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.

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.

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.

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.

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.