Fungal Allergen Genes

Allergy is a disorder of the immune system often also referred to as atopy. Allergic reactions occur to environmental substances known as allergens; these reactions are acquired, predictable and rapid. Strictly, allergy is one of four forms of hypersensitivity and is called type I (or immediate) hypersensitivity. It is characterized by excessive activation of certain white blood cells called mast cells and basophils by a type of antibody known as IgE, resulting in an extreme inflammatory response. Common allergic reactions include eczema, hives, hay fever, asthma, food allergies, and reactions to the venom of stinging insects such as wasps and bees.
Mild allergies like hay fever are highly prevalent in the human population and cause symptoms such as allergic conjunctivitis, itchiness, and runny nose. Allergies can play a major role in conditions such as asthma. In some people, severe allergies to environmental or dietary allergens or to medication may result in life-threatening anaphylactic reactions.

The causative agents of allergy are commonly eukaryotic proteins apparently mostly restricted to a number of functional classes. Identification of the genes encoding allergens is an essential first step in characterisation of the allergen and its epitopes and for studies involving diagnosis and cross-reaction where pure protein preparations are necessary. Much past and current effort has gone into discovering allergen gene sequences to define the nature of allergenic proteins and allow manipulation of allergen gene sequences for definition of epitopes, production of component resolved diagnostics or to direct design of a variety of immunotherapeutics. Fungi are estimated to sensitise ~20% of the atopic population although they may not be always the sole or causative agent. One important allergenic fungus is Aspergillus fumigatus with 20 described allergens. This fungus is also important as a pathogen of immunocompromised individuals and as a complicating allergenic factor in asthmatics. Although ~20 allergens have been described in A. fumigatus only four are known in A. oryzae, 5 in A. niger and a further 2 in A. flavus [www.allergome.org]. A possible allergen Asp ni 2 (previously Asp nd1) has also been described in A. nidulans. Other species of Aspergillus known to be allergenic such as A. clavatus, A. versicolor, A. sydowii and A. ochraeus have no allergens yet described. The genomes of several Aspergillus species have recently been sequenced and presented on this site under Aspergillus Genomes. Fungi produce ~90 allergens from a total of ~750 published in databases. A description of Aspergillus allergens including data on IgE reactivity and occurrence of allergy to specific proteins as presented here[link to website fungal allergens article]

The table below shows a list of known and predicted allergens from A.fumigatus with links to both the Aspergillus Genomes page for a particular gene (e.g. AFUA_5G02330) and to the SDAP allergen batabase for a particular allergen name (e.g. Asp f 1). A number of related fungal allergens that are of the same gene type are listed on the right of the table and the bottom half of the table shows genes in A.fumigatus that are homologous to known allergens from other sources but that have not yet been formally described as allergens in A.fumigatus

Table 2 Comparative analysis of allergen orthologues in Aspergillus genomes:

Here the known and predicited allergens from A.fumigatus from Table 1 are used to find homologues in the other Aspergillus species. Only a few of these proteins are confirmed allergens (these are shown in red text). It is noticeable that not all Aspergillus species possess all of the allergen gene homologues