Biochemical composition of Phleum pratense pollen grains: A review

Phleum pratense-pollen adaptive variations and pollen microbiome investigation under different climatic regions and prospects of allergenicity

Phleum pratense is an allergenic grass that pollinates in spring in Pakistan. Databases Allergenonline.org and Allergen.org record ten P. pratense allergens and their isoforms. Phl P 1, Phlp 5, and Phl p 11 are major P. pratense-pollen allergens with demonstrated basophil activity and skin test reactivity. Little is known about P. pratense pollen adaptive variations in different climatic regions and pollen-associated microbial diversity. In this study, we collected P. pratense-pollen and soils in the spring season 2022. Samples were collected from three climatic regions in Pakistan (R1, R2 and R3) with differences in mean monthly air temperature, mean monthly precipitation and elevation. The morphology of pollen was observed by light microscopy, scanning electron microscopy (SEM), biochemical fingerprint analysis, and composition of pollen were investigated by fourier-transform infrared spectroscopy (FTIR). The pollen-associated bacterial populations were identified through a Biolog GEN III microplate system. The pollen water-soluble proteins were isolated and stabilized in phosphate buffer saline (PBS) and tested for allergenicity responses through dot blots and western blots analysis. The morphology study found difference in pollen biochemical composition. Biolog identified Brevibacterium epidermidis and Pantoea agglomerans from P. pratense pollen. Protein extract quantification and sodium dodecyl sulfate-poly acrylamide gel electrophoresis (SDS-PAGE) gel found decreased protein expression in R1 region pollen compared to R2 and R3 region pollen. Allergenicity studies found differential expression of beta-expansin and profilin allergens in pollen obtained from the three regions. Beta-expansin and profilin were suppressed in R1 pollen and expressed in compared to R2 and R3 pollen. This is the first study to identify B. epidermidis and P. agglomerans growth on P. pratense pollen. Variable allergen expression in P. pratense pollen has also been observed in different regions. Soil pH, an increase in mean monthly temperature and a decrease in mean monthly precipitation correlated with pollen biochemical composition, and reduced beta-expansin and profilin expression involved in pollen growth and development. The findings of this research are unique, which enhances basic knowledge and understanding of P. pratense-pollen associated microbiota and climate change impacts on the pollen allergen expression.

Profile of cross-reactivity to common pollen allergens in Northwest China based on component resolved diagnosis

The prevalence of allergic diseases such as Allergic Rhinitis and Asthma is steadily increasing globally, with pollen allergy being one of the most significant sensitizing factors. However, the cross-reactivity of different pollen allergies remains unclear, posing challenges in the diagnosis and treatment of individuals with multiple sensitivities. In this study, the Component Resolved Diagnosis technique was performed to simultaneously measure the specific IgE concentrations of 52 patients against Art v and its components (Art v 1), Phl p and its components (Phl p 1, Phl p 4, Phl p 5, Phl p 6, Phl p 7, Phl p 12), Bet v and its components (Bet v 1, Bet v 2), Amb a and its component (Amb a 1), and Amb p. Additionally, sIgE inhibition tests were conducted by Art v, Phl p, and Bet v extracts. Among Art v-positive patients, 64.6% showed positivity for Art v 1. In Phl p-positive patients, Phl p 12 had the highest positivity rate (75.0%). Among Bet v-positive patients, 75.6% exhibited positivity for Bet v 2, whereas for Amb a and Amb p-positive patients, 23.7% and 29.0% respectively showed positivity for Amb a 1. The sIgE inhibition assays results revealed that Art v extract had inhibition rates greater than 73.2% against Phl p and its component Phl p 12, as well as Bet v and its component Bet v 2. Simultaneously, Phl p extract showed inhibition rates of 80.70-89.87% against Phl p 12, Bet v and Bet v 2. Bet v extract showed inhibition rates ranging from 21.9 to 59.8% against Phl p and Bet v 2, with a better inhibition rate (76.80%) against Phl p 12. In conclusion, Art v 1 is identified as the principal component of Art v. The profilin proteins of Phl p and Bet v (Phl p 12 and Bet v 2), are implicated as potential cross-reactive elements contributing to polysensitization in patients with respiratory allergies in the Northwest region of China. This cross-reactivity leads to a shared sensitization mechanism among pollen allergens such as Art v, Phl p, and Bet v.

Storms facilitate airborne DNA from leaf fragments outside the main tree pollen season

Bioaerosols are useful indicators of plant phenology and can demonstrate the impacts of climate change on both local and regional scales (e.g. pollen monitoring/flowering phenology). Analysing bioaerosols with eDNA approaches are becoming more popular to quantify the diversity of airborne plant environmental DNA (eDNA) and flowering season of plants and trees. Leaf abscission from broadleaved trees and other perennial species can also indicate the status of plant health in response to climate. This happens primarily during autumn in response to seasonal growth conditions and environmental factors, such as changing photoperiod and reduced temperatures. During this period biological material is released in larger quantities to the environment. Here, rural bioaerosol composition during late summer and autumn was captured by MiSEQ sequencing of the rRNA internal transcribed spacer 2 (ITS2) region, a common marker for taxonomic variation. Meteorological parameters were recorded from a proximal weather station. The composition of atmospheric taxa demonstrated that deciduous tree DNA forms part of the bioaerosol community during autumn and, for several common broadleaved tree species, atmospheric DNA abundance correlated to high wind events. This suggests that both flowering and autumn storms cause bioaerosols from deciduous trees that can be detected with eDNA approaches. This is an aspect that must be considered when eDNA methods are used to analyse either pollen or other fragments from trees.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10453-024-09826-w.

The Chemical Landscape of Leaf Surfaces and Its Interaction with the Atmosphere

Atmospheric chemists have historically treated leaves as inert surfaces that merely emit volatile hydrocarbons. However, a growing body of evidence suggests that leaves are ubiquitous substrates for multiphase reactions-implying the presence of chemicals on their surfaces. This Review provides an overview of the chemistry and reactivity of the leaf surface's "chemical landscape", the dynamic ensemble of compounds covering plant leaves. We classified chemicals as endogenous (originating from the plant and its biome) or exogenous (delivered from the environment), highlighting the biological, geographical, and meteorological factors driving their contributions. Based on available data, we predicted ≫2 μg cm-2 of organics on a typical leaf, leading to a global estimate of ≫3 Tg for multiphase reactions. Our work also highlighted three major knowledge gaps: (i) the overlooked role of ambient water in enabling the leaching of endogenous substances and mediating aqueous chemistry; (ii) the importance of phyllosphere biofilms in shaping leaf surface chemistry and reactivity; (iii) the paucity of studies on the multiphase reactivity of atmospheric oxidants with leaf-adsorbed chemicals. Although biased toward available data, we hope this Review will spark a renewed interest in the leaf surface's chemical landscape and encourage multidisciplinary collaborations to move the field forward.

Sporopollenin Capsules as Biomimetic Templates for the Synthesis of Hydroxyapatite and β-TCP

Pollen grains, with their resilient sporopollenin exine and defined morphologies, have been explored as bio-templates for the synthesis of calcium phosphate minerals, particularly hydroxyapatite (HAp) and β-tricalcium phosphate (TCP). Various pollen morphologies from different plant species (black alder, dandelion, lamb's quarters, ragweed, and stargazer lily) were evaluated. Pollen grains underwent acid washing to remove allergenic material and facilitate subsequent calcification. Ragweed and lamb's quarter pollen grains were chosen as templates for calcium phosphate salts deposition due to their distinct morphologies. The calcification process yielded well-defined spherical hollow particles. The washing step, intended to reduce the protein content, did not significantly affect the final product; thus, justifying the removal of this low-yield step from the synthesis process. Characterisation techniques, including X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermal gravimetric analysis, confirmed the successful calcification of pollen-derived materials, revealing that calcified grains were principally composed of calcium deficient HAp. After calcination, biphasic calcium phosphate composed of HAp and TPC was obtained. This study demonstrated the feasibility of using pollen grains as green and sustainable bio-templates for synthesizing biomaterials with controlled morphology, showcasing their potential in biomedical applications such as drug delivery and bone regeneration.

Uptake of ozone by allergenic pollen grains

Ozone exacerbates allergy symptoms to certain pollens. The molecular mechanisms by which ozone affects pollen grains (PGs) and allergies are not fully understood, especially as the effects of pollutants may vary depending on the type of pollen. In this work, pollens of 22 different taxa were exposed under laboratory conditions to ozone (100 ppb) to quantify the ozone uptake by the PGs. The ozone uptake was highly variable among the 22 taxa tested. The highest ozone uptake per PG was measured on Acer negundo PGs (2.5 ± 0.2 pg. PG^-1). On average, tree pollens captured significantly more ozone than herbaceous pollens (average values of 0.5 and 0.02 pg. PG^-1, respectively). No single parameter (such as the number of apertures, time of the year for the pollen season, pollen size, or lipid fraction) could predict a pollen's ability to take up ozone. Lipids seem to act as a barrier to ozone uptake and play a protective role for some taxa. After inhalation of PGs, pollen-transported ozone could be transferred to mucous membranes and exacerbate symptoms through oxidative stress and local inflammation. Although the amount of ozone transported is small in absolute terms, it is significant compared to the antioxidant capacity of nasal mucus at a microscale. This mechanism of pollen-induced oxidative stress could explain the aggravation of allergic symptoms during ozone pollution episodes.

Physicochemical and immunological characterization of Amb a 12, a novel ragweed (Ambrosia artemisiifolia) pollen allergen

BACKGROUND

Ragweed is an invasive plant in Europe, causing hay fever and asthma in allergic patients. Climate change is predicted to increase expansion and allergenicity. Elevated NO₂ induced upregulation of a new allergen in ragweed pollen, an enolase, Amb a 12.

OBJECTIVE

of this study was producing ragweed enolase as a recombinant protein and characterizing its physicochemical and immunological features.

METHODS

Amb a 12 was designed for E. coli and insect cell expression. Physicochemical features were determined by mass spectrometry, circular dichroism measurements and enzymatic activity assay. Immunological characteristics were determined in ELISA, in a mediator release assay and by investigation of association with clinical symptoms. Common allergen sources were screened for similar proteins.

RESULTS

Ragweed enolase was produced as a 48 kDa protein forming oligomers in both expression systems, showing differences in secondary structure content and enzymatic activity depending on expression system. IgE frequency and allergenicity were low regardless of expression system. Enolase-specific serum bound to similar sized molecules in mugwort, timothy grass and birch pollen, as well as food allergen sources, while highest IgE inhibition was achieved with peach pulp extract.

CONCLUSIONS

Amb a 12 had high sequence similarity and comparable IgE frequency to enolase allergens from different sources. 50 kDa proteins were found in other pollen and food allergen sources, suggesting that enolases might be pan-allergens in pollen and plant foods.

Three patterns of sensitization to mugwort, timothy, birch and their major allergen components revealed by Latent class analysis

BACKGROUND

Mugwort, timothy, and birch are commonly spread pollen allergens across China. Although several studies have described the rates of sensitization to mugwort, timothy, and birch in China, most of them just on specific whole-allergen extracts but little was known about the co-sensitization characteristics of its allergen components. This study aimed to explore the patterns of sensitization to mugwort, timothy, birch, and their major allergen components.

METHOD

Serum specific IgE (sIgE) levels of allergen components of mugwort, timothy, birch, and cross-reactive carbohydrate determinants (CCD) were detected in 160 patients whose serum showed positive results to at least one of mugwort, timothy, and birch allergens via EUROBlotMaster system. Skin prick testing was utilized to assess the allergic reaction of grass, weed, and tree allergens. Latent class analysis was used to identify underlying patterns of sensitization to a series of allergen components and their corresponding extracts.

RESULTS

88.8% of patients with allergic rhinitis and/or asthma were positive for mugwort-sIgE, 30% for timothy-sIgE, and 32.5% for birch-sIgE. By using the LCA model, three sensitization patterns as "Mugwort, Art v 4, Bet v 2 and Phl p 12 co-sensitized", "Timothy, mugwort, and CCD co-sensitized", "Mugwort and Art v 1 co-sensitized" were revealed based on optimal statistical fit in this study. Compared with other clusters, participants in "Mugwort, Art v 4, Bet v 2 and Phl p 12 co-sensitized" pattern were associated with higher sensitization rates of common grass and tree pollens allergen. The spearman's coefficient between CCD and timothy was larger than the corresponding values of CCD with mugwort or birch.

CONCLUSION

CCD and profilin, as minor allergens in pollens, were associated with other pollen sIgE false positives presumably due to cross-reactivity. Patients sensitized with profilin had a significantly higher risk of sensitization to other pollens.

Abundance and Stability as Common Properties of Allergens

There have been many attempts to identify common biophysical properties which differentiate allergens from their non-immunogenic counterparts. This review will focus on recent studies which examine two such factors: abundance and stability. Anecdotal accounts have speculated that the elevated abundance of potential allergens would increase the likelihood of human exposure and thus the probability of sensitization. Similarly, the stability of potential allergens dictates its ability to remain a viable immunogen during the transfer from the source to humans. This stability could also increase the resilience of potential allergens to both gastric and endosomal degradation, further skewing the immune system toward allergy. Statistical analyses confirm both abundance and stability as common properties of allergens, while epidemiological surveys show a correlation between exposure levels (abundance) and allergic disease. Additional studies show that changes in protein stability can predictably alter gastric/endosomal processing and immunogenicity, providing a mechanistic link between stability and allergenicity. However, notable exceptions exist to both hypotheses which highlight the multifaceted nature of immunological sensitization, and further inform our understanding of some of these other factors and their contribution to allergic disease.