Alec H. Sehon

Synthesis, isolation, and characterization of conjugates of ovalbumin with monomethoxypolyethylene glycol using cyanuric chloride as the coupling agent

The experimental conditions for the preparation of conjugates of ovalbumin (OA) and monomethoxypolyethylene glycol (mPEG) of a preselected average degree of conjugation, n, using cyanuric chloride as the coupling agent, have been investigated with emphasis on purification and characterization of the products. These conjugates served as prototypes of tolerogenic mPEG derivatives of antigenic proteins which were capable of suppressing in mammals the immunological response to the corresponding unmodified antigens. In other studies in this laboratory, the tolerogenicity of OA(mPEG)n conjugates was found to be a function of n. The reproducibility of the reaction leading to the production of OA(mPEG)n conjugates was shown to depend primarily on the reactivity of the mPEG-cyanuric chloride intermediate, which--for best results--had to be synthesized under completely anhydrous conditions. Isolation of the OA(mPEG)n conjugates was optimized by the use of ion-exchange chromatography whereby rapid removal of large amounts of uncoupled intermediate from the conjugate was achieved; the conditions of fractionation were affected by the degree of conjugation. This method of purification was superior to dialysis, ultrafiltration, and gel filtration. Furthermore, by the application of analytical hydrophobic interaction HPLC it was possible to differentiate among conjugates of different degrees of conjugation and to establish the absence of any detectable free OA in any of the preparations. The quantity of mPEG in the conjugates was determined directly by NMR.

Comparison of recombinant timothy grass pollen allergens with natural extract for diagnosis of grass pollen allergy in different populations

BACKGROUND Complementary DNAs coding for the major timothy grass pollen (Phleum pratense) allergens Phl p 1, Phl p 2, and Phl p 5 and birch profilin were isolated, expressed as recombinant nonfusion proteins in Escherichia coli, and purified. OBJECTIVE In this study the in vitro IgE-binding capacity of recombinant Phl p 1, Phl p 2, Phl p 5, and birch profilin and their IgE recognition frequencies were investigated by using sera from different populations. METHODS One hundred eighty-three sera from patients allergic to grass pollen were obtained from different populations in Europe, Japan, and Canada. The sera were selected according to clinical criteria, skin testing, and RAST (CAP system; Pharmacia, Uppsala, Sweden) and then tested for IgE reactivity with natural and purified recombinant timothy grass pollen allergens by ELISA and Western blot. RESULTS Most (94.5%) of the patients allergic to grass pollen could be diagnosed with a combination of recombinant Phl p 1, Phl p 2, Phl p 5, and profilin by means of ELISA. Sera that did not react with the recombinant allergens contained low levels of timothy grass pollen-specific IgE. Although considerable variability in IgE recognition frequency of the recombinant allergens was observed in certain populations, a good correlation was found between natural timothy CAP results and the combination of recombinant allergens in all 183 tested sera (r = 0.87). CONCLUSIONS Despite considerable variability in the IgE recognition frequency, purified recombinant timothy grass pollen allergens (Phl p 1, Phl p 2, Phl p 5) and profilin permitted successful in vitro diagnosis of grass pollen allergy in 94.5% of allergic individuals from different populations. The addition of other recombinant allergens (e.g., recombinant Phl p 4) would only slightly improve the in vitro test sensitivity.

Immunosuppressor T cells in tumor bearing host.

Thymus or spleen cells of tumor bearing animals (TBA) (methylcholanthrene induced sarcoma bearing A/Jax mice) were shown to possess immunosuppressor cells regulating the immune response to the tumor in syngeneic animals. The immunosuppressive activity of these cells of TBA was totally abolished by the in vitro treatment of anti-theta serum and complement. Soluble factor(s) with identical suppressive activity was isolated from the thymus cells of TBA and its molecular size was estimated to be lower than that of serum albumin in terms of its elution behaviour on gel filtration through a Sephadex G-200 column. These immunosuppressor T cells or their soluble factor(s) may be largely responsible for the growth of antigenic tumors.

Neuro-hormonal host defence in endotoxin shock

The sensitivity (LD100) of mice to lipopolysaccharide (LPS) endotoxin and to its toxic moiety, lipid A (LA), increased 500-fold after adrenalectomy (ADX). Inhibition of glucocorticoid synthesis in intact mice by metyrapone had a similar, though less dramatic, sensitizing effect to LPS. In ADX mice, the serum level of tumor necrosis factor-alpha (TNF) was 40-60 times higher than that in controls at 2 h after LPS/LA treatment. In intact mice the serum corticosterone level fell 1 h after lipid A injection to below detectable levels, which was followed by a brisk increase reaching the peak level of 48-50 micrograms/100 ml at 2 h. Both TNF production and the lethal effect of PLS/LA could be inhibited in ADX mice by glucocorticoid treatment. Plasma prolactin was increased significantly 1 h after endotoxin administration in both intact and ADX animals.

Suppression of Reaginic Antibodies with Modified Allergens

Administration of multiple injections of conjugates of ovalbumin (OA) and polyethylene glycol (PEG) or its monomethoxy derivative (mPEG) into mice which had been sensitized with 2,4-dinitrophenylated OA (DNP3–OA) abrogated both the anti-OA and anti-DNP IgE responses, in spite of additional injections of the sensitizing dose of DNP3-OA in the presence of Al(OH)3. Treatment of mice with OA-PEG in Al(OH)3 stimulated preferentially helper T cells, whereas injection of mice with OA-PEG in the absence of adjuvant elicited predominantly suppressor T cells. The unresponsive state of mice which had been treated 21 days earlier with OA-PEG could not be broken by the transfer of normal spleen cells and an additional sensitizing dose of DNP3-OA. Transfer of spleen cells from tolerized animals to normal mice dampened the capacity of the latter to mount both anti-DNP and anti-OA IgE responses; however, the suppressive effect of these cells was eliminated by treatment of the normal recipients with cyclophosphamide, which is a procedure known to inactive suppressor T cells, and hence it may be concluded that this effect was not due to the carryover of the tolerogen with the transferred cells. All these results provide strong support for the conclusion that the suppressor cells induced by the treatment of mice with OA-PEG and OA-mPEG conjugates belonged to a T cell subpopulation, and that the B cells of these mice were devoid of suppressive activity.

A canine model for reaginic hypersensitivity and allergic bronchoconstriction

Immunization of neonatal dogs with a conjugate of 2,4-dinitrobenzene and ovalbumin (DNP2-OA), using aluminum hydroxide as the adjuvant, elicited long-lasting (over 30 wk) anti-DNP and anti-OA IgE antibody responses of high titers as determined by homologous passive cutaneous anaphylaxis. Low antigen doses of 10 or 50 mug were more effective than the higher doses of 250 or 1,250 mug in inducing high IgE antibody levels. However, this method of immunization failed to elicity any detectable IgE antibody response in adult dogs. Bronchoprovocation with antigen of sensitized animals having IgE antibody titers in excess of 64 resulted in a marked increase in airflow resistance, which could be corrected by the administration of nebulized isoproterenol. On the other hand, sensitized animals with IgE antibody titers in the order of 64 did not manifest significant bronchoconstriction on inhalation challenge but developed anaphylaxis following intravenous injection of the antigen.

Induction of IgE antibodies in mice and rhesus monkeys with recombinant birch pollen allergens: different allergenicity of Bet v 1 and Bet v 2.

BACKGROUND Serologic measurements with recombinant birch pollen allergens, rBet v 1 and rBet v 2 (birch profilin), have shown that more than 95% of patients allergic to tree pollen mount high levels of IgE against rBet v 1, whereas only approximately 10% of the patients display rather low levels of IgE against rBet v 2. OBJECTIVE In this study an attempt was made to determine whether the different allergenicity of the major birch pollen allergen, rBet v 1, and a minor birch pollen allergen, rBet v 2, might be related to a different immunogenicity of the proteins as evaluated in experimental animal systems (mice and rhesus monkeys). METHODS Purified recombinant allergens were injected into mice and rhesus monkeys with aluminum hydroxide as adjuvant for elicitation of specific IgE responses. Antibody responses to the allergens were detected by immunoblotting, and time courses of immune responses were measured by ELISA. RESULTS In both animal models more than the 10-fold dose of rBet v 2 was required to induce IgE antibodies, and even then, the amount of specific IgE antibodies elicited with rBet v 1 was substantially higher than that induced by rBet v 2. It was noted that rBet v 2 formed stable polymers through disulfide bonds. CONCLUSION In two different animal models (mice and rhesus monkeys) the major birch pollen allergen, rBet v 1, induced substantially higher levels of IgE than rBet v 2. A reduced allergenicity of Bet v 2 caused by polymer formation would be in agreement with previous studies indicating reduced allergenicity of proteins on chemical polymerization.

Growth inhibition of murine mammary carcinoma by monoclonal IgE antibodies specific for the mammary tumor virus.

SummaryTwo IgE-producing hybridomas were established from spleen cells of Balb/c mice, which had been immunized with mouse mammary tumor virus (MMTV). These IgE monoclonal antibodies (mAbs) reacted specifically with the major envelope glycoprotein (gp36) of MMTV, as established by the immunoblot assay and by passive cutaneous anaphylaxis. The effect of the IgE mAbs (produced by clone A8) on the growth of the MMTV-secreting mammary adenocarcinoma H2712 was investigated in syngeneic C3H/HeJ mice. The mice were inoculated s.c. with either 105 (≈100 × LD50) or 106 (≈1000 × LD50) tumor cells and received repeated i.p. injections of 25 µg anti-gp36 IgE mAbs at 4-day intervals for 8 weeks. This treatment prevented the development of subcutaneous tumors in 50% of the animals. Similar protection was observed when the tumor cells (105/animal) were injected i.p. 4 days prior to the beginning of the i.p. treatment consisting of injections of 25 µg mAbs at 4-day intervals for 6 weeks. However, these mAbs did not protect C3H/HeJ mice against the MMTV-negative MA16/c carcinoma cells. Hence, these results support the view that IgE-mediated cytotoxic mechanisms may play an immunologically specific antitumor surveillance role and that laboratory-induced antitumor IgE mAbs have the potential of specific therapeutic agents for in vivo destruction of tumor cells.

Isolation and Characterization of a cDNA Clone Encoding an IgE-Binding Protein from Kentucky Bluegrass (Poa pratensis) Pollen

We reported previously on the isolation and characterization of several allergens from Kentucky bluegrass (KBG) (Poa pratensis L.) pollen with the aid of the corresponding murine monoclonal antibodies (Mabs). In the present study, (1) an analysis of various tissues of this grass revealed that the allergenic components recognized by these Mabs were confined to the pollen; (2) intact translatable mRNA was isolated from the KBG pollen, and (3) a cDNA library was constructed with this mRNA in the lambda gt11 expression vector. Screening of this library with a pool of six sera from KBG-allergic patients, in combination with enzyme-labeled antibodies to human IgE, led to the isolation of a cDNA clone, referred to as KBG7.2. The nick-translated cDNA probe of KBG7.2 hybridized to a 1.5-kbp RNA transcript from KBG pollen. Moreover, transcripts corresponding to KBG7.2 were found in pollens of eight other grasses, indicating that the proteins similar to the one encoded by this cDNA may be present in these grasses. The nucleotide sequence of KBG7.2 was determined; interestingly, the corresponding derived amino acid sequence did not match any other sequence recorded in the protein data banks. The peptide encoded by KBG7.2 was expressed as a fusion protein utilizing the plasmid vector pWR590.1. Whereas none of the above allergen-specific Mabs bound to the fusion protein, all the 15 individual sera from grass pollen allergic patients recognized the fusion protein.(ABSTRACT TRUNCATED AT 250 WORDS)

A method for the preparation of protein-protein conjugates of predetermined composition

A novel procedure for the synthesis of well-defined protein-protein conjugates is described using ovalbumin (OA) and IgG as test proteins. This procedure involves the highly selective and rapid reaction of alkyl halide and sulfhydryl groups, which have been grafted, respectively, onto the proteins to be conjugated. Accordingly, iodoacetylated IgG, (ICH2CO)nIgG, was prepared by the reaction of the epsilon-amino groups of IgG with the N-hydroxysuccinimide ester of iodoacetic acid (NHIA), the degree of iodoacetylation (n) being proportional to the concentration of NHIA. OA was reacted with S-acetylmercaptosuccinic anhydride (SAMSA) under conditions yielding, on the average, a monosubstituted derivative. Following removal of the protective S-acetyl group, the resulting -SH derivative of OA was reacted with (ICH2CO)nIgG. The OAx-IgG conjugates so produced were characterized by gel filtration, specific radioactivity (using tritiated OA) and immunodiffusion. It was found that the average number of OA molecules coupled per IgG molecule could be controlled by varying the degree of iodoacetylation of IgG.