Ambrosia artemisiifolia (hereafter briefly referred to as ragweed) is an anemophilous herb of the Asteraceae family that probably originated in desert areas of the USA. The plant was introduced to Europe through trade and spread as a successful neophyte during the 20th century. Although conditions are not ideal for ragweed in northern and central Europe, when the plant prefers dry, sandy soils, climate change may be a significant contributor to its spread. The pollen is considered highly allergenic, so it is possible that lower pollen concentrations are sufficient to trigger allergy symptoms compared to native grass or birch pollen. Together with its ability to spread invasively and its tolerance to harmful factors, ragweed is therefore considered a health hazard.~Determining threshold concentrations for various aeroallergens has been attempted many times in published literature. In fact, first experiments have been reported since the 1960s. However, obtaining comparable results prove difficult due to a plethora of methods, outcome measures and choices in study population. Basically, threshold concentration could be assessed by target organ specific allergen challenge, field study and allergen chamber challenge - each of which has its own benefits and drawbacks.~To date, allergen challenge chambers have been used primarily for proof-of-concept studies with antiallergic agents. Technically, the chambers are designed to maintain high pollen concentrations, which should induce symptoms in all sensitized subjects, at a constant level for hours in order to be able to determine the maximum possible effect size of the investigated therapeutic intervention. Metering and monitoring of pollen to maintain stable concentrations present technical challenges for deploying pollen concentrations in the double-digit range. Fraunhofer ITEM has successfully established low concentration pollen exposures, so that allergic patients can be titrated to effect. The pollen concentration will be escalated or de-escalated according to a pre-defined algorithm, based on interim data analysis. Eventually, a concentration range for ragweed and birch pollen can be determined that induces allergic symptoms with clinical and statistical significance.
The ragweed Ambrosia artemisiifolia is spreading in northern Europe due to climate change. The pollen are considered highly allergenic and might trigger allergy symptoms at much lower concentrations than e.g. grass or birch pollen. This study aims to determine threshold concentrations for ragweed and birch pollen in patients with seasonal allergic rhinitis. Participants will be exposed in an allergen challenge chamber that was technically modified to maintain very low and stable pollen concentrations for several hours. The study design is adaptive, where the pollen concentrations are escalated or de-escalated based on interim analysis of resulting allergic symptoms.