Is epitope recognition of shrimp allergens useful to predict clinical reactivity?

BACKGROUND

Shrimp is a frequent cause of severe allergic reactions world-wide. Due to issues such as cross-reactivity, diagnosis of shrimp allergy is still inaccurate, requiring the need for double-blind, placebo-controlled food challenges (DBPCFC). A better understanding of the relationship between laboratory findings and clinical reactivity is needed.

OBJECTIVE

To determine whether sensitization to certain shrimp allergens or recognition of particular IgE epitopes of those allergens are good biomarkers of clinical reactivity to shrimp.

METHODS

Thirty-seven consecutive patients were selected with clinical histories of shrimp allergy. Skin prick test, specific IgE determinations, DBPCFC and immunoblot assays to shrimp extract were performed. IgE binding to synthetic overlapping peptides representing the sequence of the four allergens from the Pacific white shrimp (Litopenaeus vannamei) identified to date (Lit v1, Lit v2, Lit v3 and Lit v4) was analysed.

RESULTS

Of 37 (46%) patients, 17 had a positive challenge to shrimp (11 children and 6 adults). By microarray, patients with positive challenges showed more intense binding to shrimp peptides than those with negative challenges. Statistically significant differences in terms of the frequency and intensity of IgE binding to some epitopes were observed between the two groups. Diagnostic efficiency was higher for individual epitopes than for proteins. Particularly, efficiency was highest for certain Lit v 1 and Lit v 2 epitopes, followed by Lit v 3 and Lit v 4 epitopes.

CONCLUSION AND CLINICAL RELEVANCE

Patients with positive shrimp challenges present in general more intense and diverse epitope recognition to all four shrimp allergens. IgE antibodies to these shrimp epitopes could be used as biomarkers for prediction of clinical reactivity in subjects with sensitization to shrimp. Patients with positive shrimp challenges show more intense sensitization and more diverse epitope recognition. Several IgE-binding shrimp epitopes could be used as biomarkers for predicting clinical reactivity in subjects with sensitization to shrimp.

Seafood allergy and allergens: a review

Seafoods are composed of diverse sea organisms and humans are allergic to many of them. Tropomyosin is a major allergen in many shellfish, especially crustacea and mollusks. Interestingly, tropomyosin has also been identified as an important allergen in other invertebrates including dust mites and cockroaches, and it has been proposed by some to be an invertebrate pan allergen. Different regions of shrimp tropomyosin bind IgE; 5 major IgE-binding regions have been identified in shrimp tropomyosin containing 8 epitopes. Mutations of these shrimp allergenic epitopes can reduce seafood allergenicity; methods utilizing such mutations will provide safer vaccines for more effective treatment of seafood-allergic patients, and in the future less-allergenic seafood products for consumption.

Immunoglobulin E antibody reactivity to the major shrimp allergen, tropomyosin, in unexposed Orthodox Jews

BACKGROUND

Assessment of allergic (IgE antibody-mediated) reactions to foods may become complicated by cross-reactivity that can occur among certain food families and between foods and seemingly unrelated allergens.

OBJECTIVE

The allergenic properties of tropomyosin (muscle-derived protein) have been recently demonstrated in invertebrates such as cockroaches, dust mites, and shrimp. In view of a possible cross-reactivity between food allergens and related allergens from animal sources, we designed a study to assess IgE antibody reactivity to the major shrimp allergen, Pen a 1, in an unexposed population of Orthodox Jews, who observe Kosher dietary laws that prohibit eating shellfish.

METHODS

Nine subjects, who reacted positively by skin tests to shrimp (Penaeus setiferous), were selected for the study. Subjects (two females, seven males) ranged in age from 14 to 32 years (mean 20.4). All subjects were strictly observant of Jewish tradition and had no prior exposure to seafood (regarded as a non-Kosher food). Serum was obtained from all the subjects and tested for IgE antibody reactivity to shrimp and dust mite.

RESULTS

All subjects reported symptoms of perennial allergic rhinitis, five had history of asthma, atopic dermatitis, and/or sinusitis. All had positive skin prick tests to shrimp and house dust mite (HDM) (Dermatophagoides farinae, D. pteronyssinus, or both); 2/7 subjects were positive to cockroach mix (Blattella germanica and Periplaneta americana). Sera of 4/9 subjects demonstrated specific IgE antibodies by RAST to shrimp (7.0-20.0%), 3/9 to Pen a 1 (6.3-24.1%), and 3/9 to shrimp or Pen a 1 by immunoblot. IgE binding to Pen a 1 was inhibited with either mite or cockroach extracts as demonstrated by RAST and/or immunoblot inhibition analysis.

CONCLUSIONS

These studies indicate that IgE antibody reactivity to a major food allergen, shrimp, can occur in an unexposed population of individuals; some subjects allergic to HDM and/or cockroach show substantial IgE antibody reactivity to the major shrimp allergen Pen a 1 (tropomyosin). Based on inhibition with cockroach and/or dust mite extracts, this reactivity appears to be due to cross-reacting tropomyosins.

Identification of continuous, allergenic regions of the major shrimp allergen Pen a 1 (tropomyosin)

BACKGROUND

Crustaceans and mollusks are a frequent cause of allergic reactions. The only major allergen identified in shrimp is the muscle protein tropomyosin; at least 80% of shrimp-allergic subjects react to tropomyosin. Furthermore, tropomyosin is an important allergen in other crustaceans such as lobsters, crabs and mollusks, as well as other arthropods such as house dust mites and cockroaches, and has been implied as the cause of clinical cross-sensitivity among invertebrates. In contrast, vertebrate tropomyosins are considered non-allergenic.

OBJECTIVE

The basis of the allergenicity of proteins has not yet been resolved. Thus, tropomyosin molecules provide an excellent opportunity to study the relationship between protein structure and allergenicity. The aim of the current study was to identify the IgE-binding regions of Pen a 1 and compare these regions with homologous sequences in other allergenic and non-allergenic tropomyosins.

METHODS

Forty-six overlapping peptides (length: 15 amino acids; offset: 6 amino acids) spanning the entire Pen a 1 molecule were synthesized and tested for IgE antibody reactivity with sera from 18 shrimp-allergic subjects to identify the IgE-binding regions of shrimp tropomyosin.

RESULTS

Based on the frequency and intensity of the IgE reactivities, five major IgE-binding regions were identified. All five major IgE-binding regions were 15-38 amino acids long. The major IgE-binding regions identified were: region 1: Pen a 1 (43-57); region 2: Pen a 1 (85-105); region 3: Pen a 1 (133-148); region 4: Pen a 1 (187-202), and region 5: Pen a 1 (247-284). In addition, 22 peptides were categorized as minor IgE-binding regions, and 12 peptides did not bind any IgE antibodies. No substantial differences in amino acid group composition in the five IgE-binding regions compared to the whole molecule were detected. Sequence identities and similarities of the Pen a 1 IgE-binding regions with homologous regions of allergenic arthropod tropomyosins were as high as 100%, whereas identities and similarities with homologous vertebrate sequences ranged from 36 to 76% and 53 to 85%, respectively.

CONCLUSION

Five major IgE-binding regions of the allergenic shrimp tropomyosin, Pen a 1, were identified which are positioned at regular intervals of approximately 42 amino acids (7 heptads), suggesting a relationship with the repetitive coiled-coil structure of the tropomyosin molecule. The high degree of similarity between Pen a 1 IgE-binding regions and homologous sequences in invertebrate tropomyosins and the lower percentage of similarity with homologous regions of vertebrate tropomyosins supports a structural basis for cross-reactivity of allergenic tropomyosins.

Grid-immunoblotting: a fast and simple technique to test multiple allergens with small amounts of antibody for cross-reactivity

Grid-immunoblotting is a procedure that allows the simultaneous testing of up to 20 different antibodies such as monoclonal antibody-containing hybridoma supernatants or human sera for specific antibodies to up to 20 different antigens or allergens on a single sheet of nitrocellulose membrane. Since only 150 to 200 microl of antibody-containing solution are required this technique is uniquely suited to test growing hybridomas and small amounts of sera (e.g. mouse and children's sera). Compared to a standard ELISA, approximately ten times less antibody is needed to obtain the same information.

Characterization and identification of allergen epitopes: recombinant peptide libraries and synthetic, overlapping peptides

For the understanding of the relationship between protein structure and allergenicity, it is important to identify allergenic epitopes. Two methods to characterize primarily linear epitopes are compared using the major allergen from brown shrimp (Penaeus aztecus), Pen a 1, as an example. A recombinant peptide library was constructed and synthetic, overlapping peptides, spanning the entire Pen a 1 molecule, were synthesized and tested for specific IgE reactivity. Both methods identified IgE-binding of Pen a 1, however, the SPOTs procedure resulted in the identification of more epitopes of the major shrimp allergen Pen a 1 than the usage of the recombinant peptide library. For detection of specific IgE antibodies, the usage of 125I-labeled detection antibody seems to be superior over enzyme-labeled anti IgE antibodies. The regeneration of SPOTs membranes is possible, but it is prudent to test regenerated membranes for residual activity. If a given food allergen contains significant linear epitopes, which seems to be true for stable major allergens such as those of peanut and shrimp the SPOTs system may be more advantageous than the use of recombinant peptides libraries. However, if allergens are studied that contain more conformational epitopes, recombinant peptide libraries may help to identify the relevant epitopes. It has to be emphasized that no system for epitope identification will detect all epitopes and that the relevance of identified epitopes has to be confirmed with other methods such as inhibition studies, crystallographic analysis or the immunological evaluation of modified whole allergens.

Identification of bovine IgG as a major cross-reactive vertebrate meat allergen

BACKGROUND

Although beef is a main source of protein in Western diets, very little has been published on allergic reactions to beef or the main allergens implicated in these reactions. The aim was to evaluate the IgE antibody response to beef in suspected meat-allergic subjects and assess cross-reactivity of beef with other vertebrate meats.

METHODS

Fifty-seven sera from suspected meat-allergic subjects were tested by grid blot for specific IgE antibodies to vertebrate meats (beef, lamb, pork, venison, and chicken), and the patterns of recognition of meat proteins were assessed by immunoblot studies.

RESULTS

A 160-kDa band, identified as bovine IgG, was detected in raw beef in 83% (10/12) of beef-allergic subjects but in only 24% of the beef-tolerant subjects. IgE reactivity to a band of similar mol. mass was detected also in lamb and venison, but rarely in pork or chicken. Complete inhibition of the IgE reactivity to the bovine IgG was obtained with lamb, venison, and milk. IgE reactivity to this band also completely disappeared when beef or lamb extracts were separated under reducing conditions, indicating conformational epitopes.

CONCLUSIONS

Bovine IgG appears to be a major cross-reacting meat allergen that could predict beef allergy. Further studies with oral IgG challenges should be performed to document the conclusion that in vitro reactivity correlates with clinical hypersensitivity. The role of bovine IgG in other bovine products such as milk, dander, or hair must also be studied, and the hypothesis that it is a cross-reacting allergen with other mammalian products validated.

IgE antibody response to vertebrate meat proteins including tropomyosin

BACKGROUND

Although meat is a main source of proteins in western diets, little information is available regarding allergy to vertebrate meats or the allergens implicated in these reactions.

OBJECTIVE

To evaluate the in vitro IgE antibody response to different vertebrate meats in suspected meat-allergic subjects, as well as the possible role of tropomyosin in meat allergy and to analyze the cross-reactivity between vertebrate meats and the effect of heating on the IgE-binding to meat proteins.

METHODS

Fifty-seven sera from suspected meat-allergic subjects were tested by grid blot to extracts of beef, lamb, pork, venison, chicken, and turkey and to four mammalian tropomyosins of different origins.

RESULTS

Meat-allergic subjects have IgE antibodies to proteins in different mammalian meats (43/57 subjects); cross-reactivity with avian meat was limited: less than 50% (19/43) of meat positive sera reacted to chicken. In contrast, most of the poultry-positive sera also reacted to different mammalian meats. In general, there was stronger IgE reactivity to raw meats in comparison to cooked meats; an exception was six cases in which IgE reactivity to cooked poultry was stronger. Weak IgE reactivity to tropomyosin was detected in only 2/57 sera tested.

CONCLUSIONS

Suspected meat-allergic subjects have serum IgE directed to meat proteins. In vitro cross-reactivity among mammalian meats appears to be important, while cross-reactivity to poultry is limited indicating mammalian-specific proteins. Although cooking in general denatures meat proteins rendering them less allergenic, in some cases the process of cooking may result in the formation of new allergenic moieties. The muscle protein tropomyosin is not an important vertebrate meat allergen.

Tropomyosin: an invertebrate pan-allergen

Among food allergens, crustaceans, such as shrimp, crab, crawfish and lobster, are a frequent cause of adverse food reactions in allergic individuals. The major allergen has been identified as the muscle protein tropomyosin. This molecule belongs to a family of highly conserved proteins with multiple isoforms found in both muscle and nonmuscle cells of all species of vertebrates and invertebrates. Its native structure consists of two parallel alpha-helical tropomyosin molecules that are wound around each other forming a coiled-coil dimer. Allergenic tropomyosins are found in invertebrates such as crustaceans (shrimp, lobster, crab, crawfish), arachnids (house dust mites), insects (cockroaches), and mollusks (e.g. squid), whereas vertebrate tropomyosins are nonallergenic. Studies of cross-reactivities among crustaceans and the high degree of sequence identity among them suggest that tropomyosin is probably the common major allergen in crustaceans. Furthermore, immunological relationships between crustaceans, cockroaches and housedust mites have been established and may suggest tropomyosin as an important cross-sensitizing pan allergen.

Quantitation of the major allergen of several Parietaria pollens by an anti-Par 1 monoclonal antibody-based ELISA. Analysis of crossreactivity among purified Par j 1, Par o 1 and Par m 1 allergens

BACKGROUND

Plants of the genus Parietaria, Urticaceae family, represent a major cause of pollinosis in the Mediterranean area. Different Parietaria species crossreact to a great extent, but studies on the crossreactivity among the major allergens of these pollens have not been carried out so far.

OBJECTIVE

To develop an immunochemical method to quantify the major Parietaria judaica allergen, Par j 1, as well as to verify the presence of Par j 1-like proteins in different Urticaceae pollens. These proteins would be purified in order to study the cross-reactivity among them.

METHODS

Immunoaffinity chromatography with a monoclonal antibody, solid-phase enzyme-linked immunoassays and SDS-PAGE.

RESULTS

A monoclonal antibody-based ELISA for the quantification of Par j 1 has been developed. The assay has a sensitivity of 0.2 ng/mL and shows a high correlation with the allergenic activity of P. judaica extracts determined by radioallergosorbent assay (RAST) inhibition. By means of this assay, proteins homologous to Par j 1 were detected in P. officinalis and P. mauritanica. These proteins (Par o 1 and Par m 1, respectively) were purified by affinity chromatography using the same monoclonal antibody employed in the ELISA. Crossed-inhibition experiments demonstrated that Par j 1, Par o 1, and Par m 1, competed for the binding of specific IgE from a P. judaica-sensitive patients serum pool.

CONCLUSION

The results here described suggest that shared allergenic epitopes are present in the three main allergens investigated, which may simplify the diagnosis and therapy for Parietaria allergy.

[A surveillance system for the study of the circulation of influenza in Madrid during the 1986-1991 quinquennium. The Influenza Surveillance Group of Madrid]

BACKGROUND

The creation of a surveillance system allowing the study of the evolution of the tendency of influenza and act as an alert system for undertaking control measures is necessary due to the great variability characteristic of the circulation of influenza virus. The Madrid Influenza Surveillance Group was therefore designed. The activity carried out during its first five years of existence is evaluated.

METHODS

The field work of the Group is based on the clinical study of patients with influenza, among which some are selected for virologic study with the aim to isolate and characterize the circulating virus. The data obtained by the work group itself are used as the dates of the System of Obligatory Disease Declaration and the System of Microbiologic Information as epidemiologic support to define the outbreaks observed.

RESULTS

All the virus isolated were similar to those recommended by the World Health Organization for their inclusion in anti-influenza vaccination, with their circulation being largely reproduced throughout Europe. In three of the five seasons studied the type A virus prevailed leading to earlier outbreaks and a greater number of cases than in the two seasons with type B prevalence.

CONCLUSIONS

The circulation of the influenza virus in Madrid coincides with that of the rest of Spain at both the maximum peak and relative incidence as well as the type of prevailing virus. The minor circulation detected by the Madrid Group is in concordance with the data provided by the other autonomic communities.

Isolation by mAb based affinity chromatography of two Par j I isoallergens. Comparison of their physicochemical, immunochemical and allergenic properties

We report the identification and separation of two isoallergen components of Par j I, the major allergen from Parietaria judaica pollen. First, electrophoretic conditions for consistently separating both isoforms in an SDS-PAGE system were established, and mol. wt values of 13,000 (isoallergen IA) and 10,500 (isoallergen IB) were estimated. Immunoblot, after SDS-PAGE experiments, with individual P. judaica-sensitive human sera revealed a slightly different IgE-binding pattern for each isoallergen. Four anti-Par j I mAbs were obtained from BALB/c mice immunized with a purified Par j I preparation comprising IA and IB isoallergens. Three mAbs were directed to an epitope shared by both isoallergens, and the fourth one recognized specifically one epitope on Par j IB. Dot-blot experiments with the deglycosylated allergen showed that the mAbs did not recognize the carbohydrate prosthetic group of the molecules. Affinity chromatography using the mAbs allowed the separation of the isoallergens that retained their IgE-binding ability after the purification process. Amino acid composition analyses and partial N-terminal sequencing demonstrated an extensive homology and also the existence of some structural differences between Par j I isoallergens, which is in agreement with the high, but not complete, cross-reactivity observed in competition ELISA experiments. Finally, skin prick tests performed on 28 P. judaica-sensitive patients showed that all of them recognized both isoforms and that allergenic epitopes present in Par j IA and IB are responsible for most of the allergenic activity of the whole extract.

Studies on the relationship between structure and IgE-binding ability of Parietaria judaica allergen I

The main allergen of Parietaria judaica pollen, Par j I, is a glycopolypeptide with mol. wt about 10,000. It shows a considerable charge heterogeneity which is mostly due to the carbohydrate prosthetic groups, since treatment with trifluoromethanesulfonic acid yielded a deglycosylated protein with 8500 mol. wt that displayed only a few bands on IEF, in a narrow pH-region around 5.0. Deglycosylated Par j I exhibited a specific allergenic activity slightly lower than that of native Par j I; however, no allergenic determinants should be located on the sugar moiety since both native and deglycosylated Par j I inhibited up to a similar extent the binding of specific human IgE to P. judaica-coated wells in ELISA. The decrease of specific allergenic activity following deglycosylation could be ascribed to conformational changes evidenced by CD experiments. On the other hand, fluorescence spectroscopy showed that Par j I bears unidentified yellow-brown chromophores strongly linked to the polypeptide chain. These chromophores were not removed by TFMS treatment. Finally, reduction and alkylation caused the complete loss of allergenic activity, showing that disulphide bridges are essential for the IgE-binding ability of Par j I.

HPLC purification of the main allergen of Parietaria judaica pollen

A two-step purification procedure of Par j I from the whole Parietaria judaica pollen extract is described. The first step consisted of gel filtration HPLC using a TSKG 3000 SW column, and 0.1% trifluoroacetic acid as the eluant. By this method, proteins were separated from the highly colored material present in the extract. Then, Par j I-containing fractions were chromatographed on a reversed-phase HPLC column (Vydac C4) using an acetonitrile gradient. This second step yielded pure Par j I as assessed by SDS-PAGE and CIE. Previously reported microheterogeneity was still observed, but amino acid analysis of various RP-HPLC fractions suggested that the heterogeneity of Par j I might not be due to changes in its primary structure. Allergenic activity of Par j I was shown to be retained after the purification procedure by several immunochemical techniques.

Relationship between lipoprotein levels and in vivo insulin action in normal young white men

In epidemiologic studies, hyperinsulinemia has been found to be an independent risk factor for coronary heart disease (CHD). However, the mechanisms responsible for its role in atherogenesis remain unclear. We studied the relationship of in vivo insulin action and plasma lipids and lipoproteins in 44 normotriglyceridemic white men (aged 18 to 34 years). The euglycemic, hyperinsulinemic glucose clamp technique was used to quantitate insulin-mediated glucose disposal (M/I value) at a plasma insulin concentration of approximately 100 microU/mL. The M/I value correlated negatively with plasma triglycerides (r = -0.553, P less than .0001), as well as with fasting plasma insulin levels (r = -0.483, P less than .001), independent of age, body mass index, and fasting plasma glucose levels. A negative correlation of the M/I value was also observed with very low density lipoprotein (VLDL)-cholesterol (r = -0.347, P less than .05), VLDL-triglycerides (r = -0.474, P less than 0.005), and total cholesterol/high density lipoprotein (HDL)-cholesterol ratio (r = -0.431, P less than .01). The relationship between the M/I value and the total cholesterol/HDL-cholesterol ratio was independent of VLDL-cholesterol and VLDL-triglycerides, however, not independent of plasma triglycerides. No relationship was observed between insulin-mediated glucose uptake and total cholesterol, low density lipoprotein (LDL)-cholesterol, and HDL-cholesterol values. Individual differences in plasma triglycerides, fasting insulin concentration, and the total cholesterol/HDL-cholesterol ratio accounted for about half the variance observed in the M/I value.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of Par j I, the major allergen of Parietaria judaica pollen

A component of Parietaria judaica pollen extract, previously identified as the major allergen, then reported as Pj10 and hereafter denominated Par j I has been isolated by a combination of 65% ammonium sulphate salt precipitation and gel filtration and an Ultrogel AcA54 column. The purified allergen appeared essentially homogeneous on gel filtration HPLC. The mol. wt of Par j I was estimated by electrophoretic and chromatographic techniques. All results gave values in a range from 13 K to 25 K. Analysis in SDS-PAGE under reducing conditions revealed a broad band corresponding to a mol. wt of 10 K, which retained allergenicity when tested with a patients serum pool. CIE and CRIE patterns of the isolated Par j I displayed the two precipitating lines already reported as those exhibiting the highest IgE-binding ability. Par j I showed a specific allergenic activity about 10-fold higher than that of the whole extract and was demonstrated to be the major allergen of Parietaria judaica as assessed in 25 sensitive human sera.

Monocyte-T lymphocyte interaction for regulation of insulin receptors of the activated T lymphocyte

During activation the lymphocyte attains functional insulin receptors with precise regulation, a consequence of insulin concentration manipulations. These studies test the hypothesis that insulin receptor (+) monocytes monitor insulin concentrations, so instructing the T lymphocytes. Monocyte-enriched populations were incubated with insulin (0-10(-6) M) followed by co-culture with T lymphocytes and an activating stimulus. A dose-related fall in T lymphocyte insulin receptor binding was observed that was specific for the monocyte as the signalling cell and for insulin as the signal received. Monocytes from normal volunteers during a euglycemic, hyperinsulinemic clamp were cultured with T lymphocytes and an activating stimulus. A decline in specific insulin receptor binding on T lymphocytes was observed, which Scatchard analysis demonstrated to be a consequence of reduction in receptor numbers. These studies demonstrate that the receptor (+) monocyte perceives the concentration of insulin and passes this information to T lymphocytes regulating the number of activation-induced insulin receptors. The interplay between the monocyte and T lymphocyte parallels the interaction of these cell types for recognition of antigen.

Identification of IgE binding polypeptides cross-reactive with the Parietaria judaica main allergenic polypeptide

The major allergen of the pollen of Parietaria judaica was characterized using an anti-allergen MAb AC/15.1. The antibody was able to immunoadsorb four different polypeptides (10,000, 20,000, 30,000 and 40,000 mol. wt) from the pollen proteins radioiodinated by the Bolton-Hunter's reagent. The four polypeptides have been shown not to be covalently linked, except for the 10,000 mol. wt polypeptide (Pj10), which appeared to form Pj10 dimers under non-reducing conditions. All of them contained the antigenic epitope defined by the monoclonal antibody and demonstrated human IgE binding ability. The structural relationship of these polypeptides in the native allergen is discussed.

[Evaluation of the total biological activity and allergenic composition of allergenic extracts]

In the present study, a complete procedure is presented in order to standardize allergenic extracts, the meaning of which is the measurement of the total allergenic activity and the determination of the allergenic composition. The measurement of the biological activity comprises 2 steps: Preparation of Reference Extracts and determination of their "in vivo" activity. Evaluation of the total allergenic activity of extracts for clinical use. Reference extracts were prepared from the main allergens and their "in vivo" biological activity was determined by a quantitative skin prick test in a sample of at least 30 allergic patients. By definition, the protein concentration of Reference Extract that produces, in the allergic population, a geometric mean wheal of 75 mm.2 has an activity of 100 biological units (BUs). The determination of the biological activity of a problem extract is made by RAST inhibition. The sample is compared with the corresponding Reference Extract by this technique and, from this comparison, it is possible to quantify the activity of the problem extract in biologic units (BUs) with clinical significance. Likewise, different techniques have been used to determine the allergenic composition of extracts. These techniques comprise 2 steps: Separation of the components of the extract. Identification of the components that bind specific human IgE. The separation of the components of the extract has been carried out by isoelectric focusing (IEF) and electrophoresis in the presence of sodium dodecyl sulphate (SDS-PAGE). In order to identify the allergenic components, an immunoblotting technique has been employed. The separated components in the IEF gel or SDS-PAGE gel are transferred to a nitrocellulose sheet and later on, this membrane is overlaid with a serum pool from allergic patients and a mouse monoclonal anti-human IgE, labelled with 125I. Finally, the autoradiography of the nitrocellulose membrane is obtained. In this way it is possible to compare the allergenic composition of an extract with the corresponding Reference Extract and so to employ for clinical use only those extracts with the right allergenic composition.

A competitive solid-phase radioimmunoassay for quantitation of the major allergen of Parietaria pollen

A competitive solid-phase radioimmunoassay has been developed for quantitation of the major allergen of Parietaria judaica pollen. The assay is based on: (1) the ability of AC/1.1 monoclonal antibody to bind specifically to the P. judaica major allergen, and (2) the ability of crude pollen extracts or purified allergen to inhibit the binding of 125I-labelled allergen to solid-phase-bound AC/1.1 monoclonal antibody. The assay is sensitive enough to detect as little as 10 ng of allergen. A good correlation is found when the results obtained are compared with those produced by RAST inhibition (r = 0.95; P less than 0.001). Thus, this method can also be used for the estimation of the allergenic activity of P. judaica pollen extracts. The assay is easily completed in 2 h, allowing simultaneous analysis of a number of extracts.

Stability of Lolium perenne extract

The stability of Lolium perenne extract was studied during a year in different conditions of storage. The changes of allergen activity were measured periodically by both in vivo and in vitro techniques, and structural modifications were examined by polyacrylamide gel electrophoresis and isoelectric focusing. Lyophilised extracts did not show any change and frozen samples retained full activity, but there were slight alterations in the pattern of proteins during the storage period. The activity of refrigerated aqueous extracts (4-6 degrees C) decreased gradually with time, while glycerinated samples at the same temperatures did not lose any of their allergen potency. Room temperature and 40 degrees C were unsatisfactory for aqueous extracts, but less so for preparations that contained 50% glycerol. The presence of the preservative phenol had a significant negative effect on stability at all of the temperatures studied.