In situ Localization of Pollen Allergens by Immunogold Electron Microscopy: Allergens at Unexpected Sites

Abstract

The windborne pollen grains of many trees and grasses contain a number of highly water–soluble (glyco)proteins which upon moistening, e.g. on the human respiratory mucosa, rapidly diffuse out of the pollen grain. In susceptible individuals, they may cause allergic reactions. Because of their rapid release from the pollen, pollen allergens were expected to be located in the outermost layers of the pollen grain, i.e. on the surface and in the wall (exine, intine). First attempts to localize allergens by microscopic methods in the pollen grain supported this view. However, since conventional preparation methods were used, artificial mobilization of allergens could not be excluded. Based on new, completely anhydrous preparation protocols and on the immunogold–labeling technique, pollen allergens were electron–microscopically shown to be located in the interior of the pollen grain, i.e. in the cytoplasm, often within ribosome–rich areas. This unexpected result was obtained in all strictly anhydrously prepared pollen species. The biological function of these allergens is largely unknown, however, clues as to possible cellular functions have been obtained for the birch pollen major allergen Bet v 1.

Nondiffusional Release of Allergens from Pollen Grains of <i>Artemisia vulgaris</i> and <i>Lilium longiflorum</i> Depends Mainly on the Type of the Allergen

“…For instance, profilin binds to monomeric actin molecules, thus preventing the generation of actin filaments, which are essential for pollen germination and tube growth [24]. In this regard, it has to be pointed out that proteins released upon rehydration are in most cases localized in the cytoplasm or associated with intracellular structures and organelles [8, 13, 25, 26, 27, 28, 29]. …”

“…Using strictly anhydrous fixation techniques to prevented artificial hydration of pollen grains, Grote [8]was able to localize most allergens in intracellular compartments. It has been proposed that allergens are mainly released together with cytoplasmic components upon bursting of pollen grains, as it has been shown for birch pollen grains after contact with fluids from eyes, mouth or nose [9].…”

Group 13 Allergens as Environmental and Immunological Markers for Grass Pollen Allergy: Studies by Immunogold Field Emission Scanning and Transmission Electron Microscopy

“…grasses, trees, and weeds) belong to the most potent and frequent allergen sources [1]. Pollen allergens are water-soluble proteins of a low molecular weight (5–80 kDa) which are located in the cytoplasm and, occasionally, in the wall of the dry pollen [2]. Two modes of allergen release have been described for pollen allergens.…”

Origin and Functional Prediction of Pollen Allergens in Plants

“…In contrast, the exine refers to the very resistant outer wall that provides robust protection of the pollen grain from disintegration (Shi et al, 2015). Allergenic proteins are usually located within the pollen protoplast and readily released during the rehydration process (Grote, 1999). For example, birch (Betula spp.)…”