Initiating pollen sensitization – complex source, complex mechanisms

Abstract

The mechanisms involved in the induction of allergic sensitization by pollen are not fully understood. Within the last few decades, findings from epidemiological and experimental studies support the notion that allergic sensitization is not only dependent on the genetics of the host and environmental factors, but also on intrinsic features of the allergenic source itself. In this review, we summarize the current concepts and newest advances in research focusing on the initial mechanisms inducing pollen sensitization. Pollen allergens are embedded in a complex and heterogeneous matrix composed of a myriad of bioactive molecules that are co-delivered during the allergic sensitization. Surprisingly, several purified allergens were shown to lack inherent sensitizing potential. Thus, growing evidence supports an essential role of pollen-derived components co-delivered with the allergens in the initiation of allergic sensitization. The pollen matrix, which is composed by intrinsic molecules (e.g. proteins, metabolites, lipids, carbohydrates) and extrinsic compounds (e.g. viruses, particles from air pollutants, pollen-linked microbiome), provide a specific context for the allergen and has been proposed as a determinant of Th2 polarization. In addition, the involvement of various pattern recognition receptors (PRRs), secreted alarmins, innate immune cells, and the dependency of DCs in driving pollen-induced Th2 inflammatory processes suggest that allergic sensitization to pollen most likely results from particular combinations of pollen-specific signals rather than from a common determinant of allergenicity. The exact identification and characterization of such pollen-derived Th2-polarizing molecules should provide mechanistic insights into Th2 polarization and pave the way for novel preventive and therapeutic strategies against pollen allergies.

Allergens and their associated small molecule ligands—their dual role in sensitization

“… 156 Immunomodulatory pollen‐associated lipid mediators such as leukotriene‐like molecules and phytoprostanes when codelivered with the allergen were proposed to play a key role in Th2 polarization. 7 Phytoprostane E1 has also been identified as a new ligand of Bet v 1. 14 This pollen‐derived ligand was shown to enhance the proteolytic resistance of Bet v 1 and to inhibit endolysosomal cathepsin protease activity.…”

“…Bet v 1 binds various classes of ligands in its large hydrophobic cavity including fatty acids, cytokinins, or flavonoids 156 . Immunomodulatory pollen‐associated lipid mediators such as leukotriene‐like molecules and phytoprostanes when codelivered with the allergen were proposed to play a key role in Th2 polarization 7 . Phytoprostane E1 has also been identified as a new ligand of Bet v 1 14 .…”

“…There is another category of allergens that requires either components from the matrix 7 or bound ligands 8 to act as adjuvants and whose presence is essential for the induction of a type 2 immune response 9 . Certain lipids from the Brazil nut matrix are necessary for inducing signaling pathways that ultimately result in the synthesis of sIgE against the major Brazil nut allergen Ber e 1, a seed storage 2S albumin 10 .…”

Grass pollen morphology investigation as a basis for monitoring of allergenic biological particles in an automatic mode

“…Grass pollen is not only the main factor of hay fever in the world [1], it also acts as an initiating factor that causes width lendth the development of pollen allergy in general since childhood [19,30]. However, insufficient attention is given in the scientific literature to the issue of studying the morphology of grass pollen.…”

“…Thus, currently, the pollen of Poaceae family plants has become one of the most important factors of seasonal allergy in the world [5,11]. In temperate climates, it contributes significantly in the level of sensitization of patients, along with pollen of ragweed and trees, in particular, birch [4,8,19]. According to molecular diagnostics of allergies [25], in Ukraine about 40% of patients with seasonal allergies are sensitive to grass pollen allergens.…”