Storage mites are global pests of stored food products of increasing medical and economical impact. In agricultural environments, they cause occupational allergy in farmers and grain handlers. Storage mites are also found in house dust from rural and urban dwellings and are important contributors to the allergen content, which expands their clinical significance. The storage mites belong to the Acaridae and Glycyphagidae families; our work focuses on Acarus siro, one of the most frequent and abundant species in central Europe.
More than two dozen groups of mite-derived allergens have been described in the WHO/IUIS Allergen Nomenclature database http://www.allergen.org
. Allergens from house dust mites of Dermatophagoides
spp. have been extensively studied; however, much less is known about allergens from storage mites (e.g. 7 records for A. siro
allergens) (for review, see [1
]). There is increasing evidence that mites contain epitopes that are species-specific as well as cross-reactive among species. The effect of a partial cross-reactivity between storage mites and house dust mites and co-sensitization by both groups further increases the medical impact of storage mites [4
]. A detailed analysis of storage mite-derived allergens at the protein level will be necessary to better evaluate aspects of their sensitization specificity and biochemical activity, as well as to improve diagnosis and treatment.
Group 4 mite allergens are homologous proteins of the α-amylase class [10
]. Group 4 allergens have been investigated in house dust mites such as Dermatophagoides pteronyssinus, Euroglyphus maynei
, and Blomia tropicalis
, and their sequences have been determined [12
]. The biochemical properties of Der p 4 were analyzed in detail, including its interaction with major cereal flour allergens that act as α-amylase inhibitors [14
]. The IgE-binding activity of group 4 allergens has been demonstrated for ~30% of allergic subjects in Western populations and China [12
]; these allergens may also be the major contributor to the serum activity, as found in an Australian Aboriginal community [16
]. In this work, we analyze native Aca s 4 from A. siro
, the first α-amylase allergen to be isolated from storage mites. Specifically, we describe its biochemical and immunological properties. Furthermore, we provide insight into the 3D structure of Aca s 4 with the help of a novel homology model, the first 3D model of a group 4 allergen.