane-1-carboxyl hydrazide) spacer arm to the aldehyde derivative, and then conjugated with thiolated KLH. This method gave a higher epitope ratio and yield than the direct method. The STn(c)-MMCCH-KLH conjugate induced high titer antibodies in mice against STn(c). This method may be generally applicable for large synthetic oligosaccharides.

Heat shock proteins as immunological carriers and vaccines

HSPs are among the major targets of the immune response to bacterial, fungal and parasitic pathogens. The antigenic nature of HSPs is emphasized by evidence that mammals are capable of recognizing multiple B- and T cell epitopes in these proteins. The powerful immunological features of HSPs have led to their experimental use as immunomodulators and as subunit vaccine candidates. Mycobacterial hsp70 and hsp60 have been found to be excellent immunological carriers of molecules against which an immune response is desired; in the absence of adjuvants, the HSPs can stimulate strong and long-lasting immune responses against molecules which have been covalently attached to the HSPs. When used as subunit vaccines, HSPs derived from a variety of bacterial and fungal pathogens have been found to stimulate protective immunity in animal models. These studies suggest that HSPs might be used as immunomodulators or subunit vaccines against infectious disease in man.

Immunoregulation in fish. I: Intramolecular-induced suppression of antibody responses to haptenated protein antigens studied in Atlantic salmon (Salmo salar L)

We report here evidence for intramolecular-induced suppression of the in vivo antibody response in fish, using a panel of T-dependent hapten-carrier antigens. Atlantic salmon were immunized intraperitoneally with protein antigens (Limulus polyphemus hemocyanin, chicken gamma globulin, and Aeromonas salmonicida A-layer protein) given in their native form or haptenated with either 4-hydroxy-3-iodo-5-nitrophenyl-acetic acid (NIP), 2,4,6-trinitrophenyl-acetic acid (TNP), or fluorescein-5-iso-thiocyanate (FITC). The salmon immune system responds to these hapten-carrier antigens by eliciting high anti-hapten titers whereas the antibody titers against protein determinants were suppressed 87-99%, determined by ELISA. NIP also induced suppression of the anti-FITC response when NIP and FITC were intramolecularly conjugated to Limulus polyphemus hemocyanin (LPH). The suppression was found to be independent of haptenation ratios and time after immunization. The possibility that haptenation interferes with or blocks the protein determinants is not likely because antisera raised against native LPH recognize LPH-specific epitopes even on heavily NIP-substituted LPH. Although the mechanism behind intramolecular-induced suppression is poorly understood, even in mammals, this study demonstrates that intramolecular-induced suppression may be one means by which antibody responses in fish are regulated. The possible impact of antigen-induced suppression on immune responses against vaccine antigens in fish is discussed.

Conjugation of synthetic peptides to proteins: quantitation from S-carboxymethylcysteine released upon acid hydrolysis

A method described here for conjugating synthetic peptides to carrier proteins provides a convenient method for determining peptide-to-carrier protein ratios. N-Bromoacetyl-containing peptides are reacted in situ with carrier proteins in which the disulfide bonds were reduced with tri-n-butylphosphine. At pH 7-8 and ambient temperature, the newly formed sulfhydryl groups of the carrier protein react exclusively with the bromoacetyl mokiety of the peptide to form conjugates having stable thio ether linkages. Acid hydrolyses of these conjugates release S-carboxymethylcysteine in amounts proportional to the amounts of peptides conjugated and thus allow determination of peptide-to-protein ratios.

Studies on active immunization with self antigens. II. Production of antibody related to hapten substitution

BALB/c mice were injected during neonatal life with conjugates in buffered physiological saline, prepared by coupling trinitrophenyl groups (TNP) at various densities to either syngeneic mouse serum albumin (TNP-MSA) or xenogeneic bovine serum albumin (TNP-BSA). Serum samples were obtained on days 30 and 60 after birth, on days 75 and 88 after two booster injections, and monoclonal antibodies were prepared from spleens of neonatally treated mice. The antibody titres, isotypes, and specificities were evaluated by enzyme-immunoassay. It was found that the extent of the anti-TNP immune response to TNP-MSA conjugates depends on the degree of hapten substitution, which is not the case for the anti-TNP-BSA. All the TNP-MSA conjugates induced mainly IgG and only a few IgM antibodies. These antibodies reacted essentially with the TNP group but seemed to have a higher avidity for the TNP-protein conjugate used in their induction. During the course of the immunization, decreasing quantities of TNP-MSA conjugates were needed to inhibit antibody binding. A large amount of monoclonal anti-TNP antibodies was found in hybridomas obtained after neonatal treatment either with TNP-MSA or TNP-BSA. Therefore, it appears that the anti-TNP immune response obtained after antigenic stimulation with sufficiently substituted TNP-MSA conjugates possesses all the characteristics of a normally occurring humoral immune response.

Evaluation of antisera to 5-(2-bromo-E-ethenyl)-2'-deoxyuridine for the radioimmunoassay of a potent antiviral agent

The production and evaluation of antibodies specific for 5-(2-bromo-E-ethenyl)-2'-deoxyuridine (BVDU) is described. Antibodies were raised against 5-(2-carboxy-E-ethenyl)-2'-deoxyuridine bovine albumin conjugates (CVDU20-BA and CVDU54-BA) and 5'-carboxy-propionyl-BVDU7-BA. The molar substitution ratio of the conjugates was determined by differential ultraviolet absorption or isotope dilution and compared to a newer method based upon the determination of unsubstituted protein residues. Usable antibody titers were obtained from all the New Zealand White rabbits immunized, but only one-third of the half-lop rabbits responded. The antisera were highly specific for BVDU and did not significantly cross-react with naturally occurring nucleosides, pyrimidines, or sugars. However, the lowest cross-reaction observed (0.21%) for the major metabolite bromovinyl uracil using antisera raised to CVDU-BA could not ensure adequate assay specificity under all conditions of use. An alternative approach using 5'-carboxy-propionyl-BVDU7-BA proved unsuccessful because the antisera could not discriminate between BVDU and bromovinyl uracil.

Antigenic presentation of small molecules and peptides conjugated to a preformed iscom as carrier

The aim of the present study was to elaborate a carrier system for haptens and synthetic peptides, making them immunogenic without addition of Freund's adjuvants. As carriers, preformed iscoms and micelles as well as BSA have been compared. The iscoms and micelles were prepared with envelope proteins of an influenza virus. As a model hapten, the small molecules of biotin were coupled to iscoms to determine the optimum epitope density for induction of an enhanced antibody response to the hapten. The most efficient carrier tested was the preformed iscom at an epitope density of ten biotin molecules per viral protein in the iscom. This carrier system exceeded the efficacy of both the preformed micelles and BSA, the latter with or without addition of Freund's adjuvant. A favourable epitope density could not be achieved when each of two different synthetic peptides was conjugated to iscoms. Epitope densities higher than one to three peptide molecules per protein lead to polymerization of either the peptide or the carrier. The coupling agent was glutardialdehyde.

Hapten reactive inducer T cells. II. Evidence that a secreted form of the T cell receptor induces antibody production

The biologic activity of molecules synthesized and secreted by hapten-specific inducer T cells was examined. After activation, a single inducer clone secretes both antigen-specific inducer peptides as well as nonspecific factors. The nonspecific factors augment the in vitro response of B cells to sheep erythrocytes (SRBC) and Type 2 T-independent antigens. The antigen-specific molecules (ABM) induce plaque-forming cell (PFC) responses in cultures containing ABM, B cells, and antigen that links the epitope recognized by ABM with the B cell epitope. Induction of B cells by ABM is limited to B cells expressing the same I-A allele as the source of the ABM and this reflects binding by ABM to I-A products on B lymphocytes. The data reported here strongly support the view that inducer cells can activate at least some B cells by secretion of a modified form of the T cell surface receptor.

Allergic hypersensitivity to the insecticide malathion in BALB/c mice

The widely used insecticide malathion (diethylmercaptosuccinate, S ester with O,O-dimethylphosphorodithioate) has been reported to cause allergic responses in some exposed people and in guinea pigs. In this study, IgE antibody-mediated and cell-mediated hypersensitivity to malathion was evaluated in female BALB/c mice. To elicit malathion-specific antibodies of the IgE class, a conjugate of the anhydride of the diacid metabolite of malathion (MMA) with keyhole limpet hemocyanin was administered ip with aluminum hydroxide as adjuvant. Sera collected following three sequential sensitizations were tested for specific IgE with the passive cutaneous anaphylaxis (PCA) test in Sprague-Dawley rats. MMA coupled to bovine serum albumin was used as the challenge antigen. Specific IgE was produced following the second and third sensitization in the mice receiving 10 and 100 micrograms of conjugate and following the third sensitization in the mice receiving 1 microgram of conjugate. A paper radioallergosorbent test (PRAST) was as sensitive as and showed a good correlation with the PCA assay for samples analyzed by both procedures. Malathion applied epicutaneously on 2 days or over 4 weeks failed to elicit delayed-type hypersensitivity as determined by change in ear thickness, 5-[125I]iodo-2'-deoxyuridine incorporation in the ear, and histology of the ear following ear challenge, with or without pretreatment of the mice with cyclophosphamide. MMA-specific IgE antibodies were not detected by the PCA test in the serum of mice treated epicutaneously for 4 weeks.

Allergic hypersensitivity to the herbicide 2,4-D in BALB/c mice

Following several reports of human allergic hypersensitivity, the ability of 2,4-D (2,4-dichlorophenoxyacetic acid) to elicit 2,4-D-specific IgE antibodies and delayed-type hypersensitivity in BALB/c mice was studied. 2,4-D-specific IgE antibodies were detected in mouse sera following the second intraperitoneal immunization with 1, 10, or 100 micrograms 2,4-D-keyhold limpet hemocyanin conjugate with aluminum hydroxide adjuvant. Specific IgE was determined with the rat passive cutaneous anaphylaxis test using a conjugate of 2,4-D with bovine serum albumin for challenge. The highest antibody titers and a measurable response in all mice were seen in the group that received 1 microgram of 2,4-D conjugate. Dinitrophenyl-specific IgE was measured at all intervals examined in mice immunized with a dinitrophenyl-keyhole limpet hemocyanin conjugate. 2,4-D applied epicutaneously on 2 d or over 4 wk failed to elicit delayed-type hypersensitivity as measured by change in ear thickness, incorporation of 5-[125I]iodo-2'-deoxyuridine, or histology following challenge on the ear. No 2,4-D-specific IgE antibodies were detected in serum during the 4-wk sensitization period. Similar treatment with a known sensitizer, dinitrofluorobenzene, produced delayed hypersensitivity. Following 4 wk of dosing, low titers of dinitrophenyl-specific IgE antibodies were elicited.

Lymphocyte subpopulations and antibody levels in immunized malnourished children

1. The proportions of lymphocyte subpopulations (by rosette tests) and the serum antibody levels (using haemagglutination techniques) were estimated in malnourished and well fed Nigerian children before and up to 21 d after immunization with tetanus toxoid or measles virus vaccine. 2. Significantly diminished (P less than 0.01) mean percentage T lymphocyte levels and considerably higher mean percentage null cell levels were observed in the malnourished children before immunization with either of the vaccines. 3. There was comparable in vivo increases in percentage T lymphocytes in malnourished and control children following the administration of each antigen. 4. The mean percentage B lymphocyte levels were similar in the control and malnourished children before and after the immunization. 5. There was a slight depression in the tetanus antibody levels (P greater than 0.2) but a significant diminution (P less than 0.01) in measles virus antibody concentrations in the malnourished children. 6. Rise in mean percentage T lymphocytes corresponded with the elevation in mean tetanus antibody levels in both malnourished and control children following tetanus toxoid immunization. This was however not the situation in the malnourished children following immunization with measles virus. 7. The observed depressed T lymphocyte number in malnourished children may in practice affect their handling of antigens such as measles virus in vivo.

Mechanisms of B cell tolerance: I. Dynamic nature of the induction of hapten-specific unresponsiveness by hapten-conjugated pneumococcal polysaccharide

Exposure of 2,4-dinitrophenyl (DNP)-hemocyanin-primed spleen cells to DNP-conjugated pneumococcal polysaccharide (DNP-S3) in vivo or in vitro renders such cells unresponsive to DNP-hemocyanin challenge following adoptive transfer. The unresponsiveness is hapten-specific, independent of the presence of T cells and adherent cells, and not due to either toxic effect of S3 or carry-over of tolerogenic amounts of cell-bound DNP-S3, and thus presumably represents a model of B cell tolerance. The degree of suppression induced depends upon the dose of the tolerogen and most strikingly on the duration of exposure of cells to the tolerogen. Thus 2 to 6 h exposure to DNP-S3 has an insignificant effect on anti-DNP responses, while 24 and 48 h exposures in vitro and in vivo are highly suppressive. Such a dynamic process of tolerance induction suggests a "multiple hit" phenomenon, implying the generation of suppressive signals by repeated cycles of tolerogen-receptor interactions. The process can be interrupted by removal of extracellular DNP-S3, although this does not reverse the unresponsiveness that has already been induced.

Effect of prior sensitization with hapten on the antibovine IgG antibody response to hapten-conjugated tolerogen of mice tolerized by low doses of bovine IgG

Mice tolerized by low doses of bovine IgG (BGG), immunized with arsanilated (ARS) conjugates and challenged with ARS-BGG show an augmented anti-BGG antibody response compared with controls immunized with nonconjugated carrier. Conditions optimal for generating hapten help are explored and suggest that the phenomenon is mediated by hapten-specific helper T cells. During exploration of these conditions it became apparent that the response was suppression rather than augmentation with ARS, under certain circumstances, and with 2,4-dinitrophenyl, 4-hydroxy-5-iodo-3-nitro-phenylacetyl (NIP) and sulfanilic acid, under all conditions tested. Especially important in determining the outcome of the interaction was the type of adjuvant used for hapten priming. The significance of these observations is discussed in relationship to the balance between negative and positive cooperation.

Mechanisms by which hapten conjugates of pneumococcal polysaccharide interfere with the challenge of anti-hapten memory cells

Incubation of trinitrophenylated hemocyanin (TNP-KLH)-primed spleen cells with microgram amounts of 2,4-dinitrophenyl (DNP) or 2,4,6-trinitrophenyl (TNP) conjugates of pneumococcal polysaccharide type 3 (SIII) for as little as 5 min at 4 degrees C results in a specific "block" of the 19 S and 7 S adoptive memory response to TNP-KLH. This hapten-SIII-induced block of anti-hapten memory B cell responsiveness seems to be an example of specific receptor blockade. The block is specific and can be prevented by simultaneous incubation of the primed cells with hapten-protein conjugates which presumably compete with the hapten-polysaccharide for attachment to the B cell surface via anti-hapten Ig receptors. Removal via capping of these Ig receptors by exposure of TNP-KLH-primed memory cells to rabbit anti-mouse Fab serum for 45 min at 37 degrees C renders these cells refractory to the blocking effect of hapten-SIII. Once the hapten-SIII has attached to the memory cells, these blocked cells can be "rescued" (i.e. returned to a state of responsiveness) by incubating these cells with either mouse anti-SIII at 37 degrees C or rabbit anti-DNP serum at 4 degrees C. Since a papain digest of the IgG fraction of rabbit anti-DNP did not rescue the cells while the intact IgG did, a capping off of the TNP-SIII was proposed as the mechanims for this return to responsiveness of the hitherto blocked cells. A rescue was not seen by treatment of recipient mice with such B cell mitogens as dextran sulfate, endotoxin or purified protein derivative of tuberculin.

B cell tolerance induced by polymeric antigens. II. Effects of tolerance on hapten-binding lymphocyte levels in primary and secondary antibody responses

Tolerogenic doses of hapten [2,4-dinitrophenyl (DNP)]-coupled type 3 pneumococcal polysaccharide (DNP-lys2.5-S3) totally abolished the anti-DNP rosette-forming cell (RFC) response to primary immunization with DNP-hemocyanin in mice, while lightly substituted antigen (DNP-lys0.6-S3) had little effect. Both antigens suppressed secondary anti-DNP RFC responses to DNP-KLH. Limiting doses of DNP-lys-S3 preferentially suppressed antibody-secreting cell levels, and had less effect on RFC. DNP-lys2.5-S3 was 500--1000-fold more potent in "blockading" primary RFC in vitro than DNP-lys0.6-S3, whereas both antigens were equally effective in blocking secondary RFC. These results suggest that the sensitivity of primed B lymphocytes to inactivation by DNP-lys-S3 is related to their high avidity for antigen. Furthermore, this appears to be largely due to a high density of immunoglobulin receptors on primed cells since the affinities of primary and secondary RFC for monovalent hapten were indistinguishable. Treatment of primarily immunized mice with DNP-lys2.5-S3 2 h before assay abolished 90% of RFC. Therefore, the reduction in RFC levels in tolerant mice may be due to cellular blockade by persisting tolerogen. However, it seems unlikely that simple blockade of antigen-reactive cells is the sole mechanism operative in this system.

B cell tolerance induced by polymeric antigens. I. Comparison of the dose and epitope density requirements for inactivation of primed and unprimed B cells in vivo

Hapten [2,4-dinitrophenyl (DNP)]-specific tolerance was induced in nonimmune or DNP-hemocyanin (DNP-KLH) primed mice by administering hapten-conjugated type 3 pneumococcal polysaccharide (DNP-lys-S3). The dose of DNP-lys2.5-S3 required to suppress the primary anti-DNP antibody responses was approximately ten times higher than that required to suppress the secondary response. Large doses of lightly substituted antigen (DNP-lys0.6-S3) had no effect on primary antibody responses, while small doses of this conjugate suppressed 90-95% of the secondary response. The conclusion from this (presumably B cell) tolerance model is that B lymphocytes "mature" in their susceptibility to tolerization following primary contact with immunogen, since primed cells are inactivated by lower doses of tolerogen, and by tolerogen with lower epitope density, than nonimmune B cells. These and other data suggest that the tolerance threshold of B lymphocytes is related to their state of differentiation, and especially to their antigen-binding characteristics.

B cell tolerance induced by polymeric antigens. V. Different avidities of primed and virgin precursor cells for paucivalent antigen

We have compared the avidity of virgin and primed hapten-specific precursor cells for DNP-lys-S3 (dinitrophenylated type 3 pneumococcal polysaccharide) by measuring its capacity to prevent them from binding highly radioactive DNP-hemocyanin, and thereby protect them from committing hapten-specific "suicide". Moderately substituted conjugates (e.g. DNP-lys2.7S3) protected virgin and memory B cells impartially. In contrast, DNP-lys0.6S3 protected memory cells efficiently, but protected virgin cells only at considerably higher concentrations. These results are consistent with previous evidence - from this and other systems - that there is a higher density of receptors on primed than on unprimed B cells - the significance of which is discussed.

B cell tolerance induced by polymeric antigens. IV. Antigen-mediated inhibition of antibody-forming cells

The role of antibody-forming cell (AFC) blockade in the genesis of hapten-specific tolerance induced by hapten (2,4-dinitrophenyl)-coupled pneumococcal polysaccharide (DNP-lys-S3) was investigated. Tolerizing doses of DNP-lys-S3 given to mice making antibodies to DNP-hemocyanin a day before assay markedly reduced numbers of detectable anti-DNP AFC. Furthermore, anti-DNP AFC were specifically inhibited by brief in vitro incubation with DNP-lys-S3, followed by extensive washing. This inhibition requires multivalent binding of tolerogen to immunoglobulin receptors on AFC, and appears to result from a decrease in the rate of antibody secretion per cell. A variety of data indicate that IgM AFC are more susceptible to blockade than IgG AFC, and the susceptibility of both cell types decreases with time after immunization. This probably reflects differences in the density and in the rate of loss of surface immunoglobulin receptors on IgM and IgG AFC and their immediate precursors. However, we conclude that under "conventional" tolerizing conditions, i.e. when tolerogen is given prior to immunogen, DNP-lys-S3 suppresses antibody formation primarily by inactivating DNP-specific precursor cells. AFC blockade is therefore probably only relevant in the suppression of (primary?) IgM responses by large doses of tolerogen. The relative importance of precursor inactivation and AFC blockade in tolerogenesis of IgM responses to T cell-independent antigens (such as S3) remains to be elucidated.

B cell tolerance induced by polymeric antigens. III. Dissociation of antibody formation and memory generation in tolerant mice

Hapten (2,4-dinitrophenyl (DNP))-substituted type 3 pneumococcal polysaccharide (DNP-lys-S3) effectively suppresses both primary and secondary anti-DNP antibody responses to DNP-proteins. The present experiments show that tolerizing doses of DNP-lys-S3 have much less effect on B cell memory (re)generation in three distinct situations: (i) in serial transfers of DNP-protein-primed cells, (ii) in virgin mice tolerized before priming with DNP-hemocyanin, and (iii) in tolerized, hemocyanin-primed mice boosted with DNP-hemocyanin. Under some conditions tolerized mice developed 10-50% of normal memory in the absence of significant antibody formation. Isoelectric focusing analyses revealed that many B cell clones proliferate in tolerant mice, but produce very little antibody until transferred to further hosts. Clones that escape suppression in partially tolerant mice do not appear to be resistant to DNP-lys-S3, when retested. Since there is independent evidence that the generation of B memory cells is less T cell-dependent than the development of antibody-forming cells, these data are best explained by assuming that DNP-lys-S3 blocks lymphocyte cooperation. This would be expected to preferentially suppress antibody formation, and to spare memory generation.