Chemical modifications of the major allergen of ragweed pollen, antigen E

Efficient experimental method for purifying allergens from aqueous extracts

Studying the molecular and immunological basis of allergic diseases often requires purified native allergens. The methodologies for protein purification are usually difficult and may not be completely successful. The objective of this work was to describe a methodology to purify allergens from their natural source, while maintaining their native form. The purification strategy consists of a three-step protocol and was used for purifying five specific allergens, Ole e 1, Amb a 1, Alt a 1, Bet v 1 and Cup a 1. Total proteins were extracted in PBS (pH 7.2). Then, the target allergens were pre-purified and enriched by salting-out using increasing concentrations of ammonium sulfate. The allergens were further purified by anion exchange chromatography. Purification of Amb a 1 required an extra step of cation exchange chromatography. The detection of the allergens in the fractions obtained were screened by SDS-PAGE, and Western blot when needed. Further characterization of purified Amb a 1 was performed by mass spectrometry. Ole e 1, Alt a 1, Bet v 1 and Cup a 1 were obtained at > 90 % purity. Amb a 1 was obtained at > 85 % purity. Overall, we propose an easy-to-perform purification approach that allows obtaining highly pure allergens. Since it does not involve neither chaotropic nor organic reagents, we anticipate that the structural and biological functions of the purified molecule remain intact. This method provides a basis for native allergen purification that can be tailored according to specific needs.

Insect Cell-Expressed Major Ragweed Allergen Amb a 1.01 Exhibits Similar Allergenic Properties to Its Natural Counterpart from Common Ragweed Pollen

Common ragweed pollen allergy has become a health burden worldwide. One of the major allergens in ragweed allergy is Amb a 1, which is responsible for over 90% of the IgE response in ragweed-allergic patients. The major allergen isoform Amb a 1.01 is the most allergenic isoform in ragweed pollen. So far, no recombinant Amb a 1.01 with similar allergenic properties to its natural counterpart (nAmb a 1.01) has been produced. Hence, this study aimed to produce a recombinant Amb a 1.01 with similar properties to the natural isoform for improved ragweed allergy management. Amb a 1.01 was expressed in insect cells using a codon-optimized DNA construct with a removable N-terminal His-Tag (rAmb a 1.01). The recombinant protein was purified by affinity chromatography and physicochemically characterized. The rAmb a 1.01 was compared to nAmb a 1.01 in terms of the IgE binding (enzyme-linked immunosorbent assay (ELISA), immunoblot) and allergenic activity (mediator release assay) in well-characterized ragweed-allergic patients. The rAmb a 1.01 exhibited similar IgE reactivity to nAmb a 1.01 in different IgE-binding assays (i.e., IgE immunoblot, ELISA, quantitative ImmunoCAP inhibition measurements). Furthermore, the rAmb a 1.01 showed comparable dose-dependent allergenic activity to nAmb a 1.01 regarding basophil activation. Overall, the results showed the successful expression of an rAmb a 1.01 with comparable characteristics to the corresponding natural isoform. Our findings provide the basis for an improvement in ragweed allergy research, diagnosis, and immunotherapy.

Dectin-1 Controls TSLP-Induced Th2 Response by Regulating STAT3, STAT6, and p50-RelB Activities in Dendritic Cells

The epithelium-associated cytokine thymic stromal lymphopoietin (TSLP) can induce OX40L and CCL17 expression by myeloid dendritic cells (mDCs), which contributes to aberrant Th2-type immune responses. Herein, we report that such TSLP-induced Th2-type immune response can be effectively controlled by Dectin-1, a C-type lectin receptor expressed by mDCs. Dectin-1 stimulation induced STAT3 activation and decreased the transcriptional activity of p50-RelB, both of which resulted in reduced OX40L expression on TSLP-activated mDCs. Dectin-1 stimulation also suppressed TSLP-induced STAT6 activation, resulting in decreased expression of the Th2 chemoattractant CCL17. We further demonstrated that Dectin-1 activation was capable of suppressing ragweed allergen (Amb a 1)-specific Th2-type T cell response in allergy patients ex vivo and house dust mite allergen (Der p 1)-specific IgE response in non-human primates in vivo. Collectively, this study provides a molecular explanation of Dectin-1-mediated suppression of Th2-type inflammatory responses and suggests Dectin-1 as a target for controlling Th2-type inflammation.

Sequence conservation predicts T cell reactivity against ragweed allergens

BACKGROUND

Ragweed is a major cause of seasonal allergy, affecting millions of people worldwide. Several allergens have been defined based on IgE reactivity, but their relative immunogenicity in terms of T cell responses has not been studied.

OBJECTIVE

We comprehensively characterized T cell responses from atopic, ragweed-allergic subjects to Amb a 1, Amb a 3, Amb a 4, Amb a 5, Amb a 6, Amb a 8, Amb a 9, Amb a 10, Amb a 11, and Amb p 5 and examined their correlation with serological reactivity and sequence conservation in other allergens.

METHODS

Peripheral blood mononuclear cells (PBMCs) from donors positive for IgE towards ragweed extracts after in vitro expansion for secretion of IL-5 (a representative Th2 cytokine) and IFN-γ (Th1) in response to a panel of overlapping peptides spanning the above-listed allergens were assessed.

RESULTS

Three previously identified dominant T cell epitopes (Amb a 1 176-191, 200-215, and 344-359) were confirmed, and three novel dominant epitopes (Amb a 1 280-295, 304-319, and 320-335) were identified. Amb a 1, the dominant IgE allergen, was also the dominant T cell allergen, but dominance patterns for T cell and IgE responses for the other ragweed allergens did not correlate. Dominance for T cell responses correlated with conservation of ragweed epitopes with sequences of other well-known allergens.

CONCLUSIONS AND CLINICAL RELEVANCE

These results provide the first assessment of the hierarchy of T cell reactivity in ragweed allergens, which is distinct from that observed for IgE reactivity and influenced by T cell epitope sequence conservation. The results suggest that ragweed allergens associated with lesser IgE reactivity and significant T cell reactivity may be targeted for T cell immunotherapy, and further support the development of immunotherapies against epitopes conserved across species to generate broad reactivity against many common allergens.

Allergens of weed pollen: an overview on recombinant and natural molecules

Weeds represent a botanically unrelated group of plants that usually lack commercial or aesthetical value. Pollen of allergenic weeds are able to trigger type I reactions in allergic patients and can be found in the plant families of Asteraceae, Amaranthaceae, Plantaginaceae, Urticaceae, and Euphorbiaceae. To date, 34 weed pollen allergens are listed in the IUIS allergen nomenclature database, which were physicochemically and immunologically characterized to varying degrees. Relevant allergens of weeds belong to the pectate lyase family, defensin-like family, Ole e 1-like family, non-specific lipid transfer protein 1 family and the pan-allergens profilin and polcalcins. This review provides an overview on weed pollen allergens primarily focusing on the molecular level. In particular, the characteristics and properties of purified recombinant allergens and hypoallergenic derivatives are described and their potential use in diagnosis and therapy of weed pollen allergy is discussed.

Immunologic analysis of monoclonal and immunoglobulin E antibody epitopes on natural and recombinant Amb a 1

BACKGROUND

Amb a 1 is the major allergen from ragweed pollen and more than 90% of ragweed-allergic patients react with this protein. Although Amb a 1 was cloned and sequenced in 1991, little is known of the specificity of anti-Amb a 1 antibodies or of the immunologic properties of the recombinant allergen.

OBJECTIVE

To compare binding of monoclonal antibodies (mAb) and IgE antibodies to purified natural Amb a 1 (nAmb a 1) and recombinant Amb a 1 (rAmb a 1).

METHODS

Binding of a panel of anti-Amb a 1 mAb and IgE antibodies to nAmb a 1 or rAmb a 1 was compared by immunoblotting. Chimeric ELISA was used to measure specific IgE to these allergens using 89 ragweed-allergic sera from Austria, Italy, Canada and the United States.

RESULTS

The 8 mAb bound to a 38 kDa Amb a 1 band in ragweed pollen extract and a subset of 5 mAb also bound to the 26 kDa chain of nAmb a 1. A two-site ELISA was developed using a mAb pair, which was approximately 10-fold more sensitive to rAmb a 1. There was a significant correlation between IgE antibody binding to nAmb a 1 and rAmb a 1 (n=89, r=0.79, P<0.001). A subset of approximately 40% of patients showed greater reactivity to nAmb a 1 than to rAmb a 1.

CONCLUSIONS

The data suggest that there is less reactivity of human IgE to rAmb a 1 compared with nAmb a 1. The development of more sensitive, quantitative ELISA for Amb a 1 will require the production of new mAb especially directed against nAmb a 1.

Purification and immunochemical characterization of recombinant and native ragweed allergen Amb a II

The complete sequence of a cDNA encoding Amb a II and its relationship to the Amb a I family of allergens has recently been described [Rogers et al. (1991) J. Immun. 147, 2547-2552; Griffith et al. (1991a), Int. Archs Allergy appl. Immun. 96, 296-304]. In this study, we present results generated with rabbit antipeptide antisera that recognize Amb a II or Amb a I, but not both. The specificity of two anti-Amb a II antipeptide sera, anti-RAE-50.K and anti-RAE-51.K, was verified on Western blots of recombinant Amb a II and Amb aI.1. These two sera, directed against separate regions of the Amb a II molecule, detected three individual 38-kDa Amb a II isoforms on 2D Western blots of aqueous ragweed pollen extract. These Amb a II isoforms have pI in the 5.5-5.85 range and can be easily distinguished from Amb a I isoforms with pI in the 4.5-5.2 range detected by an anti-Amb a I specific peptide antiserum. The Amb a II isoforms have also been individually purified from pollen, positively identified as Amb a II by amino acid sequencing, and visualized as separate bands on IEF gels. An analysis of Amb a II cDNA sequences generated by PCR led to the prediction of three Amb a II isoforms with pI of 5.74, 5.86 and 5.97 that are very similar to the pI deduced from 2D Western blot analysis. Recombinant Amb aI.1 and Amb a II have been expressed in E. coli, purified in their denatured form, and examined by ELISA for their capacity to bind pooled allergic human IgE. Purified native Amb a and Amb a II from pollen were shown to have very similar IgE-binding properties. In contrast, Amb a II had a markedly reduced IgE-binding capacity as compared to Amb a I.1. These data suggest that recombinant Amb a I.1 and Amb a II, isolated in a denatured form, differ significantly in their IgE-binding properties whereas the native molecules isolated from pollen do not.

Immunoaffinity chromatography of recombinant Amb a I in the presence of a denaturing agent

Recombinant proteins expressed in E. coli are often sequestered into inclusion bodies and require the use of denaturing agents in order to solubilize them. The recombinant form of Amb a I, the major allergen from short ragweed pollen, is one such protein. In some cases solubility can be maintained after the removal of the denaturing agent, particularly if the protein can be folded into its native conformation. However, not all proteins refold readily and after the removal of the denaturing agent the proteins will reaggregate and/or precipitate. In the case of Amb a I, the recombinant protein stays in solution at low concentrations but aggregates with itself and other proteins. The recombinant Amb a I is not expressed at high levels and may be toxic to E. coli. Therefore, isolation from a complex mixture of E. coli proteins was necessary. Monoclonal antibodies which recognize the denatured form of Amb a I were available, allowing for immunoaffinity purification. However, because the protein was not monomeric, this chromatographic technique did not provide an improvement in the purity level when run in normal buffer solutions. Analysis of one monoclonal antibody's stability to urea indicated it could tolerate the presence of 2 M urea and recover full activity. Use of this antibody as an immunoaffinity reagent in a column run in 2 M urea, which minimized aggregation of the E. coli produced proteins, gave a high degree of purification of recombinant Amb a I in one step. This illustrates the potential for the use of denaturing and other solubilizing agents in immunoaffinity chromatography of recombinant proteins.

Isolation and characterization of a glycoprotein allergen, Art v II, from pollen of mugwort (Artemisia vulgaris L.)

A glycoprotein allergen, Art v II, was isolated from pollen of mugwort by two different isolation procedures. Art v II-A was isolated by a combination of ion-exchange chromatography on DEAE-Sepharose, affinity chromatography on Con A-Sepharose and ion-exchange chromatography on Mono P. Art v II-B was isolated by a combination of preparative IEF in Ultrodex granulated gel, affinity chromatography on Con A-Sepharose and HPLC size exclusion on Ultropac TSK G2000SW. Art v II-A and Art v II-B were shown to be antigenically identical with the allergen we have formerly denoted Ag7. The MW of Art v II A/B was determined to be 34,000-38,000 by HPLC size exclusion, and 35,000 and 20,000 by SDS-PAGE under non-reducing and reducing conditions, respectively. Art v II was found to consist of 6(7) isoforms with pI 4.10, 4.20 (major component), 4.35, 4.45, 4.55, 4.65, (4.80). The glycoprotein allergen had a protein to carbohydrate ratio of 10:1 and the carbohydrate part contained mannose (70.7%), N-acetyl-glucosamine (17.0%), glucose (7.0%) and galactose (5.3%). In R(R)IE the purified allergen bound IgE from 5 (33%) of 15 sera from patients with clinical allergy against mugwort pollen and from 13 (52%) of 25 sera from patients selected only on the basis of a RAST-class 4 against mugwort pollen.

Epitope mapping of the major allergen from yellow mustard seeds, Sin a I

The antigenic sites on the major allergen from yellow mustard (Sinapis alba L.) seeds were studied using murine (BALB/c) monoclonal antibodies (mAb) and human IgE antibodies. Ten IgG1 (K) mAb from two fusions were analyzed. Competition and complementation studies performed with peroxidase labeled mAb reveal the existence of two main antigenic sites in Sin a I. All the described mAb failed to recognize the unordered carboxyamidomethylated polypeptide chains, with the single exception of 2B3, which binds the alkylated large chain. However, this mAB cannot react with the tetranitromethane-modified protein which retains the native conformation. This fact suggests that the only tyrosine of Sin a I, located in the large chain, may be part of a sequential epitope of the allergen. This chemical modification also alters the binding of the mAb 4A11 and 3F3 to the allergen, besides 2B3. The three mAb belong to the same complementation group. Specific IgE binding cannot be inhibited either by the large or small carboxyamidomethylated polypeptide chains, while the nitrated allergen shows a weaker inhibitory activity than the native Sin a I. 4A11, which is a tyrosine-dependent mAb, causes the greatest binding inhibition of the tested mAb on human IgE from atopic individuals, as determined from a reverse enzyme immunoassay, suggesting an important role played by tyrosine in the immunochemical recognition of Sin a I.

Characterization of allergens from spores of the oyster mushroom, Pleurotus ostreatus

Crude extracts of Pleurotus ostreatus spores obtained from a single local source were fractionated by gel filtration to resolve the allergenic components. The fraction pool corresponding to 10.5 to 25 kd molecular weight contained allergenic activity as demonstrated by both RAST and skin testing. Similar results were obtained with extracts from spores that originated in four other areas and with extracts prepared from P. sajor-caju spores obtained from commercially produced caps. The RAST-active fraction was further separated by hydrophobic interaction chromatography (HIC). HIC fraction pools were assayed for allergen(s) by RAST inhibition and immunoblotting of isoelectric focused polyacrylamide gels. RAST-inhibition data indicated that the allergen(s) was reversibly bound to the HIC column, eluting with 2, 1, and 0.15 mol/L of buffered salt solutions. After electrofocusing, these fractions yielded 15, 12, and 11 Coomassie brilliant blue-staining bands, respectively. IgE binding occurred with 7, 8, and 6 of these bands, as revealed by radiostaining of the immunoblots. These procedures help identify P. ostreatus spore allergens and allow a greater degree of standardization in the preparation of allergen extracts from basidiospores for use in diagnosis and therapy of fungal allergy.

Monoclonal antibodies to denatured ragweed pollen allergen Amb a I: characterization, specificity for the denatured allergen, and utilization for the isolation of immunogenic peptides of Amb a I

The epitope structure of short ragweed allergen Amb a I (formerly antigen E or AgE) has been investigated by characterizing monoclonal antibodies (MAbs) from mice immunized with Amb a I. The MAbs to Amb a I that we previously produced and characterized (HaA1, HaB1 and HaC1) reacted with determinants which were conformationally dependent. Denaturation of Amb a I, which is a prerequisite for peptide isolation and hence epitope localization, destroyed these determinants. We report here the isolation of 15 MAbs produced against denatured Amb a I and present their reactivities with native Amb a I, denatured Amb a I, and peptide fragments of Amb a I. None of the 15 MAbs to denatured Amb a I bind to native Amb a I, as judged by their lack of binding to Amb a I in immune complex with HaA1 and HaC1. All 15 MAbs reacted with the extensively reduced and alkylated form of denatured Amb a I and 14 of the 15 were shown by Western blotting techniques and ELISA to have activity against the isolated alpha chain or beta chains of Amb a I, but not both. In addition, several MAbs react with tryptic fragments of Amb a I which allowed us to isolate and sequence two tryptic peptides of Amb a I. Antisera raised against KLH-coupled synthetic analogs of these peptides reacted well with intact, denatured Amb a I. Finally, during chromatographic purification of Amb a I from fresh pollen extracts, various MAbs began to react with Amb a I as a function of stage of isolation, suggesting that some proportion of Amb a I spontaneously denatures during purification, converting from the allergenic form possessing two major B cell epitopes to an allergenically inactive form.

Regulatory mechanism of delayed-type hypersensitivity in mice. V. Augmentor cells for DTH responses

Mice primed with 1 microgram of reduced and alkylated ovalbumin (RA-OA) developed not only long-lived memory cells for delayed-type hypersensitivity (DTH), capable of differentiating into DTH-effector T cells (DTH-Te) against ovalbumin (OA) when restimulated in vitro with OA, but also spleen cells capable of augmenting recipients' DTH responses to OA when transferred into cyclophosphamide (CY)-pretreated mice. The augmenting activity in spleen cells, upon transfer, was found 7 days, but not 21 or 91 days, after priming with RA-OA, although memory DTH-Te were present throughout the period of observation. The loss of augmenting activity after day 7 of priming was not due to the presence of suppressor cells; spleen cells taken 21 days after priming failed to suppress, upon transfer, the augmenting activity in 7-day-primed spleen cells as well as induction and expression of DTH responses to OA. When 7-day-primed spleen cells were fractionated on a discontinuous bovine serum albumin density gradient, the augmenting activity was found only in the medium-density-cell layer, although memory DTH-Te were separated in the high-density layer. Augmentation of DTH-Te generation could also be demonstrated in vitro when 7-day-primed spleen cells, but not 21-day-primed spleen cells, were added to cultures of spleen cells from CY-pretreated mice. These results indicate that, in the 7-day-primed spleen, there is an augmentor cell population which is different from memory DTH-Te and interacts with CY-resistant unprimed cells to facilitate DTH-Te generation.

Regulatory mechanism of delayed-type hypersensitivity in mice. IV. Effect of suppressor T cells on the development of memory T cells involved in accelerated generation of DTH-effector cells in vitro

The effect of suppressor T cells (Ts) on the induction and the subsequent development of memory T cells for delayed-type hypersensitivity (DTH) was examined. The memory cells were induced in the spleens of mice primed previously with a low dose of reduced and alkylated ovalbumin (Ra-OA), and they generated DTH-effector T cells (DTH-Te) in a significantly accelerated fashion when cultured with OA in vitro. Ts were obtained from the spleens of mice which received OA-coupled spleen cells i.v. 4 days previously, and they inhibited antigen-specifically the induction of DTH responses in the recipient mice sensitized with alum-absorbed OA only when transferred with 5 weeks before sensitization. The spleen cells from mice given Ts together with the priming antigen 7 weeks before culture failed to generate DTH-Te in an accelerated manner on restimulation with OA in vitro. The memory cells from primed mice also did not cause accelerated generation of DTH-Te, when cultured with Ts in the presence of OA in vitro. These results indicate that both the induction of the memory cells by priming with antigen in vivo and the subsequent development of memory cells to DTH-Te by restimulation in vitro are inhibited independently by Ts. This corresponded well with the effect of Ts on the development of DTH-memory in vivo.

Correlation between production of inflammatory substances and generation of effector T cells mediating delayed-type hypersensitivity in mice

In vitro exposure to human serum albumin (HSA) of splenic lymphocytes from mice sensitized for delayed-type hypersensitivity (DTH) against HSA resulted in the release of substances that could induce a footpad inflammatory reaction with a maximum of 6 hr after injection into normal mice. The substances were fractionated mainly in a molecular weight range of 30,000 to 70,000 daltons on Sephadex G-200. The ability of sensitized lymphocytes to produce the substances was dependent on T cells, was antigen specific, and correlated well with the ability of the lymphocytes to mediate DTH reactions. Moreover, the substances were produced efficiently by the DTH effector cell population generated in the in vitro culture system and also by the effector cell-enriched fractions on discontinuous bovine serum albumin gradients. These results suggest that the substances are produced by DTH-effector cells.

Regulatory mechanism of delayed-type hypersensitivity in mice. III. In vitro analysis of memory T cells involved in augmentation of DTH responses

The memory of delayed-type hypersensitivity (DTH), manifested by the augmented responsiveness upon challenge with alum-absorbed ovalbumin (OA), was induced in mice primed 7 days, 21 days, or 90 days previously with 1 microgram of reduced and alkylated OA. The memory cells involved in the augmentation of DTH responses were analyzed in the in vitro induction system of T cells which mediate DTH against OA. Spleen cells from the primed mice generated DTH-effector T cells (DTH-Te) in a significantly accelerated fashion, compared with unprimed spleen cells, when cultured with OA. The accelerated generation of DTH-Te in vitro was induced antigen specifically and was dependent on a certain T cell population in the primed spleen. The T cell population was found in the spleen of primed mice for at least 3 months after priming, corresponding to the persistence of DTH-memory in vivo. Moreover, it was fractionated in the high-density layer by discontinuous bovine serum albumin gradient centrifugation. The high-density cell population decreased in density with increase in the time of culture and developed into DTH-Te, which were separated in the low-density layer on day 4 of culture. These results indicate that the T cells involved in the accelerated generation of DTH-Te in vitro are long-lived DTH-memory T cells, which are probably precursor cells, capable of differentiating into DTH-Te upon challenge with the antigen.

Treatment of ragweed hay fever with urea-denatured antigen E

Urea-denatured antigen E (UDE) has lost the major determinants of antigen E (AgE), eliciting neither IgE nor IgG antibodies to native AgE in mice. UDE, however, stimulates T cells so that repeated injections result in specific but partial suppression of ongoing IgE responses to native AgE. An attempt was made to apply this property to the treatment of 10 ragweed-allergic human volunteers by repeated subcutaneous injections of UDE over about 18 mo. Local and systemic allergic reactions limited the dose to 4 to 75 microgram UDE per injection. Little or no antibody response to AgE was induced. Five patients had increased basophil sensitivity to UDE after 4 mo of injections. Five of eight patients who completed the study had evidence of suppression of IgE responses by exhibiting a 20% or less increase of IgE antibodies to ragweed on natural seasonal exposure. Three patients still exhibited this evidence at the next season of exposure 10 mo after the last injection. The two patients who received the lowest doses had greater than usual seasonal rises of IgE antibodies. There was no clinical evidence of improvement of hay fever symptoms. The results indicate that the immunologic properties of UDE in humans are similar to those in mice. The clinical applicability of these properties remains doubtful.

Preparation of protein conjugates with alkoxypolyethylene glycols

Alkoxypolyethylene glycols can be converted to O-alkoxypolyethyleneglycoxy-S-carboxamidomethyldithiocarbonates. These dithiocarbonates are useful for the preparation of protein conjugates with alkoxypolyethylene glycols. Studies with model compounds suggest that sites of reaction are primarily the amino groups of proteins and, to a lesser extent, the aliphatic and phenolic hydroxyl groups. Antigen E, which is an allergenic protein from ragweed pollen, was modified with different alkoxypolyethylene glycols by the above procedure. The size and the hydrophobicity of alkoxypolyethylene glycols used were found to influence the reduction in antigenic activity of conjugates.

Isolation and characterization of cal allergens

A crude (saline soluble) extract of cat skins capable of eliciting a strong positive prick skin test in cat sensitive individuals was fractionated on Sephadex G200. Active fractions were pooled and successively fractionated on isoelectric focusing gradients of pH 3-5 and pH 4-5. Allergenic activity was localized in two peaks with mean isoelectric points of 4-1 and 4-35 respectively. On immunoelectrophoresis the allergen with pI = 4-35 was associated with a protein which was subsequently found to be immunologically indistinguishable from serum albumin and to have a molecular weight of 69,000 daltons. The allergen with pI = 4-1 migrated in the alpha2-region on immunoelectrophoresis and had a mean molecular weight of 55,000 daltons. This allergen was isolated and analysed for amino acid and carbohydrate content. A combined extract of both allergens coupled to microcrystalline cellulose and used a RAST procedure readily distinguished between two groups of individuals classified as skin test positive and skin test negative to cat allergen.

Localization of coliphage MS2 A-protein

The purification of coliphage MS2 dinitrophenol (DNP) conjugates provided a system for localization of the single molecule of A-protein in the capsid of the MS2 phage particle. Three A-protein preparations isolated from unconjugated MS2, overconjugated DNP-MS2, and purified 78S DNP-MS2 were tested for the presence of covalently bound DNP. The binding characteristics to Dowex 1-X8 and rabbit anti-DNP bovine serum albumin (DNP-BSA) immunoglobulin G of the 78S DNP-MS2 and overconjugated DNP-MS2 A-protein preparations indicate that the A-protein is located on the surface of the phage particle where it can be covalently conjugated with hapten. Extensive enzymatic iodination of the A-protein of intact unconjugated MS2 substantiates this conclusion.