This study aims to profile the siderophore-content in the human gut from allergic and non-allergic subjects and to assess their contribution in iron homeostasis.

Iron is an essential nutrient for the majority of commensal bacteria, which commonly secrete siderophores to liberate iron from their surroundings. In several studies, a misbalanced microbiota has been demonstrated in allergics suggesting that also their siderophore profile is severely attenuated.

There are currently no data and very limited knowledge present on the composition of bacterial surviving factors in humans, or on their impact on the human immune system.

As such, 1) the iron status, 2) the microbial biota composition and the 3) siderophore-profile in allergics and non-allergics will be assessed.

Inclusion Criteria:

• allergic and non-allergic volunteers

Exclusion Criteria:

• Patients will not be considered for the study if they have co-morbidities such as diabetes mellitus, disorders of the liver including hemochromatosis or kidney, autoimmune or metabolic diseases and malignancy or if they use of medications (e.g. antibiotics, PPIs) that influence the iron, inflammatory or microbial status. Further exclusion criteria are pregnancy, lactation; veganism, zinc, and iron supplementation and smoking. Volunteers will be asked to cease blood donation for at least three months' before recruitment and to cease other supplements for at least two weeks, e.g. vitamins, fish oil or minerals (other than zinc and iron).

Allergics and Non-Allergic subjects over 18 years.