Molecular cloning, expression and immunological characterisation of Pas n 1, the major allergen of Bahia grass Paspalum notatum pollen

Nanofluidic point-of-care IgE test for subtropical grass pollen for rapid diagnosis of allergic rhinitis

BACKGROUND

Widening of subtropical climate zones globally and increasing grass-pollen exposure provide the impetus for developing a more precise and accessible diagnosis of allergy.

OBJECTIVE

To evaluate the utility of recombinant allergen components of Panicoideae and Chloridoideae pollens for specific IgE testing in a rapid, point-of-care device.

METHODS

Recombinant (r) Pas n 1 and Cyn d 1 were expressed, purified, and tested in the nanofluidic device for measuring serum specific IgE (spIgE) in a well-characterized Australian cohort. Concentrations and classes of spIgE to rPas n 1 and rCyn d 1, and total IgE were compared with skin prick test results and spIgE with grass pollen.

RESULTS

Correlations between commercial and academic laboratories for 21 sera were high for rPas n 1 spIgE (r = 0.695) and total IgE (r = 0.945). Higher spIgE to rPas n 1 and rCyn d 1 fluorescence was detected in the patients with grass-pollen allergy and with clinician-diagnosed allergic rhinitis (n = 134) than in participants with other allergies (n = 49) or no allergies (n = 23). Correlation between spIgE concentrations to rPas n 1 (r = 0.679) and rCyn d 1 (r = 0.548), with Bahia and Bermuda grass-pollen spIgE, respectively, was highly significant (p<0.0001). The positive/negative predictive agreements of spIgE classes for rPas n 1 (73%/82.5%) and rCyn d 1 (67.8%/66.3%) between the nanofluidic and ImmunoCAP measurements for Bahia and Bermuda grass pollen, respectively, were substantial.

CONCLUSION

Point-of-care nanofluidic tests for spIgE to rPas n 1 and rCyn d 1 could increase access to more precise clinical diagnosis for patients with allergies in subtropical regions.

Identification of carboxymethyl (CM)-binding proteins derived from Lolium multiflorum pollen extract and antibody reactivity in Brazilian allergic patients

Lolium multiflorum grass is the major pollen allergen source in the southern region of Brazil, but most of its allergens remain poorly characterized. The aim of this study was to investigate antibody reactivity to L. multiflorum crude and carboxymethyl-ligand extracts in allergic patients and healthy individuals. Ion exchange carboxymethyl (CM) chromatography (CM-Sepharose) was used to isolate proteins (S2) from L. multiflorum crude extract (S1), which were assessed by SDS-PAGE. S1- and S2-specific IgE and IgG4 levels were measured by ELISA using sera from 55 atopic and 16 non-atopic subjects. Reactive polypeptide bands in S1 and S2 were detected by immunoblotting, and the most prominent bands in S2 were analyzed by mass spectrometry (MS-MS). Similar IgE and IgG4 levels were observed to both S1 (IgE median absorbance: 1.22; IgG4 median absorbance: 0.68) and S2 (IgE median absorbance: 1.26; IgG4 median absorbance: 0.85) in atopic subjects. S1 and S2 had positive correlations for IgE and IgG4 (IgE: r=0.9567; IgG4: r=0.9229; P<0.0001) levels. Homology between S1 and S2 was confirmed by IgE (84%) and IgG4 (83%) inhibition. Immunoblotting revealed that the 29-32 kDa band was recognized by 100% of atopic subjects in both S1 and S2. MS-MS analysis identified similarity profile to groups 1 and 5 grass allergens. This study revealed that carboxymethyl-ligand fraction played an important role for pollen allergy diagnosis by containing clinically relevant allergens and constituted a promising candidate for allergen-specific immunotherapy.

Metabarcoding airborne pollen from subtropical and temperate eastern Australia over multiple years reveals pollen aerobiome diversity and complexity

eDNA metabarcoding is an emergent tool to inform aerobiome complexity, but few studies have applied this technology with real-world environmental pollen monitoring samples. Here we apply eDNA metabarcoding to assess seasonal and regional differences in the composition of airborne pollen from routine samples collected across successive years. Airborne pollen concentrations over two sampling periods were determined using a continuous flow volumetric impaction air sampler in sub-tropical (Mutdapilly and Rocklea) and temperate (Macquarie Park and Richmond), sites of Australia. eDNA metabarcoding was applied to daily pollen samples collected once per week using the rbcL amplicon. Composition and redundancy analysis of the sequence read counts were examined. The dominant pollen families were mostly consistent between consecutive years but there was some heterogeneity between sites and years for month of peak pollen release. Many more families were detected by eDNA than counted by light microscopy with 211 to 399 operational taxonomic units assigned to family per site from October to May. There were 216 unique and 119 taxa shared between subtropics (27°S) and temperate (33°S) latitudes, with, for example, Poaceae, Myrtaceae and Causurinaceae being shared, and Manihot, Vigna and Aristida being in subtropical, and Ceratodon and Cerastium being in temperate sites. Certain genera were observed within the same location and season over the two years; Chloris at Rocklea in autumn of 2017-18 (0.625, p ≤ 0.004) and 2018-19 (0.55, p ≤ 0.001), and Pinus and Plantago at Macquarie Park in summer of 2017-18 (0.58, p ≤ 0.001 and 0.53, p ≤ 0.003, respectively), and 2018-19 (0.8, p ≤ 0.003 and 0.8, p ≤ 0.003, respectively). eDNA metabarcoding is a powerful tool to survey the complexity of pollen aerobiology and distinguish spatial and temporal profiles of local pollen to a far deeper level than traditional counting methods. However, further research is required to optimise the metabarcode target to enable reliable detection of pollen to genus and species level.

EAACI Molecular Allergology User's Guide 2.0

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE-mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE-mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well-defined, highly pure molecules for component-resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the "EAACI Molecular Allergology User's Guide" (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state-of-the-art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Tracking seasonal changes in diversity of pollen allergen exposure: Targeted metabarcoding of a subtropical aerobiome

The importance of grass pollen to the global burden of allergic respiratory disease is well established but exposure to subtropical and temperate pollens is difficult to discern. Current monitoring of airborne pollen relies on light microscopy, limiting identification of taxa to family level. This informs seasonal fluctuations in pollen aerobiology but restricts analysis of aerobiological composition. We aimed to test the utility of DNA metabarcoding to identify specific taxa contributing to the aerobiome of environmental air samples, using routine pollen and spore monitoring equipment, as well as assess temporal variation of Poaceae pollen across an entire season. Airborne pollen concentrations were determined by light microscopy over two pollen seasons in the subtropical city of Brisbane (27°32'S, 153°00E), Australia. Thirty daily pollen samples were subjected to high throughput sequencing of the plastid rbcL amplicon. Amplicons corresponded to plants observed in the local biogeographical region with up to 3238 different operational taxonomic units (OTU) detected. The aerobiome sequencing data frequently identified pollen to genus levels with significant quantitative differences in aerobiome diversity between the months and seasons detected. Moreover, multiple peaks of Chloridoideae and Panicoideae pollen were evident over the collection period confirming these grasses as the dominant Poaceae pollen source across the season. Targeted high throughput sequencing of routinely collected airborne pollen samples appears to offer utility to track temporal changes in the aerobiome and shifts in pollen exposure. Precise identification of the composition and temporal distributions of airborne pollen is important for tracking biodiversity and for management of allergic respiratory disease.

Biogeographical variation in specific IgE recognition of temperate and subtropical grass pollen allergens in allergic rhinitis patients

Objective

Globally, grass pollens (GP) are major aeroallergen triggers of allergic rhinitis (AR) and asthma. However, patterns of allergic sensitisation to pollen of temperate (Pooideae: Lolium perenne) and subtropical (Chloridoideae: Cynodon dactylon and Panicoideae: Paspalum notatum) subfamilies in diverse climates remain unclear. This study aims to evaluate the level of allergic sensitisation and IgE specificity for major GP allergens representing the three subfamilies in biogeographically distinct regions.

Methods

Participants (GP‐allergic with AR, 330; non‐atopic, 29; other allergies, 54) were recruited in subtropical: Queensland, and temperate: New South Wales, Western and South Australia, regions. Clinical history, skin prick test (SPT), total and specific IgE to GP and purified allergens (ImmunoCAP) were evaluated. Cross‐inhibition of sIgE with Pas n 1, Cyn d 1 and Lol p 1 by GP extracts was investigated.

Results

Queensland participants showed higher sensitisation to P. notatum and C. dactylon than L. perenne GP. sIgE was higher to Pas n 1 and Cyn d 1, and sIgE to Pas n 1 and Cyn d 1 was inhibited more by Panicoideae and Chloridoideae, respectively, than Pooideae GP. Conversely, participants from temperate regions showed highest sensitisation levels to L. perenne GP and Lol p 1, and sIgE to Lol p 1 was inhibited more by Pooideae than other GP.

Conclusion

Levels and patterns of sensitisation to subtropical and temperate GP in AR patients depended on biogeography. Knowledge of the specificity of sensitisation to local allergens is important for optimal diagnosis and choice of allergen‐specific immunotherapy to maximise benefit.

The molecular allergology of subtropical grass pollen

Grass pollens are amongst the most important aeroallergen sources world-wide triggering allergic rhinoconjunctivitis and asthma in sensitised patients. Much of what we know about the allergen components of grasses is informed by research on pollen of temperate (Pooideae) species that are abundant in the temperate climate zones. However, climate changes are altering the biogeographical distribution as well as timing and allergenicity of grass pollens. This provides an impetus for better understanding of the contribution of subtropical subfamilies of grasses to pollen allergy globally. Pollen of Chloridoideae (e.g. Cynodon dactylon; Bermuda grass) and Panicoideae (e.g. Paspalum notatum; Bahia grass or Sorghum halepense; Johnson grass) subfamilies are clinically important in subtropical zones of Australia, Asia, India, Africa, and America. These grasses differ ecologically and phylogenetically from temperate grasses and, importantly their allergen composition is qualitatively different. For example, subtropical grass pollens appear to lack the major group 5 grass pollen allergen family. In this review we summarize current knowledge of the epidemiology and immunology of subtropical Chloridoideae and Pancoideae pollen allergens, describe the biochemical characteristics of known isoforms and variants as well as properties and structures of subtropical pollen allergen components. Whilst only one subtropical allergen component; Cyn d 1 of Bermuda grass pollen, is available commercially for diagnostic use, in a natural purified form, a number of allergens of Panicoideae grass pollen; Zea m 1, Zea m 3 and Zea m 13 of maize, Pas n 1 and Pas n 13 of Bahia, as well as Sor h 1, Sor h 2, Sor h 13 and Sor h 23 of Johnson grass, have been discovered. Research effort is directed towards making available subtropical grass pollen allergen components as innovative treatment and diagnostic options that more specifically address the needs of patients from warmer regions of the globe.

EAACI Molecular Allergology User's Guide

The availability of allergen molecules ('components') from several protein families has advanced our understanding of immunoglobulin E (IgE)-mediated responses and enabled 'component-resolved diagnosis' (CRD). The European Academy of Allergy and Clinical Immunology (EAACI) Molecular Allergology User's Guide (MAUG) provides comprehensive information on important allergens and describes the diagnostic options using CRD. Part A of the EAACI MAUG introduces allergen molecules, families, composition of extracts, databases, and diagnostic IgE, skin, and basophil tests. Singleplex and multiplex IgE assays with components improve both sensitivity for low-abundance allergens and analytical specificity; IgE to individual allergens can yield information on clinical risks and distinguish cross-reactivity from true primary sensitization. Part B discusses the clinical and molecular aspects of IgE-mediated allergies to foods (including nuts, seeds, legumes, fruits, vegetables, cereal grains, milk, egg, meat, fish, and shellfish), inhalants (pollen, mold spores, mites, and animal dander), and Hymenoptera venom. Diagnostic algorithms and short case histories provide useful information for the clinical workup of allergic individuals targeted for CRD. Part C covers protein families containing ubiquitous, highly cross-reactive panallergens from plant (lipid transfer proteins, polcalcins, PR-10, profilins) and animal sources (lipocalins, parvalbumins, serum albumins, tropomyosins) and explains their diagnostic and clinical utility. Part D lists 100 important allergen molecules. In conclusion, IgE-mediated reactions and allergic diseases, including allergic rhinoconjunctivitis, asthma, food reactions, and insect sting reactions, are discussed from a novel molecular perspective. The EAACI MAUG documents the rapid progression of molecular allergology from basic research to its integration into clinical practice, a quantum leap in the management of allergic patients.

Specific IgE recognition of pollen allergens from subtropic grasses in patients from the subtropics

BACKGROUND

Pollens of subtropical grasses, Bahia (Paspalum notatum), Johnson (Sorghum halepense), and Bermuda (Cynodon dactylon), are common causes of respiratory allergies in subtropical regions worldwide.

OBJECTIVE

To evaluate IgE cross-reactivity of grass pollen (GP) found in subtropical and temperate areas.

METHODS

Case and control serum samples from 83 individuals from the subtropical region of Queensland were tested for IgE reactivity with GP extracts by enzyme-linked immunosorbent assay. A randomly sampled subset of 21 serum samples from patients with subtropical GP allergy were examined by ImmunoCAP and cross-inhibition assays.

RESULTS

Fifty-four patients with allergic rhinitis and GP allergy had higher IgE reactivity with P notatum and C dactylon than with a mixture of 5 temperate GPs. For 90% of 21 GP allergic serum samples, P notatum, S halepense, or C dactylon specific IgE concentrations were higher than temperate GP specific IgE, and GP specific IgE had higher correlations of subtropical GP (r = 0.771-0.950) than temperate GP (r = 0.317-0.677). In most patients (71%-100%), IgE with P notatum, S halepense, or C dactylon GPs was inhibited better by subtropical GP than temperate GP. When the temperate GP mixture achieved 50% inhibition of IgE with subtropical GP, there was a 39- to 67-fold difference in concentrations giving 50% inhibition and significant differences in maximum inhibition for S halepense and P notatum GP relative to temperate GP.

CONCLUSION

Patients living in a subtropical region had species specific IgE recognition of subtropical GP. Most GP allergic patients in Queensland would benefit from allergen specific immunotherapy with a standardized content of subtropical GP allergens.

An immunodiagnostic assay for quantitation of specific IgE to the major pollen allergen component, Pas n 1, of the subtropical Bahia grass

BACKGROUND

Pollens of the Panicoideae subfamily of grasses including Bahia (Paspalum notatum) are important allergen sources in subtropical regions of the world. An assay for specific IgE to the major molecular allergenic component, Pas n 1, of Bahia grass pollen (BaGP) would have immunodiagnostic utility for patients with pollen allergy in these regions.

METHODS

Biotinylated Pas n 1 purified from BaGP was coated onto streptavidin ImmunoCAPs. Subjects were assessed by clinical history of allergic rhinitis and skin prick test (SPT) to aeroallergens. Serum total, BaGP-specific and Pas n 1-specific IgE were measured.

RESULTS

Pas n 1 IgE concentrations were highly correlated with BaGP SPT (r = 0.795, p < 0.0001) and BaGP IgE (r = 0.915, p < 0.0001). At 0.23 kU/l Pas n 1 IgE, the diagnostic sensitivity (92.4%) and specificity (93.1%) for the detection of BaGP allergy was high (area under receiver operator curve 0.960, p < 0.0001). The median concentrations of Pas n 1 IgE in non-atopic subjects (0.01 kU/l, n = 67) and those with other allergies (0.02 kU/l, n = 59) showed no inter-group difference, whilst grass pollen-allergic patients with allergic rhinitis showed elevated Pas n 1 IgE (6.71 kU/l, n = 182, p < 0.0001). The inter-assay coefficient of variation for the BaGP-allergic serum pool was 6.92%.

CONCLUSIONS

Pas n 1 IgE appears to account for most of the BaGP-specific IgE. This molecular component immunoassay for Pas n 1 IgE has potential utility to improve the sensitivity and accuracy of diagnosis of BaGP allergy for patients in subtropical regions.

Grass pollen allergens globally: the contribution of subtropical grasses to burden of allergic respiratory diseases

Grass pollens of the temperate (Pooideae) subfamily and subtropical subfamilies of grasses are major aeroallergen sources worldwide. The subtropical Chloridoideae (e.g. Cynodon dactylon; Bermuda grass) and Panicoideae (e.g. Paspalum notatum; Bahia grass) species are abundant in parts of Africa, India, Asia, Australia and the Americas, where a large and increasing proportion of the world's population abide. These grasses are phylogenetically and ecologically distinct from temperate grasses. With the advent of global warming, it is conceivable that the geographic distribution of subtropical grasses and the contribution of their pollen to the burden of allergic rhinitis and asthma will increase. This review aims to provide a comprehensive synthesis of the current global knowledge of (i) regional variation in allergic sensitivity to subtropical grass pollens, (ii) molecular allergenic components of subtropical grass pollens and (iii) allergic responses to subtropical grass pollen allergens in relevant populations. Patients from subtropical regions of the world show higher allergic sensitivity to grass pollens of Chloridoideae and Panicoideae grasses, than to temperate grass pollens. The group 1 allergens are amongst the allergen components of subtropical grass pollens, but the group 5 allergens, by which temperate grass pollen extracts are standardized for allergen content, appear to be absent from both subfamilies of subtropical grasses. Whilst there are shared allergenic components and antigenic determinants, there are additional clinically relevant subfamily-specific differences, at T- and B-cell levels, between pollen allergens of subtropical and temperate grasses. Differential immune recognition of subtropical grass pollens is likely to impact upon the efficacy of allergen immunotherapy of patients who are primarily sensitized to subtropical grass pollens. The literature reviewed herein highlights the clinical need to standardize allergen preparations for both types of subtropical grass pollens to achieve optimal diagnosis and treatment of patients with allergic respiratory disease in subtropical regions of the world.

Unique and cross-reactive T cell epitope peptides of the major Bahia grass pollen allergen, Pas n 1

BACKGROUND

Bahia grass pollen (BaGP) is a major cause of allergic rhinitis. Subcutaneous allergen-specific immunotherapy is effective for grass pollen allergy, but is unsuitable for patients with moderate to severe asthma due to the risk of anaphylaxis. T cell-reactive but IgE nonreactive peptides provide a safer treatment option. This study aimed to identify and characterize dominant CD4(+) T cell epitope peptides of the major BaGP allergen, Pas n 1.

METHODS

Pas n 1-specific T cell lines generated from the peripheral blood of BaGP-allergic subjects were tested for proliferative and cytokine response to overlapping 20-mer Pas n 1 peptides. Cross-reactivity to homologous peptides from Lol p 1 and Cyn d 1 of Ryegrass and Bermuda grass pollen, respectively, was assessed using Pas n 1 peptide-specific T cell clones. MHC class II restriction of Pas n 1 peptide T cell recognition was determined by HLA blocking assays and peptide IgE reactivity tested by dot blotting.

RESULTS

Three Pas n 1 peptides showed dominant T cell reactivity; 15 of 18 (83%) patients responded to one or more of these peptides. T cell clones specific for dominant Pas n 1 peptides showed evidence of species-specific T cell reactivity as well as cross-reactivity with other group 1 grass pollen allergens. The dominant Pas n 1 T cell epitope peptides showed HLA binding diversity and were non-IgE reactive.

CONCLUSIONS

The immunodominant T cell-reactive Pas n 1 peptides are candidates for safe immunotherapy for individuals, including those with asthma, who are allergic to Bahia and possibly other grass pollens.

Subtropical grass pollen allergens are important for allergic respiratory diseases in subtropical regions

Background

Grass pollen allergens are a major cause of allergic respiratory disease but traditionally prescribing practice for grass pollen allergen-specific immunotherapy has favoured pollen extracts of temperate grasses. Here we aim to compare allergy to subtropical and temperate grass pollens in patients with allergic rhinitis from a subtropical region of Australia.

Methods

Sensitization to pollen extracts of the subtropical Bahia grass (Paspalum notatum), Johnson grass (Sorghum halepense) and Bermuda grass (Cynodon dactylon) as well as the temperate Ryegrass (Lolium perenne) were measured by skin prick in 233 subjects from Brisbane. Grass pollen-specific IgE reactivity was tested by ELISA and cross-inhibition ELISA.

Results

Patients with grass pollen allergy from a subtropical region showed higher skin prick diameters with subtropical Bahia grass and Bermuda grass pollens than with Johnson grass and Ryegrass pollens. IgE reactivity was higher with pollen of Bahia grass than Bermuda grass, Johnson grass and Ryegrass. Patients showed asymmetric cross-inhibition of IgE reactivity with subtropical grass pollens that was not blocked by temperate grass pollen allergens indicating the presence of species-specific IgE binding sites of subtropical grass pollen allergens that are not represented in temperate grass pollens.

Conclusions

Subtropical grass pollens are more important allergen sources than temperate grass pollens for patients from a subtropical region. Targeting allergen-specific immunotherapy to subtropical grass pollen allergens in patients with allergic rhinitis in subtropical regions could improve treatment efficacy thereby reducing the burden of allergic rhinitis and asthma.

Functional immunoglobulin E cross-reactivity between Pas n 1 of Bahia grass pollen and other group 1 grass pollen allergens

BACKGROUND

Grass pollens are major triggers of allergic rhinitis and asthma, but the immunological relationships between pollen allergens of the subtropical Bahia grass, Paspalum notatum, and temperate grasses are unresolved.

OBJECTIVE

To assess serum IgE cross-reactivity between subtropical P. notatum and temperate Lolium perenne (Ryegrass) pollen allergens.

METHODS

Serum IgE reactivities of grass pollen-allergic patients with P. notatum, L. perenne and Cynodon dactylon (Bermuda grass) pollen extracts and their respective purified group 1 allergens, Pas n 1, Lol p 1 and Cyn d 1, were compared by immunoblotting, ELISA and basophil activation.

RESULTS

In a cohort of 51 patients from a temperate region, a high frequency of IgE reactivity with each grass pollen was detected, but reactivity with L. perenne pollen was substantially greater than with P. notatum and C. dactylon pollen. Similarly, serum IgE reactivity with Lol p 1 was greater than with Pas n 1 or Cyn d 1. For seven of eight sera studied in detail, asymmetric serum IgE cross-reactivity was observed; L. perenne pollen inhibited IgE reactivity with P. notatum pollen but not the converse, and IgE reactivity with Pas n 1 was inhibited by Lol p 1 but IgE reactivity with Lol p 1 was not inhibited by Pas n 1 or Cyn d 1. Importantly, P. notatum pollen and Pas n 1 activated basophils in grass pollen-allergic patients from a temperate region, although stimulation was greater by pollen of L. perenne than P. notatum or C. dactylon, and by Lol p 1 than Pas n 1 or Cyn d 1. In contrast, a cohort of 47 patients from a subtropical region showed similar IgE reactivity with P. notatum and L. perenne pollen, and reciprocal cross-inhibition of IgE reactivity between L. perenne and P. notatum.

CONCLUSIONS

Pollen allergens of the subtropical P. notatum, including Pas n 1, show clinically relevant IgE cross-reactivity with pollen allergens of L. perenne but also species-specific IgE reactivity.

The dominant 55 kDa allergen of the subtropical Bahia grass (Paspalum notatum) pollen is a group 13 pollen allergen, Pas n 13

Bahia grass, Paspalum notatum, is an important pollen allergen source with a long season of pollination and wide distribution in subtropical and temperate regions. We aimed to characterize the 55 kDa allergen of Bahia grass pollen (BaGP) and ascertain its clinical importance. BaGP extract was separated by 2D-PAGE and immunoblotted with serum IgE of a grass pollen-allergic patient. The amino-terminal protein sequence of the predominant allergen isoform at 55 kDa had similarity with the group 13 allergens of Timothy grass and maize pollen, Phl p 13 and Zea m 13. Four sequences obtained by rapid amplification of the allergen cDNA ends represented multiple isoforms of Pas n 13. The predicted full length cDNA for Pas n 13 encoded a 423 amino acid glycoprotein including a signal peptide of 28 residues and with a predicted pI of 7.0. Tandem mass spectrometry of tryptic peptides of 2D gel spots identified peptides specific to the deduced amino acid sequence for each of the four Pas n 13 cDNA, representing 47% of the predicted mature protein sequence of Pas n 13. There was 80.6% and 72.6% amino acid identity with Zea m 13 and Phl p 13, respectively. Reactivity with a Phl p 13-specific monoclonal antibody AF6 supported designation of this allergen as Pas n 13. The allergen was purified from BaGP extract by ammonium sulphate precipitation, hydrophobic interaction and size exclusion chromatography. Purified Pas n 13 reacted with serum IgE of 34 of 71 (48%) grass pollen-allergic patients and specifically inhibited IgE reactivity with the 55 kDa band of BaGP for two grass pollen-allergic donors. Four isoforms of Pas n 13 from pI 6.3-7.8 had IgE-reactivity with grass pollen allergic sera. The allergenic activity of purified Pas n 13 was demonstrated by activation of basophils from whole blood of three grass pollen-allergic donors tested but not control donors. Pas n 13 is thus a clinically relevant pollen allergen of the subtropical Bahia grass likely to be important in eliciting seasonal allergic rhinitis and asthma in grass pollen-allergic patients.

Clinical and immunobiochemical characterization of airborne Delonix regia (Gulmohar tree) pollen and cross-reactivity studies with Peltophorum pterocarpum pollen: 2 dominant avenue trees from eastern India

BACKGROUND

Delonix regia and Peltophorum pterocarpum pollen are important aeroallergens for type 1 hypersensitivity in the tropics. The IgE-binding proteins of D regia and their cross-allergenity with P pterocarpum pollen have not been evaluated.

OBJECTIVES

To isolate and characterize the IgE-binding proteins of D regia pollen for the first time and to investigate the cross-allergenity with P pterocarpum pollen belonging to the same family (Leguminosae).

METHODS

Allergenic activities were determined by in vivo and in vitro analyses. Pollen extract was fractionated by a combination of 2 columns (diethyl amino ethyl Sephadex and Sephacryl S-200). Protein components were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, periodic acid-Schiff staining, and immunoblotting. In vitro inhibition tests were performed to evaluate the cross-reactivity.

RESULTS

The skin prick test results of the patients with respiratory allergies in Calcutta, India, showed 31.1% positivity with D regia pollen. Nine IgE-reactive protein components were found in the crude extract. An optimum IgE-reactive fraction was resolved into 4 subfractions. Subfraction A, which showed maximum IgE reactivity, contained 2 (96- and 66-kDa) IgE-reactive protein components. The 66-kDa component was found to be glycoprotein. Remarkable cross-reactivity between D regia and P pterocarpum pollen was found on IgE enzyme-linked immunosorbent assay inhibition and dot blotting. Shared IgE-binding components (66, 56, 32, 28, 25, and 23 kDa) were observed between D regia and P pterocarpum pollen extracts, whereas the 96- and 43-kDa components were specific to D regia.

CONCLUSION

The purification of the IgE-binding proteins and the identification of the shared/cross-reactive proteins in these taxonomically related pollen members should be helpful for the diagnosis and therapy of patients susceptible to these pollens.