Fully synthetic immunogens. Part II. Studies on parallel dimerization of the human IgG1 hinge-fragment 225-232 with N- or C-terminal gastrin related extensions.

The bis-cysteinyl hinge-fragment 225-232 of human IgG1 has been extended at the N- or C-terminus with Nle15-desamido-human-little-gastrin-[5-17] and Nle15-human-little-gastrin-[5-17]-NH2, respectively. Thermodynamically controlled air oxidation of the resulting bis-cysteinyl-peptides led to the predominant formation of the corresponding dimers in parallel alignment despite the incorporation of the immunoglobulin-unrelated gastrin-sequences. These surprising results confirm the high degree of structural information inherent in the hinge-sequence and its intrinsic tendency to fold into the correct structure in terms of cysteine pairings. This protein subdomain-the hinge-peptide-is therefore well suited as core molecule for the design of fully synthetic immunogens with multiple attachment of antigenic determinants.

The T-lymphocyte proliferative response to synthetic peptide antigens of defined secondary structure.

Immunodominant sites in proteins recognized by T lymphocytes are segments consisting of at least 7-8 amino acids. It has previously been proposed that these sites in proteins are alpha-helical and amphipatic structures. We synthesized and investigated the immunogenicity of three synthetic peptides (MP7, MP8, and MP9), each consisting of the same 15 amino acids, but differing with respect to sequence. Based on information analysis and circular dichroism measurements, MP7 was shown to have an alpha-helical secondary structure and, based on previously assigned hydrophilicity indices, was also strongly longitudinally amphipatic. MP8 also was conformed as an alpha-helix, but was amphipatic in the sense that the N-terminal half of the molecule was hydrophilic and the C-terminal half hydrophobic. MP9 had neither an amphipatic nor alpha-helical structure. All three peptides were immunogenic in some strains of mice but none was immunogenic in all strains. This supports other studies concluding that amphipaticity per se is neither a necessary nor sufficient requirement for immunogenicity of a peptide. On the other hand, the present experimental data suggest that longitudinally amphipatic alpha-helical peptides may function better as T-cell determinants than the other peptides investigated.

Interaction of anti-DNA antibodies with synthetic polyanionic antigens.

Autoantibodies to DNA (anti-DNAab), found primarily in systemic lupus erythematosus (SLE), cross-react with a variety of antigens. The binding of these antibodies to naturally occurring mucopolysaccharides such as heparan and chondroitin sulfates has led to the suggestion that anti-DNAab have specificity for a polyanionic epitope. In this study, to avoid the use of endogenous immunogens to which humans may have become sensitized, we have used the synthetic polyanions, dextran sulfate (DS), polyvinyl sulfate (PVS) and the semi-synthetic antigen, pectic acid (PA) to evaluate this hypothesis using SLE sera (n = 15) and sera from healthy individuals (controls; n = 15, age and sex matched to SLE group). Inhibition of binding with 125I-DNA was optimal at 1 mg/ml for DS and PVS, and resulted in significant inhibition of binding by both SLE and control sera of native DNA (P less than 0.01, each group); no inhibition was observed with PA, nor was a significant inhibition observed with any antigen on binding of SLE or control sera groups to denatured DNA. We conclude that while on quantitative grounds reaction of anti-DNAab with polyanions may not be clinically relevant, it is clear that, unlike polycarboxylates (e.g. PA), polysulfated polymers, whether aliphatic, as in the case of PVS, or glycosidic, such as DS, react with a subpopulation of anti-DNAab in such a manner as to block significantly the ability of these antibodies to bind DNA.

Multiple antigen peptide. A novel approach to increase detection sensitivity of synthetic peptides in solid-phase immunoassays.

We describe a novel approach to detect antibodies to synthetic peptide antigens in solid-phase radioimmunoassays, using a multiple antigen peptide (MAP) system. The MAPs consist of multiple copies of peptides that are synthesized as single units on a branching lysyl matrix using a solid-phase peptide synthesis method. The efficacy of the MAP approach in solid-phase immunoassays was compared with the conventional approach using a monomeric peptide of the immunodominant epitope of the circumsporozoite proteins of two species of malaria. Two monomeric peptides with 12 and 17 residues were found to bind poorly to plastic surfaces at a concentration up to 30 micrograms/ml, and showed no immunoreactivity to specific polyclonal or monoclonal antibodies, while the corresponding MAP-containing peptides showed excellent binding capacity and immunoreactivity at a concentration of 0.11 microgram/ml. The immunoreactivity of MAP-containing peptides was also superior to that of monomeric peptides conjugated to a protein carrier. The effects of various arrangements of lysyl branching of MAP on antigenicity were also studied, and the optimal number for lysyl branching of MAP was found to be octameric. Thus, the MAP, by enhancing the coating capacity and the avidity of synthetic peptides, provides increased sensitivity and reliability for the use of synthetic peptide to study antigen-antibody interactions on solid surfaces.

Carrier-bound synthetic peptides. Use as antigen in HIV-1 ELISA tests and in antiserum production.

Chemically synthesize carrier-bound peptides have been used as antigens in diagnostic test systems (ELISA) and for raising antipeptide-specific antisera. The method does not require prior cleavage of the peptides from the support used for the solid-phase synthesis. Using the same resin for both the synthesis and the subsequent applications it was possible to avoid expensive and time-consuming purification procedures and artificial recoupling to solid supports. A quick and specific ELISA-based diagnostic test system for HIV-specific antipeptide antibodies in human sera was established. In addition the carrier-bound peptides were shown to be potent antigens for raising antibodies in animals.

[Antibody formation to o-aminoazotoluene via the administration of conjugated antigens synthesized by enzymatic and chemical methods]. / Obrazovanie antitel k o-aminoazotoluolu pri vvedenii kon''iugirovannykh antigenov, sintezirovannykh fermentativnymi i khimicheskimi metodami.

Two new methods are developed for synthesis of conjugated antigens of o-aminoazotoluene-bovine serum albumin (o-AAT--BSA): (1) from the microsomal fraction of the guinea pig liver which contains the cytochrome-P-450-dependent monooxygenase enzymic system and (2) from the m-chloroperbenzoic acid. A possible mechanism of the covalent binding of o-AAT with albumin under the effect of monooxigenases and of their chemical model is considered. Differences of antigenic determinants in conjugated antigens of o-AAT--BSA synthetized by the chemical and enzymic methods are detected.

Enzyme immunoassay of blasticidin S with high sensitivity: a new and convenient method for preparation of immunogenic (hapten-protein) conjugates.

An antibody against blasticidin S (BLS), an antibiotic effective for blast disease of rice, has been produced in rabbits immunized with a blasticidin S-protein conjugate prepared by a novel and convenient procedure devised to couple BLS to bovine serum albumin (BSA) after sodium borohydride reduction of its disulfide bonds, using N-(m-maleimidobenzoyloxy)succinimide (MBS) as a cross-linker. BLS-MBS-BSA conjugate contained about 16 BLS per BSA molecule. Enzyme labeling of BLS with beta-D-galactosidase was performed by utilizing another cross-linker, N-(gamma-maleimidobutyryloxy)succinimide by means of a convenient labeling method which we introduced last year. A double antibody enzyme immunoassay of BLS which could determine as little as 100 pg per tube of BLS was developed using labeled BLS and anti-BLS antiserum. Various commonly used drugs were found to have little reactivity in this immunoassay, indicating that the anti-BLS produced is highly specific. The titer of the anti-BLS was excellent and 10,000,000-fold diluted solution could bind with the enzyme labeled BLS.

The development and application of a radioimmunoassay for dihydrodigoxin, a digoxin metabolite.

The cardioinactive digoxin metabolite, dihydrodigoxin, has been conjugated to bovine serum albumin and to bovine pancreatic ribonuclease by the periodate oxidation method. Rabbits immunized with the dihydrodigoxin-bovine serum albumin conjugate formed antibodies which bound a radioiodinated dihydrodigoxin-ribonuclease conjugate. This binding was inhibited by dihydrodigoxin. After affinity chromatography on a digoxin-ribonuclease-Sephacryl immunoadsorbent to remove antibodies which cross-reacted with digoxin, dihydrodigoxin was 300 times more effective than digoxin in inhibiting the binding of tracer by antibody. Digoxin-absorbed antidihydrodigoxin antibodies were coupled to Sephacryl and were used to develop a solid-phase radioimmunoassay capable of detecting 250 to 500 pg of dihydrodigoxin in 1 ml of human serum or urine. This radioimmunoassay has been used to define the pharmacokinetics of the metabolite in four normal human volunteers who ingested 125 to 500 micrograms of dihydrodigoxin by mouth. Dihydrodigoxin was quickly absorbed, with maximal serum concentrations achieved within 45 to 105 min, followed by a rapid fall in serum immunoreactivity over 2 to 4 hr and then by a slower, more gradual decline. The terminal half-life (beta) in serum varied from 4.24 to 11.9 hr (mean +/- S.E. = 8.1 +/- 1.3 hr). Most of the administered dose was excreted in the urine, with cumulative urinary recovery varying inversely with the dose. Urinary half-lives averaged 13.8 +/- 2.1 hr, and renal clearance rates were similar to those of creatinine. Dihydrodigoxin is rapidly absorbed and excreted in man and appears to be eliminated from the body at a faster rate than digoxin.

Radioimmunoassays for cannabinoids.

The simplicity, sensitivity, and specificity of radioimmunoassay have made it an attractive procedure for the analysis of delta-9-tetrahydrocannabinol (THC) in biological fluids or tissues. The presence of closely related compounds such as metabolites may interfere with radioimmunoassay results. Appropriate design of immunogens may diminish such interference. This work has been directed towards the use of the amyl side chain for linking cannabinoid compounds to proteins to form immunogens. Although the amyl side chain is metabolized to some extent, the metabolites are not quantitatively significant in most cases. 5'-Carboxy-delta-8-THC and 5'-carboxy-delta-9-THC were linked to bovine serum albumin. Immunization of rabbits with the resulting conjugates resulted in the formation of antisera with high selectivity for delta-9-THC vs. its carboxylic acid metabolite, 11-nor-9-carboxy-delta-9-THC. Delta-8-THC radioligands (4',5'-tritium and 5'-iodine-125) could be used with these antisera for analysis of delta-9-THC in plasma. Sensitivity with tritium-labeled material is about 2.5 ng/ml. 5'-Oxo-11-nor-9-carboxy-delta-8-THC was used to prepare an immunogen which led to the generation of an antiserum highly specific for 11-nor-9-carboxy-delta-9-THC. This antiserum and iodine-125-5'-iodo-11-nor-9-carboxy-delta-8-THC were used to develop a highly specific assay for 11-nor-9-carboxy-delta-9-THC in plasma.

Evidence for cross-linking of cyclic AMP to constituents of brain tissue by aldehyde fixatives: potential utility in histochemical procedures.

The amount of cyclic AMP recovered from unfixed tissue sections of brain carried through immunohistochemical procedures was found to be small (less than 2 pmoles/mg protein) and constant despite wide variations in the amount accumulated prior to freezing and sectioning. However, treatment of brain slices with glutaraldehyde or formaldehyde in buffered sucrose solutions for one to two hours at 0 degrees rendered insoluble as much as 60% of the total accumulated cyclic AMP as judged by filtration of homogenates of treated tissue. Immunoreactive cyclic AMP was recovered from filters by extraction with warm, dilute acid. The fraction of filter-bound cyclic AMP was relatively constant over a wide range of initial tissue levels. The persistence of insoluble cyclic AMP was greatest in homogenates of slices treated with formaldehyde when maintained above pH 8.5; about 40% of this fraction was lost after two hours at 0 degrees. Incubation of tissue homogenates with formaldehyde and radioactive nucleoside or nucleotide derivatives of adenine, guanine, and cytosine resulted in a time-dependent appearance of insoluble radioactivity; compounds lacking an amino function were inactive. Pure proteins, including polylysine, also reacted with formaldehyde and 3H-cyclic AMP to produce radioactivity resistant to adsorption by charcoal. The reaction between cyclic AMP or adenosine, formaldehyde, and alkyl amines was examined using UV spectrometry. It is tentatively concluded that at 0 degrees formaldehyde is capable of rapidly producing a methylene-bridged adduct between primary alkylamines and the N6-amino function of purine nucleosides or nucleotides. Application of these results to the development of immunohistochemical procedures for the cellular localization of cyclic AMP will require the generation of antibody preparations with high reactivity for cyclic AMP derivatized at the N6-position.